12A Teardown Pictures
 

So I finally got a chance to tear apart my car's original engine... I don't think this one's coming back.

Front housing had some pitting around the edges near the exhaust port.

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Rear housing was a little bit worse. Bottom, just before the exhaust port:

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Top:

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This engine never ran under my ownership, so I have no idea what kind of history it had. What kind of failure could cause that much damage?

A combination of issues. Bearing failure and/or over-rev caused the rotor to take those bits out of the housing :( I have a similar motor that was originally in my car, it was stolen, taken for a joyride, and never ran right again. Inside was a very similar story. I bet the stat gears are pretty munched too.

Isaac


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The stat gear appears to be in decent shape...

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The apex seals were all accounted for, and all looked fine (unbroken, smooth) to my untrained eye.

that front housing is pretty nice for used, the rear one looks more normal...

i think that huge amount of flaking is either due to the engine running a little hot for a long time or a lack of metering oil.

i had an 83 LE that actually ran pretty well, i took the motor apart and the chrome was gone!

this thread worries me as im about to teardown a 12a i pulled out of a parts car that ive never seen run

then run it and don't worry about it until it blows!

Wrd. That's what's going to happen to the engine in my car right now. It was $150, so it's just to hold me over until I can build a new one.

That heavy flaking looks to me like a combination of extreme wear, possibly combined with being somewhat short on OMP oil, followed by extended storage time in a damp environment that let water condense and corrode the steel under the chrome plating.

Say, like, someone leaving a spark plug out for about a year? Cause that definitely happened before I bought it.

WOW!! I am about to tear apart a 12a tonight! Pulled it out two days ago. I think it will be OK, it ran great, just doing some surgery to reduce oil consumption!

On the two engines i have pulled apart that were this bad, the large areas that were missing chrome had mechanical damage, not just flaking. You can see that the chatter path extends all the way across the housing even where chrome remains.

it screams overrev to me ... and, as mentioned, possibly inadequate OMP lubrication.

its already out and sitting in my friends garage, its hopefully replacing the one that's currently in my 83 gsl with 125k on it

over rev was my first thoughts as well. looks to have had water sitting in it as well.

Just pulled my 12a apart and had similar chatter damage. Is there some reliable way to repair this type of damage? I came across a website http://jhbperformance.com/services.php that claims to be able to repair this. Has anyone heard of this procedure/website?

I've never heard of that company in particular, but I've read that you can indeed refinish housings, I know that's one of the easier ways to rebuild a 12A, actually. Good condition housings are rarer and rarer that it's easier to just send your old ones away. I'd probably just email that company a picture of the damage and have them tell you yes or no.

JHB does cermet coating

is there anyone actually running recoated housings?

lots

I'm so glad that recoated housings exist now. I was scared that I would have to do a 13b swap but I get to keep my 12a :D

good. so i take it they're just as good as original. i have some rotor housings i'd be interested in getting done(depending on the cost) that r the original ones to my engine and were ported when it was first built by one of roger mandeville's guys. they have some chatter marks in them and was afraid to reuse them when i did the rebuild which has been more than 5 yrs ago now. i've lost count since then but rough guess it's got round 80k on it now.

That type of wear is pretty much to be expected from a 12A. The 3mm seals will cause this type of wear. Especially with over revving. People wonder why Mazda went from 6mm, to 3mm, to 2mm. The thinner seals have been proven to be easier on the housings.

I have heard both good and bad stories of recoated housings. I have also heard of guys over in Australia taking 13B housings, and having them machined down to the width of the 12A housings.