1995 4.3 bad compression test

[beachbum2425]

Re: 1995 4.3 bad compression test

All the valves on the cylinder 1-3-5 head all looked identical. Although, I have not removed the valves yet.

 

[RogersJetboat454]

Re: 1995 4.3 bad compression test

Have a good look #3 exhaust valve when you pull them.

 

[Bamaman1]

Re: 1995 4.3 bad compression test

You can send the heads to any good auto machine shop to get the valves ground--and have the head cleaned up.

If you've gone this far, pull the engine and inspect the pistons and condition of the block. Wouldn't it be nice if you could just do a slight cylinder honing--and install new rings? If you need help, find a good independent auto mechanic to reinstall the timing gear, degree the cam etc. Rebuilding these engines is not rocket science, and a good Chevy mechanic could put the engine back together in a very short time.

Pulling inboard outboard engines is really a easy, relatively quick job--when you get around to doing it. It's just resealing with those darned bellows that give me a headache.

 

[beachbum2425]

Re: 1995 4.3 bad compression test

I would first like to thank everyone for their help and advise. Although I am new to boating, I have had some experience with small block Chevy's in 4x4's.

I do have a couple of questions. After reading the shop manual for engines removal, there does not seem to be any bolted connection to the transom or out drive. You just unbolt the 4 engine mounts and pull the engine. I have already removed the out drive. Is this correct?

My other question has to do with the cause of the problem I have with #3 cylinder. If everyone agrees that the piston erosion was caused by detonation, why only #3 cylinder? Some of my observations are 1st: #3 had a different spark plug than the others, which I believe was a colder plug (the porcelain part of the plug was more recessed into the threaded part of the plug, exposing less porcelain into the combustion chamber). This I believe would lessen the chance of detonation. My 2nd observation is the heads and block where remarkably clean, no sludge build-up in lifter valley or under valve covers. Also, no rust build-up was observed in any of the water cooling ports of the heads and block. The only rust build-up I saw was in the thermostat housing and exhaust manifolds/risers. Could my problem be caused by overheating? When I repair this engine, I do not want the same thing to happen again.

Any and all advise would be greatly appreciated.

 

[RogersJetboat454]

Re: 1995 4.3 bad compression test

I do have a couple of questions. After reading the shop manual for engines removal, there does not seem to be any bolted connection to the transom or out drive. You just unbolt the 4 engine mounts and pull the engine. I have already removed the out drive. Is this correct?

The two bolts that hold the flywheel cover to the transom shield are the engines connection to the transom.

My other question has to do with the cause of the problem I have with #3 cylinder. If everyone agrees that the piston erosion was caused by detonation, why only #3 cylinder? Some of my observations are 1st: #3 had a different spark plug than the others, which I believe was a colder plug (the porcelain part of the plug was more recessed into the threaded part of the plug, exposing less porcelain into the combustion chamber). This I believe would lessen the chance of detonation.

You are backwards on your hot/cold plug info. The more porcelain exposed to the combustion chamber, the colder the plug. The porcelain acts as a heat sink to wick the heat away from the center electrode and into the head. The less porcelain present, the hotter the electrode will be. Just look at surface gap spark plugs used on some of the outboards. They have a center electrode completely surrounded by porcelain (no gaps), and are stone cold to prevent detonation. That spark plug could very well be the cause of all your problems. You assume that it was installed while someone was trying to diagnose the problem with the engine. For all you know, either the previous owner, or some rookie wrench broke the correct spark plug during some routine maintenance and in turn riffled in a spark plug they had on hand because they were either lazy, cheap, dumb or all of the above.

My 2nd observation is the heads and block where remarkably clean, no sludge build-up in lifter valley or under valve covers. Also, no rust build-up was observed in any of the water cooling ports of the heads and block. The only rust build-up I saw was in the thermostat housing and exhaust manifolds/risers. Could my problem be caused by overheating? When I repair this engine, I do not want the same thing to happen again.

Generally overheating is going to affect all cylinders, or at least a bank of cylinders. All your troubles are more or less localized to #3. If say you had a 400 small block with steam ports and siamesed cylinders, you would be more likely to get localized overheating in one cylinder. But the 4.3 has nice wide open coolant passages below the deck that should not allow any localized overheating to occur. It may be worth it to take a look in the cooling passages around cylinder 3 to make sure there is no mud or sand packed in around the cylinder. Chances are it will be clean like the rest of the passages.

 

[beachbum2425]

Re: 1995 4.3 bad compression test

I have included the following pictures of the spark plugs. The shorter plug is the plug from #3 cylinder and the longer plug is correct plug and what was in the other 5 cylinders. Excuse the quality of the following pictures, my batteries were dying and I could not use the live screen.







Notice how the center electrodes look brand new. The bottom picture shows #3 on the left side.

 

[beachbum2425]

Re: 1995 4.3 bad compression test

I have pulled the engine and disassembled it and I found #3 not only had a gasket problem, it also had frozen rings. Below are the ugly pictures of #3 piston.






Click on pictures to enlarge

The main and rod bearings and journals were remarkably spotless, but cylinder bores have some corrosion which means new oversized pistons are needed I believe. Unless someone has any other ideas?

 

[RogersJetboat454]

Re: 1995 4.3 bad compression test

but cylinder bores have some corrosion which means new oversized pistons are needed I believe. Unless someone has any other ideas?

If It were mine, I would probably start fresh, and have it bored .030 over. Is there a ring ridge at the top of any of the cylinders? If there is, you need them bored. If there isn't, you could see if honing the cylinders will remove the damage, then have them measured to see if they are with-in STD bore specs, but thats a decent amount of work that may all be for nothing if the cylinders don't measure up.

 

[bnicov]

Re: 1995 4.3 bad compression test

Do a full rebuild on the engine, bore out the cylinders however much they need, have the crank and rods inspected, new bearings, new pistons and rings, have the heads redone, a new cam and you'll know what you are working with, a fresh engine that will give you years of faithful service as long as it's maintained and not abused too much.

 

[beachbum2425]

Re: 1995 4.3 bad compression test

There was no ridge on top of cylinder, just a small amount of carbon. I pushed the pistons out with my hand. I have not done any bore measurements yet, trying to find someone with the right micrometers and snap gauges. I hope this engine did not get a lousy rebuild and just sit for along time. I will post the measurements when I get them.