Valve chatter on an 82

[jdp6000]

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

 

[AKRAY4PLAY]

sounds like detonation to me. try higher grade gas and/or 2* less timing.

 

[Twin_Turbo]

check if your knock retard system is working, do you have a scanner? If not, download win ALDL and build the simple interface connector, then when engine is running and the scanner on, tap the block w/ a hammer (don't whack, just tap) and watch if the knock counts go up, if not the system is at fault.

Check the simple stuff first though, check if the knock sensor is still connected, it's in the pass. side coolant drain hole. The stock one has a mushroom style conenctor and a lead that has a rubber square block w/ a metal retainer clip. The cable is a thick shielded cable. If you need an ESC/interpreter, I still have one from an 82. I think these are discontinued.

 

[jdp6000]

Thanks Twin. ECM is brand new. I never thought to check the knock sensor.
what is an EST/interpreter???Where is it??

Jim

 

[wishuwerehere82]

Can you still do the old hammer test where you watch the timing marks while you strike the block with a hammer?
When the hammer strikes, the ESC sees the strike as a knock and the knock sensor tells the ESC to retard the timing advance.

My timing was jumpimg all over the place and it turned out to be a broken ceramic insulator on the Knock sensor that was spinning around randomly firing the ESC.

 

[Twin_Turbo]

that's supposed to be ESC, typo! This is the ESC:

It's bolted to the back of the ECM bracket, on the wall behind the seat. Next to the battery you see the ECM, between that and the metal wall you'll find the ESC 9electronic spark control). It's the spark controller/interpreter. It's sort of the amplifier box for the knock sensor where the sensor is the microphone, the ESC signals the ECM which in turn signals the EST (electronic spark timing) .. the "module" in the distributor to take out timing.

You can do it with a timing light but it's much easier to see w/ a scanner and the knock counts.

 

[jdp6000]

Thanks guys.

I don't have a scanner. Maybe its time I built one. Where do I download ALDL? I suppose I need a connector to fit the plug under the ashtray...where do I get that?

My chatter is only on the one side...passengerside. Same side that had the collapsed rod. Can the knock sensor/ESC system cause this? Or should the chatter come from both sides? I'll try to check the system this weekend.

Turbo...your right...dealer still sells the knock sensor...but not the ESC. How much do you want for that part? Just in case I end up needing it.

Also I'm running synthetic oil. Just wondering if this may be contribution to the problem.

Jim

 

[Twin_Turbo]

it's winALDL ALDL = Assembly Line Data Link ..the connector behind the ashtray.

http://winaldl.joby.se/

The system only eliminates knock. If it's on one side it's most likely a mech. problem. What do you mean w/ collapsed rod? Did you replace rod bearings???

The oil won't be the problem, unless it's a real thin oil that also thins out a lot, like 10W30, a 10W40 or 50 oil will maintain a higher viscosity at hihger temps. However, that's a bandaid...if there's a problem it's usually a rod, big end stretching giving too much slack on the bearings.

Dunno what the ESC is worth, make an offer. anything else you need? i have mostly everything from my 82 apart from all the stuff that I already sold but as far as eletronics go, I have pretty much everything left.

 

[wishuwerehere82]

Jim,

I'm having a hard time grasping the exact nature of the problem.
When you say a valve chatter, do you mean a knock or ping coming from the cylinders or do you mean a clattering like sound coming from the rocker arms.
Since it is only from the passenger side, I am concerned it could be an oil delivery or valve adjustment problem if it's a clattering. Or a coolant flow issue if it's a pinging.
When you say a collapsed pushrod, how was it collapsed? At the end, or bent?

Can you provide more details into the sounds and the conditions it occurs under?

EDIT* After reading your post on the Crossfire vault.
I would say the you need to examine your pushrods and look at the balls on the ends. They can wear to the point that they are razor sharp where the oil holes contact the lifters and moreso the rocker arms. This can lead to a lack of oil flow to the rockers and also wear out the mating surface on the rocker arms. This might explain the looseness in the valve train and it will continue to get worse as it wears. Maybe time for a new set of pushrods and rocker arms.

 

[jdp6000]

Thanks Twin and Wish. I see I have the attention of the two Crossfire Masters!!

Twin I'll check around and see what that part is worth. I want to be fair. I'll send you a PM when I find some info.

