Low compression wet and dry

[1gcrazy]

So I know that my results point to a little bit of both, valve seals and rings but I wanted to get every bodies consensus.

Left to right, dry/wet

92/112 94/104 100/115 60/75

I can understand the rings being "tired" but with what they're supposed to be... would it be safe to say that new valve seals could freshen this motor up enough to drive it a bit?

I'll be rebuilding a different motor for this car shortly but I'd rather drive it in the mean time...

 

[brassc2007]

if you did a wet test and it brought the numbers up then it is most likely the rings that are bad and the valve guide seals are fine. The valve guide seals main purpose is to keep oil from seeping into the cylinders not to help hold the compression, that is the valve seats purpose. Also i have a question when you did this compression test what was your engine temperature was this a hot or cold compression test?

 

[Calan]

If that's a 4g63 and those are accurate compression numbers, I'm surprised you're still able to drive it at all.

 

[1gcrazy]

Valve guides, my mistake.

I understand that if they go up it must be my rings but they didn't go up a whole hell of a lot... just about 15%ish...

 

[brassc2007]

was your motor at running temp when you did this test?

 

[1gcrazy]

Thats the only way to DO The test. Well correctly that is...

Yes it was as warm as it gets.

 

[brassc2007]

You could perform a leak down test to see where the compression is going that would give you a better idea but i would say if it is running now id just keep driving it the only thing that would worry me is the 60/75psi cylinder otherwise they are roughly close together

 

[1gcrazy]

The body is trash. It got hit in the back and isn't repairable I was going to put this motor in my shell and drive that while I rebuilt a good motor. Ultimately this car is getting parted out and my shell is getting driven.

 

[Calan]

With those numbers, it looks like your rings are worn to the point that adding a capful of oil isn't really going to seal them much, so I'm not surprised that the compression didn't increase a whole lot.

Personally, I wouldn't bother with doing anything to the head until you take it apart for a full rebuild. I doubt if you'll gain much (if anything) with valve work alone.... so why pull the head twice?

Just my .02 of course.

 

[1gcrazy]

With those numbers, it looks like your rings are worn to the point that adding a capful of oil isn't really going to seal them much, so I'm not surprised that the compression didn't increase a whole lot.

Personally, I wouldn't bother with doing anything to the head until you take it apart for a full rebuild. I doubt if you'll gain much (if anything) with valve work alone.... so why pull the head twice?

Just my .02 of course.

Yeah, well I value those couple of pennies. I guess i'll just hurry up with the rebuild. I was trying to get this all done before my birthday on the 20th. Kind of a bday present to myself.

 

[Calan]

Well happy early b-day!

 

[dsm-onster]

Just a note. Adding oil to the cylinder ALWAYS raises compression. Because wh have dished pistons, the oil doesn't trickle down to the rings. It puddles un the piston crown. So your compression is not going up because of your rings being wet. Therefore it could be something other than your rings.m Like a REAL bad headgasket. Or slightly bent valves.

 

[1992awdlaser]

if you did a wet test and it brought the numbers up then it is most likely the rings that are bad

This is a complete guess when it comes to our cars. The reason for this is because when you do a wet test the oil will sit on top of the piston. This is going to raise compression every time because there is less room for the air when the piston is at tdc. Everything else you have said is correct though (and this is for flat top pistons also).


My suggestion is add air to each cylinder when at tdc via a compressor. Just set cylinder 1 to tdc with all valves closed(compression stroke). Add air to that cylinder. Pull out the dipstick and see if you can hear/feel air coming out of the dipstick tube. Going around the car and see if you can feel/hear air coming out of your exhaust. Also check the coolant for bubbles.

If there is air coming out of the dipstick tube, rings. If there is air coming out of the exhaust, valves or valve seats. If the coolant is bubbling, hedgasket.

 

[1gcrazy]

What should my psi be set at for this? Just full blast?

 

[brassc2007]

im not sure what psi you would set it at but im gonna guess not a full blast, a full blast im sure just like on my v8 in my truck would be enough pressure to push the piston down. Im going to say somewhere between 60 and 100 psi. From what i have read anything over 100 will push the piston down

when you are testing for rings throw your finger over the dipstick tube and feel for air, if you cant then with the valve covers of lightly tap the valve with a rubber mallet if there was air coming out the exhaust and after tapping lightly it stops then your valve seats are wore out, And last if there is bubbles in your antifreeze then your head gasket is gone. If you want you can go to google.com and type in leak down tester and there are tons of cheap ways to make your own with a 100 psi gauge that way you can tell your percentage of leaking. For example if you put 100 psi of air into the cylinder and it leaks down to say 80 psi, that would be taken as a 20% leak and that is horrible.