Been a while but here is one i just came across. I put a Cometic DLS gasket from Cyclex in my 77 CB750 rebuild and it seemed fine. After about 500 Miles of break in I decided to hit the highway for a while and see how it performed. Worked great - but next morning #4 puffed out some blued smoke for about a minute and then cleared. This happened after every start up from then if the bike was sitting for a few hours - but not on restart after a short time. My theory was that oil from above was seeping into the cylinder while it sat.
Just got around to pulling the motor and checking the gasket which seemed to have not sealed properly around the oil drain next to #4. After careful inspection I found the head side of the joint had a couple of little circles pressed into it around the drain holes at #1 and #4. These were made by the dowel pin at the drain hole sticking out to far from the block side and hitting the head. This, I think, prevented me from properly torquing the gasket at these points. The block was resurfaced at the rebuild and I found the dowel sticking out a few thou past the .040 gasket thickness.
Adjusted the dowel length so that they did not stick up past a .038 feeler gauge and I hope that is it. I did later find this mentioned on the CycleX gasket web pages..
