SpeedOfLife

iTrader: (16)

I'm rebuilding a motor for my '87 TII right now and I'm concerned about how I sit with regard to irons.

A few weeks ago I took my irons/housings/rotors to Arnold Motor Supply to have them hot tanked and I had the guy there check the irons for flatness. I'm pretty sure the shop guy told me that my irons are flat to .01", and he said that was very flat, but he doesn't know rotaries. It might be very flat for the head on a 1996 Neon, but I doubt that's the case for reusing irons. I read on NoPistons that taking .005" off the surface is recommended against as the nitriding is only about that thick, what would you guys recommend I do? The deepest part of the wear is where the corner seals rode. As far as I can tell everything else looks pretty good... I'd hate to have to buy more parts, as I thought I just finished and could start porting/building soon, but if these irons won't help make a solid engine to eventually make 300+ hp reliably and hopefully last 40k+ miles then I don't have much choice. I'm trying to make this motor as strong as I can.

This brings up questions about lapping/grinding and other surface prep as well. Please bestow upon me your expert wisdom, oh rx7club.

slo

iTrader: (1)

usually when they make a statement like that they aren't saying its .01" off.

He probably did what he does for head/blocks which is most likely laying a strait edge on the iron and trying to get a .01 feeler gauge under it, or trying to drag a strait edge around the with a .01 feeler gauge. It either did drag the strait edge, or didn't slide under the strait edge, so he just called them flat.

SpeedOfLife

iTrader: (16)

That's understandable. Just today I started looking for a straight edge of my own, and I have a nice set of feeler gauges. Once I have a straight edge and it isn't insanely cold outside I'll go check the actual wear for myself. However, my memory tells me that .006" wear would not be surprising. I could not only feel where the corner seal grooves were, I could see it pretty well.

Like I said, I'll have to check myself, but either way I still need to know what iron clearances should be.

[I should just bring the motor inside for most of the prep work... I have a small work closet for things like that]

Captain Jean-Luc Picard

I would much rather run a mildly worn iron as-is than try to lap it, take off the factory hardness coating, and have it wear extremely quickly after the rebuild, all the while paying several hundred dollars for the lapping service and shipping to boot.

I have seen several engines that I suspect were lapped during a previous rebuild attempt, have extreme wear on the irons that resulted in chewed up corner and side seals, and very weak compression. It also meant that of course the irons, which the person was several hundred extra dollars invested in, were also junk.

The only way I would trust lapping is if the coating could be reapplied, but I am not aware of any builders who offer this service.

Unlike reusing rotorhousings that have wear on them, reusing irons with wear does not seem to cause any significant compression loss or seal wear. Due to the factory coating, the irons do not wear too much.

About 0.005 is normal wear and acceptable in my opinion. Of course there are many armchair builders here who insist on nothing but 5 grand worth of new parts in their 20 year old 200hp rotary build, and if they can afford that then more power to them.

slo

iTrader: (1)

+1

except one thing, irons aren't coated there gas nitride'd.

This is not a coating but a process of case hardening.

There is also a coating called titanium nitride (probably others with similar names and different process's), this is not the same thing as gas nitriding. There are also other process's of hardening that do similar things applied in different ways with similar names.

There are probably places around the country where you can get the housings re hardened.