Mr.modified's GTR Four Zero

redlinemotorsportts wrote:

Im willing to bet the arc flywheel is lighter than 18lbs. I mean, aluminum is aluminum, and it for sure will spin a engine up faster with one on.

Im tellin you man, ditch the opposed if you wanna save weight! Drillin' in a shifting arm?

I don't have a billet flywheel here to weigh, but all I know is shipping weight listed on their site is 18lbs. Looks like the whole thing is a lot thicker than a stock flywheel. Aluminum is almost 1/3 the weight of cast iron, but the flywheel still needs the magnets and that adjustable part for timing probably adds some weight. Maybe they add weight on purpose too.

I'll have to check the weight of the opposed and see how it stacks up against singles. Just what engine would you suggest? I don't have too many engines around that will put out close to 20hp to use. Not to mention the opposed will sound cool and fit in the frame pretty nice.

And as far as drilling holes in stuff, that shift arm is just the beginning of my super weight savings program. Need I remind you of the Porsche 917 balsa wood shift knob again???

"But an engine is nothing without a body to put it in, and fortunately, the 917 had an impressive one. It featured a lightweight aluminum frame that weighed just over 100 pounds (45.4 kilograms), and included a variety of weight saving measures like a gearshift knob made from balsa wood. The body itself was made of fiberglass"

Now the ignition key of the 917 is pushing it too far. Of course they probably did it for a joke more than anything.

Working on cleaning up to casting edges in the ports. This is an intake port. I'd like to fill the bottom a little, but I don't know what's good to use that will hold up. I've heard of people using JB weld. I guess some type of fuel resistant epoxy would stay in there if I got all that carbon cleaned out. Wouldn't want a big piece of epoxy getting past the valve and jamming through the top of a piston.


The matching Tecumseh carbs that I plan on using. They don't look super bad inside. Exactly the same carb except one doesn't have an adjustable high speed jet.


I bought a high speed jet for the older carb, so now all I have to do is clean them out and assemble. My idea is to weld up some short manifolds, probably about 2" long. Make my own air filter "housing" from thin aluminum with a foam filter.


Another thing I was thinking of changing was the location of the spark plug in the stock heads. I don't think they are in the most efficient place in the sides of the heads and behind the intake valve. I might use the two heads from the more beat up engine to do some experimenting. I think the main reason briggs and stratton put the plugs where they did on opposed heads is for clearance, not because it's the best place to put them. I should get some stuff to cc the heads if I'm going to grind on them much, otherwise both sides won't match.

i had a similar idea on filling the valves bowls there with something so it would be a straight out smooth surface so it would work hellova alot better then porting it and the edges ect but im lost as well i know jb weld would work ok for a bit but like on my tiller i used some on my 3 hp tillers coil where one of the bolts broke off so i used it to hold it on and from the vibration and heat it didnt last too long 2 seasons of tilling was it maybe 7-9 hours total

I know a guy with an aluminum welder. Maybe If I stuck a junk valve in the guide so no weld splatter or anything gets in, you could just fill it in. At least it would be permanent that way.

o yea that would work pretty dang on good then!!

So to save weight, I bought the super budget stamped pillow blocks vs cast iron. They probably would bend and flex on their own, so I'll have to weld in some gussets. I would say they're a little heavier steel than exhaust pipe. Here they are under the frame which would be easier on the stamped bearing holders, but it makes the center of gravity way too high. The opposed is going to stick up pretty high as it is. Could have Z'ed the frame to drop it, but I didn't want to mess with that may cuts and angles.


With the frame on top, you get a little more than 8" of ground clearance.


Frame underslung gives you about 5" of clearance. That should be plenty for some pretty rough terrain given how short the wheelbase is going to be. Obviously, your not going to be in the woods with it, but rough trails or rough gravel roads shouldn't be a problem.


This way the frame will be hanging off of the stamped pillow blocks. I think once I brace them up a bit, they should hold up ok. There will be a third bearing in the center next to the drive gear, I'll add an extention off the frame to mount it.

I know you probably already know but some may not, It helps to drill slight indentations into the shaft for the set screws on the bearings. This helps to keep the shaft from sliding through the bearings. Just my 2¢

Actually, I was going to weld a washer or something onto the axle to hold it since the bearings will be trapped with my setup anyway. I suppose the set screws might be enough to hold it if I put some indentations like you said. I guess I could try just relying on them first and weld something on later if they don't hold up. All my simplicity 5010 has to hold the front wheels on is a collar with one set screw, so I guess with two screws each in three bearings, that should be enough to hold the axle in place.

