I saved this post by John.
What is meant by "Dry Ring Installation?"
With the introduction of engine oil friction modifiers in the mid 1970's a piston/ring installation procedure became popular in the US. Tried and true ring installation methods that were used for generations of mechanics, basically swamp the cylinder and the rings in engine oil, gave problematic results. The engine would smoke.
Some of my first experience with problems with modern engine oil and ring break-in was with Triumph T140's that would "smoke" right out of the crate. It was worse if it was filled with
Castrol 20/50 engine oil during set-up. It was typical to re-ring these engines at the 500 mile check-up.
During this period our shop was doing a lot of Japanese performance work, and turned out several
Honda 750 fours kitted out with
Honda 350 twin pistons making it an 836cc engine a week. These engines also became problematic when assembled with the new, slick, engine oil. At startup they would rival any device designed to turn oil into smoke. The sheer volume of these engines we were doing meant we had to come up with a way to overcome this. The advice I received back then was from Ken Tipton of MTC Engineering. His web site, some 25 years later, still recommends "Dry Ring" installation for his high performance piston kits.
The oils available today, formulated to be even more "slippery," and thus let the engine get better fuel mileage, is many times more problematic than oil was in the late 1970's.
So what has this to do with and what is meant by "Dry Assembly?"
First the cylinder is prepared with a honing stone that provides the proper finish, or grit, for the type of ring chosen. If you have chosen a ring made from grey cast iron ring you would choose a honing stone with a 150 (recommended by Triumph) to 220 (recommended by Hasting) grit. If you have chosen a ring made from Ductile Iron or Steel you would chose a honing stone from 280 to 400 (plus) grit. It is important to match the surface finish of the bore to the ring you have chosen.
A cast iron ring, which requires a certain bore surface "tooth" or surface finish to seat the ring, will not "break-in" in a bore that is finished with a 280 plus finish. Conversely, a 150 to 220 (coarse) finish can remove the protective coating from the face of the ductile or steel ring. These coatings are required, as neither ductile iron or steel is compatible with the iron cylinder. With out these coatings the ring will rapidly wear the cylinder bore.
After honing the cylinder should be washed in HOT soapy water. The bore scrubbed with a stiff brush. The idea is to remove any remaining stone chips from the hone that get imbedded into the cylinder wall.It has been found that washing in solvent does not remove these chips. The marks left on pistons, where all of the stone chips haven't been removed, are easy to identify.
After washing, a lint free rag which has a small amount of engine oil (or what is popular with a lot of engine builders, automatic transmission fluid) is rubbed on the bore until the rag comes out without any grey haze on it.
Then everything, EXCEPT THE RINGS, is given an appropriate coating of oil:
1. The wrist pins are coated with assembly lube.
2. The skirts of the pistons are given a very thin coating of engine oil (not assembly lube).
3. The rings are left DRY.
4. The cylinder is left with only the light coating of engine oil or automatic transmission fluid. No additional oil is put on the cylinder.
This is what is meant as "dry assembly." It is important to understand that the rings, while not flooded as in past assembly techniques, do not have dry metal to metal contact with the cylinder. I like to call it "drier" assembly.
John Healy
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