View Full Version : 4 stroke race buggy... er, truggy Update: 7/13 Fan Mount

09-27-2005, 10:51 PM
Hello all, I'm a new member around here, but far from a stranger to the r/c scene. Anyway, recently I've had an idea kicking in my head and I think it's time to let it out.

First off this story starts with a talk to one of my neighbors back home. Apparantly someone opened a new r/c shop in a shopless town and things are looking up. So much, in fact, that they plan on opening an off-road track next spring. Long story short, I got talked into taking a step into the 1/8 scale buggy market.

Of course I could just go out and buy a buggy with a fire breathing engine, but what would be the fun in that? ;) Since my old project, Quagmire (a twin four stroke 6x6), has been put on an extended delay, I've been thinking of ways I could put the two FS 40s I had collected to use. Obviously this buggy is a perfect candidate. :banana:

The ultimate plan is to build a single engine setup that can hang with the big dogs. Since I'm starting with an airplane engine it's going to take a little work, but that's where all the fun is. Ultimately the project is pointing towards these ideas:

*Modifying the fs-40 through head porting, a different carb, stiffer valve springs, knife edged con-rod, and a rebalance job. And if that doesn't net the rpm and power output I want, I'll start considering forced induction. Yummy.

*Building a better clutch. I've never been satisfied with the old centrifugal clutches. They work well with a two stroke, but you just can't get the force you need to really make them grab with a four stroke. Because of this I want to build a compact disc style clutch. I'm still trying to figure out if I want to build it as an automatic clutch or a semi-manual one.

*Multis-peed is the way to go. There's no way I can get a four stroke to put out the 37000 rpm range that modern 2 strokes can handle. Because of this I'm severly restricted between going with all out acceleration or top speed. Since I want both it'll at least need to be a two speed. Three speed preferable. Manual is the cat's meow. I'm really not sure what the heck I'm going to do in this department though.

Hopefully the buggy itself won't need too much modifying in the suspension department. I'm assuming that it'll take all the extra weight in stride. Getting it to perform, however, is going to be a real pain.

Anyway, the project should be something like this:

Plus this.
Equals this!

09-28-2005, 06:09 AM
Hey Welcome to scale4x4, :chug: havent seen you much since the old days of RCMT, before the dark times....before the empire....erm.... :blink: :crazy:


anyhoo sounds cool.... but wheres the other fs 40 going? :blink:

btw will you be allowed to race a 4 stroke? I mean its unlikely to be banned for being faster than the 2 stroke ones, but it may simply be so different that they might not allow it....

as for the clutch ideas, I've no idea how you would do a good car style clutch well, especially as an auto, but have you seen the centax style clutches where the centrifugal force is used to push the clucth shoes both outwards and forwards into a conical clutch bell for a greater surface contact? a system like this might work in a modified way for a car style setup? I am not certain as I have no practical experience of nitros or their clutches but it seems a good idea from what I've seen in RC mags...


09-28-2005, 09:04 AM
Hey Spoon! Yeah, I'm not sure what I'm going to do with the second four stroke. For now it's just a spare one for any parts I may screw up in the modification process. Altough if I get real stupid, it may go on the buggy as well, but I'm going to hold off on that for now. :unsure:

I was actually thinking about something like what you were talking about for the clutch. Right now the plan is to use a few 6mm steel ball bearings and a conical washer setup to create a sort of wedge effect to generate the clutch pressure.

As for the racing, right now it's not going to be an official ROAR deal. Just a bunch of guys getting together and racing. I'm not too worried about going to fast anyway considering my neighbor got himself a Hyper 7 and has a 3.5 hp powerplant coming in the mail. <_<

09-28-2005, 09:25 AM
You just had to wait so you could get to be member #400 didn't you :)
This is an awesome idea, i'll be glad to help out in ways that i can (My M196 truck is going to need a wet clutch.. with like 10 plates).

As for the transmission, it's going to be a while though before i will be able to cut annealed steel gears and then temper them back up to hardness. I've never done those yet. But making compact, multispeed manual transmissions is something i really want to do at some point.

Good to see you here man! You should start up a Quagmire thread too, even if its on hiatus! :)

09-28-2005, 09:48 AM
It's just a shame I couldn't have waited four more users, eh? I may make a quag post later on down the road once I dig up all of the old photos of it.

In all honesty though, the main reason Quag is in hiatus is because I need to design the clutch and drivetrain. It just happens to be that it'll probly be heavily based off what goes into this buggy. :)

09-28-2005, 10:37 AM
it makes sense to have a testbed vehicle which is otherwise largely ready for action as soon as you've worked out the drivetrain issues.....then hopefully quagmire will be up a chugging in no time.... :lol:

a thread about quagmire would be pretty cool here, many of our members wont have seen it on RCMT back in the day....also I seem to recall one of the most hacked up pajeros I've ever seen posted by you a while back(?) still got it? :huh:


09-28-2005, 11:33 AM
:lol: Yup! I still have the old Hackjero. It's in need of some major reworking though. The new sideplates need to be lightened and I almost need to get a new chassis to cut apart. The current one has way too many stripped screw holes on it.

09-28-2005, 04:04 PM
Just a quick update. I now have a general idea of how I want to layout the drivetrain so I'll give you guys this sketch for now.


The idea is to connect the engine to the transmission using a boat flywheel and short dogbone shaft. Then the clutch will be an external part of the transmission itself. The benefit to this is that it'll allow me to drop the engine as far down onto the chassis as possibly to get a low center of gravity. Since the clutch design is about 1.5 inches in diameter, I couldn't do this if the clutch was connected directly to the engine.

For initial testing, however, I'm going to leave the stock drivetrain in place and use the flywheel and clutch I had originally built for another project of mine, Quag.

That is a 1.6x.375 puck of steel along with a pair of steel shoes. Lots of rotating mass, but boy does it let those four strokes idle down and rumble. It's like listening to a Harley... with one piston. :nice:

09-29-2005, 01:45 PM
cool.... thats a meaty clutch!! :blink:



09-29-2005, 01:57 PM
I don't recall Quagmire, although the name is familiar!

09-29-2005, 02:49 PM
Jugg: I'll see if I can make a post for Quag later on down the road.

