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No compression on 250

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I just put a new piston on my RMZ250. I get no compression. Oil does stay on top of piston so the ring isn't leaking. I've rebuilt it with the same results 3 times now. I've had the local shop go thru the valves and non are bent. I've reshimmed the valves to spec tolerances. I've even air tested it and for valve leakage and non. Timing is set to the book. Obviouly doesn't start and can't find the reason. And no return phone call from Vertex. What am I missing??? :thumbsup:

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WOW THAT SUX! it could be a million things,decomp,piston in the right way,valves (i know you said you had it checked out but who knows) How much oil is on top of the piston? not much help here but good luck!

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well first, the oil on the piston is the oil I put on it to see that the ring wasn't leaking. Piston is in with the arrow forward as it should. Valving they have check twice. Vertex has called me but was of no help. Plus the factory in Itialy is closed for the month. Oh well chalk it up to another aftermarket typical. I always get burned by no matter who they are :ride::thumbsup:

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I don't think the piston is your problem. It could be a million other things that you could have done during re-assembly. It's only a motorcycle, not the space shuttle, go through everything very carefully starting with checking for spark and fuel.

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I have the Vertex 298cc kit for my blue bike (YZF). It bolted on perfectly and started up straight-away, just like a stock bike. I couldn't be happier with its quality and performance.

Assuming you have the obvious stuff right (piston in right, rings in right, gaskets in right, bolts torqued right), I would focus on your valve clearance and cam timing. It sounds like you have your valve clearance set and confirmed, plus if you bike ran fine before, the valves will work fine when you put it back together. Which leads us to cams. You say you have them timed right, but something is MAJORLY out of whack if you have no compression. Check to make sure the cams aren't out 180 degrees.

I would tell you to lean out your jetting a bit, but that is more for after you get it running. The main and pilot jet don't effect starting anyways. Besides, if you don't have any compression, you have bigger problems than jetting. It's got to be the cam timing or the cams being out 180, again, assuming all the other obvious stuff is right.

After you have all this checked and confirmed (or before), try your spark plug and air filter. Did you clean and oil your air filter lately? If so, the fresh oil will often foul an otherwise good spark plug. Try a new spark plug, and make sure you don't have any excess oil on your filter. Good luck. :thumbsup:

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Well everything was right. The filter was new, piston in right, etc. all the way down to the timing punches were perfect. I was scratching my head along with a few other parts trying to figure this out. It was making my head go :applause: Seeing this wasn't my first motor ever to rebuild having built hi horsepower motors in my cars in the late 70s early 80s in didn't think I was that rusty at it but I never figured this to ever happen as easy as it did. I bought new cams (hot cams) figuring that what the piston kit changes is pretty hard to screw up and everyone I talked to was saying timing which I agreed but I was right on the marks. So I air testing the motor and never could stop the air from leaking. Once I got the new cams I discovered that somewhere down the line the sprocket on the intake cam had spun and the cam was off. So with that I finally got it running and it's running great :ride::applause: I would of thunk that those sprockets would of been pressed in there a little better then that. Tonight it will go to the track and see how it does there in practice.

CBDaddy and sn22 I'm assuming you guys are from Vertex in Ohio. Thanks :thumbsup: for your input on the phone. There's one for your troubleshooting book.

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I am in Ohio, but I do not work for Vertex. I am glad to hear you got it dialed in. If your RMZ runs like my big bore YFZ, you will have a smile on your face all the way around the track. Just remember, big bores like to lug. Don't try and hold it on the bump box and ride it like a 125. I assume you are more of a short shifting lugger than a high-revving screamer since you are going so big on the bore. Grab a higher gear, stay in the meat of the power, and your big bore will treat you right! :thumbsup:

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