Remanufactured rotor housings

[Ian Habicher]

Greetings!

Man, aren't those rotor housings getting tough to find in good shape
these days?

I was wondering if anyone had heard of any existing company that
remanufactures the trochoid housings? Mazda wants over a thousand bux
for one housing, I have been tossing many ideas around in my noggin
about how to build a machine to grind the trochoid profile.

I could grind off the chrome down to the cast iron, then have them
replated locally, and then regrind the chrome plating into the proper
profile. Provided I could grind the hard chrome, it wouldn't be much of
a problem as long as the cuts were very light and the grinding wheel
didn't skip over the chrome instead of cutting it! Perhaps a diamond
grinding wheel would work.

So, am I dreaming, or would there be a market for these things,
especially if the chrome was new and they were sold at 1/3 the price or
so of brand new Mazda factory ones? Be interesting... Would I have any
buyers? Building the grinding machine would be work, and interesting,
and perhaps tricky, but by no means impossible.

Does anybody know if it's a particular pain in the butt to chrome plate
cast iron properly?

Ian
87 T2

[The Raven]

"Ian Habicher" <ihab...@hotmail.com> wrote in message
news:3C205B8A...@hotmail.com...

> Greetings!
>
> Man, aren't those rotor housings getting tough to find in good shape
> these days?

Yup

>
> I was wondering if anyone had heard of any existing company that
> remanufactures the trochoid housings?

No-one does it because it needs to be specially applied, the right type of
porosity, and then machined to close tolerances over a surface that most
machine types can't duplicate (NC machines excluded). Even if all this was
done, the chome plating could still flake.

> Mazda wants over a thousand bux
> for one housing,

Which country? Last I checked they could be had for $500+ (depending on year
and type).

> I have been tossing many ideas around in my noggin
> about how to build a machine to grind the trochoid profile.

Easy done once you see how the shape is generated.

Have you figured out how to deal with worn combustion/water seal grooves
(early housings)? I think this is why Mazda moved the seal grooves onto the
side plates, it meant that a housing replacment wouldn't replace the grooves
and ensured machining the side plates was less tempting. It's harder to
rebuild a newer style engine now.

> I could grind off the chrome down to the cast iron, then have them
> replated locally, and then regrind the chrome plating into the proper
> profile.

I believe most chrome platers have a method of chemically, or electrically,
removing existing chrome. Grinding would just ruin the tolerance the housing
had, you couldn't be that accurate with a grinder.

> Provided I could grind the hard chrome, it wouldn't be much of
> a problem as long as the cuts were very light and the grinding wheel
> didn't skip over the chrome instead of cutting it! Perhaps a diamond
> grinding wheel would work.

Don't try it.

>
> So, am I dreaming, or would there be a market for these things,
> especially if the chrome was new and they were sold at 1/3 the price or
> so of brand new Mazda factory ones?

If it could be done cost effectively you'd be rolling in cash. I believe the
properties and application of the chrome are very specific and something
that would be near impossible to do on an old housing. Additionally, you'd
have to be extremely careful with the housing sides as you could easily ruin
the machined surface/tolerance (remember you have to chrome right up to the
very edge).

> Be interesting... Would I have any
> buyers? Building the grinding machine would be work, and interesting,
> and perhaps tricky, but by no means impossible.

Definitely would be interesting for someone with the time and money to test
the theory out.

>
> Does anybody know if it's a particular pain in the butt to chrome plate
> cast iron properly?

Don't even think about the side plates, if that's what you're thinking. Yes,
cast iron can be chromed as they do it with old rotors to make clocks and
paperweights. As for chroming the inside face of a housing, the underlying
insert is steel not cast iron.

--
The Raven
** Undisputed President of the ozemail.* NG's
** since August 15th 2000.
** Conqueror of the uunet.* NG's

[Rex Burkheimer]

Seems to me new housings run about US$300, with racers discount.
I think you are wasting time trying to rebuild them. As Rachel points out,
it would be easier to build new ones than re-do damaged ones.

But....Does anyone know what kind of milling machine is used to resurface
the side housings?

--
Rex Burkheimer
Parts Plus Marketing Director WM Automotive Whse., Fort Worth TX

"Ian Habicher" <ihab...@hotmail.com> wrote in message
news:3C205B8A...@hotmail.com...

[Chas Hurst]

Rex Burkheimer <r...@wmautomotive.com> wrote in message news:u223bu3...@corp.supernews.com...

> Seems to me new housings run about US$300, with racers discount.
> I think you are wasting time trying to rebuild them. As Rachel points out,
> it would be easier to build new ones than re-do damaged ones.
>
> But....Does anyone know what kind of milling machine is used to resurface
> the side housings?
>
>
> --
> Rex Burkheimer
> Parts Plus Marketing Director WM Automotive Whse., Fort Worth TX
>

I have resurfaced older (pre RX7) side housings. A blanchard grinder is required, a big one. And considerable talent by the
operator. It is my understanding that a new process is used on RX7 side housings (gas nitrideing) and the hardened surface is not
sufficiently deep to allow resurfacing.

Chas Hurst

[Kenneth McKenzie]

"Ian Habicher" <ihab...@hotmail.com> wrote in message
news:3C205B8A...@hotmail.com...

