Cracked head? Leakdown test...

[pmartino]

97 Jetta 2.0... running rough, changed the coil and cat converter, did the head gasket a little while ago.

Compression reads 180-90-180-180. I did a leakdown test and all are fine except 2... the air seems to be coming out around the spark plug hole. At first I thought it was just a bad seal but after retrying it is definitely different than the other cylinders, and the pressure won't get up past 40 or 50 as oppose to 100+ on the others.

Cracked head I assume?

[boschmann]

Are the plug hole threads stripped? I would expect the plug to blow out if that were the case. Make sure the air isn't coming out the intake or exhaust (cylinder #2 must be on TDC). Helicoil makes a spark plug thread repair kit, available at most auto parts stores.

[pmartino]

I had #2 on TDC when I tested... hard to get the piston NOT to move once the pressure builds up.

Anyways at first it was coming out the intake, so I popped the valve top with a hammer and that freed it. Then the leak was from right around the plug. I tried putting plumbers tape on the threads (probably not a great idea to have that fall in the engine, I thought later) but I had the same result. I put a water/dish soap mixture on it and it was bubbling a lot all around the hole.

The timing slipped on it about a month ago in the extreme cold... I think the engine was basically frozen. I tried push starting it a few times with no luck, then figured out it was the timing and retimed it. Ever since its run rough. I am going to take the head off and get it examined, if I can somehow get that last exh manifold nut off.

[boschmann]

Unfortunately I'd say it slightly bent the valve. Try on another cylinder & see if a little air leaks out the plug hole on it also.

[pmartino]

I tried it on the others and they seemed to hold the pressure fine, with no air coming out the plug hole.

Well if I've bent a valve that's better news than a cracked head... will get it off and see what's up.

Thanks

[boschmann]

Have the machine shop check that plug hole out also.

[pmartino]

I removed the head, stared at the valves, etc for a while, everything seems OK. I took the cam off, laid the head upside down, put the plugs in #2 and 3 and put gas on top of the valve cutouts for both. No leaks at all after about 20 min, so I think my valves/head are OK.

I put the head back on, leakdown test again... #2 seems to hold a little better pressure but still air escaping. I am pretty sure it is coming out of the oil passage which is right in front of the 2 valves on that cylinder. Is this a problem, bad rings or oil seal maybe?

[pmartino]

Did the teaspoon of oil trick for the compression test... and it jumped to 210. I guess I have a ring problem... not sure how that happened, but a big job awaits.

[veedubmechanic]

Re-ringing is not that bad, you dont even have 2 remove the engine to do it.

[boschmann]

Ar you replacing the head gasket & using new bolts each time?

[pmartino]

Changed the head bolts and gsket the first time only... my Haynes book says the mfgr doesn't specify they need to be replaced but it's recommended.

As for the ring job, I read up on and its not that bad. What other parts should I change at the same time...

Oil pump and pickup?
Oil pan gasket?
??

[boschmann]

You cannot re-use the head gasket. Re-using the head bolts is not advised as they are stretch bolts & you cannot be sure the torque will be correct. Did you let a machine shop cehck the valves?

[pmartino]

I'll have to get another head gasket and bolts I guess. I think the head/valves are fine, my compression is good an all cylinders but the bad one. I'll do the rings and go from there.

Thanks for your help.

[boschmann]

Compared to the cost of all this, a qiuck machine shop check is inexpensive.