Well, the Scrambler is no longer running after less than 2 hours on the fresh rebuild. It started this morning, idled for 5 minutes and I rode it onto the trailer. Ran fine. I got it to the lake to ride around for a while, and it started ok. Idled for about a minute and then just shut off. With each pull attempt to restart the machine, I could feel the compression dropping. A compression test would be pointless at this point since there was no resistance with each compression stroke when pull starting. The spark plug was dripping black, probably from my 32:1 premix for break-in. I got the top end taken apart and everything looked fine. No broken rings, broken skirt, or majorly scuffed cylinder. The piston-bore clearance was about .006" when assembled, and ring end gap was about .016"...both more than recommended, but should have been tolerable. Well, here's the measurement I have now...all taken with a dial caliper:
20 over Wiseco=3.279" front to back, 3.285" across wrist pin. Apparently it's not round.
cylinder bore=3.289" top and bottom
ring end gap= .022"

I know all those tolerances are excessive and a bore job and 30 over Wiseco are going to be needed. I measured a new standard bore stock piston at 3.266". Why the hell doesn't my 20 over Wiseco measure 3.286" and why isn't it round?? I wish I knew what a 30 over Wiseco measured so I could get my cylinder bored. If you haven't guessed, I am frustrated. I was hoping to get at least a year out of this top end, but only 1 gallon of gas run through!?!? What's a guy to do???

 

Oh yeah, here's a few pics of the piston if they'll tell anything about the situation:

http://i29.photobucket.com/albums/c2.../piston002.jpg
http://i29.photobucket.com/albums/c2.../piston001.jpg
http://i29.photobucket.com/albums/c2...ATV/piston.jpg

Of course, my computer is being a POS, so I can't post a direct link. Sorry.

 

I would give Rick Ritter a call and let him set you up with a good bore and piston. Just my $.02

 

Hey. The same thing sort of happened to me. My scrambler blew just a little after it was bored. It was so bad it wasnt worth fixen. I just sold it for parts. There was other things missing as well. The top of the piston looked like ground beef!!![img]i/expressions/face-icon-small-shocked.gif[/img]

 

Well, this ATV is not worth parting out since everything looks new on it still. The top of the piston looks new besides a little black carbon residue. I wanted a modded Scrambler when I was 16. I finally got one in great shape and built it the way I wanted it built. There's no way I parting it out after this incident.

 

Yea they are pretty nice quads. I hope to get another one soon.

 

RICK RITTER,
Wiseco pistons aren't round, they are oval is shape, wide at wrist pin hole and narrow at intake and exhaust sides to allow for expansion. And I believe the skirts are bigger than the top of piston.

I run my piston at .0035 to .004 and a good breakin.
On the 440 Aaen kit .005 to .008 because of harmonic vibration due to cylinder wall thickness.

You bore the cylinder to the piston, pistons can be off a little.

The measurements you gave gives you more than .006 clearence on piston to cylinder wall.

Call Rick, if he is busy try Bubba297.

What about the base gasket or the crank seals? You do the leak down test.


good luck.........................handycap

 

Handycap-
I replaced the crank seals when I rebuilt the engine and I retorqued the base stud nuts twice after rides. The base gasket looked great when I pulled the cylinder off yesterday. I have a 30 over piston on the way here and will get the bore job done once I have the piston.

 

Send the cylinder to rick to get hm to port it to match your piston. He is much more reliable than a random shop boring it to what you tell them to bore it to. Obviousyl something was wrong with the last rebuild, either the bore was wrong, or the assembly was wrong.

Get rick to do the boring, and he will also walk you through step by step on the rebuild if you need help. Something is wrong, he will find it.

 

When WIscrambler got the jug it had already been honed. We knew that the clearance was going to be a little large, but with .005-.006 and only .016 ring gap it should have run for awhile with a forged piston. The only other reason I can think of would be if whoever honed it used too rough of a stone and allowed the rings to scrub against the wall and increase clearance.

I feel your pain. When I put my first big bore together the clearance was not marked on the piston bkx. The shop set it up at the normal .003, It ran for about 30 seconds down the road before seizing, and that was after a good warm up. I also had my wife's bike bored to .020 and it was a little tight and seized. It's a huge pain and very frustrating to tear them back down again.Chalk this one up as a learning experience, it will help you out in the long run.