dpfarrell

I have a 1967 427/435 with the factory aluminum heads. If I do a cold start, after about 1 minute I get BAD oil smoke out both sides of the exhaust. If I let it run for 3 or 4 minutes it will clean out and there is no evidence of oil burning at all after that. I replaced the valve seals which did not help the problem. Ive owned the car for about 10 years but have not driven it much. The engine looks to have been rebuilt before I got it. If I just let it sit a couple of hours and restart it,it will not smoke any. It only seems to smoke after the engine returns to room temp. Any help??

survivor66

Have you done a compression test? Sounds like bad rings.

Mike Terry

I would do a compression check to start out with.

dpfarrell

No I have not but Ive been told that a compression test may not be of much help.
Would bad rings cause it to smoke bad when cold then not at all when warmed up?
What would I look for with a compression test or how when would I do it? Hot or cold?
Thanks in advance for any direction.

jimh_1962

Both hot/cold then a leak down test.

emdoller

What color is the smoke? Does it smell like oil? Is it condensation? Have you checked your coolant level and/or your oil level?

Ed

65 396

My guess would be bad valve seals. They are easily replaced with the heads on.

emdoller

That's what I would have guessed but he stated he recently changed them...

kingwoodvette

He already tried that, see post #1

GTOguy

Could be valve guides, as well, causing the seals to leak. Classic case of oil seeping down the valve stems and into the cylinders.

dpfarrell

99%sure it is oil smoke. Antifreeze level is ok and oil is down some. Just got back from purchasing compression and leak down gauges. Will check and post results. I have looked at plugs when cold and 15 seconds of running and they are dry. Then after about 1 minute it starts the big smoke out. I have checked plugs at the height of the smoke and they are oil soaked.
Thanks and I will keep you posted.

Bluestripe67

Did you replace the seals or did a shop replace them? Could the wrong seal have been installed? Dennis

dpfarrell

I did make sure with the help of an engine builder that I installed the correct valve seals. Did not change the smoke issue any.

So I just did a cold compression test 155-160 on all cylinders
Cold leak down was 20 plus or minus on all cylinders.

I also did both tests hot on just a couple of cylinders with no real change in readings.

Any ideas?

GTOguy

20% leakdown is a bit high for a newer engine....Most healthy engines have less than 10-15%. Still should not be a cause of smoke out of the tailpipe, though. Out of the breather, possibly.

leif.anderson93

I think he's saying 20 lbs not 20%. That would throw it into a pretty decent range of 12-13%

GTOguy

All the leakdown testers I have used read in percentage, not PSI....but anything is possible. True leakdown testers aren't too cheap, and most home mechanics don't have one.

DansYellow66

It's been awhile since I did a leak down but don't they typically suggest 100 psi air pressure (or is my memory failing me)?? If so 20 lbs is the same as 20%.

OP - could you tell where the leakage was going - into the crankcase or into the exhaust/intake manifold?

Powershift

Are you CERTAIN that the exhaust cloud is oil and not unburned hydrocarbons (unburned gas) from a poorly performing choke??

Your symptoms suggest a carb choke problem to me............but I have been wrong before.

Larry

dpfarrell

I believe that it is 20%. I just bought a this unit to do this test. The needle was right in the middle of the "Good" zone. Not sure what that means..
I am sure that it is oil smoke. It is definetly not gas or a choke issue. Looks and smells like oil smoke. What makes no sense to me is that it only smokes on cold start up, and I mean a smoke screen. It takes about 1 minute or so to start smoking and lasts for about 3 minutes. Then it clears out and no evidence of smoke after that. It does NOT appear to be oil draining in the cylinders after it is shut off.

DansYellow66

That's a pretty classic description from what I've always heard, of oil leaking past the valve seals/guides after shut down and pooling on top of the valve or in the chamber. Then when the car is restarted the oil is burned and exhausted as smoke.

I'm no expert but if it takes a minute or so to start smoking, I wonder if that is a symptom of oil leaking past the exhaust valve guides/seals. Then as the engine starts the oil is blown into the exhaust manifold/head pipes (instead of into the combustion chamber which would be typical of intake valves). Only after the manifold and exhaust get hot does it burn off in smoke.