Anyway, more concept stuff. This time it's the transmission and clutch combo. I'm already running into one problem though. Right now the input (top) and output (bottom) shafts are too close together for how big the clutch may be. As you can see, the clutch and shaft overlap a bit.


10-14-2005, 08:31 PM
Time for another update! I finally got the lathe I had ordered from harbor freight a week or so ago and decided to start work on converting the four stroke from an airplane carb to a buggy carb.

As you can see, it's not a direct bolt up. :lol: The plan is to build an apapter that converts the 13mm carb outside diameter to a 8mm outside diameter that will be drilled into the cylinder head. The center hold of the adapter is 6mm. The same as what the head has.

The first step was to chuck the carb into the lathe and trim the end down to just 3/16 of an inch.

CHIPS! :banana:

As I found out, a 13mm drill bit is about as big as I can fit on the lathe. :lol:

Not too shabby. In hindsight I should have shot for 8.10 and not 8.00.

Unfortunantly my mill didn't have enough height to do this job so I can to resort to the drill press. Luckily it didn't have too much play though as the fit is decent. Not as tight as I wanted, but some sealant will fix all.

And wallah! At least now I can actually mount a filter on the engine. :lol: What you don't see is the set screws that will hold the carb to the adapter and then the adapter to the cylinder head.

The buggy also came in the mail. I ended up tearing it down and cleaning off all the parts as well as straighten some bent pieces on the front end due to a collision the previous owner had. <_<


Here's the four stroke just sitting in place. I ended up thinning out the edge of the flywheel because it was making contact with the rear brake disc.


That's all for now! Next up should be a test fire on the engine with the new carb, and then maybe some engine mounts if I ever get around to securing the vise to my mill. <_<

10-15-2005, 05:16 AM

you should get some MT2 shank drills, I just got a load off ebay cheap* - the drills I got range from 5/8" to 27/32" and most sizes inbetween they fit driectly into the tailstock as the shank is an MT2 taper with tang ends....

I have a lathe just like that one - its a clarke CL300M but its obviously a generic asian 7"x12" lathe as sold by companies like grizzly, taig etc...

good work on the carb mods tho... :chug:


*see the auction here: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?Vie...AMEWN%3AIT&rd=1 (http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=7547574560&rd=1&sspagename=STRK%3AMEWN%3AIT&rd=1)

10-15-2005, 10:02 AM
Awesome work Maxzillion! This is just the kind of stuff I like to see. ;)

10-24-2005, 09:47 AM
Thanks for the compliments guys!

Spoon: I forgot all about those drill bits! I'll have to start making myself a collection so I can actually drill a part that sticks out farther than 1-2 inches. :lol:

Anyway, after my yearly trip to the sand dunes, I've come to a basic conclusion. Rather than going with a bulky custom built 3 speed transmission, I'm going to try and develope a CVT setup.

After watching some crazy with a Kawasaki VForce 700 go at it on the dunes, I've come to realize that belt drives really aren't that bad. :)

I've already picked up a torsen diff from my neighbor for a great deal of only $10 and I'll use it as a base to build everything off of. In the end this will solve several problems all it once. It'll cut down on the rotating mass, eliminate the problem of stripped spur gears (instead now I just gotta watch out for belt stretch), and it doesn't require a heavy duty clutch because it's one in itself!

Anyway, if you guys don't know what I'm talking about, take a look at some go-cart or snowmoble drives. The real trick though is going to be finding a 1/4-3/8 inch wide belt with a 4-6 inch circumference.

10-24-2005, 02:25 PM
cool project!

actualy , i had a fs 26 scx in my maxx (http://community.webshots.com/album/103031894tLNbby)

had a lot of overheating problems , since there is no cooling on this thing
but when i ran good it was a torqy little monster! and cool sound too

made a mount for a 15cvx carb , never got to test it since the piston rod and camshaft said farewell.. <_<

10-26-2005, 09:38 AM
Mmmm... this is going to be interesting... i eagerly await how the CVT project comes out! Hopefully, http://www.sdp-si.com might have one of the belts that you are looking for...

10-26-2005, 11:33 AM
Hummer: Very nice! How did that heatsink extension work out for you on the engine?

Weeb: Thanks for the link. I have a feeling that I'm going to have to settle on a sort of timing belt, but I have my doubts as whether they'll handle the compressive forces they'll see from the sides with a CVT setup.

What I'm wondering is if there's a way for my to cut a V-belt and shorten it to the lenth I need. The problem is coming up with a reliable way to rebond them. Right now it looks like I'll need a belt that's around 7-8 inches long. Sdp definently has those lengths for the timing belts, but none for the v-belts. <_<

One other thing I was thinking about is this, but I have a feeling that it'd stretch too much. https://sdp-si.com/eStore/PartDetail.asp?Op...780&GroupID=168 (https://sdp-si.com/eStore/PartDetail.asp?Opener=Group&PartID=69780&GroupID=168)

10-26-2005, 11:49 AM
This also looks promising.


10-28-2005, 01:02 PM
SDP does custom sizes for things too. They are super-responsive about custom sized parts. Thought it might cost an arm and a leg in some cases.

Give them a call and see- they do a lot of manufacturing in-house so its entirely possible that those belts are actually made internally instead of drop-shipped from somewhere else...

10-28-2005, 03:46 PM
how do they bond V belts anyway? it should be too hard once you know how its done - lets face it the one in my cheapy drill press is as tough as nails and I'm certain its not made as a loop, it must have been bonded in the first place.

if those guys make those belts a slightly different length shouldnt be too much bother tho.... :nice:


10-28-2005, 05:09 PM
Yeah, even if they won't custom make a belt for me, I think I know of one product that can bond a belt together. Worse comes to worse I may just have to buy a 10 inch belt and stick a second engin in there to take up all the slack. :lol:

11-02-2005, 09:10 AM
Welp, I contacted sdp-si a couple of days ago and I'm now waiting on a reply from them. I've started designing the CVT drive pulley in AutoCAD and I'm beginning to realize one tiny little problem. How the heck am I going to operate this thing?! :lol:

Right now I don't have a long enough crank on my engine because I had shortened it to work with the custom flywheel and clutch I had made. Hopefully my parts engine still has an unmolested crank that will hopefully be long enough to fit all the junk I'll need to actuate the pulley.

