A lot of very smart, very reputable engine builders assemble the top end dry. Almost none of the best automobile manufacturers do, and neither do I. In the case of the car companies, it has nothing to do with storage, as the engines are running within hours of assembly in almost every instance.
Consider these undeniable truths about four-stroke engines.
>In operation, with a healthy top end, there is basically no oil at all on the compression rings. They are lubed by the fuel. This is not true of the piston, of course.
> During break in, moving, lubricated parts, new and perfectly machined and sized as they might be, are in a rough state, and need the break in period to match themselves to each other more perfectly. During this time, lubrication is more important than ever to prevent undesirable galling or excessive material loss.
Properly finished cylinders and modern ring materials allow the rings to seat almost immediately, regardless of whether they are oiled or not, and any oil that is present on the compression rings at first startup will be gone in a matter of seconds, leaving no trace that it was ever there, so in what way does oiling the rings delay the seating process in a significant way? On the other hand, not oiling the cylinder will allow the piston, a critically lubed part, to run up the first few strokes totally without oil. Sounds like a bad idea, to me.
I oil all of my top ends on assembly. That does not mean I dunk the piston in a bucket, though. I like to provide the piston adequate prelube, but I do think there's merit in not over oiling the combustion chamber, too. So on engines where the piston goes in the bottom, I do this:
Apply a drop or two of oil to the rings and spin them on the piston to distribute it.
Smear oil on the piston skirt fairly liberally, and assemble the ring compressor.
Wipe the cylinder with an oily rag and then wipe out most of that so thatthe cylinder has a light film of oil on it.
Insert the piston, and once it's up in there a little, I'll wipe a little more oil on the bottom of the sleeve, then bolt down the cylinder.
After it's assembled, I run the piston to the bottom, and wipe out any excess above the piston.
The only difference in that and how I do engines where the piston gets inserted from the top is that on those I oil the cylinder without wiping it out afterward, and just let the rings shove it out as the piston goes in.
In the most recent example of a motorcycle engine that I built this way AND tested was my son's old 250F. After the first two hours of running, it was below 1% on a leak down test with a used cylinder. That's good enough for me.
Bottom line is that my engines work the way I do it, and I don't like the risks, small as they might be, associated with the dry assembly of anything that's going to burst into life at 3-4000 rpm all of a sudden.
Thanx.....I would find it hard not to use a few drops....and a light film on the bore...Interesting though..
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