I can see flames coming from exhaust and stones flying from rear tires. Excelent idea me likes.

And don't forget half the rear fiberglass fender flying around in the breeze from the trees you slid into on the last turn.



Guess your from finland, ever see much rally action before? I guess there is some rallying in the united states, but as far as I know, mostly on an amatuer level and I don't think it's too popular. Too many people complain about everything here I guess. Not much shutting down public roads in the U.S. for any kind of racing really since the early 1900's.

Hopefully I'll have all the pillow blocks braced up tommorrow.

From Finland yes. Seen rally action yes.

Sorry about writing offtopic. I am from middle Finland so about 20 miles to closest world rally action. Every summer here is world rally competition neste rally finland. I have not seen groupe b rally cars but maybe I will go to see some historic rally action. Under 50 miles from my home have lived or lives big rally names like Juha Kankkunen, Tommi Makinen, Harri Rovanpera and Mikko Hirvonen.

I will be watching this topic closely. Nice work so far.

That's pretty neat. Nice to live close to things like that, makes it a lot easier to get there.

So... I welded up two of the three pillow blocks. Took a little longer than I thought it would. I think this probably falls into the category of "seemed like a good idea at the time." I guess it's not all that bad. We will see if they hold up or not. The bracing should be a big help. If they bend too bad, it's not the end of the world. I can always convert to cast iron pillow blocks later if I need to. I primed the one, figured I would top coat with grey or silver so when paint chips off the galvanized parts, you won't notice as much.



The original and modified versions. The ones I welded up look a little rough as far as the braces being the same size. The problem is cutting the pieces out, which are only about the size of a quarter and fairly thin steel. Tough to hold in a vice and cut them without bending. If your cut isn't right in the perfect spot when you start, it's pretty noticable since your working with such a small piece.


Started working on the exhaust ports. I've read the exhaust ports should be about 95-100% of the exhaust valve diameter. Probably talking about high rpm stuff of course, but I figured it's not going to hurt much either way to have the exhaust port too big when your headers will be larger than the threads. The most important thing is...it looks cool.


One exhaust port with pipe threads removed. Decent increase in diameter. Like I said, who knows exactly what changes help what. All of your performance books and junk are dealing with much higher engine speeds where sizes and shapes of things are more critical. So your kind of guessing as to what is going to help at fairly low lawn tractor engine speeds. My theory is that the intake port has more effect on things on an engine as "de-tuned" as these are. You could play around with things if you had a dyno and the patience.

Started working on one of the junk cylinder heads to move the spark plug out into the middle of the combustion chamber. Carefully cut the fins and then broke them out of the way with needle nose plyers. Just needs to be wide enough for a plug socket.


Marked out about where the plug will be and started cutting down what's left of the fins.


Now I can drill a hole and tap to the correct size, then try to get a flat enough surface for the gasket to seal. If it works out ok, maybe I will do another one and use them on the engine. If not I can use the stock heads. Takes quite a long time to cut the fins out of the way and flatten it off. I think it should be thick enough for the threads of the plug. I checked a head from a briggs 400cc single (12hp maybe). The four head bolt holes around the cylinder are the same, but around the valves are far off enough where you can't just drill new holes in the single head to make it fit an opposed. The holes would be right on the inner edge of the gasket surface. The original plug hole will be plugged off with a steel billet.

You can always use another spark plug to fill old hole just for testing.

Got some tips for porting for you. I'll do the exhaust. It all comes down to your target rpm's, for low to mid range rpm you just want to clean up the bowl area with attention to the short radious, keeping the runner small and just cleaning up the high spots, the idea is to have the gasses move fast through a small pathway which will help draw in fuel/air on the overlap of cam. Mid range rpm you want to open up the bowl and runner evenly with attention to the short radious so when the exhaust valve opens, it will fill the bowl and then through the runner at ofcourse a faster speed, which in turn will help draw in more fuel/air on the cam overlap. At high rpm, open up the bowl with attention to the short radious with the runner opened up a little bigger then the bowl, this will establish flow direction and increase suction the most for the fuel/air charge on the overlap of cam. For extreme example of mixing up the port job, if you do a high rpm port job on a low rpm exhaust port, it will literally suck part of the fuel/air charge out the exhaust port, loosing power. You also want to match the pipe to the port to because a missmatch pipe will loose efficiency also. Small pipe for small runners with big pipe for large runners. Bad example of wrong pipe is a big pipe on a low rpm runner will have an effect of when the gasses exit the engine block into the big pipe will expand and create more suction then normal and suck some of the fuel/air charge out the engine before the exhaust valve closes. Hope it helps. Got tips on intake also if interested.

