Originally Posted by smikeb
So I've searched for threads about smoking SB's and read about a hundred postings about all kinds of things and learned a lot already. However now I'm confused about which advice actually applies to my situation. So here goes.
I have a mid 70's SB 327 in my 911. Unknown number of miles or years since its last rebuilt. Its got quite a high lift cam, edlelbrock manifold and carb, HEI distributor. The exhaust is completely seperate for each bank. On acceleration I get a big cloud of blue smoke only out the left tailpipe. There is no smoke on starting, even after sitting for a few days, there is also no smoke when I rev the engine up to about 4000rpm while in neutral. It only smokes when its loaded and driving. I did a compression test and got between 135psi and 155psi. Checked the plugs and #3 on the left side is oily and black, the rest are dry and brown. That cylinder #3 had 150psi compression.
Since it only smokes out one side, I've discounted oil getting sucked in from the PCV. And since it doesn't smoke on start-up, I think the valve seals are ok right? So I'm left with head gaskets or rings? Is there a way to confirm which it is? I'm optimistic its not rings because of the good compression test, am I right?
Cheers and thanks in advance.
Given the condition of only smoking when getting on it, I rather suspect that the increased pressures are upsetting something. This does sound like a ring problem where blowby is being trapped between the first and second ring causing the second ring (which is really an oil control ring) to loose contact with the cylinder wall. Then when backing off the throttle the pressures between these rings have time to diminish and the ring returns to normal function.
Another place to consider is the loss of a cam lobe. This upsets normal function in the cylinder which will pull a lot of oil. Since you already have a suspect cylinder, pulling a valve cover and checking this action should be pretty quick.