I have a friend that owns a 1971 SB. I own a '69 SB, but I am far from an expert. The issue with the '71 is that after he drives it for a period of time (say 30 minutes or more), he notices some light blue/black smoke when its left to idle for 5 min or more. We took his 71 and my 69 out for a spin on Saturday. We did not see any smoke or issues during startup and did not witness anything while we were driving around (I was following behind for part of the road trip). However, when we got back to his house we left both of the cars idling for a couple of minutes to do some comparisons. After about 5 min of idling, we both noticed the smoke from his exhast. He has had his car for several years (its got around 100K miles on it) and only started to see this recently. I drove it a couple of times this past Summer when I was looking for a vette and learing about them and I did not see the smoke issue in the warmer weather. He drives it about once every 10 days or so during the Winter.

Any ideas on the root cause of this? I thought it may be related to the colder temperatures and the lower amount he drives it in the Winter. I was also concerned about the engine temperature (his temp gauge does not work), but there was no evidence of the radiator getting hot that I could see. Any help would be appreciated and passed on to my friend.

Thanks............

 

Bad rings

 

What would it cost to replace those?

 

Valve seals?

 

as said could be rings or valve guides or burned vlave. The quick old school check is to do a compression test on all cyl. when you find a low one comparitively, drop about a table spoon of fresh oil in the spark plug hole and re-check.

if the compression goes up, its rings if not its valves


cheers


tim

 

Maybe it's just loading up from idling too long. The carb may be out of adjustment. However, if you're sure it's BLUE it's probably oil. Valve seals or rings. Compression test and leak down test is the next course.

 

I would rule out valve stem seals or valve guides, you will most generally see smoke at start up if the seals are bad, if guides are bad you will see smoke all the time.
Piston Rings are a possibility, do a compression test for sure. If this doesn't yeild any answers, there is a few more possibilities. There is a possibilty that the intake gaskets are leaking, the engines vacuum will pull small amounts of oil into the intake runners on the heads through the lifter valley, but this will most likely cause a rough idle condition. If the engine has had aftermarket valve covers installed, make sure that there is a baffle for the PCV valve.

best of luck

Lance

 

with the last 2 posts.

The baffle under the pcv valve is something many people wouldn't consider, but if oil is being slung up off the rocker arms right into the valve, next stop intake manifold.

A weak spring in the pcv valve will also be sucking more crankcase vapors than it's supposed to.

I'd go with the carb adjustment and new pcv valve for starters, then the leak-down test.

 

Thanks guys. I will pass along the information.

 

I assumed that the PCV system was in shape. If that is not the easy fix then you need to do the compression check for rings. If it were the valve/seals it wuold smoke on start up.

Bad rings tend to allow oil to pass when there is no load as with idle.

I had a very nice '64 in 1983 and it did the same thing. Turnd out that the rings were getting gummed up becase the car had an origionl 36K mi and sat alot. I was driving it more that it was used too. I replaced the rings in the car and freshened the heads. It was very noticable of the power loss I had with the old rings.

With gummed up or just worn out rings it will smoke at idle, stop lights, or any other non load condition.

I hope it's just he PCV

 

I would also fix the temp guage ASAP. Hate to loose a motor because it overheats or runs very hot.