Lapping and Seal Question
 

After lapping the steel housings, what is the "ideal" Ra value that you want to go for? I just had all of mine done and got an Ra of about 5 which is pretty darn mirror smooth. I hope it's not too smooth and the oil will not cling a little like it's supposed to.

What do you guys normally go for with an Ra value?

anybody know anything about this?

TBH, I've never heard of anyone on here talk about this.

but do you mean you can actually measure how smooth the housings and stuff are?



but jus so ya know, oil likes smooth surfaces, and the smoother it is, the better it'll want to stay next to it ;)

i've never used them but yes there is equipment that will measure the finish of a machined surface.

to smooth will result in oil consumption to rough is bad as well
if you look at new housings they have a finish that would appear to be about
what you would get if you sanded them with 600 to 800 grit sand paper .
you need to be more worried about how much you took off lapping them
taking away the hard surface and if there is enough groove depth left for the
coolant o rings.
my 2 cents
matt

Off topic: Turbo3, those two rotor housings u sold me a couple years back were a couple of winners! The motor is great, lots of torque and idle vacuum.

um.... you arent supposed to lap the surfaces of the side housings. The side housings are soft nitrided by soaking them in an atmosphere of ammonia and rx gas at 570 degrees. This leaves a layer about 0.01 millimeters thick of a much harder surface. This gives them a surface hardness of nearly 900 on the vickers scale. The surface hardness of the iron is between 250 and 300. This soft nitrided coating also gives the side housings a much lower coefficient of friction, leading to less parasitic "bearing" losses, and less heat generated from friction. The surface is much less rough than the iron could ever be, and it is very resiliant to wear.

I believe Racing Beat states that the wear is not seriously compromised when nitriding is removed.

Perhaps we are talking about an engine that will go to 200,000miles plus (stock nitrided) as compared to only 100,000miles w/ lapped plates?

But when there's grooves worn in the housings badly enough to warrant lapping, the nitriding layer's been compromised anyway. So they need either lapped or replaced. A lapped housing is better than a worn out one and cheaper than a new one.

If it's not bad enough to need lapping, then they don't need lapping, so no problem.

Re-nitriding after lapping is not expensive.

I have my housings blanchard ground (to ensure parrellism. Then Nitrided and then wet-honed to final finish.

BanzaI: How much this set you back? I have two engines worth of housings, that barely need lapping. I'd hate to junk them, if i could bring them back to life.

I am experimenting with a new type of hardness coating right now (part of the reason for the question) and definitely agree that it should be there but the coating is only 0.0002" thick so the Ra value of the housing is definitely going to be a factor. My fear was that if it was too smooth, the oil wouldn't stick, the seals wouldn't seat, and I would get blow-by.

I think you guys are somewhat agreeing with me but nobody has provided any empirical data of which the Ra value (smoothness) is which I was trying to find out.

88IntegraLS - good, very glad to hear your're happy and all is well. I only sell good products so I'm pleased to know how it turned out.

Bonzai is basically doing what I am but I won't need the wet-honing because of the existing smoothness. We also bought a "true" stone piece of granite to ensure that all the housings were not off by more than 0.001-0.002" at the most.

I don't think it matters how much you polish the stock cast iron surface of a side plate for oil retention since it will have the natural porosity of the cast iron structure.

I mean look at a finely polished Japanese sword- you can actually see the variances in grain structure in the Hamon (not talking about the patterns from the lamminations you can see even better).

Now if you surface coat it... ????