4.3GL One Cylinder Zero Compression!

[dtescher]

97 4.3GL PLKD. Reinell. Started to idle rough but was ok mid throttle but bad again at high throttle. Found zero compression at center cylinder starboard side of engine. How bad is this? Where do I go from here?

 

[Bt Doctur]

Re: 4.3GL One Cylinder Zero Compression!

engine temp, oil pressure ? previously overheated? Get an old spark plug, remove the center section, tap for air fitting, inject air.
out the exaust = exaust valve, out the carb= intake valve, out the dipstick= hole in piston

 

[Scott Danforth]

Re: 4.3GL One Cylinder Zero Compression!

As Bt Doc mentions, do a leak test. you could simply have a stuck valve. that would indicate a rusted valve guide and stem which would be an easy fix compared to broken piston.

 

[funk6294]

Re: 4.3GL One Cylinder Zero Compression!

Boat doctor has the right idea. Other thought is to pull the valve cover on that side and look to see if a valve is sitting high or low. What ever you do don't run it again until you fully diagnosed it. I had this issue last year and thought it was a stuck valve because it would jump back and forth from zero comp and 90psi. Well after restating it to work on the "sticky" valve the engine dropped an exhaust valve seat in the number 8 cylinder which trashed the head and piston and scored the wall. All in a matter of seconds. Had I just pulled the head off to begin with I likely would have only been in for a valve job instead of a full rebuild.

 

[Pesimist]

Re: 4.3GL One Cylinder Zero Compression!

And, if you had a hole in the piston - the blow-by into the crank case would have been noticeable, even at cranking speeds (without spark of course).

 

[Walt T]

Re: 4.3GL One Cylinder Zero Compression!

Why bother with air leak test?

Leak test shows valve leak. Pull head to fix.

Leak test shows piston problem. Engine probably done but you're gonna pull the head out of desperation and to make it look like you know what you're doing to the neighbor's hot wife who is out watering the spring flowers in a bikini top with their twin supercharged 502 Formula that makes your boat look really tiny in the driveway which leads you to the conclusion that size really does matter.

You're gonna pull the head no matter what

 

[dtescher]

Re: 4.3GL One Cylinder Zero Compression!

Do I have to remove the distributor before I remove the intake manifold?
Or, what's the proper order of dis-assembly?

Thanks to all who responded especially Walt T - You had me laughing. I'm in the process of disassembling the motor now.
But, since I've never taken one apart. It's taking time because I'm labeling and bagging every nut & bolt.

 

[funk6294]

Re: 4.3GL One Cylinder Zero Compression!

It's not as daunting as it may seem. The distributor needs to come off to pull the intake manifold. Btw, drain the the block first to help keep the water from running into the chambers when you pull the head.

 

[dtescher]

Re: 4.3GL One Cylinder Zero Compression!

Looks like stuck valve? Let me know what you think.

 

[Bondo]

Re: 4.3GL One Cylinder Zero Compression!

Looks like stuck valve? Let me know what you think.
View attachment 229164View attachment 229165View attachment 229166View attachment 229167View attachment 229168

Ayuh,.... Lotsa Rust,... Probably time for Manifolds, 'n risers,...

 

[dtescher]

Re: 4.3GL One Cylinder Zero Compression!

Should I do a valve job as well? If I replace intake and exhaust manifolds and risers, which I am going to do. Will that solve the steam coming from the valve cover problem?

 

[Bt Doctur]

Re: 4.3GL One Cylinder Zero Compression!

Unless its the pic, it looks like 2 pieces of piston missing and a valve strike.Also look like some water ingestion. that will pucker an exaust valve too.
Have the heads checked for cracks, and your missing the motor mount bolt.
head gasket looks a bit funky between 4 and 6

 

[MikDee]

Re: 4.3GL One Cylinder Zero Compression!

Unless its the pic, it looks like 2 pieces of piston missing and a valve strike.Also look like some water ingestion. that will pucker an exaust valve too.
Have the heads checked for cracks, and your missing the motor mount bolt.
head gasket looks a bit funky between 6 and 8

I agree, but it is Cyl#3, or Cyl #4, because it's a V6, not a V8. Yes that stuck valve looks funky too?

 

[Bt Doctur]

Re: 4.3GL One Cylinder Zero Compression!

Your right , a V6 .that would make it #4 cylinder then

 

[MikDee]

Re: 4.3GL One Cylinder Zero Compression!

Your right , a V6 .that would make it #4 cylinder then

True, just noticed where the (bolt missing) motor mount is, so it is #4

 

[Walt T]

Re: 4.3GL One Cylinder Zero Compression!

Valve strike and piston damage. Move that piston down in the bore see what the walls look like. Just for curiosity. I'd say that motor is done. Never know though, I've seen guys put heads back on some pretty nasty looking cylinders and run all summer.

 

[dtescher]

Re: 4.3GL One Cylinder Zero Compression!

There is definitely a valve strike. The piston damage is a reflection off the sides. The cylinders are in perfect shape. No water got below the heads. What causes a valve strike? I was hoping that a valve job and new risers, intake and exhaust manifolds all with new gaskets and she'd be done.

 

[dtescher]

Re: 4.3GL One Cylinder Zero Compression!

Anybody?????

 

[dypcdiver]

Re: 4.3GL One Cylinder Zero Compression!

Valve strike is caused when the valve does not close properly and the piston comes up and contacts it , can be due to several possible causes, rust on the stem, carbon build up, bent stem, even valve timing out etc.
Get the heads checked for cracks and deformities and as this is your first rebuild you might want to ask the shop to check the valve guides and regrind the valves. Or just do some reading and do it yourself.

 

[Bondo]

Re: 4.3GL One Cylinder Zero Compression!

Anybody?????

Ayuh,.... With all the Rust visible, I'm guessin' the manifolds are shot, 'n the valve rusted Open,...