A couple of years ago I picked up an 82 corvette. Mechanically it was a mess. One of the push rods on the passengerside was collapsed....its been replaced. It wouldn't run or idle....

I have been able to get it to a point were it runs quite well. I have replaced every electronic part on the engine. Balanced the throttle bodies, etc. New 85 fuel pump.

I still have a rough idle. I get what I call "valve chatter" on excelleration. It happens only under load. Just wondering what might be causing this. Any guesses? Valve spring? Collapsed lifter? Cam? Combination of some or all??

Jim

 

Sounds like your ignition timing is advanced too much.

 

That sounds like detonation also called pinging. Very bad for a motor with stock pistons. Check your timing and retard it until it goes away. You should have no more than 48-52* total and 36-38* mechanical only when full in around 2800 rpm.

 

Thanks for the replies.

I know how to set the timing but how to I check for no more than 48-52* total and 36-38*? How do i do that? Run the RPM upto 2800 and see what it is??

Jim

 

There are a ton of posts on setting timing. This is one I refer to often: http://forums.corvetteforum.com/show....php?t=1059896

Total refers to mechanical + vacuum. To check mechanical only, disconnect the vacuum hose to the canister on the dist and then run it through the rpm band. Unless you have an external rpm meter, get an assistant to run it in 200 rpm increments and write down the readings as you increase from idle on up.

 

The question is, is the chatter in the valve train or in the cylinder. Although this does sound like a vaccum advance issue, why did your rod collapse? I had a rod bend and brake in my 383 Stroker. When I took off the valve covers and manifold, everything looked innocent enough. The lifter was still in it's bore, the valve wasn't stuck, etc. I thought maybe I was lucky and it was just a bad rod that wasn't heat treated properly. Then I removed the lifter. It was worn concave. I looked down the bore and could see the lobe of the cam was worn and rounded. So, the bent rod was just a symptom of a more serious problem. If you didn't check the lifter and cam when your rod bent, you may want to check it now. The begining of a worn cam/lifter can cause chatter and poor idle.

 

The rod collapsed at the top....not the bottom. When I got the car it was surging, not idling and backfiring through the intake. The TBI's were leaking. Everything was wrong with it. Anyway first thing we did is pull the valve covers off. We found the callapsed rod. We replaced it. It took a long time to get this thing running the way it is now. Just about everything has been replace...electronically. This valve chatter is that last thing. I don't know why th rod was callapsed. It could be the cam and lifters.

I'm not sure of the symptoms of a bad cam and lifters. The idle is somewhat rough not erratic. The car runs okay. When you hammer it you can hear the chatter from the engine on the passenger side (this is where the collapse rod was).

The mechanic did adjust the valves on the passenger side at the same time the collapsed rod was found. He said oil was coming up on all lifters. Next thing replaced was the plugs and wires. It ran like crap for about a year after...possibly fouled the plugs???

The timing was set with the EST wire disconnected at 6 degrees...that factory for this car. I'll check this again other parts have been replaced since it was done...i.e injectors, IAC's, balanced TBI's and ECM.

I take it to replace the lifters the intake needs to come off. Assuming the cam is fine can the lifters and rods be replaced without doing the cam??


Jim

 

I was convinced that this was a timing issue until you said the chatter only comes from one side, and the same side as your bent rod. That doesn't sound like timing. Did the mechanic check to make sure you don't have a sticking valve? Also, when a lobe wears down there is usually chatter and bad idle quality, and can include a popping and backfiring through the carb. Rods generally don't fail for no reason. I would want to find out why it collapsed, and that means checking your valves, cam and lifter. Actually, you can visually check it by taking the valve cover off, and rotating the assembly by hand (remember to take it out of gear or put it in neutral and pulling the spark plugs makes it easier). Watch the rocker where the rod bent. If the valve appears to move smoothly and if it does not appear to travel the same distance as the others (of that type meaning, intake or exhaust), you may have a worn lifter, cam lobe or both. At that time, it's time to tear the manifold off and pull the lifter out of the bore. From there you can look at the bottom of the lifter, and look down the bore with a flash light at the lobe. If either one looks worn, it's time to pull the cam. If a lifter is worn on the bottom, you'll have to replace the cam.

I hope that this is NOT what you have, but there's the info I have.

Good luck.