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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.

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