Barely any valve overlap with the stock cam. Pretty much just trying to get things where they should be for the stock rpm range. At least make some improvement anyway.

Finally got around to checking rod clearance for the heck of it. Looks like about .003

Picked up this snapper that someone used for racing at one point. Had a single cylinder 2 stroke on it. Spindles look usable for the GTR and bearing hubs might be usable too. Front rims are bad so I would need to drill lug holes in the rims I have or find different wheels.


Front axle welded up from cast iron pipe by the looks of it. I drilled holes in the GTR frame to mount the rear axle bearings, so now I can start on the front suspension.

I have one of those Snappers, with a seized 11hp engine on it(I might have overstressed the engine when I swapped the 12hp carb on it without adjusting it downwards).

That thing is a freaking TANK, weighs as much as one, but tries to turn in its own length. I'm debating between junking it, putting my spare 12hp on it and continue using it, or stripping it for some future project. If I go for the last one, it may cause marital problems on the issue of storage.

The front end on this mower is bulletproof. Good choice if you ask me, but it is going to be heavy for your build.

I did see someone turn some of those pillow blocks sideways and use them for steering gear. Just a seed for an idea. Either way, I cant wait to see this build running.

This is coming along real well. That drilled out key is just too funny. Leave it to Porsche, I bet the blank costs 20x more than a regular Chevy blank even though it has less metal in it. Why? Because Porsche.

The steering knuckles on this snapper aren't real bad weight wise I don't think. They probably look bigger in the picutres than they actually are. I think they are go cart parts that they welded up. Got the front axle off the tractor and took the rims off. Hubs have sealed bearings I think and turn real easy for sitting outside for years. Front rims were split rims. Looks like it was fairly cheap parts to start with, kinda light looking. I'm going to cut the old axle maybe half an inch from where they welded it and weld in my A-arm tubes from there. I didn't really have a good plan for the steering before, these should work pretty nice. Just have to get some rims or make them up. Maybe this weekend I will start on the front end.

Scavanged two pedals. These were E brake pedals from a mercury sable and a ford taurus around the same year. About the same car of course. I'll use these for clutch and brake. Just have to take the rubber off and then weld up my own stems for them.


Made all eight billets for the suspension joints from nuts with the correct thread. Had to do some grinding. Now I can press them into the a-arm tubing and spot weld the inner one, then weld around the edge of the outter one. When they are inside the pipe, I'll have them arranged about how they are on the joint in this picture. I've got them so they press in pretty snug.


What it will look like when it's all assembled. Joints will be both adjustable and replaceable if needed. Originally I thought I was going to have to step down a size with the pipe after the joint, but now I see how small/short the a-arms will be, I'll just stick with that size all the way to the spindle. Next step is to weld brackets to hold the joints on the frame, then put the a-arms together. After that I can deal with mounting the front shocks. That pipe is push mower handle, pretty thick wall stuff. Painted, but at least not rusty. I'll be painting it anyway later.

Some slow progress. Working on some engine parts. Worst of the valves.


Most of the other valves cleaned up ok. This one has some deep pits on the seat. I should have a good extra from my parts engine.


Drilled a pilot hole in the experimental head. Here is where the plug is supposed to end up. Been trying to get a 14mm x 1.25 tap for a few days...

Thanks, good to see your still around. I'd like to spend some more time messing around on here myself, but I've been relatively busy. Hopefully I'll have the main parts of the front suspension roughed out in the next few days.

Finally some work getting done at the GTR research and development facility. Measured things out on cardboard so I would have a flat surface to work on and also so I could tack weld things without getting weld splatter on the frame. Trying to keep the inside of the tires out 1.5" from the main sides of the frame rails.


Cut some tubing from the push mower handle. Set the billets and joints in the tubes without welding.


Steering will be in front of the suspension. Threaded rod holds everything in place while trying to line it up.


Welded the tubes together in the center and tacked some places. The spindle bolt/king pin (whatever it's called) is set in place to help keep things square. Had to eye ball things because there isn't an easy way to measure it out. Bunch of different angles at once.


Ended up with a usable part (I think). Close to being pretty straight and where I wanted it.


Next to cut out and drill the brackets that will hold the joints. Then weld to the frame. I think the best way to go about it would be to weld on the brackets for this side and also the opposite side so they match on the frame. Then make the opposite a-arm to fit. I've gotta get moving on this thing or I'll never be done by the cut off. Still all that fiberglass work to do at the end...