Engine Well Damn - Low Compression

[Airtime]

I've been trying to address a slightly rough idle. Did plugs, wires, adj carb & timing etc. ...finally broke down and bought a compression gauge (evidently I own a leakdown checker but not a compression guage???). Anyway, 7 cylinders read 130psi - 135psi and cyl #4 reads 65psi. Dumped some 15w40 in there and compression went to 90psi. Google says that could be stuck rings and I have now soaked for days different things. I tried mm oil, seafoam, atf, a 50/50 mix of atf & acetone...now still at 65psi.

It runs fine and I drove it 2 hrs round trip a few weeks ago and got 15mpg. I almost wish I didn't know compression is the issue...but now that I do I have to fix it. I'm going to try to do it without pulling the engine. It's got 108k on the odometer but sat for at least the past 10 yrs.

Today or tomorrow I'll start by pulling the intake/carb and passenger side head. I'll look at everything I can from there.

Actually, just now I'm thinking. Maybe I should pull the oil pan 1st. That way I can see the cylinder wall. If it's smooth then pull the head.

Thoughts?

 

[TSB8C]

Agree on dropping the oil pan and check the cylinder wall. If it's scored than you know what needs to be done. If not and it's smooth, then you could just pull the head and check for a broken or stuck ring and make a decision from there.

 

[jzak]

Why you looking for problems bro! Just add some motor honey every once in a while, and you're good to go. Seems like everyone nowadays wants to pull an engine the second you hear some piston slap or rod knock. My dad drove his ford country squire 50K on zero compression. No problems.

 

[Belizean]

My number 4 is a little lower on compression also, but not enough that I’m going to do anything yet either. Not nearly as much as yours though.

 

[Airtime]

 

[Airtime]

Just replace the exhaust valve and put it back together? What causes this?

The rings, bore, & rod journal all look great.

 

[Apple]

Any number of things can cause a burnt valve like that. If everything else of okay a quick fix with a new valve will get you back running.

 

[Airtime]

Got the valve in and together enough to crank. Compression right in line with the other 7 now. Today I'll get the valve cover and exhaust manifold back on then add oil and coolant so I can start it up.

 

[Airtime]

 

[CJ]

Got the valve in and together enough to crank. Compression right in line with the other 7 now. Today I'll get the valve cover and exhaust manifold back on then add oil and coolant so I can start it up.

Great! Compression is a good thing!

 

[Jeep Soup]

I know this is a late post....
Lean Out can cause a Burnt Valve. That one looks like it Cracked Too, and Burnt following UP the crack.
Have you run it out of Gas during or right after a hard load on the Engine? No. 4 cylinder is in the Middle of the Manifold, and closest to the exhaust pipe connection, and 5&6 exhaust gases are passing before No. 4's Runner also. So it can Amplify Lean Out.

Just a guess

 

[pat76cj]

Based on the valve shaft and burn spot, It looks like the valve quit rotating as it should. Probably got some debris in the guide, causing it not to spin.

Assume the lobe and all were decent?

 

[Airtime]

Yes, everything else looked great. It runs so smooth now, I'm very happy with my repair.

 

[CJ]

Yes, everything else looked great. It runs so smooth now, I'm very happy with my repair.

It is so happy to hear that old school real repairs work!