What I've been thinking of is a pretty simple ball weight setup. In between two plates, one flat and one concaved, there would be a set of ball bearings. As the engine speeds up, they would sling outward and apply a pressure to the pulley causing it to squeeze the belt, providing the initial engagement and then changing the gear ratio as the engine rpm increases. Unfortunantly it's about... 10mm too long.

I guess if worse comes to worse I could always setup a microcontroller controlled servo to adjust the gear ratio. ;)

Otherwise it looks like the cvt may work. Right now I have it designed to give a low ratio of 2.8:1 and a high ratio of 1.9:1, effectively giving it a top speed of 45 mph while still providing enough of a low end that the buggy could theoretically crawl along at 25mph at wot. :)

One neat thing I've noticed though is that by shifting the engine away from the driven pulley, I can adjust the top speed of the buggy. It's beginning to look like I'll have to design a set of engine mounts that can be adjusted side to side with a couple of screws. Then if I want to kick the speed up to 50-55 all I need to do is shift the engine over half an inch or so. :burnout:

11-02-2005, 02:50 PM
QUOTE]Hummer: Very nice! How did that heatsink extension work out for you on the engine?[/QUOTE][

it help'd alot
i think u'll get some cooling issues if you dont make another cooling head...

anyway , when its done , post vids! :chug:

11-06-2005, 09:44 PM
More lathe work! I didn't get as much done as I wanted, but here's the start of the cvt drive pulley. This part will act as the main flywheel and provide the incline needed for the ball bearings to apply pressure to the pulley sheeves.



As you can see, it was made from two parts for ease of machining... I have enough trouble trying to machine a flat surface let alone watch what the cutter is doing inside a 1 inch hole. :lol:

I even managed to get the four stroke running on the buggy carb! :banana:

It's a little bit of a pain to start that way. So far the only way I could get it to fire was to pour a little fuel down the carb. Once I get a bump starter I don't think it'll be as big of a problem though since it should be able to turn it over fast enough to suck some fuel in.

Video! (http://members.cox.net/maxzilla/images/4stroketest.wmv)

Another thing I did to the four stroke was slightly port the head and attempt to lighten the rocker arms. I can't say for sure whether or not it helped much, but I'll take everything I can.


The idea is to make the valvetrain as light as possible to reduce valve float. I'm also considering making aluminum spring cups for the valves. Chances say that in the end I'll need to steal the springs from the FS-40-C to really help the engine with it's max rpm capabilities.

11-06-2005, 09:57 PM
Man does that sound better then a 2 stroke!!! :nice:

11-07-2005, 03:39 AM
I have no words.
That's an amazing work :nice:
Really IMPRESSIVE man ;)

11-07-2005, 04:45 PM
Outcast: You're darn right! I'm already thinking of a way to make a flowmaster style chambered muffler and then route the exhaust all the way to the back end of the buggy. We'll see if we can get this baby to rumble. :burnout:

Rik: After witnessing some of your projects, that comes off as one heck of a compliment. :nice:

Just as a quick side update:

I still don't know what to use for the belt. I think I'm just going to order a few different belts from SDP that are the length I need and see if any of them will work.

Right now I'm thinking of how to butcher one of my mini PC fans so I can use it as a crank driven fan. One interesting thing is that I have generated power with a PC fan so I'm left to wonder if I can use this one to power the RC equipment. :huh:

I also saw the. Coolest. Thing. Ever. You guys remember that joke concept drawing on the first page with the massive air scoop intake? Well I was just at the store today flipping through a magazine and I ran across the Kyosho Giga Crusher DF which, get this, has a functional hood scoop! I think I'm definently going to get myself one of those. B)


11-07-2005, 09:10 PM
Eh, a little bad news. I got some mail from sdp today saying that they couldn't make the belt I needed. However, they do have a double sided timing belt that may work so I'm going to order that and a few others tonight to see if I can find one that will work.

11-11-2005, 08:36 PM
Welp, I ordered a selection of belts for a grand total of about $26... not too shabby I must say.

Anyway, I managed to get my hands on AutoCAD 2006 so naturally the first thing I had to draw was the cvt. :)

The first two pieces on the left are what I have some pictures of earlier in this post. The third is the thrust side of the pulley while the fourth is the fixed side that also serves as the nut to hold the entire assembly together. The way it'll work is that between the thrust plate and the flywheel there will be 4 3/16 inch steel balls. As the engine speeds up, they will provide the force on the pulley assembly. One thing missing in these drawings is the spring assembly I'll likely need to hold the thrust side back at engine idle.


11-13-2005, 08:50 PM
Sweet project so far, good CAD skills too. Not to go too far off topic but I want to make a trail/ mud truck based on one of the 6th scale lids I have and was debating on nitro or electric and 2 stroke vs 4 stroke. I could get a big block .28 for $130 shipped or go considerably more expensive and run a nice 4 stroke. How do your 4 strokes perform, I seem to remember a vid of quag running but dont remember what it had for motors at the time. I could be delusional of the vid but thought i saw one. The horsepower numbers throw me for a loop too, they are so low compared to two strokes half their size, yet everything I've read claims they are absolute torque monsters and sometimes hard to gear for because of how low (numerically) the gear ratio has to be.

Could you shed some light on the above for me?

11-13-2005, 09:42 PM
Oh yeah, four strokes are the kings of torque. Those videos of quag was with clod tires and 1/8 scale buggy gearing. The only problem I really had was that the truck weighed too much and had a tendancy to smoke clutches. I still remember ruining a set of aluminum clutch shoes in 2-3 tanks of running. Still, it was rather comical to listen to the truck because you could pin the throttle and the engine would instantly find one rpm and hold it steady as the speed steadily increased. At one time I had considered a clutch from a weedwaker because it was obvious that any buggy style clutch just wasn't going to cut it. :lol:

I cannot stress how important it is to have a good clutch for a four stroke, but if the vehicle is fairly light it shouldn't be that big of a problem.

