Rotary Resurrection - Tech Section

Most of my rebuilds, and most of everyone else’s, utilize used rotorhousings. Since the rotorhousing provides much of the compression surface for the seals, their condition is fairly important to how the engine performs, both in the beginning and long term. IT takes experience to judge the quality and wear of a used housing, and most people reading this probably lack this experience. So I am willing to share some of it here, and shed some light on this. This will also show why it’s hard to rebuild any 12a or older 13b (85 and prior engines) with used housings, and why I do not rebuild them myself.


Here is a like-new housing…not brand new, but very low mileage, in great condition. No chrome flaking off either edge. No odd wear patterns around the exhaust port. No deep groove on the rear side. You can note a ring around the rear edge, which is where the apex corner piece rides…later on in life, chrome flaking and wear will occur here. Housings in this condition are highly desireable for any rebuild and will develop compression between 110 and 130 depending on the rest of the components. Most housings that look like this have under 100k miles on them, usually closer to 50k or less.
A nice, flat compression surface…
Here is a housing with considerably more wear. Note that some chrome has actually flaked off the rear edge, approaching the exhaust port (this is where it will usually be worse). Also note some wear occurring on the front edge. These housings are still useable in a rebuild, however compression will suffer a bit, being especially low before breakin. They still develop 100-115psi compression, most of the time. Most of the housings that look like this have between 75k and 125k miles.
You can see the area where chrome has flaked off…
Here we have a housing with a bit more wear on it. Note more chrome flaking on the rear edge, and some on the front edge as well. Also some odd wear patterns on the edges, near the exhaust port. Most 86-88 housings will look about like this. They are still useable, however, compression will never build up really well, so you should evaluate your needs for the engine. Expect 85-110psi compression out of housings like this. Most of the time these housings have 100-200k miles on them.
Here is a GSL-SE housing from an 84 model. Here you can see significant chrome flaking all around the housing. This is why it’s difficult to rebuild an older engine (85 and earlier) with used housings…even with 50k miles, you start to see flaking like this, and it gets much worse with time. I do not consider these housings useable in a rebuild, however the engine would run with housings like this, just never have much compression. And probably would suffer from hot start problems.

I do not offer used housing rebuilt 85 and prior 13bs due to these problems, since any used housing you acquire will have this wear present, and most all my rebuilds are used housing. Instead, I use 86+ 13b block parts to build a hybrid engine, and install the older 13b front cover and oilpan for use in the original car. Or, in the event that the customer wants to stay all original (for whatever reason) and has a larger budget, we can get new rotorhousings, or send the existing housings out to be resurfaced with cermet ceramic.

Here is an old 12a housing. This is just more of the same, severe chrome flaking everywhere. Again, this is why it’s difficult to rebuild a 12a with used housings, therefore I do not offer these. These are all of the same housing, btw.
Here’s a different 12a housing…
And another one.
Rotary Resurrection - Tech Section
Rotary Resurrection
is located in
Morristown, TN,
1 hour east of Knoxville.
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