bad crank bearing?

[holtzer1]

ok, heres the story, i ported a motor for someone on a blaster and they didnt want to bore it out or anything, just put in a stock bore wiseco....i was hesitant, but did what they asked, we went riding and he was out drag racing...unbroken in mind you, and the engine shut down. so i look at it, when i kicked it over, it would kick just fine, but have this horrible intermittant grinding noise coming from the engine...and it wouldnt start. i messed with it a while and it finally cranked up...and it was just this nasty grinding sound like if you take a piece of metal and shove it into a bench grinder as fast as you can to get the wheel to stop...that kinda "krrrr" noise. hard to explain. but anyway, i pulled the top end off and found the piston just slappin around in the cylinder...it was ovaled out about .030, so my thinking was the piston was kickin so much causing it to chatter and get hung in the cylinder. i just got it together last night and kicked it over...nice new .040 wiseco, perfectly fitted to the cylinder etc etc.. and it does it still, when i had the top end apart, i spin the crank by hand as fast as i could and never felt any resistance or binding. but now that there is compression...it does it, every time you kick...cruch....any ideas, all i can think of is crank bearing. oh, and i kicked it over without the head on it..so there ws no compression fighting and it never made the noise.

[fiveOnick]

Wow that is a head scratcher. The only way I could possibly see the crank as the cause, since you said it spun free by hand, is if the force exerted from the compression on the system is loading a bearing that has something in it that isnt noticable until loaded with a force. Thats seems like a long shot though, I think you should be able to feel something in that crank by hand. I hate to ask the obvious questions since you seem pretty damn sharp and if your porting for people you should be. But your sure there is no contact with the head of any kind, or with the head gasket? Are the ports chamfered, if not the force on the rings from the compression could cause them to catch. If you didnt do this after porting it then if who ever bored it didnt relieve them thats a possibility. Not much else comes to mind right now.

[ONLY2STROKES]

maybe the flywheel nut backed off and/or sheared the key?

[370banshee]

might be a sheared key... they make a nasty noise and that woudl explain your not firing then your firing and running.

[fiveOnick]

A sheared key should act different than what I read. Yes it would act pretty screwy with the ignition on but with off it should kick over just fine, compression or not. Now if it was catching something inside the cover I could see that too, but not if it spins over fine without the head. I guess the main question should be when kicked over with the head on, was the ignition on. If so the key could be the problem, if not then it shouldnt have anything to do with the rotating assembly. Not to mention this guy seems sharp enough to know if it was out of time from the start of all this.

[370banshee]

a sheared key will sometimes ride against the nt till it loosens then will let the flywheel spin across the crank taper.... seen it a few times.... and it makes a horrible grinding noise

[fiveOnick]

Originally Posted by 370banshee

a sheared key will sometimes ride against the nt till it loosens then will let the flywheel spin across the crank taper.... seen it a few times.... and it makes a horrible grinding noise

I can see this making sense if the ignition was on when kicked and the off timing put a reverse load on the crank opposing the flywheel causing it to spin on the crank and make the sound your talking about. Otherwise if the flywheel was loose enough to spin freely from simply the rotation of the crank it should have been noticed when it was kicked over without the head on. You see what Im saying, there has to be some force opposing the flywheel causing it to spin if it doesnt spin when kicked over without the head, cause obviously the force of kicking it over without any compression to put a reverse load isnt enough to cause a problem. I dont know if Im doing the best job at explain what Im getting at here but its a try.

[holtzer1]

I'M GONNA CHECK THE KEY....ooops, caps on.if its not the key, i'll report back.

[holtzer1]

it IS the key, the degree key sheered clean off, i'm gonna put a stock one back in it....that flywheel was just spinnin as free as it could, i took the nut off by hand...odd, i tightened it down with an impact.

[holtzer1]

well, i put the key in it just now...2 kicks on a brand new top end and whallah....perfect. thnks for your help guys, i was so damn flustered about this thing i wasnt thinkin straight. thanks alot.