Compression test numbers

[J_lope82]

Based on you alls experience what are acceptable numbers for cylinder compression test? I have cylinder #5 that was a little low compared to all others. It tested at 110 psig compared to all others at ~120-145. Should I be worried about the 110? Cylinder #5 has a slight misfire but I think it’s the injector. Car does have a PI head swap on the stock bottom end.

 

[RAU03MACH]

Rings
Head gasket
Slowly loosing compression

 

[J_lope82]

That’s kind of what I dread. I don’t want it to leave me stranded. How long do you think before it goes really low?

 

[RAU03MACH]

It could last a couple of years
Just depends on if you get on it

Valves could be leaking also

 

[J_lope82]

Yeah I didn’t add oil to test the piston rings.

 

[RAU03MACH]

Just do yourself a favor and monitor it
Do the test evey oil change to see if droped

 

[RAU03MACH]

You can do it it dry or wet
Oil is messy

 

[96blak54]

I can promise you them pi exhaust valves are the leak. They terrible for any type of valve seat sealing. All the pi heads ive ever torn down, the exhaust valve sealing surface was pitted bad. The seat looked ok, the valve was terrible. And these were from great running engines. Pull the heads and do a valve job.

 

[RAU03MACH]

Based on you alls experience what are acceptable numbers for cylinder compression test? I have cylinder #5 that was a little low compared to all others. It tested at 110 psig compared to all others at ~120-145. Should I be worried about the 110? Cylinder #5 has a slight misfire but I think it’s the injector. Car does have a PI head swap on the stock bottom end.
View attachment 26656

haven't seen that book in a while

 

[J_lope82]

I can promise you them pi exhaust valves are the leak. They terrible for any type of valve seat sealing. All the pi heads ive ever torn down, the exhaust valve sealing surface was pitted bad. The seat looked ok, the valve was terrible. And these were from great running engines. Pull the heads and do a valve job.

How long do you think they will last like that?
What’s a good permanent solution to the leaking valves?

 

[RAU03MACH]

Any time

 

[J_lope82]

I’m thinking of running some seafoam through it to see what it does.

 

[96blak54]

The mating surfaces of the valve and valve seat is what i was talking about. The valve surface pits easily. Removing the heads to get a valve job is the fix.

 

[J_lope82]

The mating surfaces of the valve and valve seat is what i was talking about. The valve surface pits easily. Removing the heads to get a valve job is the fix.

I understand. I just want to try seafoam in one last tiny hope that a valve might have some build up causing sealing issues and the seafoam will break it free.
I think it started with the injector issue and then maybe that lead to bigger problems. I’m about to change the injector then I’ll try the seafoam.

 

[Dubsport]

You can run an engine flush as well, Permatex 637 works well as does Seafoam in the crankcase and helps any stuck/gummed up rings release... I have bought engine back from the dead (tech for 25+ years)... worth a try?

 

[98darkhorse.com]

for a head gasket, start the car with the radiator reservoir open and check and see if you see bubble popping up constantly. if so that is a sign of exhaust gas in the water. mine was doing it for a year then it started leaking from the head with drips above the exhaust. Thats when I PI swapped. after the swap, I was closer to 180 on all my compression test. sounds like something isn't holding 100%

 

[J_lope82]

I can promise you them pi exhaust valves are the leak. They terrible for any type of valve seat sealing. All the pi heads ive ever torn down, the exhaust valve sealing surface was pitted bad. The seat looked ok, the valve was terrible. And these were from great running engines. Pull the heads and do a valve job.

Your were spot on. The driver side head is leaking out the exhaust on #5. Now to find me some heads or maybe fix these. The piston is also missing a little chunk on top. Trying to figure out what to do next that is within my budget. I can’t afford a coyote just yet my daughter just started college. Maybe I’ll just tell her to get student loans.
There’s a guy that sells me a coyote for 3K, apparently it’s in good shape.

 

[96blak54]

Piston missing a chunk? That doesnt sound good. What do you suppose caused the missing chunk? Did that cylinder experience a popped sparkplug dropping sparkplug remnants? Or maybe detonation breaking the piston ring lands? Possible debri thru the cylinder? Definitely keep us posted with your findings.

 

[J_lope82]

I’m not sure what happened but it’s a small piece on the outside. I couldn’t see anything wrong with any of the valves so I’m guessing it might have happened to the previous owner.

 

[J_lope82]

I think the valve issue started to happen after I started playing with the WOT box.