my buddy was driving down the road and his T/A just shut off. when we try to start it back up, it just cranks and backfires out bouth ends. i just wanted to see what yall think before we start pullin his engine apart

 

If the timing chain was broken, it wouldn't be firing at all.

 

The timing chain virtually NEVER "breaks" or gets "thrown".

Rather, what happens, is that the phenolic teeth strip off of the chinesium center of the cam gear; and the chain just sort of drags around on the "gums" that remain, such that the cam turns somewhat, but not at anywhere near the speed it's supposed to. It just gets a little jerk now and then.

Typically, what an engine will do when the gear strips and you just hold the key down and whirl it over for a while, is it will just almost try to start; then start to backfire through the exhaust; then won't really do much of anything for a while; then will seem like it has no compression whatsoever; then the compression will seem to come back; then it will spit back through the intake a time or 2; then it will try to start; and the cycle will repeat.

If that's how it's acting, then the gear has lost its teeth. Quit running the battery down. Don't touch the distributor. Just change out the gears and chain (yes you MUST change the cam gear). Since the chain has had lots of slop for a time, you may find that it has worn a hole in the timing cover, on the pass side at the bottom; so have a new one of those on hand when you tear into it. You'll almost certainly be needing it.

 

you would have alot of bent valves if your timing chain broke..

 

On an interference engine there'd be bent valves, but stock SBCs are all non-interfering, as far as I know.

I thought that the factory gave up on nylon teeth on the cam gears sometime in the last 70s as well.

 

Until you get into dome pistons and/or valve lifts well over .600"....

Don't worry about bent valves, or any other damage, besides the timing set and maybe the timing cover, and maybe even the water pump... while you're there.

Actually, the last SBCs I looked at were about a 88 L98 and a 87 L69; seems to me they both had the plastic/chinesium cam sprocket. I'm quite sure the L69 did because we replaced it with an iron one.

 

yeah, thats pretty much what it's doing. we got new gears with the chain and a spare engine to rip a cover off of if we need to. tnx, chris