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I am reviving a 1940 110 that was parked for 20 years. The problem that has developed is after 200 miles of driving is that it blows blue smoke when accelerating and when it idles for along time. I have taken the head off and decarbonized the top end. the cylinder walls and pistons look new, the valves look fine. Took of the pan and the bottom is the same, clean!
So that leaves a broken ring, a stuck ring, or a valve not seating.
I think!
Does some one have an idea to isolate the problem before I start to rebuild what appears to be a perfect engine?
The car has 71,000 original miles.
Thanks
John

Add worn intake valve guides (or worn intake valve stems) to your list of things to consider. If the intakes are worn, chances are the exhausts are worse. They don't quite fit your symptoms which sounds more like rings, worn intake guides symptoms are generally blowing blue smoke after a long decelleration and then stepping on the gas, but they deserve a look anyway.

EDIT - HH makes a good suggestion!

Don't know if vacuum wipers but if so does it have a vacuum section on the fuel pump that might have deteriorated and allowing oil to be sucked in?

Thanks for the suggestions. I have electric wipers so the leaves the rings suggestion. Any thoughts on how to free up rings?
I remember that my dad who was an auto mechanic in the 30's and 40's had a list of symptoms for exhaust smoke to isolate the problem. about all I can remember is white smoke=water, blue=oil and black gasoline. Does anyone remember what the exhaust symptoms for ring problems, valve problems and low compression, he could tell which cylinders had weak compression by holding his hand over the exhaust and having someone accelerate and let drop to idle speed.
Any one out there remember these techniques I think it would make an interesting and useful post. Especially for those of us who drive our cars on road trips or do not have the latest diagnostic equipment.

John

You may want to do a compression check. If you don't have a compression tester, you can get one fairly inexpensively at places like Amazon.

Do the check once with cylinders dry, then add a teaspoon of oil to each cylinder before you check again. If any cylinder shows significant improvement, that is the cylinder with ring/piston/cylinder wall problems.

If you have a bad cylinder and compression does not improve with oil then there is probably a valve problem.

Tom

Tom, thank you will do tonight.
Will let you know the results.
John

A puff of blue smoke on startup, bad intake valve guides. Smoke on acceleration, bad rings.

The best cure may be to drive it. Sometimes old rings will come back to life after you drive a car a few hundred, or a few thousand miles. You have to get the engine thoroughly warmed up short trips won't do much.Add some Rislone or Bardahl and go for a drive.

Or you may need a ring and valve job. This was a standard service procedure on prewar cars. Believe it or not, they usually needed a ring and valve job after 20,000 to 30,000 miles.

A compression test will tell you a lot. If compression is low retest after squirting a little oil in the cylinder. If it comes up, the rings are bad.

Driving may free things up but depending on how bad or persistent, may not really be much of an option in the San Joaquin Valley where we live. Being further North, Modesto may be a bit better off but because of the same blue smoke problem, a good friend and his 54 daily driver was turned in to the air resources board by some person with nothing better to do. He was cited, fined, and given two options--fix it or park it.