Exhaust coming out of valve cover

[DEPUTY101]

I have an enormous amount of exhaust coming out of my valve cover oil fill cap and no compression in 5 out of 6 cylinders. Could this be the piston rings shot and exhaust blowing by the rings through the block? HELP! This is my primary vehicle, hehe

 

[Robb]

The only way exhaust is getting into your valve covers is if the valves aren't seating. This would also explain the lack of compression. Which 4.0 do you have? How many miles are on engine? Is it treated nicely?

Robb

 

[Robb]

Sorry, for got to look, it's a '91 4.0 OHV.

 

[BigOne]

What you likely have is what is called "blow-by". This is usually caused by gasses passing the rings, getting into the crankcase and being vented up through the engine. Remember the PCV valve on the valve covers? That is a "Positive Crankcase Ventilation" valve and what it does is allows those gases to be passed (one way valve) out of the engine and into the intake air to be burned, on vehicles so equipped.

Significant blow by is a sign of piston ring wear.

If the rings are so bad that you have no compression they have likely broken and the pieces have gone into the engine.

The other possibility is that you have valves stuck open. There are several possible causes for this but most likely broken springs/spring retainers/valve stem.

But as it is in 5 of the six cylinders, I am suspecting blown head gaskets.

I take it you noticed the blow by before the current problem of no compression as with no compression in 5 of 6 cylinder the engine will not run.

 

[88vert]

Doesnt sound good

 

[DEPUTY101]

Okay gentlemen, here's the deal. Believe it or not, my baby DID run! (just barely!)We finally got the engine out last night, and I have never seen pistons that looked so bad. every ring on every piston was collapsed and one piston was cracked through the middle.two had broken skirts, three had broken ring guides and all the bearings were a nice shiny copper color, hehe. I will be having a short block done this week. Thanks for all your help guys.

 

[Alec]

Ouch! How did it get so bad?

 

[BigOne]

WOW

Must have a TON of miles on it to be that far gone.

 

[Derrick]

I'm gonna hafta go with either stuck open valves or improper seating, pop off the valve covers and check it out...