Oil smoke from 1971 350 SL

When I start the cold engine and drive 4 to 5 minutes, suddenly a heavy oil smoke sky come from the exhaust system, like the smoke from a steam train. After some minutes the smoke disappear.
I have drive the car the same way several times ,and the same
recur . I have change the Supplementary air valve, and my be the problem are a little less. When the engine have normal tempratur, the engine does not smoke at all.
Any idea ?
From Norway Arvid

[neileg]

What colour is the smoke?

If it is white, then it is just water vapour that has partially condensed in the cold exhaust system. When the exhaust is hot, the water vapour stays as a gas and is colourless. This is a normal feature of any engine, just more noticable.

If it is blue, then it is oil burning. This is probably caused by oil running past the valve stem oil seals when you turned off the engine. This then burns off when you start her up again. Renewing the seals is a relatively simple job.

Hi Neileg
The color of the smoke are blue, and it smell burmed oil.
Are the possible for the oil to run into the exshaustystem from the valve stems? And the oil are burning when the exshautystem goes hot?
I run the car today , and it smoke VERY HEAVY after some minutes.
After 10 minutes the smoke was gone. The engine runs very fine, an no smoke at all when the car are goes warm.
But it does not smoke every times I run the car.?
I,m desterat
Regards Arvid

I think I have found the problem with the oil smooke.
I took a jam glas and conect one rubber hose to the valve cover outlet, and the other to the supplementary valve.
When i start the engine the come ca. 0,2 liter oil in the glas!!!.
If I dont have the glass , oil will go into the intake pipe.
But I dont know wats wrong. Any idea???????

[neileg]

Sound more serious than I thought.

To pump the oil out like this, there must be pressure getting into the crankcase. The two favourites for this are blow by and head gasket.

Blow by is caused by bore wear - the cylinder walls and or the pistons, or possibly the piston rings being worn. When the engine is cold, the seal between the pistons and the cylinders is poor and the pressure from combustion can leak past into the crankcase which will pump the oil out. As the engine warms up, the pistons expand, and the seal improves, the problem goes away.

If the head gasket is leaking, then it may seal when cold, but as the engine warms up, it may leak between the cylinder and the oilways. This will pressurise the crank.

You will need to get this tested. Checking the cylinder compressions or better, a leakdown test, will help to show up bore wear. Otherwise, you may have to take the heads off to check for the gasket.

If you are very, very, very lucky, you may have siezed piston rings. It is possible that a Redex treatment may unstick them. I have tried this many times. It has worked only once!