When rebuilding the 2nd gen do the cast iron housings need any treament or
can they be used as is? Cylinders ina piston engine are usually honed so
new rings can seat what about side seals? Thanks for any help
Joe Berki
Below is an answer that I posted on the "Nopistons" news group. A good source of rotary information.
This applies to street engines and competition engines in severe use.
You can lap the surface youself and you can get it ready with a random orbital sander. Used dry with 180 grit paper,
this alone will get most of the surface close to one color. You can run the front iron against the front side of the center iron with oil and valve grinding compound in between. Wipe it off now and then to be sure all of the surface
has a flat finish with no shiny spots. This will produce a very satisfactory result on both irons. About half way through, rotate the top iron 180 degrees so the ports are not together the whole time. If you have a mill or access to one make a bar and plate with holes in the plate to mount a bearing on a bolt. Plant the bearing in the center hole, so it impinges the iron about one inch. Run the mill slowly and keep adding grinding paste as you go along.
A few layers of Visqueen under the bottom plate will keep the mill clean and allow reuse of the paste. Bolt on a rod of some kind and run the rod through a fixed bracket or just any bracket on the bed to keep the iron from spinning. Then you flip the center iron over and do the same again with the rear iron. If you drill press has an electronic speed control that allows for very slow rotation, you can use it as well.
This method costs nearly nothing and produces very flat irons with a nice oil holding finish. Clean the irons at the car wash with high pressure water and soap. Spray with WD-40.
You can do this by hand as well, but it will take all day long. This can be done quite a few times without bothering the nitride. Piece of cake. This has to do with finish, and is not much help with wear grooves since it removes very little material.
Lynn E. Hanover
There should be no attempt to reduce the surface enough to remove the wear marks (Groove along the plugs side of the iron). This groove is caused by hot metal wearing more quickly than cooler iron. So, the groove forms from the side seal moving in a somewhat vertical path. The same exact wear would occur on the opposite side but for the cooler iron. Right? The wear limit of this groove depth is .004". It can be removed by grinding and lapping. That is reducing the entire surface exactly the same amount. Or just lapping for a very long time. Either operation is acceptable. The irons should be renitrided after either process.
One light lapping probably would leave a nitrided layer since it starts out at about .003" deep. This is for street engines that do not get disassembled often. It makes no difference in a race engine.
You hone a piston engine cylinder to remove the glaze. That is the chrome like finish of the bore walls caused by the rings wearing away some of the surface. New rings installed in a slick chrome like bore will take years to break in. The oil scraper ring will remove all oil from the bore on each stroke and the new rings will spoil from over heating.
Same thing in the rotary. To remove the glaze. The shiny surface, and replace it with a rough surface that will hold a supply of oil to help lubricate the side seals. The side seals are the piston rings of the rotary.
The object here is to remove the glaze with the rather course 180 grit paper on the random obital sander. A air powered 5" round aluminum oxide disc is what I use, but an electric unit would be fine. I run the disc dead flat on the iron long enough to remove all of the staining done by water in the seal grooves. Go real light on the legs. Material comes off real fast with high unit pressures, Then a fancy lapping session or glue some wet or dry silicone carbide 400 grit paper to an old disc pad, and wet the iron with kerosine and run over it again nice and flat just long enough to get a flat grey look to it. About 5 minutes, and keep it wet. A new dry 180 grit disc and a new silicone carbide disc for each iron face. You can do the wet part in the cleaning tank for less mass making.
Then off to the car wash for a long wash and wrinse. Then dry with old clean towels and spray with WD-40. Now you have a finish that will last through several rebuilds. Provide quick break-in, and long life and high compression
form the side seals and corner seals. The swirl marks from the 180 grit will outlast the irons.
Just don't use a synthetic oil in a fresh rebuild. Run a few hours with dino oil, then dump it and change filters, and run what you want. If the OMP is in use, a good brand of dino oil and if you premix, a synthetic racing oil in the sump.
Lynn E. Hanover
There are pictures of a set of irons done with this method on the web site.
For irons that exceed the .004" wear limit (the depth of the groove along TDC on both sides) you can surface grind to just reduce the surface to below the .004" then treat as above. Or, surface grind to .003" and power lap to zero groove depth. In most cases this will be through the Nitride, and the irons must then be retreated. Early irons were not nitrided, and could exceed the .004" wear limit before 100,000 miles. About 10 years of flying. I would suspect you would look inside a few times before then.
With synthetic oils the irons might even last longer, Nitrided or not.
Lynn E. Hanover
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