The best case of four stroke mania that I can remember is someone from Maxxtraxx who installed a modified FS-52 into a revo. In the videos it was passing other revos with big blocks down the straights and it could still manage to lift the front end high in the air if the driver goosed it hard enough. :blink:

11-14-2005, 02:19 AM
heh...reminds me of the old days on maxxtraxx, when someone first put a .40 in a T-maxx...it was smokin!(literally) but it could also hang with the then big block T-maxxes(using .21's lol).


11-14-2005, 07:40 PM
4 stroke sound better then a 2 stroke? BLASPHEMY! Ok so maybe in RC, but everytime I hear a snowmobile with a set of twin pipes and an aftermarket can on it, I get an erection..... :blink:

This is amazing that your making a CVT for this thing, just think of it, unlimited gear ratios! What are you going to do for the secondary?

11-14-2005, 11:24 PM
I'm not sure yet. The plan for the secondary was to make a simple spring loaded setup. I still haven't gotten around to designing it yet though because I still need to trim the gear off of the torsen diff I have.

11-15-2005, 11:42 AM
New goodies! They even tossed in a free pocket knife! :banana:


I messed up the order for the neoprene round belt by ordering one that was 7 inch in diameter and not 7 inches in circumference though. :lol:

Anyway, I think the timing belts will do the trick just fine. They've got much more support than I thought they would, although two of the belts may be too hard of a compound to get any decent grip and the neoprene timing belt may be too soft and wear out quickly. Time will tell.

One thing I need to figure out is how to make a jig so that I can use a dremel and a sanding wheel to put a 20 degree chamfer on the edges of the belts. Right now all the edges are squared off.

11-27-2005, 12:22 PM
I finally got the time to make these today. Roughly 3 hours for both now that I'm finally getting the hang of my lathe. :lol:

I still need to chuck a couple of pieces into the mill so I can machine some grooves, but otherwise the lathe work is done for the most part for the drive pulley. :banana:


Here's how it should look when the engine is at idle:

And when it's at max rpm:

11-27-2005, 03:26 PM
nice work! :chug:

lathe work can take a while, especially making sure the cut your setting up now doesnt screw up the last one you made so carefully.... :banghead:


11-27-2005, 10:15 PM
It'd help if I wasn't forced to take off only .030 every pass and don't have my dial indication setup yet! :lol:

So far I've been eyeballing all the length dimensions using the end of my calipers so I'm led to wonder when that's going to come back and bite me in the butt. :unsure:

11-28-2005, 02:28 AM
I'm still impressed

11-28-2005, 07:41 AM
Impressive for eyeballing it!

01-29-2006, 09:17 PM
Well, I decided to drop the CVT portion of the project for now. It's taking up too much time. So for now I'm testing some steel clutch shoes I made a while back that you saw on the first page. :)

Anyway, I finally got my mill running after owning it for two years! :blink: I think I broke 'er in well. :owned:

I should have cleaned up my work bench before turning on the mill though. As you can see it made a mess of everything that was in the immediate area.

And as a result I have this trick one piece engine mount made!


I still need to mill some fins in it for added cooling (and looks), but otherwise the engine is finally stuck on the chassis. :nice:

01-30-2006, 06:34 AM
great stuff!!


03-11-2006, 07:42 PM
Hot dang, it runs! The track here in town is finally complete so I slapped the final pieces together today to go run with the guys at the track. Unfortunantly I only got about 5 minutes of run time with it, but holy smokes is it quick!

Just putzing around, a quick stab of the throttle will instantly make the car squat and send the front tires a-light. It's ridiculous. :excited: Some thicker grease in the center diff is definently a must.

However! It does need a lot of fine tuning. Right now the steel clutch shoes are way too heavy for the clutch spring. At the moment it won't even fully disengage and easily over powers the brakes. That being said, it's making the car a bit of a pain to drive. I may go to aluminum clutch shoes since the car is obviously light enough, but if I can I'm going to try to run a tighter clutch spring. The steel shoes work amazingly well, believe it or not.

The engine still needs a cooling fan as well, along with a true exhaust system so that I don't keep smoking out the rear wing and maybe get the engine to have a throatier growl. I also need to put some stiffer springs in the rear since this engine is obviously a little heavier than your normal big block two stroke.

However, the input I got was immense! Even though I couldn't even come close to pushing the car, a lot of guys were impressed with how the 4 stroke ran. Of course they all loved the sound the most. :nice:

Anyway, no pictures this time since the look of the car hasn't changed at all aside from some fuel line and a throttle linkage. Videos will be long coming since I need to buy myself a starter box as well. I had to borrow one today to get it running. :cryin:

03-11-2006, 08:40 PM
Can I have the other engine? (Eye's 1/8 monster truck)

03-11-2006, 09:30 PM
Nope, sorry. That's for Quagmire. :P

03-12-2006, 08:36 AM
Hi Max

Sounds like great fun well done for getting it up and running :nice:

I am particularly interested in the clutch issues.

I was thinking of using a heavy duty 3 shoe clutch system but doubling the diameter of the clutch bell and doubling the number of shoes to 6. This will require stronger springs at idle to keep the clutch disingaged but should give the shoes way more bite and less slip when you speed things up.

Thats what I am thinking anyway. keep us posted on how you work things out.

I am watching you now :blink:

Great stuff :nice:

03-12-2006, 11:12 AM
glad to hear you got it running Max! :nice:

Spitfire: I dont think there's room for a double diameter clutch bell - look at the pics further up the page, there aint much room between that clutch bell and the rear brake/bearing support....

unfortunately I dont have much to suggest for clutches(bit of a Nitro N00b meself) other than my previous enquiry about those centax style clutches (from what I've seen they use conical shoes and get pushed forwards rather than just out and as the clutch bell is also conical it gives a larger contact surface per shoe in a small clutch unit...), alternatively if you wanted to use more clutch shoes, why not move the engine back a little and make a clutch that could use dual clutch shoes side by side so if you see what I mean the clutch would be twice as long and have 2x the surface area, but you also have to make or modify the clutch bell to work otherwise it would only engage one set of shoes...


03-12-2006, 12:18 PM
Yea I concede the clearence will be an issue. its allways a nightmare trying to work with existing chassis and layouts etc.

Are you using the same springs from the aluminium clutch shoes for the new steel shoes???
Cos that might be why your clutch is dragging like mad at idle. The springs are being overpowered by the heavier clutch shoes even though the rpms should be lower than a 2 stroke at idle.

