ShadowLightCSU

iTrader: (1)

I know this isn't LS1 related, but I bet this problem can be solved in context of thinking about an LS1.

My little brother was driving his LT1 this morning and he said he was just rocking out with the radio on, then suddenly heard a loud pop from the motor and now it's totally dead. It will turn but makes a funky noise, but definitely won't attempt to start.

Any ideas?

383?

30th droptop

iTrader: (-1)

Could be a timing chain. Check compression. If it's the timing chain, you'll have little or no compression. The loud pop might have been a backfire, which is typical when a timing chain fails. To diagnose a timing chain in the old days, we used to pop the distributor cap and check to see if the rotor was turning during cranking and that timing was correct. That's pretty hard to do on that front-mounted LT1 distributor!

Good luck! The timing chain looks like a pain in the butt on the LT1.

Boostaholic

iTrader: (4)

lt1 valvecovers are easy enough to remove, and you could see if the timing chain had a problem with the valvecover off.

If it is broke though, you have some serious problems.

Camaroholic

iTrader: (1)

When my cam timing gear on my 94Z let go, I bent all the intake valves. Mine made a funny noise and then stopped working... it would crank, but not start. If you pull the valve cover and some of the rockers are very loose, and/or the valves are at different heights with the rocker arms removed, that's bad.

30th droptop

iTrader: (-1)

Yeah, you could remove a valve cover, crank the engine, and see if the valves move. But if the timing chain has just jumped a tooth, everything may appear to be OK. To me, it would be easier to just pull an easy spark plug or two and check compression. The readings will be non-existant or VERY low if there's a timing chain problem. It is a more positive test and, to me, it's easier.

I don't know if the LT1 is an interference motor in stock form. In an interference motor, the valves travel into the area that the pistons occupy at TDC. As Camaroholic alluded to, an interference engine will often bend the valves if the timing chain lets go - that's when you'd see the valves at different heights with the rockers removed. Most pushrod engines are not interference engines in stock form, but, if you've got an aftermarket camshaft or high-ratio rocker arms, you'll likely have a problem.

Since you've already been cranking the motor, any valve bending is probably already done. A compression test shouldn't hurt anything. If it indicates a problem, then pull your valve covers and rocker arms to see if the valves are bent.

SSPerformance

iTrader: (76)

I had to try it out

98Mayhem

iTrader: (18)

If the opti took a crap it could backfire. Check for spark before you tear into stuff.

ShadowLightCSU

iTrader: (1)

Thanks for the advice guys, we're gonna start tearing in to her Sunday night. I'll have him check out the valves. So far everything thinks its the timing chain, that really sucks if that is the case.

Oh well, I guess he's got an excuse for heads and cam.

jmX

Moved it in here since you seem to have gotten some good feedback now.