> Greetings!
>
> Man, aren't those rotor housings getting tough to find in good shape
> these days?
>
> I was wondering if anyone had heard of any existing company that
> remanufactures the trochoid housings? Mazda wants over a thousand bux
> for one housing, I have been tossing many ideas around in my noggin
> about how to build a machine to grind the trochoid profile.
>
> I could grind off the chrome down to the cast iron, then have them

Ian

I believe the housings are made of alunimium that use a metal spraying and
casting technique known as TCP - transplant coating process. It is a
process of a thin layer of steel is sprayed on the inner epitrochoid core of
the die. This is pre heated before the alunimium is poured in. The result is
a steel coated die cast rotor housing that is machined and then chrome
plated.

I have been advised that chrome doesn't properly adhere to cast iron. If you
want to know how to make the "epitrochod shape inner chamber" let me know.
(It in fact isn't a epitrochod shape that is created by a point of a radius
of a generating circle that rolls along another circle creating a curve. The
trochoid is also a poor description for the shape of the rotor)

The simplicity of the design for machining and grinding the housing should
be pleasing. It can be made to utilize standard machine tools for less than
$500

I have pictures of it on my site.

cheers
Ken McKenzie

www.starapex.com

[David]

I have seen a local company advertising re-chroming housings. I doubt
they would be anywhere near as good as an original though. They were
advertised as about half the price of a new housing from Mazda - about
AUS$250.

Try ordering new housings from here in Australia, or New Zealand. They
run to AUS$500 to AUS$600ish here in Oz(last time I inquired anyway).

--

Dave

****

"It's all just a load of Klatchian to me..."
Rincewind

****

[Glenn Wittrock]

I had my (83 12A) side housings surfaced by a freind at a boinger shop.  He used a planer/mill that they ordinarily use for heads etc.  It was just wide enough to do the cut and my god to hear him bitch and moan about how hard the job was.  I believe him when he says he used about 100 dollars worth of cutting disc.  He also said he would never do it again, this is the rotary's downfall, technological density.  I had the good fortune at the time to work at a machine shop with a hardness tester and the faces were all unchanged by the process.

As far as milling your own rotor housings the best machine for the job will likely be eccentric-shaft based.  Your next challenge will be a drive arrangement that varies the speed of the shaft such that you can maintain your cutting tip speed uniform.  I f you simply rotate the shaft at a uniform speed you'll spend too long on the narrow sections,  overcutting them, and fly too quickly through the top and bottom undercutting them.  How exactly you are going to measure the chrome thickness left, I haven't got a clue!

-- 

Glenn Wittrock

Linux: when you need to run like a greased weasel.

 

[Chas Hurst]

What sort of finish resulted from resurfacing? Ready to go, or did you need to polish it. Most head resurfacers intentionaly leave
a pattern. How much was removed? Was the resurfaced face still parallel with the other side?

Chas Hurst

Glenn Wittrock <rock...@pluggedin.ca> wrote in message news:3C21FA55...@pluggedin.ca...

[Glenn Wittrock]

The surface was very smooth and passed inspection by a rotary mechanic aquaintance of mine with no polishing.  The depth of material removed was the absolute minimum to remove the typical triangular wear on side housings. If I recall correctly the micrometer readings were delightfully precise at the perimeter and center of the center-housing.
The material removal was profoundly minimum as it was the hardest object Ron had ever milled.

[Rex Burkheimer]

"As far as milling your own rotor housings the best machine for the job will likely be eccentric-shaft based.  Your next challenge will be a drive arrangement that varies the speed of the shaft such that you can maintain your cutting tip speed uniform.  I f you simply rotate the shaft at a uniform speed you'll spend too long on the narrow sections,  overcutting them, and fly too quickly through the top and bottom undercutting them.  How exactly you are going to measure the chrome thickness left, I haven't got a clue!"

 

OK, I've got it:

 

Mount a front casting, with bearings.
Insert eccentric shaft

Mount a replated housing (which would be tighter than spec)

Modify a rotor to accept 3 high-speed cutters in place of the apex seals. Perhaps 3 Roto-Zips with cylindrical cutters the length of the rotor,  in a diameter that puts the cutting surface right at the finished surface dimension.

Turn on RotoZips and rotate the rotor through several cycles.

Repeat with polishing stones

 

 

 

[Glenn Wittrock]

I'm with you except for 1 critical issue:  I think you are going to remove too much chrome at the "waist" and not enough at the top and bottom.  I think you need to use a single cutter and to two idlers then you can manipulate the shaft speed to allow your cutter to have a reasonably uniform speed of travel over the face of the housing (patent pending yukyukyuk).

 Burkheimer wrote:

"As far as milling your own rotor housings the best machine for the job will likely be eccentric-shaft based.  Your next challenge will be a drive arrangement that varies the speed of the shaft such that you can maintain your cutting tip speed uniform.  I f you simply rotate the shaft at a uniform speed you'll spend too long on the narrow sections,  overcutting them, and fly too quickly through the top and bottom undercutting them.  How exactly you are going to measure the chrome thickness left, I haven't got a clue!" OK, I've got it: Mount a front casting, with bearings.

Insert eccentric shaftMount a replated housing (which would be tighter than spec)Modify a rotor to accept 3 high-speed cutters in place of the apex seals. Perhaps 3 Roto-Zips with cylindrical cutters the length of the rotor,  in a diameter that puts the cutting surface right at the finished surface dimension.Turn on RotoZips and rotate the rotor through several cycles.Repeat with polishing stones