Double depth will work so long as there are more clutch shoes fitted ie for more clamping effort you need more force ie same speed but more wieght or same wieght but more speed ie larger diameter.

I am not so sure the shape of the clutch makes much difference. or the surface area.

True cone clutches tend to be very harsh and often dont let go when they should due to the wedge action actuarlly gripping the male part of the clutch.

An increase in the surface area will allow better cooling but unless the shoes have more mass the clamping effort psi will be less so the overall ability to transmit torque doesnt change.
And because we are using a 4 stroke aero motor we dont get the same rpms which in turn means the centrifugal force on the clutch shoes is way less. And to make matters worse we are trying to transmit a bucket load more torque at these lower revs.

I dont see an easy answer without loads of mods.

Maybe Double depth and double wieght shoes might make it reliable. But as Spoon says you would have to move the motor back and make a new clutch bell.

All adds up to loads of work :blink:

Anybody know what the big 1/4 scale car racers use???

Good luck. let us know which way you go :nice:

03-12-2006, 10:23 PM
Yeah, the spring I'm using now is pretty much a normal 2 stroke clutch spring, only on the heavy side. So far I haven't seen any that are heavier. Although I know that at one time Kyosho did make springs for 4 stroke setups.

I can't say I like the idea of a double depth clutch. By then your shoe pins about about an inch long. Imagine the twist that'd be placed on them!

Larger diameters is surely the way to go. Even kyosho did that with their 4 stroke conversion kits. However, the steel shoes I have seem to be working very well. I'm going to give them a final horrah before going to aluminum shoes, that's for sure.

06-21-2006, 09:03 PM
Bit of an update:

I finally broke down and bought a starter box at the grand old price of $91. The good news is that it is huge and can continually turn the 4 stroke over as long as it isn't loaded with fuel.

I may also continue running the steel clutch shoes. The engine has such a low idle that it really isn't a bad thing that the shoes never fully disengage and the brakes are powerful enough to stop the car. I just fear that anything such as an aluminum shoe won't handle the stresses and easily get too hot. Either way, just putzing around this thing has ridiculous torque and has managed to bust loose the glue on two front tires now. I really need to thicken the center diff fluid. :D

I've also begun work on a side exhaust so that it looks like a 2 stroke buggy from the outside. Then I need to make a fan shroud and mount an electric fan in it. After that it's simply a matter of upgrading the electronics and this beats should be ready to hit the track. 8)

06-21-2006, 09:09 PM
Could you drill a hole in each shoe to lighten them a bit, but keep the durability? Balance may be an issue, but it could be done.

06-21-2006, 09:15 PM
Already stuck about 4 holes in each shoe. I'll look into grinding a little metal off next, but otherwise they're about as light as they're gonna get. I suppose something I could do is convert it to use the newer style multi spring setups rather than a band style spring. I think the newer ones can be found in some pretty stiff options. I've already got about as heavy of a band spring as I can get with the kyosho 4 stroke piece.

07-14-2006, 10:02 PM
Welp, I have good news and bad.

The good news is that I got the buggy running well enough to actually race it. Even better is that it kept up with the 2 stroke buggies coming out of the hole!!! :nice: It does, however, top out way too early, but it was a good shakedown none the less.

That night I came to two very important conclusions. The .21 carb is way too big for the four stroke (as if that comes as any surprise). I had some trouble with the buggy flaming out when throttle was applied too quickly from low revs. The carb was letting the engine run too lean, but richening the high end needle far enough to combat this led to the engine running too rich to really stretch it legs, effectively making the buggy rather slow.

The other problem was the exhaust. I had built a setup to pipe the exhaust to a side pipe like a normal two stroke buggy. This was mainly to keep corner marshals from burning their hands on oddly placed exhaust pieces. This worked for a while, but unfortunately it managed to blow a silicone coupler apart. I don't know if the pipe I had was doing a tuned pipe effect and pressurizing the exhaust system or of the coupler couldn't handle the increased heat over a two stroke. None the less I need to find a better solution. Likely with metal couplings rather than silicone. The exhaust on this thing gets so much hotter than a two stroke that it'll melt anything plastic that comes in contact with it.

I think what I'll likely end up doing is running a simple straight exhaust over to the side. The four stroke is a good deal quieter than it's two stroke breatherin and with a straight exhaust inches from the head, it was still quieter than all the other buggies! :huh:

I finally got some more time to tinker with it today and made a simple carb adapter that bolts on (rather than clamp) and holds a OS 12LD carb onto the back of the head. This setup is a little bit more compact that before, however, there is no flange to hold an airfilter in place. Hopefully I'll find a good solution before the races tomorrow.

None the less, it ran a good deal better today. I was able to sustain a much lower idle with the buggy and bottom end response became a good deal more crisper. However, my starter box burned out the only two four stroke glow plugs I had so my tuning session was cut short and I wasn't able to work the low and high speed needles into a good and balanced setting. From what I can tell, it's still running a bit rich on the high end. Could be rich on the bottom end as well. I've leaned it out a good deal on the bottom with good results, but then startup becomes a bit of a hassle with it and I have to back it out around a half turn.

Something interesting I noticed today while I swapped over the modified cylinder head (for the 21 carb) back to the untouched head was that one of the valve spring retainers had literally been HAMMERED APART! I guess the valve float was so extreme with this engine that the retainer for the intake valve couldn't handle it any longer. For now I'm going to run the same setup for the race this weekend, but I definently need to find a way to install stiffer valve springs or incorporate a way to limit the maximum rpm of the engine. Amazingly enough part of the retainer had wedged itself into the groove on the valve and managed to keep it all together for god knows how long.

Annnnyway, I'll see if I can FINALLY get some videos and updated pictures of the buggy tomorrow. I'm sorry that this project has been drug out so long. Time has been a little short for me lately so progress has been slow. The good news, at least, is that it is coming along.

