i pulled a motor apart that has sat for years without being cranked over, the irons are in good shape except for this one that has black marks on it from the rotor. ive tried using a scotch brite pad, engine cleaner, carb cleaner, and a magic eraser. nothing seems to work so it ok to put teh engine back together like this?

 

i personally would have the irons surface ground...but thats just me

 

ya the only place around here i know of is that new shop FNR racing or something, im goign to stop by tomorrow and see how much lapping would be but i think it will be too much for my low budget project, the irons themself are all in spec to the FSM and are smooth but now im just annoyed with those stupid black marks, theres gotta be something to clean it off with??

 

There is an excellent post in a thread on the "other forum" written by a very knowledgeable person, that describes how to do this with sandpaper.
I don't believe a direct link is allowed on this forum.

 

sorry i dont know what the 'other forum' is because im only dedicated to this one lol..is it nopistons or whatever?

 

yes

 

The 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

 

/\
l
l
That??? I undertsnad that is from a reputable guy but im so lost now im sorry im goign to need some help understanding this method!!

so hes saying use 180 grit paper on a orbital sander and literally sand the face of a iron?? with 180 grit? and then use 400 grit wet paper with kerosine? and then pressure wash it?

i was unde rthe impression that iron faces need to be smooth, and have that nitrite coating intact and shiny

sorry for noob language here guys

 

Yes.
(Quote=Lynn E. Hanover)One light lapping probably would leave a nitrided layer since it starts out at about .003" deep.(Quote)
If you want to question what he is saying, go on that forum.

 

ok so the trick is actually to have the irons roughed up before a rebuild? makes sense, its just liike honning...but is this only best when you use new rotor seals?

 

got it! just surprised me how much i dont know about rotaries yet lol i think im going to do that but i dont know if i want to use 180 grit right away, maybe 320 or so

 

Razor blade. The staining you see won't come off until you cut into the nitrided surface, but that's a big no no. So run a razor blade across the surface to knock down any high spots. That's it.

 

you know if you had a question about how lynn does something you could just ask him.

 

yep i asked him and although its a very intersting method, i just assume leave them the way they are or look for better ones

and thanks for the razor blade trick jeff