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Just a reference pic of an old 550 piston sitting next to one out of the 86 ATC250R
The bore is somewhere around 92mm, or about 3-5/8"; about the size of a piston from a Chevy 305.
And here's one of the blown up cylinders
This was the first meltdown. Turns out there are multiple thicknesses of base gaskets that can be used. We wanted more power, so we used the thinnest one. That produced enough compression to result in severe detonation. Funny thing about a 550 single; it's so dang loud at high RPM that you can't hear it.
Rattled the wrist pin clip out, got sucked up a transfer port and wedged itself between the piston and cylinder wall. Broke the sleeve and the cylinder. You can still see a chunk of the clip imbedded in the cylinder wall.
So we got another cylinder and piston and proceeded to do the same thing again, just not as catastrophic; this time the cylinder was saveable with a new sleeve, but we found a used one and ran that with a new piston. Back then, pistons were only available from KTM, only in standard bore size, and were just under $400. Pistons have been obsolete now for years. Luckily, this piston / cylinder only has a handful of hours on it - even though it was over a decade ago.
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Only thing I've found to be junk is the front brake is completely seized up; that's OK, I never used it anyway.
While I'm messing around with the front end, what do you guys think about flipping the forks around so the front axle is to the rear of the forks? Should handle a little better (in theory), but it might just expose the front tires inability to float on top of the sand like a regular ATV tire would.
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Been putting the memories together in my head; the last time this bike ran was in 2000 at dune fest. One of the things that killed it was the noise restrictions at the Oregon Dunes, IIRC they went into affect in 1999. The year prior to that I was riding the bike still as a motorcycle and the Staters were doing free noise tests in preparation for the upcoming noise restriction. I don't remember the exact db reading, but lets just say there was no way in hell the 550 was going to be that quiet. Readings taken 12" away from the side of the cylinder (instead of off the exhaust like there supposed to be), was something like 102db - coming from the cylinder
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Took a bunch of stuff apart over the weekend; flushed the cooling system out, new brake fluid, got front brake working again, cleaned the carb out (float level was set WAY too low), adjusted the rear shock (I'm about 40 pounds heavier than I used to be). Also has to weld a tab back onto the subframe, and rebuild a couple of brackets that weren't up to par. It's kind of fun to study my fab skills from back when I was just out of high school; although my current standards for fit and finish are considerably higher.
Should have a new water pump seal in the next day or two, and I'll be ready to see if she will run again.
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Awesome fab work OP. A sweet wheeler for sure..
37 goin on 20..
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Had a test fire tonight. Rolled it over a couple times, then gave her one he- man kick and it started right up for the first time in over a decade.
One problem though, the clutch drags really bad. I remember it happening before due to the clutch plates digging grooves in the basket. But it now has a new clutch basket. I can see the top of the clutch through the fill plug, and with the clutch lever in their nice and loose.
I tried to click it into gear at an idle, and it killed the motor, then I tried to put it in gear with some throttle and the front tire left a 10 foot skid mark up my driveway before I got it shut off.
Anyone have any ideas why its dragging so much?
Last edited by bikemaker; 08-25-2013 at 11:03 PM.
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Hey bikemaker you want to sell those wheels on that ford crew cab?
Are those weld wheels ??? If so are they 16's or 16.5's?
If its on the internet its got to be true they can't put any lie's on the internet
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OMG That thing is awesome! and begging for a Jason Hall front end! .....Wonder what Camexican will think of this one??
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I need to put a bigger pilot jet in it, and go through the clutch. After that, I'll fire it again and try to get a video of it running.
I don't think I can widen the front end without changing the tank and maybe even relocating the radiators; I'd like to widen it, but I'll save that project for this winter. This thing needs to visit the dunes first.
The wheels on my truck are 16.5 x 10 Welds. Not for sale for now, but they might be in the future: it's getting hard to find 16.5" tires these days.
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The clutch is dragging because it sat dry for so long.take the plates out and unstick them and oil em up real good and you shouldn't have a problem
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That's pretty much what I figured, I just didn't want to open it up again.
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That's a sweet trike. Bet it'd be fun on the dunes.
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Got the clutch feed up, changed the pilot out, and spent the last 3 mornings kicking the snot out of this thing; can't get it to fire.
My ankle hurts, my thigh is sore, and I have a bruise on the arch of my foot.
I think I have the crankcase loaded full of fuel at this point, so I'm going to take it out to my dad's this weekend and try to pull start it.
Hopefully that does the trick. This thing has always been temperamental to start; as of today it's got me walking around in a circle.
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Did you go to big on the pilot?
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Oh yeah.
I've since come to learn that the stock jettings specs in my manual are nothing to go off of.
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