rebuilt yfz450 no compression

[lpmaster]

well my piston cracked in half due to what looked to be a wristpin failure anyways.

i had the cylinder honed since there was almost no damage to it and the piston was still kind of intact.stock bore j.e. 12:1 piston. and a cometic top end gasket kit. i just got done putting her back together. and the thing has less compression than the cracked stocker i had in there. i used new headbolt torqued via fact service manual. anything you guys think i missed. i triple checked cam timing i dont think thats it. also it MIGHT have compression however when i hit the starter it spins reaally frely and doesnt even try to start or make any puffing noises...any help is greatly appreciated. im thinkin maybe the hone took off too much from the cylinder?

[rt20ps]

Unless you have a diamond hone you didn't take anything off of that plated cylinder. You should have checked you piston to wall clearance as well as the ring end gap. That would tell you if the cylinder is worn out. My first guess would be that you timing chain slipped off of the crank behind your flywheel. Did you crank it over before you put the valve cover on??

[lpmaster]

the local shop ALBA did the cylinder hone and it came back looking perfect. my ring end gaps i filed to .002 as recomended for my application.

i did spin the crank a bit however. i set the crank to tdc again before re-aligning my cams so could this still be a problem? thanks for the help btw

[rt20ps]

Take the valve cover back off and see if the cams are turning when your trying to start it. Double check your timing marks.

[JoeTeamMayhem]

I've had a small piece of dirt get between the shim and where it rides on the valve springs, and once a bucket (the round thing that goes over the valve springs that the cams ride on) got tweaked and stuck a tad open. A valve must be stuck open or you slightly bent a valve or 5. We did one that broke the piston and the valves looked fine. When we got it back together it didnt have any compression so we took the head back off. you couldnt tell they werent sealing untill you stuck the ports up to your eyes as tight as you could. Then you could BARELY see light coming through 2 intakes and an exhaust valve. It doesnt take much to make it not wanna start. When you time the cams it doesnt matter how much you spin the crank...As long as the timing mark on the crank is lined up with the case and the cams are lined up it is TDC.

[lpmaster]

thats what i figured since the compression stroke is only relevant to cam timing. i guess i'll check the head for leaks. probably spray some solvent in and see if any leaks in the cylinder befor ei pull it back off. also anyone know exactly what the piston/wall clearance is supposed to be in a stock cylinder?

[lpmaster]

meh figured out the problem. when i labled my valve spring buckets. i labled them 1,2,3 for intakes and 1, 2 for exh. well. i thought i had em organized properly however i installed the cams with the head off and what do ya know, 2 of 3 intake valve are wide upon while the lobes face outwards. so basically label your valve buckets better than i did. also i am fortunate there was no piston.valve contact.

[JoeTeamMayhem]

What a relief right! A little luck never hurt anybody!