So, how about it. Has anyone ever had to plain and surface the plate facings for their engines? If so, then about how much did you take off? Whats a safe number? this is about all the info I lack before I can get my engine out of the shop and into my car. ANY info would be great, thanks much

Well, to start with, how much ware are you trying to repair by grinding the irons? Slide a dial indicator across the iron so that the probe passes over the good unworn iron under the rotor housing and into the groove worn by the side seals. If it is .004" or less I wouldn't do anything. If .005" or more, take off .005".



You will be at the last of the nitrided surface, and without nitride the next overhaul will require new irons.

So even if the wear is more than .005" just take off .005".



Whoever is doing the grinding will not like you. Grinding nitrided iron is a slow process. I used to run over the freshly ground iron with a DA (air powered orbital sander) with a piece of 220 silicone carbide paper glued to the pad, and kerosene flooded onto the iron.



Paul Yaw grinds first to get a square and flat surface and then laps to get the great finish. But he is a perfectionist. I think the 220 paper on the DA gives an adequate finish, and have done it many times.



Scrub everything well in solvent, and then to the car wash for a high pressure blasting. Wipe the iron off and wipe on some oil when finshed.



The second time you do this, the engine will be shortened enough for the rear stationary gear to move forward enough to run the rear main bearing onto the radius at the rear throw. So you need to scrape the front end of the rear main bearing, or make up a gasket of about .020" to .025" to mount under the front stationary gear. Then nothing touches anything.



Lynn E. Hanover

I use a specialized lapping shop, great service, great results

Lynn is a wealth of information but everything he relates to is pre-86. You can't take .005" off the 86+ irons or it will compromise the integrity of the o-ring land. The suggested limit is often said to be .003" for the newer irons. We've went .004" without issue but it's not something I'd recommend since so many say not to go that much.



We use a grinding shop with excellent results. We had the surface finish of a brand new factory iron measured and the shop we use produces a finish about 50% smoother with grinding. Lapping is certainly able to produce a smoother surface but is the price justified when you can replicate the factory finish or better with grinding?

The place I use charges me $45 per side

Real good point there. I just do 12-A stuff with the "O" ring grooves in the rotor housings where they belong.



I have a 13-B rotor, and some day I may come up with some other 13-B parts to look at.



My driver retired, and I sold the older car. I think I will retire also. So I must learn some 13-B talk so I can build an engine for my BD-4 airplane kit.



Lynn E. Hanover

That's a good price for lapping. I get them ground for $25.

Wow, okay you guys answered exactly what I needed. I am truely thankful to all who posted a response to my question.

.004 is that in inches? How much would that be in mm? (I'm European)