Mr.modified's GTR Four Zero

General Idea: Basicly what i'm going for is a purpose built race car type look. What i've been intrested in recently is group b rally cars from the 80's. Anything not absolutely nesseary won't be used. No battery or starter. Things that aren't structural but still need to be there, or are there mostly for looks, will be made extremely light. I'm thinking plastic mesh grill, fiberglass fenders and hood so light that they flex just setting them on the tractor. Dash and seat mount will be thin aluminum over an electrical conduit tubing structure. I was going to try making the rear look like a Lancia 037 rally car, front will just end up however it fits best. Anywhere that I have to use heavier steel parts, like rims, steering u-joint, or cam gear in the engine, I'll attempt to lighten them as best as I can without comprimising too much strength.

Chassis: 1-1/4" square steel tubing will make up the frame. Engine and trans will sit on 1" square aluminum cross members bolted to the frame rails. Full lenght aluminum skid plate and Rear axle will be 3/4" solid bar in pillow block bearings. Rear brakes only, via a go kart style band brake. Front end will have Independent front suspension. Nothing too extreme, maybe 2" of travel. 3/4" steel tubing A-arms with coil over bicycle shocks. 6" standard lawn tractor wheels front and back. Either sears or simplicity spindles will be used. Seat wil be hinged on a bicycle shock with the rear axle solid to the frame.

Engine: 40CI Briggs and stratton opossed twin, started out as a 14hp. Dual techcumseh adjustable butterfly carbs, headers, maybe some light port work and lightening of some stock parts like the valves, wrist pins, and cam. Possible gravity fed oil cooler. To save weight, I won't be using electric start, but I will keep the charging coil to run lights. Rope starter will need to be bolted to the crank.

Transmission: Peerless 700 5 speed. Delete reverse, oil fill, add seal/vent. Going to support the input shaft and probably beef up the case with some type of bracket which will double as a scatter shield.

Body: I am planning on keeping a tractor appearance. My idea was to have rear fenders one piece and hood and front fenders one piece. I was going to use fiberglass and keep it pretty thin and flimsy. They would probably be pinned on and lift off as a unit. Probably some ultra light plastic mud flaps behind the rear wheels.

Lancia 037 Rally car


Most of the parts...


Aluminum go kart steering wheel, some used heim joints, water pump pulley should make a nice brake drum.

Uh oh, do I smell billet parts? Yea know, the flywheel is pretty dang heavy. Much easier to love my 46ci around without it on. Weight and power, might need a sponsor.

wow will most definitely have ya hands full on this one

I'm thinking probably not on the billet engine parts, just because I think I would start with a larger displacement engine to start with. I'm possibly thinking of a turbo setup for a future build. And sponsorship? I've got my representatives speaking with people from castrol... We'll see how this turns out, I hope putting the frame and suspension together will go smoothly, then I can spend more time on the fiberglass work.

This oughta be cool... Good luck!

some one was going to do a 4x4x4 4 wheel drive, 4 wheel steer, who was that? was in you?

No, 4wd wasn't me, although that would be neat. And while I'm thinking about it, GTR is supposed to stand for Garden Tractor Rally. The four zero is for the engine size of course...Don't want anyone thinking I just came up with some random letters or anything.

OK good luck!

Did some measuring and found out that 40 and 42CI opposed blocks are pretty much the same. The 42 is basically just a stroked version of the 40CI engine. Since I have a decent 42CI crank and rods to use, might as well upgrade. My 42CI block's cylinders are pretty beat, which is why I have to use the 40CI block and pistons. Didn't look too close to see if webbing is beefed up on the bigger engine yet, but I'll probably swap over either way.

Pics?

Judging by last years Baja Sears this should be great.

Couple of pictures from when I first got the engines about 6 months ago maybe. This is the 40CI block, was half full of water. It was in a guys back yard in a plastic crate. Looks good wear wise on all the surfaces, just some rust here and there.


Inside the 40CI block when I first took it apart.


Picture taken as of this date... 40 on the left, 42 on the right. I plan on using the 42 engine as a mock up while i'm working on the frame. That way I don't have to move around a heavy engine with flywheel, crank, ect. Also, If I want to weld something while it's there, I don't need to worry about weld splatter or anything since the cylinders are junk on the 42CI anyway. Meanwhile I can put the good engine together. Cleaned them both up a little. Good block is ready for test assembly to make sure 42 crank fits ok, then I'll probably need to go buy some gaskets, piston rings, and hone the cylinders. Pics of frame contruction soon...

