Quote:
Originally Posted by Roberd42
Yep all what he said, I usually don't lube the Pistons, rings, or cylinders (beyond a very thin layer of oil for rust prevention) to prevent any glazing. With these engines I guess it doesn't matter much being older and lower performance. Here's an excerpt from klemm vintage (two stroke guys but same concept):
About “Dry Top End Assembly” - One step that helps reduce break-in times is to assemble the top end with no oil at all on the piston skirt or cylinder walls. This step has a history worth telling.
In the middle 1960s and early 1970s American muscle-cars were a very popular item on automotive showroom floors. At that time, it was standard procedure for Detroit manufactures to assemble all automotive engines with a generous helping of oil on the cylinder bores and pistons. When these muscle-cars were first fired up, the assembly oil on the bores would burn onto the bores as a glaze that took a very long time for the rings to wear through before sealing.
Unfortunately, this assembly process caused problems for salesmen in the showroom. When prospective buyers took a muscle-car out for a test drive, it was a given that there would be at least one full throttle blast involved. During that full throttle blast, the poorly sealing rings allowed considerable oil to pass, and the brand new muscle-car would leave a big plume of unattractive blue oil smoke that could be seen in the rear view mirror…. Buyers were understandably put off by anything that appeared to be “already burning oil”.
This was a very real problem that Detroit had to address. In time, they learned that if they assembled the top ends dry, with no oil on the bores or pistons, they could avoid this initial burned on cylinder glaze. The result was much shorter ring sealing times (because the rings didn’t have to wear through that glaze), and the absence of blue smoke from those important test drive blasts.
This same rule applies to two-strokes … vintage or not. Some owners shy away from this assembly process because they fear scoring the piston … but it is an unfounded fear. On such assemblies, we do apply assembly oil to all the lower end bearings. In the first moments of initial combustion, that lower end assembly-oil disperses on the bore in even quantities that are easily enough to avert any kind of scoring. In addition, it bears noting that the lubrication needs of an unloaded engine spinning at very low rpms are very minimal. We have been assembling high performance two-strokes in this way since the early 1970’s. It works … and it results in greatly reduced ring sealing / break-in times.
|
I am in this corner having raced 2 strokes for many years. I did however use just a hint of 2 stroke oil in the top ends but definitely used a sufficient amount on the bearings.
I have always practiced the same thing with 4 strokes and have never had a problem until this particular problem. Whatever caused this, happened all of a sudden and I doubt it had anything to do with assembly lube not being used.
I talked to the mechanic that I am going to bring my cylinders for re-bore and he thought along the lines I did that it was a two fold issue. After market pistons combined with a tighter than usual wrist pin fitting. This side was tighter than the other or the old pistons. He told me that he bets that the cylinder got a little ovaled on the inlet and exhaust side because the wrist pin wasn't allowing the piston to move as it should.
Kind of makes sense I guess.