Long time lurker, old-time RX-7 owner, first time poster. Searched for this but didn't have much luck.



I'm about to rebuild my second 13B ever, first NA motor ever. I'm rebuilding a high mile (180k) NA with new rotor housings and a set of low mile irons. I picked up the irons and while they measure out fine as far as grooving / scoring goes (no measurable scoring), there are some discolored areas that I'm not sure about. Different texture than the smooth areas of the iron. Is there some standard way to clean up the irons before a rebuild? I have not hit them with any chemicals.



Thanks everyone.



JV

A few close up pictures would be helpful. If the surface is level it will be fine no matter what color areas may be.



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

Lynn,



Thanks for the information. I do need to snap a photo of the iron I'm concerned about - I've been so busy yanking the old motor out of this car that I haven't had a spare moment.



Regarding your procedure below - I do not have access to a mill. I want to make sure I understand what you're getting at here so bear with me please. With the random orbital sander, the goal is to knock down any small grooves that might be there as well as eliminate any discoloration on the surface? I don't have a feel for how aggressive this technique is. I imagine it's kind of a "feel" thing. How do I know when I've done enough with the sander?



Next you say to run the front iron against the front side of the center iron with compound and oil between. I'm assuming this is to polish away the roughness left behind by the sander and leave a flat surface.



If I don't have access to a mill - is this the point at which I'm done?



Thanks again,



John

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

Lynn,



Thanks again. I understand now. The grooving is less than .001" at its worst for the irons I have.



I'll follow your procedure this weekend and report back with pictures of the results.



John

Here are the irons before:



https://i368.photobucket.com/albums/...oresanding.jpg

https://i368.photobucket.com/albums/...oresanding.jpg

https://i368.photobucket.com/albums/...oresanding.jpg



Here are they after:



https://i368.photobucket.com/albums/...r/HPIM1670.jpg

https://i368.photobucket.com/albums/...r/HPIM1671.jpg

https://i368.photobucket.com/albums/...r/HPIM1672.jpg



How do they look?

Nicely done. Exactly what you are looking for.

I agree, they look fine.



Lynn E. Hanover

Thank you both, I'm sure I'll have more questions as I start assembling this weekend.



John

Do you do anything to the rotor housings?