So I found a post that told how to prep irons for a rebuild. Start with 180 on DA, then block sand with 400 grit with kerosene. I did mine and want to see if I did it right or if I need to work on them more with the 400 grit. I can still see some black on the edges. Pics below and let me know if they need more work. I don't want to go too deep and ruin them (first rotary rebuild and first rotary owned so nervous).

 

I'm not sure that you would want to use a DA on a machined surface like this. You could easily make the surface uneven that way.

When the irons are "lapped" it is done on a machine similar to one used to resurface cylinders heads and blocks to ensure the surface is "flat."

Another consideration depending on how much sanding you did, is that the surface nitriding is only so deep. Typically, the irons are nitrided after being lapped.

Vince

 

Thanks for the reply. I might just end up getting another set of plates as I found a chip in the coolant jacket . Anyway here is the post I was reading. I didnt really see how the method could be done properly either as far using a DA. I know there are people who provide the service but I also remember reading its not a good idea to have them done, but cant remember why as it was a long time ago I was researching it.



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Originally Posted by John V View Post
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.

 

This is interesting, I would like to know if other people are resurfacing this way.

 

To be honest, with the money you're saving on labor, just send the irons to Chips Motorsports to be lapped.

Vince

 

Indeed.


Alright thanks I will check them out and hope I didn't ruin all 3 plates lol.

 

I think you have the right idea. Lynn Hanover wrote that how-to post and he's forgotten more than most people know about building rotaries.

It makes sense to just break the glaze on the surface. If you have gouging that would need the surface ground down to repair, that's more of a call for a "real" lapping job or lapping/re-nitriding.

I don't see any harm with this technique, makes a lot of sense. Just go slow and just knock the glaze down, make sure you keep moving the sanding block/DA so you retain a nice, even surface and don't go too far on any one surface.

Dale

 

Well now I'm debating....I was inspecting the front plate this afternoon and found a chipped coolant jacket. I have 2 options I guess... Buy another used one or bite the bullet and just buy all 3 new plates and have peace of mind. What is average price for a good front iron? I found one for like $370 but for another hundred more I could have a new one....

 

Used irons aren't super hard or pricey to sell. I've bought and sold a few for about $150 a pop, may want to look around more to find a good deal.

It's much easier to find a good iron than it is to find a good rotor housing or rotor.

That's why you do cleaning and inspection, find problems like this now and not when the motor is together and pumping water!

Dale

 

I have been blocking down all my plates when rebuilding my engines for 30+ years and find they bed in quicker and end up better engines and make good hp and seem to last longer

 

Alright thanks. And yeah I am glad I found that now and not later lol.

Using the same or similar method I used?

 

you could use these coolant seal saver rings

https://www.rx7club.com/group-buy-pr...ntion-1006993/

 

I'd really like more specific details from you..... I find it hard to believe that removing material from the iron faces will yield any positive benefits.

 

16+ years of the same... I think a lot of people do not understand the how and what are the important steps, so they just believe all the misinformed "builders" out there who say you HAVE to do this or that way. When in reality, a lot of the less expensive and "simpler" methods are not only perfectly fine to do, but also, if performed by the right, knowledgeable individual, can in a lot of cases provide superior end results!

-J

 

If you inspect any plate you will see dirt and slight un even wear marks on them. all I am doing is removing any dirt and minor wear and roughness off the face with 240 grit wet and dry enery paper on a block of cork with white spirits in my cleaning bath .I also shampher the edges of the inlet and bridge ports to stop side seal wear and or the chipping of the side seals as they pass over the ports .I have built 1000 + engines this way with out any noticeable problems or failures due to this process .
Is similar to what you do to any block and head when building a piston motor to help the sealing of the head gasket to make sure it is clean and burr free

 

Another possibility (shamelessly stolen from an aviation rotary guy Chuck Dunlap)
Barry

 

Barry thats a great idea thanks for posting, also you can spray glue onto a sheet of glass and place 240 wet and dry sheets onto glass, place glass sheet on a very flat table and place white sprits, wd 40 or oil to lap you plates, because glass is very flat and level.

 

I strongly advise against using a da on the irons. At most I will take a sanding block and hit them with wet 1500 and then 2000 grit very lightly. Any irons where the scratches that won't come out this way will have to be lapped and should be re-nitrided. Remove the nitride coating and the irons wear very quickly. The break in the coolant seal retaining wall can be repaired with a tig welder and nickel rod. Because it is cast iron, you really want to pre-heat the entire iron plate first before welding. There are several places that can do this for you: Chips Motorsports, Goopy, Racing Beat, Judge Ito. However, since the iron eroded through in one area, you should examine all of them and see if the retaining walls are wearing thin elsewhere.

 

This seems like the most viable feedback... I guess its like what you get with all car parts and services. You get what you pay for.

 

I thought you were referring to removing so much material as to minimize the nitride coating, i.e. the da method mentioned at the beginning of the thread.

Sounds like you're simply evening things out a bit and knocking down any minor high spots.

 

I have my own lapping machine I built myself. It uses an oil stone on a random rotating head with adjustable pressure. You need the lapping to be even and have the correct finish across the plate- the finish needs to be similar to a fresh honed cylinder bore in a piston engine.

I'd love to post a video of my machine up here, but I'm not sure of the best way to do that.

 

block with 320 / 400
and then turn the plates in figure 8's against each other with some treflex ( lapping paste ) between them

just a clean up and to knock off high spots and edges and nothing savage

 

Yes virtually just cleaning up the surface and any minor high spots the same as you do on an engine block before you fit the head on

 

Wel I already hit them with the 180 and 400 so they can probably be presumed worthless? I guess I could still ship them to Chips for "lapping service" (might be cheaper and better than buying new). However, if I remember correctly, I remember reading that lapping and re-nitriding the irons isn't a good idea but cant remember why. It was about a year ago when I read this and might not have even been talking about side housings.

In all honesty, I am thinking about just buying new irons from mazdatrix or wherever and starting with a fresh motor but this will be absolute last resort. I appreciate all the replies and now I know what to do and what not to do on the irons.

 

Just be lucky you dont have a 20b with those same broken tabs on the thick center iron. Due to the cost of those, I had to reweld mine.