Now, as a final thing. Does anyone happen to know where I can find a crank shaft driven cooling fan like what Kyosho equipped on the QRC vehicles (wild dodge ram, some sort of beetle, and a van) or the nitro blizzard? I've been toying with a few setups, ranging from pc fans wired to batteries, or modified pc fans to be driven by the crank. The electric setups are too heavy in my mind and the PC fans aren't made from a durable enough plastic. For now I've just been running the buggy and making sure to keep it moving, but as it sits, it usually hangs aorund 250 F and tops out around a horrendous 300 F if the buggy sits for too long. :blink:

07-15-2006, 04:48 AM
sounds good, its bound to have a few 'teething troubles' like the exhaust coupler disintegrating....

as for the fan, there is a new Nitro blizzard coming out - the DF300, which should still use the fan unit, might it be possible to adapt this to your engine? I mean you know its durable enough for a .15 engine in a tank or small MT, and its not like the 4stroke will run it too high RPM...

I mention the new blizz cuz it may be easiest to get spares whilst its new (being kyosho)...


07-15-2006, 11:23 PM
Yeah, sadly tower hobbies no longer carries kyosho parts so I can't just look back to the blizzard and get pieces (or pictures) for it.

Sadly, I'm afraid I lied to you guys. With some carb problems today I couldn't get any photos or movies. I should be able to at least get some pictures tomorrow night though.

It did pretty damn well today at the races. I initially had a problem with the engine vaporlocking once it was warmed up, and it liked to stay around 280F with no cooling aids... not too bad, not too great. I had a heat isolator that came with the carb and that seemed to help out a lot. It did still flame out every now and then, but at about 4 minute intervals. Restarts with a hot engine were a real pain, however, as it wouldn't fire up on vapor and I would have to richen the low end immensly to get it to even pop.

However, while it was running, it was FAST! My friend Darren, the track owner, made a comment that I was the ONLY person he didn't pass and he was the fastest out there with his Jammin' truggy. I'm happy! :D

07-16-2006, 01:06 PM
cool! ^_^

Kyosho are setting up their own distribution, trying to mimic Tamiya America:


their shopatron link has some parts on it tho I couldnt find the fan unit under blizzard spares(seems to be only cosmetic parts listed, wtf?? :huh: )


07-16-2006, 07:37 PM
Yeah, I was looking there, but unfortunately since they have very few photos of parts... I'll find something though, it'll just take a bit of time and research. Thanks for the lead!

07-16-2006, 08:24 PM
Here it is in all of it's post practice glory!:banana:

The engine: (note the blued clutch bell)

The new carb:

The old exhaust system:

And the broken valve retainer (right side). :huh:

10-16-2006, 09:57 PM
Yet another teaser picture. After a bit of deliberating and seeing how the 4 stroke performs, I think it'll shine much better with a little more... traction.

That being said, I've decided to join the local truggy racers and give them a little show. Right now I have a set of Sportwerks a-arms up front and some Jammin a-arms will go in the rear. The caster is a little too much for my tastes in the front, but I'll test it first to see how it works out.


10-17-2006, 06:47 PM
Do you need the fan anyway?I have one somewere in my shop from a Quick Field Baja Beattle.that I destroy.LMK if you still need it.

10-17-2006, 07:21 PM
I could still use a fan, but I think I may have figured out a way to increase the cooling surface area of the engine.

Either way, what do you think the shipping would be to send that to the states? I see that you've listed yourself as being in Puerto Rico and I haven't had an experience with receiving items from other countries.

10-17-2006, 07:33 PM
Pm your address to calculate shipping.This is for free

10-22-2006, 07:52 PM
I've had a little time lately and it turns out that bringing the mill and lathe to school was a good call.:banana:

The piston skirt was shortened roughly 5.6mm and a 2.5mm cut was done on either side of the piston. The skirt may be a little on the short side, but the cold fit in the cylinder liner is good and unless everything opens up too much at running temps, I can't see piston slap as a problem. The connecting rod has a 1.5mm cut (half the thickness) down the middle done by a 3/16 inch ball end mill.

10 grams approximately, not including the piston ring (snapped it off the spare piston).

And the stocker... 12 grams. So that's a 17% decrease in weight.:blink:

Hopefully this setup will hold. If not, I'll just have to leave a little more material in the next set! :lol:

10-23-2006, 02:37 AM
I hope so too, that looks like a lot of material to remove! :D

10-24-2006, 07:14 PM
More engine fun. :chug:

I managed to source out some stiffer valve springs from a source that will remained un-named for now.

And they fit perfectly! Surprised the heck out of me considering it's a metric engine with quarter inch valve springs.:huh:

Old Busted Hotness
10-24-2006, 07:41 PM
Max, keep an eye on the camshaft. Since you're relying on splash lubrication, cam wear could be an issue with the stiffer valvesprings. It'll definitely get you more useable rpm though, assuming the piston holds together. I'm a bit worried about the pin bosses.

10-24-2006, 08:10 PM
Very good point, I hadn't considered that. However, I am doing something that OS did with the car version of the engine that I think will help a great deal. The airplane engines have a crankcase vent in the back of the engine while the car version has one located behind the front crankshaft bearing. This should place a good amount of lubrication in the cam area and should hopefully keep everything slicked up.

The pin bosses are the biggest worries I have with the piston. However, it just may hold considering that the amount of material in the pin bosses is the same if not more than at either end of the connecting rod. A big trick here is that the pins are largely supported at the top where all the big pressure will be during the power stroke.

Old Busted Hotness
10-24-2006, 08:25 PM
Pistons and rods don't fail during the power stroke. It's the top of the exhaust stroke that kills 'em, when the piston has to reverse direction and the material in the pin boss area is in tension.

Funny Car and Top Fuel engines (which are rebuilt after every run) have their rods measured, and typically shrink about .002-3 per run, due to the extreme pressure exerted by the blown nitro (running a 2:1 mix doesn't help, either). The rods are thrown away when they shrink by .008

Gasoline engines (and model nitro engines) suffer from rod stretch, but lightening the piston will help there. Did you take any weight off the crankshaft's counterweight? If not, you're in for a bit of a rough ride.

10-24-2006, 09:21 PM
I haven't rebalanced the crank yet, but I intend to. Either way, it is impossible to perfectly balance a single piston engine.

