Source of blue smoke. Valves or piston rings?

[mulrik]

I have blue smoke coming out of the tail on idle and acceleration, and I'm using about a liter of oil on 200 km. Now my question is: Where would you estimate it is coming from? Here's the story:
The blue smoke problem appeared from one day to the other. On the first day I had it up to 6000 RPM to test the ignition which we recently overhauled. The next day I noticed the blue smoke problem. I tested the compression a month ago and it was 165 psi on all except two neighboring (#2 and 3)cylinders (suspect a blown head gasket). It has allways (more than a year) had blue smoke at start up especially cold starts. I checked the spark plugs and on # 4 and 6 traces of oil are coming out of the plug hole even while the plugs are tightly in. On the threads of the plugs (only #4 and 6) I can see oil, but the "tip" is just the right color on all plugs.

Where do I start? I suspect the valve seals more than the piston rings, but do you agree? Could I have blown the perhaps already worn valve seals going to 6000 RPM (warm engine of course). Any other ideas as to what has happened?

Best wishes and thanks for your input!!!
Ulrik


'67 250 SL Papyrus White 113043-10-000023

[knirk]

Ulrik,
What compression value did you get on cyl #2 and #3?

I had blue smoke at acceleration and also on retardation, and my plugs clogged up by oil debries and needed cleaning for every 250 miles. I overhauled the complete engine since I had it out and didn't know the milage. My blue smoke came from worn valve stems and valve guides.

Per G. Birkeland
69 280 sl aut 834
Norway

[mulrik]

I'm pretty sure it was ~145 PSI, on #2 and 3.

Per, what do you mean by blue smoke at "retardation"? And your overhaul was that complete with balancing pistons and crankshaft and how long time did it take?
Ulrik


'67 250 SL Papyrus White 113043-10-000023

[A Dalton]

As you noticed it right after high fevs , my first check would be to see if the valve seals caps have popped off...common fault w/some seal kits

[Benz Dr.]

I think he means deceleration.

 Sounds like valve guides to me.



Daniel G Caron

[knirk]

Yepp, I ment deceleration.

This is what I replaced:
Cylinder head: All 12 valves, valve guides, valve seals, timing chain, chain guides, 3 rocker arm clamp springs and cylinder head gasket. A local shop checked the head for warpage, installed the valve guides and grinded the valve seats.

Cylinder block: Piston rings, big-end bearing shells and main bearing shells. The local shop checked the rest for wear and honed the cylinders.

I took a chance and did no balancing at all. The cylinder block had no wear at all and had previously been bored once.

Per G. Birkeland
69 280 sl aut 834
Norway

[Malc]

If you mean, when I take my foot off the accelerator (gas pedal) and I get blue smoke

most likely....Valve guides and or seals
Classic symptom associated with BMW's too![:p]

especially if your compression is ok
Malc

[rwmastel]

quote:Originally posted by mulrik

I checked the spark plugs and on # 4 and 6 traces of oil are coming out of the plug hole even while the plugs are tightly in. On the threads of the plugs (only #4 and 6) I can see oil, but the "tip" is just the right color on all plugs.

Mulrik,
I've heard that you can have something loose in the head that allows oil to leak down to the spark plug area from above.  Something in the valve train system, I believe.  Others having direct experience with this will hopefully explain in better detail.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[ja17]

Hello Mulrik,
With this amount of oil consumption the problem should be easy to spot. Oil deposites will show up as a hard crusty build up on the spark plug or plugs. If you find no crusty deposites the problem can be a loose exhaust valve guide. This will dump oil into the exhaust system without fouling the spark plugs. You can remove the valve cover and with a strong light look at each guide through the valve springs. The bad guide will always have its valve seal off! Read your plugs and check back with us.
If your lucky, as ADalton mentioned, possibly just the seals have come loose!
Oil leakage around the extermal parts of the spark plug are usually not related. The threaded ball stud holes above the plugs sometimes seep oil

Joe Alexander
Blacklick, Ohio

[mulrik]

Thanks everyone for your contributions.

The answer to my problem was that a valve guide was loose. The exhaust valveguide of cylinder number 6 was loose and could be removed by hand. It can also be rocked from side to side just a little bit. The valve was COVERED in crusty carbon deposits. Also the intake valve guide of cylinder number 4 could be removed by hand, but doesn't rock. None of the seals had come loose.

Do you guys recommend that I replace all valve guides or just the loose ones? And what about the lower seals, should they be replaced??


'67 250 SL Papyrus White 113043-10-000023

[ja17]

Hello Mulrick,
It would be foolish not to have the entire head reconditioned while it is off. Find a good automotive machine shop or experienced technician who can check it out for you and recondition it.

Joe Alexander
Blacklick, Ohio