Hey guys,

This is my first rotary rebuild and have some questions about one of the housings. In the pics below, you can see some scratches that are in one of the housings. Rubbing a finger in the direction the rotor moves, it is smooth but if a fingernail is run across the grain, it catches in the scratches. The other housing is very smooth. There are no scratches or gouges in any of the apex seals.

Can I still use it or should I replace it? If I have to replace it, what is the best price for a new one and what should a good used one cost?


After I bought the car, which is an 87 T2, I drove it from Key West to Atlanta and the motor never smoked and ran very well. Before I pulled the engine, I did a compression test. It had even bumps on the gauge at 30-35 psi while holding the needle in on both rotors and pumped up to 100psi on both while the gauge was holding pressure.

 

if that's where a seal rubs, trust that it ain't gonna get better.
I think that it isn't on a corner of a seal thow... so it's kind of a go either way thang.. if u wanna be safe, replace it. If you don't, chances are you'll never regret it.

 

Don't use it.

B

 

It looks like a chunk of debris got pinched in there at some point.

Would it work? Yes.

Would I use it? No.

The cost of a decent condition used housing is cheap compared to the total cost of a rebuild. It's not worth reusing a questionable housing for anything except a "test" motor (as in, one you're planning to blow up within a short period of time to test stuff).

-=Russ=-

 

dont use it.

 

If you can afford to replace, sure.
That's the easy answer.

Now for the long answer...
The first pic looks like the grooves are right before the exhaust port?
That area is not that big a deal for rotor chamber sealing.
The second pic looks like on the intake side opposite of the spark plugs right?
That area is also not a big deal.
Grooves after the intake port and before vertical prior to the spark plugs side are vastly more critical.
If you really end up using that housing(s?), knock down the ridges as much as you can with some sandpaper before using them in a rebuild.
The areas where they are located in are not very important when it comes to rotor chamber sealing - it will not really affect power that much.

Good, used rotor housings can easily fetch up to $100 each.
Brand new ones from the Mazda dealer are $500+.

Good luck!


-Ted

 

Thanks for all the responses.

I can afford to replace if I can find a good used one for 100 or so but 500+ from Mazda is a definite no.

If all the edges are knocked down, what could possibly happen other than slightly lower compression? Just hypothetical.

 

listen to him ^^

 

If you think about it, you can probably figure it out yourself.

For the lower gouge right under the exhaust port, the burning combustion charge is already going into an expanding area since the apex seal is sweeping that area.
There might be some slight blow-by due to the groove, but it is not going to affect anything significantly.

For the gouge right under the intake port, most of the combustion charge has already exited the exhaust port, so any blow-by is going to be minimal.

*IF* the groove had been on the opposite side, you'd get serious blow-by from a rapidly burning intake charge (remember, it just got ignited by the spark plugs) that will blow-by into the incoming fresh intake charge of air and fuel - that's BAD!
This is why I said grooves after the intake port and before the vertical on the bottom are very bad areas.
Grooves outside of those areas do not affect engine operation that significantly.

Just make sure the edges of the groove(s) are flat, as any significant edges will kill your apex seals.


-Ted