Old Busted Hotness
10-25-2006, 04:37 AM
True dat :lol:

Slyp Dawg
10-25-2006, 02:38 PM
nice work on those pistons! tho if these pistons fail, leave a bit more material around the pin bosses and do a little milling on the inside of the piston (between the connecting rod and the inside of the piston itself, if that makes sense). also, I suggest getting another con-rod and knife edging it (literaly, make it so that it can cut something, then round the edge off with a sanding wheel. most knife edge conrods I've seen have had a knife edge and then a flat spot where the sharp edge should be)

10-25-2006, 03:39 PM
Yeah, I already have a game plan if the piston should fail and it'd involve leaving .5mm more than before to leave a little extra material behind. If it breaks again, I'll make it 1mm thicker. Obviously this will continue till I find something that lasts. I just need to hope that it doesn't waste in other internals in the process.

Concerning the connection rod, I would have knife-edged it, but that would require some tooling that I can't make here while I'm at school. The main intent here is to reduce the reciprocating mass anyway, not cut down on windage losses.

11-08-2006, 09:14 PM
Hey Maxzillian! Good to see that you're still pounding away at this project... Have you considered using a heatsink from a CPU for helping radiate and conducting out some of the excess heat of the engine? Granted, a fan would help also, but the two in tandem might be of great use...

Perhaps even a heatsink with heat pipes might help out, through i question what the upper end thermal limit and vibration resistance of one of those delicate things meant for desktop computers that don't move would be...

11-08-2006, 11:09 PM
It lives! :D

Yeah, I have one engine block that had the side fins machined away for heat sinks. I just need to get my hands on some thermal paste epoxy to affive some heat sinks to the block or find a means to mechanically secure them.

In other news, Leorosa was kind enough to send me a fan off a nitro blizzard for the cost of shipping so at least have a fan that should move some air while being durable enough to handle the rigors of a race.

I actually considered stealing the heat pipe off the passive cooler I had for my video card, but as you said, durability may be a concern. Also, aren't heat pipes typically filled with mercury?

Edit: I did some research on heat pipes and found all the info I needed. What I have may or may not work since they are supposedly tuned for the application, but it is worth a shot since I'll have an abundance of chassis space beside the engine now that I removed the radio box.

Slyp Dawg
11-09-2006, 05:27 AM
Weeb! glad to see you back on the boards! for the cooling system, I suggest getting some brake line and bending it around the engine block, then running it to a water pump, powered by the engine, and then through a radiator. that should be choice for this application, tho low speed engine cooling may be a problem

11-09-2006, 09:17 AM
Water cooling has crossed my mind many times, but weight is always a concern here. The four stroke is already considerably heavier than a comparable two stroke.

Slyp Dawg
11-09-2006, 02:41 PM
but they also put out more torque than a 2 stroke. it may even work to use fuel tubing instead of brake line to cut down on weight. ofcourse, you could just cut a larger hole in the body and not run at low speeds much :lol:

11-09-2006, 05:24 PM
Water cooling probably wont be very effective unless you could actually get it in and around the cylinder. I was thinking some sort of forced induction would work well, and since your racing, low speed cooling shouldn't be too much of an issue. I'm thinking incorporating some sort of scoop into the body to route air in and around the engine and an exit out the back. It would be most effective to keep the air around the engine, maybe some tubes or lexan to channel it in and out would work best. At the rear you could place an exhaust fan to draw the air out. I drew a quick little diagram to more clearly represent my idea. http://img176.imageshack.us/img176/5710/ideacz7.jpg

Great work by the way!

11-10-2006, 01:58 AM
Liquid cooling is easy you just need a marine head, a pump, a tank, and a radiator. I liquid cool a maxx back when they first came out. It would be easier now days since they make small radiators for computers.

Of you could try this, take a small generator/electric motor, put a pinion gear on it and mount it so it spins off the spur gear, the electric motor should produce electricity, which in turn could power a fan, for extra cooling.

11-10-2006, 08:19 AM
Wow, many ideas! Thanks for the help, guys!

In all honesty, liquid cooling is not the way to go with this thing. Weight and reliability would be too much of an issue, not to mention that I can only cool the sides of the cylinder since that'd be the only place I could place any cooling blocks. There was a marine version of the original FS-40, but nothing for the newer Surpass series I'm using.

Partsbreaker has it about the best. I do intend to use the Nitro Blizzard cooling fan as it doesn't add much weight at all and is driven off the crankshaft. It may get a shroud and it may not. If the fan alone can get engine temps down to about 240 on a 100 degree day, I'd be happy.

At one time I did have a PC fan on the engine, but I wasn't happy with how much air it was moving on a 9 volt battery. Not to mention I was concerned about it busting apart from the hard impacts a truggy sees during racing. At one time it was converted to a crankshaft driven setup just to test the idea, and that seemed to work the best. Naturally the fan didn't last long, but it proved the concept. :lol:

11-10-2006, 10:46 AM
Have you considered using one of the ducted fans from an backyard flyer aircraft? Some thing like one of those GWS units, for instance. Those can take a real pounding, and they're cheaper than CPU fans in some respect.... they're simple brushed DC motors too, so they're inherently stronger than those little muffin fans....

11-10-2006, 03:20 PM
Have you considered using one of the ducted fans from an backyard flyer aircraft?

Already covered! :nice:

11-10-2006, 03:24 PM
Wow, that looks even better than the ones i had in mind...


11-10-2006, 03:31 PM
Thanks Slyp :) It's good to be back... You mentioned brake line and i just thought of something related yet unrelated... using a tubular chassis as the water input/return pipes for a radiator to the engine block.

Oh well don't mind me, i'm just babbling again :)

Weeb! glad to see you back on the boards! for the cooling system, I suggest getting some brake line and bending it around the engine block, then running it to a water pump, powered by the engine, and then through a radiator. that should be choice for this application, tho low speed engine cooling may be a problem

12-21-2006, 10:22 PM
A bit of an update:



The engine has undergone it's "final" build. I moved the case drain towards the bearings to promote the movement of the fluids towards the cam and bearings, and to hopefully reduce the amount of oil shot out of the front bearing. This dumps into a simple fitting in the elbow of the exhaust.

