L24 smoking badly. Teardown pics... any opinions?

[tstewart]

I have a 72 240 with the factory L24 that smokes pretty badly. I did a compression test several weeks ago and found compression to be good in all cylinders and almost no difference in compression between cylinders. I then purchased a leak-down tester and performed a leak-down test. The test revealed a problem with cylinder 4. The cylinder would not hold any pressure and leakage could be heard most distinctly when listening at tailpipe.

I removed the head today. As you can see, when I pulled the exhaust manifold, I found the exhaust port for cylinder 4 to be pretty nasty. I also posted pics of the combustion chamber and cylinder/piston for cylinder 4. I don't see any evidence of a burned valve, so I was thinking bad valve guides or seals. Additionally, I've heard that clean edges around the piston are indicative of oil leaking around the rings but the crud is uniform here... which backed up my suspicions about valve guides or seals. But...

Inspection of the cylinder bore reveals no obvious scoring. However, near the top of the bore, there is a small pit (for lack of a better word). It is somewhat irregular in shape and is approximately 1/4 tall by less than 1/2 inch wide. It looks like a rust spot caused by condensation in that area. It is very shallow, so much so that if I hadn't seen it, I probably would not have found it by touch alone. I pulled out my telescoping gauges and outside micrometer set today to check out the cylinder bore, but my mic set only goes to 3 inches. I'll probably pick up a larger mic or a dial bore gauge and check it out.

Anyone have any opinions based on the pics? Anything else I should look at while I'm here?

[d240zx2]

Since your leak-down test failed on #4, I'd say that your compression ring is shot. Drop the pistons, re-ring 'em, new bearings/seals, hone the cylinder walls with a good strong etch. Do a good valve job w/ new seals, too. Put it back together and I'd wager your problem will be over for at least another 100K miles.

FWIW

[280~Master]

Sounds like d240zx2 wants you to rebuild the engine. I would say to heck with it and drop an L28 in its placce that runs better. Now if you have matching numbers keep the old one and rebuild it. If money is an issue go with L28 if not then go crazy with the L24.

[sblake01]

What d240zx2 proposes is not that expensive if you can do the work yourself. I can do bearings/rings and cylinder honing and the valve job myself. The only thing I'd have done at the shop is the cylinder head surfacing. Overall, it would cost less than purchasing and sorting out another engine.

[tstewart]

As it happens, I have a newly manufactured crate motor sitting around that I was planning on using for another project. I've since decided to go with a turbo L28 on the other project, so I'll probably just drop the crate motor in this one. The numbers do match on this car, but I'm not too worried about it as it is a rust bucket that I drive back and forth to work sometimes. Way too far gone for me to consider restoring.

[d240zx2]

Sounds like a good program to me. Let me know how it works out as I'm considering the same thing once I blow up my 2.4.

Regards,