Single Piston Ring Replacement

[TimD]

Looking for a bit of advice here. I am in the process of removing my cylinder heads to have them refurbished (surfaces, valves, exhaust studs). I did a compression test before I removed them and one (#4) cylinder was low (90psi vs 130-140 on others). I dripped a bit of oil into it and it came around to 120psi. After repeating this, I'm fairly confident this is bad rings on #4. My question for my case; Should I have the liner honed? If so, should I remove it? If I do, is the procedure to reinstall straightforward? If I don't remove it, what am I looking at? What other considerations should be made?

The engine is in the car right now btw and runs pretty good all things considered.

Thanks,
Tim

[vwdmc16]

Perform a leak down test to confirm if the piston rings are the main leak, it could be the intake or exhaust valve that is the main leakage.

[TimD]

Ok, but if this confirms the rings are the culprit, what of my original questions?

Thanks,

[vwdmc16]

In my opinion, if you are going to do one and the heads are already off. Might as well do them all.

Ive never taken out a cylinder with the bottom end assembled, id bet its possible but quite hard. You will need to do alot of cleaning and go through the whole cylinder shimming procedure as the manual says. Hone the cylinders, snd return them to the same place and position they came from.

[Bitsyncmaster]

When you hone a cylinder you use a "lubricant" which can be solvent or water so you really need the cylinder removed or have the pan removed.

You will need the pan removed anyway to pull the piston and rod from that cylinder. You use a ring compressor to install the piston so I don't think you can just pull that cylinder with the piston still bolted to the crank.

[David T]

It would be unusual to have just 1 cylinder leaking badly because of the rings. To do a cylinder you WILL be removing the pan and the rod bolts to remove the piston before removing the liner. As mentioned you aren't going to get the liner back in with the piston still in there. The thing to do is verify you have a problem with a cylinder and determine, to the extent possible, what the problem is.