Jeff's Classics

I bought my '72 442 convertible in Feb '13. It has ~85K miles, and looks completely stock. The last two owners did not rebuild the engine or do any major work on it. It ran pretty well with a fresh numbers matching carb, new plugs, wires, cap, rotor, etc. But on a recent drive with my wife it suddenly developed a rough idle and a noticeable miss. I let it sit for a while (weeks) since our baby boy was about to born (June 3). I just had time to mess with it again and here's what I found.
The plugs for #5 and especially #7 had some oil, although they weren't fouled. I replaced them but it didn't seem to help. While they were out I ran a compression test, and all cylinders were around 155-160 psi, except #4 which was ~133 psi. My Olds service manual says all cylinders should be within 70% of the highest one, with none below 100 psi. Well, it's within spec, but I'm not too happy with that reading on #4.
So I put oil in it and it went up, which corresponds to leaking rings.


So I guess I'm looking for opinions and suggestions. I'd rather not pull this motor and rebuild it now, as I'm knee deep in my Javelin 401 build, house projects, new baby boy, etc, but I guess it's going to have to come out and get rebuilt to run correctly again.


One more big question...should I build a 455 for it instead? This is a #s matching engine/trans, but I don't have the 442 documentation and I plan to keep the car so maybe just go 455? I have an Edelbrock Performer and JR exhaust manifolds for the 350 so I could build a nice 350 with what I already have.


Look forward to your thoughts and input.
Thanks,
Jeff

MDchanic

Those compression numbers are completely fine for a fairly well used engine.
The one slightly low cylinder should not be the cause of your problem - it's probably been like that since well before you bought it.

I would go over the common tune-up items first, thoroughly and carefully, and then reassess.
Cap, rotor, points, condenser (maybe), spark plug wires, dwell, timing, confirm operation of mechanical and vacuum advance, and confirm fasteners tight and proper operation of carburetor, including correct float level and needle and seal sealing.

I can't say which without more information, but it's probably one of those things.
I can say that when I've had missing and rough running problems with these cars in the past, with the car in frequent use and everything reasonably well maintained, the cause has usually been points rubbing block wear, leading to points closing, or a bad spark plug wire.

- Eric

oldcutlass

Also hook a vacuum gauge to it and make sure you have a good steady vacuum. If you have old fuel in it run it out and don't do anything major until your have fresh gas in it.

MDchanic

Yup. I'm not pushing the "low vacuum" theory yet, as it sounds like the car is rough while driving as well as at idle, but I agree that a vacuum gauge will tell a lot, and, of course, checking vacuum lines and connections is part of the tune-up rundown.

- Eric

rustyroger

It may be that a piston ring decided to break when it suddenly developed rough running, although I would expect the low reading cylinder to be the one that was oiled.
To rebuild or replace with a 455?. You already have a 350, which is matched to your current transmission, cooling system, suspension etc.
Unless you want to go drag racing I would settle for a well built 350, particularly if it is the original engine. For the cost of transplanting a bb you can wake up a 350 quite considerably.

Roger.

67442nut

Since you've recently done the usual tune up stuff, you might want to pull the valve covers
to check for a bent push rods and/or a broken rocker arm bridge.
Do you have an oil pressure gauge? If so, is oil pressure normal?

Jeff's Classics

Hi Guys,
Thanks a million for the replies. MDMechanic's reply made me question whether the "low" compression reading was really an issue. I pulled the car out today to check the timing, and pull the spark plug wire off #4, since it had the low compression. I accidentally set my work glove over the carb while putting the other on, and the idle didn't change. I would have expected the engine to get rougher or die, so I suddenly realized I must have a big vacuum leak. Got the carb cleaner spray out and long story short the cruise control bracket I removed had a bolt that went into the #1 cylinder intake runner...MASSIVE vacuum leak. Plugged it with a bolt with Teflon sealant my car is like new! The good news is that all the usual wear parts have been replaced (wires, coil, plugs, points, condenser).
Thanks again!
Jeff

MDchanic

There ya go!

It's almost always something simple.

And rather than throwing parts at it, you found that it cost nothing to fix.

We here at ClassicOlds are just the toolbox, giving you the tools you need to fix your car yourself. ®

- Eric