Working on finding correct bearings and stamped pillow blocks for rear axle. Started cutting frame rails. Having a scale drawing to work with helps line things up a little as long as you don't forget stuff that will be in the way later. Once I have a rolling chassis, I'll just fit everything in where I can.


Mocking up wheelbase, width, and rough engine location before I get too out of hand cutting the frame rails. I've mocked it up before, but I wanted to make sure I didn't miss anything. Engine will need to be back far enough for the front suspension to clear.


Only about an inch or less wider than redline's springfield mini tractor and a little longer. It'll be intresting to see how front to rear weight distribution turns out. My goal is to have the frame welded up by friday of next week. Front coil over shocks are on order, so I've gotta get the frame done, rear axle mounted, and then start on the front suspention. No idea on ground clearance, maybe in the range of 4-6".


A bit cool at the GTR research and development facility.

Cut my frame angles with this delwalt chop saw deal. Doesn't always cut exactly where you want it, the clamps are kind of loose fitting. If your careful, you can get close. Better than trying to get it straight with a hack saw though and at least you get close to the angle you want.


About what we're going for. Stuff is relatively thin, 16 guage.


Clamped the sections to a piece of angle iron that looked pretty straight, then double checked with a straight edge. The box steel itself isn't exactly perfect and the edges get warped slightly when you cut them. Overall, I think everything so far came out good.


High tech holding device.


Decent enough looking weld. Nice when your not welding rust.

Wait, what happpened to the lazer cut pieces that were percicly drawn up on CAD, and then tig welded with a water cooled torch?

I guess this will have to do...

Come on, I told you, the thing has got to be all hand built... They didn't have all that fancy stuff back in the old days. Once the main frame is done, next step is to mount the rear axle, then a arms up front, then mount shocks. So I'll need to figure out gearing pretty quick, because I'm planning on a one piece rear axle assembly. Mostly for easy construction. Bearings, brake drum, and drive gear will be trapped on the axle with the rims permanently welded in place on the ends. I may weld hubs onto the axle and bolt the brake drum and gear on. Then you could cut them off and replace with split ones later if needed. Any suggestions on what kind of speed I should gear this for? I'm thinking around 40mph max would be fine and give a good range for both trails in the woods or open dirt road running.

Yes it is. Much easier to deal with than having to grind a bunch of rust all the time. I can actually take close ups of the welds this time...

Main frame is completely welded, got the cheapo coil over shock in the mail, ready to hone out the 40CI opposed block so I can test fit the 42CI crank ect. I figure I'll test assemble it without rings on the pistons. Then once everything is ok, I have to order gaskets, piston rings maybe, and stick it together.

750lbs each. Should be able to mount them at a good angle, hopefully they aren't too stiff.

Frame completed. Wired the shocks there just to see what it's going to look like.


Rear corners. Had trouble making 45 degree cuts. The more angle you have, the more it pulls the wheel over on the grinder. Front two came out ok, but I decided to just weld them square in the rear. Cut out square plugs and welded them in so the frame is sealed up.


Shocks will probably need to be at a steeper angle than this. I'll see how it goes.


Also honed out the cylinders on the engine.

Wow mate! You`re getting on far better than me. I haven't even started my frame yet. Good Luck!

Dang thats beautiful. nice welds

Thanks. It came out pretty good so far. Probably the first time I bothered doing that much measuring. Usually I just hack job it. I think everything is pretty close to being flat and both sides parallel. The welds come out pretty nice if you don't start and stop too much. I tried to do each side with one pass if I could. A few connections weren't angled quite right and I had to fill in a slight gap. Once I go to make the tubing structure up front to support the shocks, I was thinking of using electrical conduit. The only problem is that paint doesn't stick to galvanized too well in my experience. I'm not sure if I should just use heavier steel tubing, sand/grind off the galvanized, or try finding other thin non galvanized pipe. Keeping the weight down is top priority, and with the amount of bracing I was thinking of doing up front, the thin conduit should be adequate strength wise. I bought some steel tubing for the front suspension arms, but it's probably three times as thick as I need for the shocks.

Use the conduit, and then clear coat the hoops in paint so the welds dont rust... Viola!

That's a neat idea, but I don't know. I was thinking of painting the whole frame a dark grey color and of course then the tubes wouldn't match. Or I could clear coat the whole frame, thought about that too. Think the clear coat is about as durable as paint is? Not sure exactly how the tubes are going to end up, but I want to end up with tubes connected just behind the Z in the frame. In other words, kind of cage that front narrow section where the front suspension is and brace it back before all those welded angles. Don't want any frame bending when you go over a jump and land on one front wheel...