Blue smoke while rolling downhills

[MowagW200]

When I drive downhills no foot on the pedal at about 2500 rpm, after a really short time blue smoke comes out of the exhaust pipe. Afterwards when the road is flat and I put my right foot back to the pedal after a while the blue smokes stops coming out of the pipe.
When the truck stands still and I hit the pedal to accelerate the engine few times, then behind the truck I could smell the taste of burned oil.
A friend of me thinks the rings at the pistons are weared. I think the caps around the stems of the valves are old. What do you think?

[wittyhoosier]

That totally sounds like a question from an ASE test: Technician A says bad rings. Tech B says bad valve stem seals. Who is right?

A Tech A
B Tech B
C Both
D Neither

I say, valve stem seals. With the throttle closed you are drawing much more vacuum during the intake stroke, pulling the oil along the stem.

[MountainMoparRobin]

How about start up?
if you have blue smoke at start up then yes the stemseals

[MowagW200]

If I would have a cloud of blue smoke after a cold start I would be glad. But I'm afraid there is no cloud at all after a cold start.

Only if the engine is hot and was sitting for about 5 to 10 min, it's rather hard to start the engine. Then it exhaustes a bigger or a smaller cloud (black). That looks like it gets too much gas when hot.

Very rare I could see a blue cloud during an upshift of the gear box, especially when the engine is not fully warmed up.

[achille]

Have to agree with wittyhoosier,sounds (more) like valve stem seals/guides.

[MowagW200]

Furthermore last summer I noticed that one spark plug was glossy black (like from burned oil). As long as I remember it was from cylinder 5 (second last on the pass side).
At home I've got a complete set of stem gaskets (8 for input stems 8 for the output side, the parts are different for the input and the output side). I would like to mount it w/o removing the heads.

By the way:
Because I'm useing a slightly hotter camshaft from (http://www.camcraftcams.com/) the vacuum rised from about 5 (with the stock camshaft and the stock 2bbl carb) to 15 hg at idle (with the new camshaft and a 500 cfm 4bbl edelbrock).
How does a broken piston ring sound when the engine is running with idle speed (+/- 550 rpm)?

[MountainMoparRobin]

If you have a broken ring, well, you would have heard a terrible metal sound for a period long enough for it to accomodate for the metal thats not supposed to be their, and you'd see something in the oil when you drain it, you could do a compression test that would help confirm that also.
By the way 383's were natorious for the blue smoke when backing off, nothing to do about it, just a charataristic of the engine

[MowagW200]

Thanks a lot for your answer, MountainMoparRobin. Because I don't hear a metallic sound (clatter or so) I don't think that a ring is broken. About two years ago I got results from a compression test. All cylinders were mor or less at the same level. At this time it was putting out blue smoke under the same conditions. But not as much and not as fast after releasing the throttle.

When I was very you a neighbor of me owned a Plymouth Fury 3 hardtop (1967) with a 383 super commando. His car was putting out blue smoke every time he started the engine after sitting for few hours (only from one tube, there was - I guess - a factory dual exhaust system installed). At that time this car was about 10 years old.

If my truck would do so, I would be sure the gaskets of the valve stems are worn. But I'm astonished because it's a poly that should never putting out blue smoke. - my truck has only 22900 mi (36850 km) on the clock.

[tom-adc]

One more vote for valve stem seals. I think the older 318's age wise that is have a problems with the seals getting brittle and cracking.

[birddog_mopar]

The engine builder I use, who is now my good friend, told me that it is a common misconception that oil consumption is caused by piston ring wear. In fact, in most cases it is the intake valve stem seals, due to the vaccuum the intake stroke pulls from the valve to suck oil into the cylinder, thus causing the engine to burn oil. Now your truck could have 500 or 500,000 miles it doesn't matter, the valve stem seals are made from rubber, and just like tires, over time the will rot and go bad. I am assuming your truck has the original untouched engine and after 40 years the seals being bad is normal. If you want to redo your selas while the heads are on you will need a kit to screw a compressed air fitting into your spark plug hole to hold the valve up (something like this one, http://store.summitracing.com/partdetai ... toview=sku ). Now you must then remove your valve covers and take the valve spring retainer, retainer locks, and valve spring off to get to the valve stem seals. You can then pull off the seals and replace them. Remeber you must repeat this process 16 times and it can be quite a pain, but it is possible without removing the heads. The best thing to do is get the good steel jacketed Viton rubber seals if they are available for your application. I know they make a tool to remove the valve springs from the head for big blocks and I think small blocks but I don;t know about poly's.

[MowagW200]

Thanks very much. I just ordered a kit screw. First I thought if I have to drill out an old spark plug. But this kit screw seems to be better.
End of August or End of September I hope I'll get some time to mount the new seals. At this time I'll mount new valve springs as well. All these parts are at my home.
Thank you very much.
Dieter