What I mean by collapsed is the top was mushroomed down and there was a slight bend in the upper part. Almost like the previous owner over tightened the valve. All that was replaced was that one rod....can't recall which...it was two or three up from the front on the passenger side. When I first got the car mechanically it was a mess. The objective was to get it going good enough and long enough to do all the usual adjustments and tests. Originally I expected that I would have to replace the cam, lifter and rods. I'm wondering now if this is a valve adjustment issue or something else before I get into tearing the engine apart.

As for the sound. its not a knock and its not a ping. Its hard to describe but I'll give it a shot. Its sounds more like a rattle...like the rod or rods are rattling around. On gradual excelleration It sound like an exaust leak...like a minor leak in a header. This might suggest the culprit is in one of the exhaust valves??? If you floor it the engine kicks in nice...no hesitation or miss...but you hear this rattle...if you can imagine...3000 rpm on the tach and an a rattle at 20 rpm...you can almost count the rattles...almost like shaking a glass full of marbles....I guess as Wish called it "clatter". BUT it doesn't do it when you give her gas in park or neutral so its only under load. The car idles at a constant 550 but there is a miss..not regular or patterned but still a miss.

Anyway I have to start somewhere. I'm going to change the oil to what specs call for. The dealer has an oil additive for unsticking sticking lifters, I'll try it. I'll check the rods for any unusual wear. Actually now that I think of it I should probably check and make sure the mechanic put the identical length rod back in...never know with those guys...actually the sound is kind of having a rod too short and moving around...is that possible with hydrolic lifters?? Maybe adjust the the lifters. So here is the question. Can I replace the rods without doing the lifters? Can I replace the lifters and rods without doing the cam??

Thanks Again,

Jim

 

[Jack]

actually the sound is kind of having a rod too short and moving around...is that possible with hydrolic lifters?? ... Can I replace the rods without doing the lifters? Can I replace the lifters and rods without doing the cam??Thanks Again,Jim

Pushrod too short ... possible but not so likely. Pushrods without new lifters ... YES. Lifters & pushrods without new cam ... YES.
JACK:gap

 

[Twin_Turbo]

If it was a mechanical problem with the valve train it'd be there regardless if the engine was under load or not and you'd notice it as a constant sound that is doing it at half the crank speed. A noisy tappet or loose rocker is a very distinkt clack clack sound and it's frequency changes w/ rpm.

The fact that it's a problem under load may point to the direction of a rod big end problem as noise there can very well be dependant on cylinder pressures. However, a rod problem is usually a banging noise, like thump thump...and you can ehar it down under.

Have you tried listening to locate the sound? If you don't have a stethoscope put a length of vac hose with a long tight fitting rod in the end or a long screwdriver in 1 ear and an ear plug (or a finger) in the other and use the end of the hose to probe the engine, you will be able to pinpoint where the noise is coming from, if it's a rocker, pushrod or tappet problem you should be able to pick it up by holding the hose on the valve cover. If it's a rod it should be audible down in the block.

Your problem may very well be something stupid like arcing over the spark plug wires, especially # 5 & 7 are prone to that because they are next to each other and next in firing order (1-8-4-3-6-5-7-2), a serious miss will occur that can be dependant on load because of the ignition timing, making it more pronounced.

Does it do it when you stand on the brakes and rev the engine (forcing it into the stall ???) if so, that's a good way to diagnose it. Pull 1 plug wire on the offending side and test it w/ the wire off, when the noise disappears when you pull one of the leads then there's where your problem is at. The engine will run rougher on 7 cilinders but it should still run good enough to diagnose.

It can also be as simple as a cracked flex plate

 

[wishuwerehere82]

The fact that one rod was mushroomed means that it was worn thin enough for the steel to collapse. The rest of them are probably just as worn too.
Mine were worn paper thin in 47,000 miles, and the holes at the ends were razor sharp, but didn't collapse. The sockets on the rocker arms were gouging out to match the balls on the rod ends, and the pivot points on the rockers were wearing to the point that they might have pulled off the studs soon afterwards. Two of the cam lobes were completely rounded off too.

All you need to do to inspect them is to pull the valve covers, remove the nuts on the rocker arms, and pull the rods out. Run your finger over the ends of the rod ball holes, and if they are sharp they need to be replaced.

Since the noise is not consistant with RPM, it is possible that something is sticking, either a lifter, rocker, or valve.
But is preferable to find the location of the sound before you end up tearing everything apart in vain.
Could even be the A/C compressor clutch?

Let us know what you find.