Overheated engine

[gradon]

I bought a 95 xj off craigslist($300) that had been overheated, ran rough and needed a headgasket(this the 3rd one I've bought broken in order to fix and resell in the past 8 months). I took the head off, cleaned the ports out real good, cleaned the piston tops, reinstalled w/ a new headgasket(I knew I'd be using a hg sometime soon strokedwj). Welded cracked header, replaced bad motor mount, cleaned tb and intake mani, new wires, cap, rotor, and plugs, reinstalled all and fired her up. Idles rough, but once you get above 1500 its good. Drive around and it feels like half the power. So today I did my first compression check (cold--didn't know engine should be warm until plugs were alreaedy out). Started with 1:115, 2:60, 3:75, 4:30, 5:150, 6:150. Anyhow, was there anyway I could've known the rings were bad w/ a blown hg? I just want to learn a lil for future reference.

[Muad'Dib]

I dont think there would really be a way to know without doing a compression check as you already have done... and you cant really do that properly without replacing the gasket... cause for all you know the lost compression could be from the gasket not the rings...

Unless there is a way to look down onto the piston when the head is off and see something... but i doubt that is the case. Either that or actually remove a piston... which requires more work.

[SilverXJ]

If you knew which cylinder the head gasket was leaking on you could measure compression on the rest and ignore that one. If you need to determine which piston was leaking past the head gasket you would do a leak down test and check for bubbles in the coolant, air from the valve cover, or air from an adjacent cylinder to which you are testing. I suppose you could also listen for leaks from the intake manifold or the exhaust to see where the better cylinders are leaking from, if they are.