Farm boy’s Rattle-can Racer

Compression test : 110psi on both cylinders, but the tester sits at the top of the plug holes, so that number is a bit lower than what it will be with plugs in. I’m satisfied with these readings.


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Was mocking up a shitty fibreglass inner fender when i realized i probably would want a bracket across the frame at the top to help stop it vibrating to pieces.
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Unfortunately i became distracted with life’s big questions like,

“Would a rotax 503 top end fit with proper stud arrangement?”

And

“Do the pistons have the same wrist pin size?”

Short answers... no and yes.

Pistons are for 71.5mm bore, and share the same wrist pin size.

Unfortunately the cylinders don’t quite fit the bill.

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It’s a shame, because these look like they are only a boost port away from matching the xr05 cylinders, and the damn pistons would fit!!!!
 
Those will fit with a little welding and moving studs... I went through as similar exercise for a GT750 - looking at RM250 top ends and triple sled cylinders and the issue on a triple is that two of the cylinders are too close together and that would require changes to teh crankcases as well as crank spacing and that all made my head hurt.

I think the 500 has wider cylinder spacing than left and center on a 750 triple, so it might be a touch easier to fit something less antiquated. Maybe a pair of XCR800 cylinders and case reeds might work for you.... Or maybe build this motor and keep thinking and build a spare big hp water cooled motor.
 
farmer92 said:
Was mocking up a shitty fibreglass inner fender when i realized i probably would want a bracket across the frame at the top to help stop it vibrating to pieces.

Q: does it need to stretch back behind the rear of the seat? Depending on what you are planning at the very back of the bike, you may be able to secure that fender to the cross tube behind the motor - or add "wings" to attach it to the tubes from swingarm pivot to top shock mount like a TZ/TD3. That way it's more like a hugger, but still long enough to keep crap out of the motor. Just no good for riding in the rain....
 
teazer said:
Those will fit with a little welding and moving studs... I went through as similar exercise for a GT750 - looking at RM250 top ends and triple sled cylinders and the issue on a triple is that two of the cylinders are too close together and that would require changes to teh crankcases as well as crank spacing and that all made my head hurt.

I think the 500 has wider cylinder spacing than left and center on a 750 triple, so it might be a touch easier to fit something less antiquated. Maybe a pair of XCR800 cylinders and case reeds might work for you.... Or maybe build this motor and keep thinking and build a spare big hp water cooled motor.

for sure this motor is going together the way it is, i just happened to find the box i had these stuffed into while i was looking for some scrap steel.
The cylinders are about 20-30mm to wide for it to work, and there is nowhere near enough cooling on these 503 cylinders.

The rear fender is going to be cut in half, just enough to cover from the swingarm to the top frame rails. Just enough to keep shit flying into the air filters.

Stuck some loctite metal putty down by the stator, should help hold it in place a bit. Hopefully when cured i can drill and tap it.
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Locktite putty worked spot on, stator no longer drops onto the rotor when the top bolt is removed, and the bottom one can now be snugged lightly into the putty for a little extra hold.

Printed patterns for the tapered section of the 1970 tr500 spec pipes (i believe).
Going bug eyed after cutting out 2 of them.

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Screen shot of a few different sets of pipe measurements.

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Ribbed for pleasure...
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Been dicking around with autodesk and their handy dandy frame analysis tools.
Blatant copy of Tony Foale's backbone frame, 2"x.095 chromoly tube
Total frame weight 18.8lbs
Here's an exaggerated simulation of the frame with
900 lbs of force forward on the rear shock mounts
1800 lbs of force down along the spine
1800lbs of force down and back on the swingarm pivot

still need to test for twisting forces and fine tune the simulations.
I think this frame will be the next step after everything is up and running in the current frame.
 

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I just came back to dtt after a little break from bikes and I come across your T500 project. Sounds very interesting i'll be following along :)
 
Dude how's that exhaust coming along? Love to learn me some fabrication skills like that, looking forward to see how it shapes up
 
I forgot i was out of gas for the mig and haven’t had time to go get a refill, but i made up the the header with some innershield wire as a mock up.
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It looks like shit, it splattered a lot, and it runs to damn hot for this thin steel, but it will line up properly so it should be good to go when i get time to fill up on gas.
Don’t know when that will be, hopefully before i end up in the fields for spring.

It’s kind of sad actually, I would have been better off with some 1/16 rod instead of the innershield. The wire is easier to fill in a hold if you blow through though.
Conclusion: i need a tig.
 
Just because it’s built not bought doesn’t mean it has to look like i welded it when i was 10

I think once i get the gas refilled and the thinner wire back on it will go okay. As it was, any more than 1 second of continuous welding would blow through it, and the fit up was almost perfect. The good side was that distortion was minimal like this, and the inside of the pipe was pretty smooth other than the first joint.
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Teazer, i have an old set of O/A tanks, but they are way past their pressure test date, i’ll have to ask what the protocol is when i get my shielding gas filled.
 
farmer92 said:
Teazer, i have an old set of O/A tanks, but they are way past their pressure test date, i’ll have to ask what the protocol is when i get my shielding gas filled.

I don't know the process in Canadia, but I do know that here in Ohio, it depends on the distributor. I have used Praxair a couple times, only because they would exchange tanks regardless of the date on them, where Delille and O.E. Meier would not. It may pay to shop around on that if they will not take the exchange.
 
I haven't had an issue exchanging tanks at either AirGas or Praxair. I normally use Praxair, but both have taken any tank I give them even competition.
 
irk miller said:
I haven't had an issue exchanging tanks at either AirGas or Praxair. I normally use Praxair, but both have taken any tank I give them even competition.

I generally use Delille here. Im pretty sure they are local though, at least to the Midwest. I used Praxair when the high school welding instructor here owned a small weld supply store and was a distributor for them, but now id have to drive 45 minutes or so to get to one since he closed down.
 
I use Airgas and took in a pair of brand new empty tanks and they gave me back a pair of full and very crappy old tanks. They are responsible for pressure testing tanks and to throw out any that don't meet spec.

If you get your own tanks filled that's a different story.

But TIG is best IMHO followed by Oxy. Oxy puts a lot of heat into the welds unless you are skilled and fast and stitch them together to minimize distortion. You do not want to see the last set of pipes I welded up. They look like they were shat upon by a blind weld pigeon.
 
teazer said:
You do not want to see the last set of pipes I welded up. They look like they were shat upon by a blind weld pigeon.
A surprisingly accurate description of this header...
The real question here is: How did they hold up?

I don’t so much care how they look, but i don’t want to be fixing cracked welds every second outing with them. Several layers of rattle-can bbq paint will fix the looks.
 
That is what I use to try to cover my sins. I built a drag bike so they only have to last about 20 seconds a time (including burnout). :)
 
Any Mig is rubbish for pipes, great for tacking but oxy or tig is good for the welding part. Here is one i did with oxy.
 

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