442 Compression and Cylinder Leakage Test

Good evening all,


I bought my 68 442 400/400 last winter expecting to have to rebuild the engine as it has 126k known miles on it. It runs, albeit rough due to carb issues. I'm not driving it at this point as it needs a total restoration. I spoke with the owner prior to the one I purchased it from who bought the car from a lady in her 60's when it had 86k miles on it around 1980. The only engine work he did is to replace all of the lifters - but not the cam shaft - when one lifter failed. He indicated no major engine work had been done prior to his ownership and the guy I bought it from stated no engine work was done in the 12 years he owned it either. The car sat for over 10 years before I bought it last December. I started the engine with fresh gas after pre-lubing the engine with a pressure tank. As stated, the engine ran rough but I was able to drive it at low speed about 2 miles earlier this summer. It would not run beyond burning the gas used to prime the bowls through the air vents when I tried starting it last week.


Where I'm at now is to determine if I need to rebuild the engine for certain. My thought is it's unlikely I'll put more than 10k miles on it in the time I'm likely to own it and I've read of 400's clocking close to 200k before rebuilding. I'll be driving it as a weekend cruiser. So, in an attempt to make the decision, I performed both compression and cylinder leakage tests last week. Both tests were performed on basically a cold engine after trying unsuccessfully to keep it running as described above.


All cylinders are within 20% of each other in compression, with no cylinder below 100psi as specified in the Chassis Service Manual. Most sources recommend having all cylinders within 10% however. The cylinder leakage test correlates fairly well with the compression test, with those cylinders having lower compression numbers also having higher leakage numbers. Focusing on the weakest cylinder, #1, the leakage of 53% seems extreme to me and it's also nearly double the leakage of the best cylinder. All cylinders leak into the crank case with audible air hissing out of the oil fill and valve cover vent pipe. Cyl. #1 is by far the worst and there's enough air blowing into the block that I can't contain it with my hand on the oil fill pipe as I can with the others. No leakage from any cylinder can be heard from the carb or exhaust, and there's no bubbling in the radiator.


My thoughts are the engine is tired and needs a rebuild, for my enjoyment, reliability, and future resale of the car at some point. But, I'm looking for thoughts and your comments. Thanks - Don


Here are the results:

 

I would figure out why it wont run right first. Get some miles on it, then run your leakdown and compression tests again. I bet you see a noticeable improvement. The engine is probably gummed up from sitting for so long.

When you did your compression test, did you have all the plugs pulled out, and the throttle held wide open? The idea is to eliminate all the variables, removing the plugs will increase the cranking speed and keep it the same. Secondly, ideally the test should be done with the engine warm. I remember correctly, the textbook results is the first pump of compression should be at least half the final reading, if not, the ring seal isnt the greatest.

 

I agree with the above. I would also remove plugs, squirt some ATF in cylinders, crank and repeat for a few days. Then do a wet compression test with some engine oil squirted into cylinders. My bet is stuck rings, corroded cylinder walls. But you should see how well you can get it to run before jumping right into a rebuild. Opening it up can add problems if not done well.
Is it noisy?
How is the oil pressure warm and with a mechanical gauge?

 

Good recommendations - I'll have to hook up a mechanical oil pressure gauge and get it running. My best guess is a fuel delivery issue as carb runs dry after it burns the gas I prime the bowls with. Fuel tank and pickup are new, but fuel lines are possibly cracked or porous. Carb is a mid-70's QJ from an Olds 350 with multiple stubbed off vacuum lines. I have the correct QJ core for rebuilding so I may proceed with that to get it running again. I'm curious to re-do the compression and leakage tests on the engine when warm to see how much difference it makes. I'll post back with updates as I move forward. Thanks for your advice! Don

 

Sounds like fuel delivery is an issue. Have you checked/replaced the fuel pump? That's a pretty quick and easy task, at least without A/C! Old and dried out hoses can work surprisingly well if they haven't actually broken.

FWIW, I ran a 350 that had a weak #1 for years. Still ran well and was tons of fun. Just depends on what you want from it.

 

Compression test is not bad at all. Sure cylinder 1 is a little low, but it's still okay. My #1 cylinder is a little lower than the rest in my 350 and it runs okay. It's not a hot shot by any means, but she's got a lot of life left in her.

I agree, I would figure out the carb/fuel delivery issue(remove the line and put it into a cup/bowl) and crank the starter, see how much fuel you're getting.

It'd get it running and drive it around a little, close to home, but get it up to temp and run it. Even through a bottle of Rislone yellow bottle engine treatment in it and run it.

Then re-do the tests and see where you are.

Even a worn 400ci motor will have enough juice in it to make you smile. Is it tired, probably. Does it need a rebuild? I wouldn't say that yet. It might last a long time as it is.

IF you get the car done, and a couple years down the road the engine gets worse, have it rebuilt then. More money is available and you've enjoyed the car in the process.

 

Good points - I have suspected the fuel pump as being weak and am planning a flow & pressure test. The body and front end bushings are in such poor condition it is not really that fun to drive at this point. If I have to lift the body to replace bushings, it seems to be a good time to pull the engine. The trans leaks and slips and needs some attention as well so if I do need/want to rebuild the engine it would be easier to do at the same time. But, if I can get the miles I want out of it, I'm not against doing the other work and just keeping the engine as is for now - I can always pull it later if needed. I do want to get this car out and drive it, even if I do end up pulling it off the road for more extensive work an a few years. I'm planning to move forward with more testing next week and hope to get it running enough to warm up and re-test. The weather's still good here next week it looks like so I may get a few miles on it. I'll let you know. Thanks for your great suggestions! Don