I removed the stock radio box and built a radio tray using some machined stand-offs and some sheet aluminum. Luckily enough I got away with using holes already in the chassis. The battery is held in place with some cushioning foam, I can assure anyone that it won't go anywhere. Quick, simple, effective. :)

The front suspension is finally "done." I don't like how the tower extension looks, but it does the job. Right now the steering linkage limits travel the most at an acceptable 2.25 inches.

I'm hoping I can get it rolling before the 18th rolls around, by then I have to head to school and I can focus on other things such as getting a body prepped and finding the fail safe unit I lost. :(

12-28-2006, 06:59 PM
I finally got it fired up today. I had a hell of a time for about 2-3 hours trying to keep it idling smoothly and running well until I finally got the bright idea to pop the pressure line off the muffler. What do ya know, 10 times better! Turns out that the loctite I used to secure the nipple had beaded up on the inside and blocked it off. Unfortunately by the time I got that sorted out and had it tuned, the receiver battery died. :P

But, I did run about half a tank through it while it was running right and I just have to say... wow! It's not lightning fast, but it sure doesn't have a bit of trouble moving around. I finally got the clutch dialed in to where it disengages at idle and the suspension worked surprisingly well. Most surprising of all, the engine didn't blow apart! :lol: It definitely has a fair increase in maximum RPMs, but I don't know if I'm still floating the valves or not. I'm hoping it's running out of carb to run on so I can at least save the valve train.

Because of the large amount of caster, I was concerned that it would have trouble turning, but so far it feels great and is nice and stable. Now I just need to mount a body, buy some tires for the MT wheels I have, and take it out to a track to dial the suspension in. :D


The drive shafts were lengthened using sections of 1/4 inch steel rod. A 2.75 inch long piece was cut out, then had 4 or 4.5 mm holes drilled a half inch in either end. The halves of the original drive shafts were then welded together to form the 1.75 inch longer drive shafts needed for the longer suspension.




02-18-2007, 03:55 PM
The weather finally permitted.:banana:

First off, I finally bought some truggy tires for it about a week ago and have been waiting for the temperature to slowly rise. The second it touched 50 today, I was out the door!


Overall it measures out to be 16 inches wide with a 13 5/8 wheelbase. Right about where I want it. The dry weight comes in just shy of 9 lbs with a 46/54 balance.:chug:

Now, as for the video...

Just to narrate a bit, the video starts with me firing up the engine at a nearly cold state around 100 F. I then try to crank the engine idle as low as possible until it eventually stalled out. The first shot of it accelerating was after a 60 second idle period and the rest is just me dicking around. Enjoy!


03-21-2007, 04:34 PM
How has nobody replied to this in over a month? :huh:

That thing is awesome!!!! I love the sound of the 4 stroke pullin hard.

Nice job man:nice:

04-11-2007, 10:01 PM
Beats me. It's been another month and still no updates, but thanks for the compliments! :lol:

05-02-2007, 07:04 AM
I know it's kind of late but I have been out of the site for a while. Man that is awesome. I am a noob to nitro and actual engines but thats a four stroke so it runs on gas right? Whats the top speed like? That is an amazing trugbug lol. Do you actually race it? If so how does it do. Sorry for the slew of questions but I am in awe! I think you made me get a truggy lol.

mt2 destroyer
05-03-2007, 05:12 PM
im going to have to get a 4 stroke for my mta4(mgt) now as it sounds a load better

05-04-2007, 09:42 AM
I know it's kind of late but I have been out of the site for a while. Man that is awesome. I am a noob to nitro and actual engines but thats a four stroke so it runs on gas right? Whats the top speed like? That is an amazing trugbug lol. Do you actually race it? If so how does it do. Sorry for the slew of questions but I am in awe! I think you made me get a truggy lol.

It still runs on the usual r/c car two stroke blend. Lubrication in the engine is provided by any unburnt fuel/oil that seeps past the piston ring and into the crankcase.

I'd say the top speed is around 30-35. Maybe faster, it's hard to gauge how quick something this small is. Obviously it's not incredibly quick, but it's not made to be. This truggy is built primarily for short tracks.

I haven't been able to race it yet. I'm waiting for my semester to end so I can head back home where all the tracks are. Then I need to toss a cooling fan on the engine, buy a body, and do a final tweak/tune. Then it'll be ready for the races.:chug:

07-13-2007, 08:18 PM
So I didn't want to work on the real car today and decided to fire up the mill again. Just to see if I could still wield a cutter. ;)



This will sit over the front of the engine, hence the large opening at the bottom. Assuming I don't get dragged off, I should be able to drill the chassis tomorrow and hopefully have it ready to test and tune on the track that we'll be building in town on Sunday. :)

07-15-2007, 04:37 PM
Mounted and works like a charm. :D The highest I saw the engine get yesterday in 95 degree weather was about 190-220 on the carb side of the head (I monitor this side since the head temperature determines whether or not the engine will vaporlock.)

Eventually I will need to install bearings as the fan has about a 50-75% overdrive on the engine which means it's turning from 25000-30000 rpm. Fast enough that at one point the fan pulled itself off the hub. :lol:

I'm thinking I may machine an aluminum hub with an e-clip to retain the fan as well as house a decent set of bearings. However, for now the setup works extremely well.




07-20-2007, 09:52 AM
wow i just came across this and read.... incredible... it is my dream to put a 4S in a machine and will be a projet that ill undergo soon, is money permits, just gotta finish everything else im making..

great stuff.. any more pics of the body?

07-21-2007, 05:00 PM
Body is the last thing on the list of things to buy. :lol:

Old Busted Hotness
07-21-2007, 06:46 PM
You may have covered it earlier, but why use a 2-stroke pipe?

07-22-2007, 07:52 PM
How Much Power is that fan taking from the engine? O and good job :nice:

07-23-2007, 07:10 PM
You may have covered it earlier, but why use a 2-stroke pipe?

The two stroke pipe was more of a muffler. It came off a duratrax buggy so I wasn't too worried about it trying to pulse the exhaust back into the engine. ;)

Either way, it's now a straight pipe setup using quarter inch brakeline. Soon to be 5/16. Now the noise is about on par with your average two stroke.

How Much Power is that fan taking from the engine? O and good job :nice:

Beats me. Not enough to concern me. ;) And thanks!

07-24-2007, 07:32 PM
Ok cool