Project79RX7

I'm hoping someone might be able to answer a few "rookie" questions I have. I'm rebuilding a freinds '79 RX7 (with a 12A motor) and I've come across a strange situation with this motor......and to add to the fun, I'm a newbie when it comes to rotary engines.



The problem is that the motor sat (completely still) for about 16 years....and wasn't driven all that much prior...it only has 37,000 miles on it. About 3 months ago a "mechanic" got the engine running and my buddy drove the thing 1200 miles. When they first got it running, suposedly it ran fine.....maybe a little weak on power. 1200 miles later the thing is burning some serious oil.......and blowing enough blue smoke to asphixiate a small village. So.....we took the motor out and broke it down. And, what we found was that the side rotor housings had corroded (see attached pic....it's typ[ical of all 3). The 1200 miles manange to clean most of the corosion off, but you can still see a light sheen of 'rust' on the side housings (hard to see in the pics, but the surface is pitted ever so slightly). So obviously, the housings need to be resurfaced.....and probably replacing the side seals too. I haven't measured everything up and checked all the tolerances yet (that's tomorrow nights job) but, I'm wondering what I can get away with when it comes to the machine work.





What is a "typical" first grind on a rotary side housing?



What is the total allowable grind on the side housings?



Assuming the surface is within tolerances, and the corrosion could be taken off with lapping only, is it a good idea to just lap the surface?...or is getting it ground more of a requirement?



Is grinding a side housing something any reputable machine shop can do, or do I need to find someone who specializes in rotary motors?



If I have the side housings ground.....and the motor is now that much shorter......isn't the length of the eccentric shaft a concern? Seems to me I'd need an undersized thrust bearing to keep the shaft in it's proper place...but this "thing" uses a roller bearing.



A visual inspection of the rotor side and oil seals didn't reveal anything ugly....the look nice and smooth. So.....assuming they are within spec, can I re-use them? or should I just assume the corrosion took it's toll and replace them?



Any help is appreciated. Iv'e rebuild my share of engines......but those all had metal parts being thrown back and forth. ....none of this spinning stuff.

Project79RX7

I just got finished checking all of the engine clearences. The only thing that was past the acceptable tolerances was the wear on the side oil seals. The FSM says the allowable wear is 0.5mm and the outer ring measured almost 0.7mm. Also, the inner rubber seals (for the side oil soils) are a bit stiff and miss shappen. Which explains the oil burning problem......looks like it was bad side oil seals.



Everything else looked amazingly good.....infact most of the stuff barely showed any wear at all.



I'm still stuck with the question of what to do about those rotor housing irons. The runout on the surface didn't even measure 0.001" (I know, I'm mixing units) and the factory spec is up to 0.004". But, the surface is ever so slightly pitted and corroded (not even sure you could meaure the depth of the pits...it's that minor). I want to do something about it, but I'm not sure what to do. I'm thinking at this point I can just lap the surface.....but, as I mentioned I'm new to these motors....



Can someone offer some advice?

diabolical1

if you're still looking for an answer, lap the side housings.

roatery_love8812

help any one. so i'm new to the roatery world. i'v bilt piston engines for a few years and have taken a deep interest in the roatery world. im getting ready to bild a 13B TT and a 20B. and ideas whayer to start or and reading materials i could pic up to help me out on what to do.

Lynn E. Hanover

Pitting is generally not a factor. I sand irons with a random orbital sander with 320 dry paper. This roughs up
the surface and installs little grooves with overlapping circles. Then lap the irons against each other with valve grinding compound, in circles about the size of a quarter.
Then scrub them with a stiff brush and laundry soap. Then take them to a car wash and high pressure wash and wrinse them. Blow dry and spray with WD-40. A nice flat grey color is fine. Replace the rubber "O" rings.

Clean out the apex seal grooves and the side seal grooves. Reassemble per manual. Become aware of the "Handedness" of the oil scraper drive springs. There are front and rear springs.

Irons can be ground on large machines and sanding tables. Anyone who grinds large truck heads. Looking for a large diameter grinding wheel. The wheels are very slightly run at an angle, so marks only run from one side.
Grind off just enough to remove wear marks. Not more than .004". This cups the surface very slightly, and lapping or sanding and lapping must follow grinding as above. The rear stationary gear moves foward by the total amount removed. You can grind off the total removed from the irons from the front face of the gear, or, build a shim of that thickness to install under the gear flange. Check for the bearing touching the radius on the crank.

Lynn E. Hanover

roatery_love8812

Lynn E. Hanover. thanks a bunch. that gave me a graet start on my first build.

roatery_love8812

ok. so i need help just once more. i have a 93-95 mazda rx7 13b twin turbo engine. does any one have any ideas on wayer i can get the full repair manual for it.

FernandoLuna

Mazdatrix sells a video and all the repair manuals