atc 200x engine kaput...what to expect?

[michaelwbrenner]

Hey guys. I figured out that after rebuilding my 1985 200x that I set the camshaft timing to the F mark on the flywheel instead of the T mark. Then I timed the motor using a timing light on the F mark at idle once the motor warmed up. I ran the motor this weekend and my girlfriend ran it hard for about 10 minutes until it lost all compression but did not sieze. What happened? Is the timing set at F at idle correct? With the camshaft timed on the F mark did I burn a valve or the rings or both? Just wondering what to look for when I tear into it soon. Thanks for any advise/insight.

[speed20]

If it was out of time...it would either not run....or run like crap. your valves may be too tight (keeping the valves open too long) clearance for them are supposed to be .003 ( 3 thousandths). as for timing....i sold my manual so i couldnt tell you!

[Kevin in Ohio]

Just a quick question. Did you replace the cam chain when you rebuilt the motor? I've seen way too many junked out because of chain jumps from overstretched chains. Just a thought. Kevin

[hondaATCman]

Hmmm...if you're lucky, the cam chain jumped a few teeth and is now out of time which is causing the valves to open at the wrong time and also cause a loss of compression. If you're not lucky, it jumped time at a high RPM and bent a valve, most likely the exhaust valve, letting the motor turn over freely but of course have no compression.

Also, when you do a rebuild, ALWAYS replace the cam chain and reset the tensioner.

[kilabeez0]

i didn't replace my cam chain. uh oh

[michaelwbrenner]

I'll post pics. I think it was running way lean and maybe the fuel wasn't of the best quality. Now you've got me thinking the cam chain slipped. I will replace it. I did reset the tensioner and the valves appear to be good. I'll dissassemble the head too and take pics tomorrow night. I'll post them right away. You guys can advise me then. I already took the top end apart and didn't notice if the cam chain was off. damn. That could have been it. But the rings look like hell and the piston has a white/grey tint to it. it is rough and seem abbraided in some way. I measured the ring end gap and it was ok upon reassembly. The cylinder showed 5 distinct areas of wear running the full stroke of the bore and guess what.... there are 5 rings. top, 2nd, 2x oil, and the oil retainer. The bore looks kinda crappy. I'm gonna post all kinds of good pics later.

[hondaATCman]

Maybe pre-detonation? But...unless there is a hole in the top of the piston, the sudden loss of compression has to do with the valves/timing.

[Kevin in Ohio]

If the chain is stretched beyound it's service limit the tensioner can not take up the slack. Too much slack allows the chain to jump a tooth or two as HondaATCMAn stated. Most often happens after a rebuild because of the compression being higher again and the engine working harder. Stress goes to the weakest link if you will. Easier and cheaper in the long run to change it the first place.