TimWilbers

iTrader: (1)

First picture is rear housing showing area of maximum flaking. Has been described as a useful paperweight.

Next four are the front housing.

Atkins has the retooled 13b's to 12a's for $750 each (seems pricey).
ebay has some at varied prices, one comparable to my front housing (cheap).

Suggestions welcomed.

erick31876

iTrader: (8)

don't use them there's a decent set on eBay right now for around 300

ray green

iTrader: (14)

I'm inclined to agree, as much as I hate to see 12A rotor housings reach the end of the line, that rear housing is fit to be a paper weight and the front one has well over the Mazda recommended amount of chrome loss for a rebuild.

Decent used 12A housings are hard to find, but patience and a lot of looking can pay off.

Here's a nice one on ebay, but the price is too high in my opinion for an early 12A housing:

Mazda RX7 12A Great Condition Rotor Housing RX 7 RX3 RX2 Racing Beat | eBay

Here's what looks to be a good pair from the pictures, but at $788 the price is way up there:

1979 1985 Mazda RX7 12A Engine Rotor Housings Qty of 2 | eBay

This one looks pretty good and the price is right at $120, but it does have more than the recommended chrome loss. If you wanted to get away cheap you could pair it with your front housing and probably get a decent motor, at least for recreational use:

1979 1985 Mazda RX7 12A Engine Rotor Housing | eBay

Here's a pair that ended last week that probably would have suited your needs nicely, but housings like these don't come along very often:

Pair of Excellent 12A Mazda RX 7 RX7 Rotor Housings 1979 1985 | eBay

Hopefully these posts will give you a sense of what's out there. If you have a few months to look, I'd keep an eye on ebay and here on the parts forum, something should come up that will suit your needs.

On the other hand, if you have the money and want it done right, the retooled 13B housings by Atkins are worth considering (I nearly got some of the Atkins housings last year before a couple used 12A units finally came my way). At least with Atkins you should get excellent housings backed by a reputable company with lots of experience with the 12A housing problem.

Of course if you go the Atkins route you will also want to make sure that all the other engine parts, rotors, irons, bearings, etc are up to Mazda standards, plus the price of a rebuild kit and a competent engine builder, which can add up, but at the end of the day you should have an engine that will last another 20-30 years.

I just noticed you are located in Ohio. You might want to check with Dave (mazdaverx713b) for parts and advice. He's in Vermillion Ohio, maybe close enough for a visit and personal inspection of your current and future 12A housings.

Here's a recent post of his for a 12A and 13B short block, I'm not sure if he currently has any later model 12A's.

https://www.rx7club.com/1st-generati...locks-1062497/

TimWilbers

iTrader: (1)

Ray,

Agreed on the first three links, and wish I had seen the fourth one when it was available. (Didn't know the condition of the housings until Easter weekend.)

I did consider the 3rd link as a pair to my front. Yes, just for recreational use.
I only put 3,000 a year on it as it is and that would be the economy rebuild. I don't think the state will let me drive in 30 years due to my age.

I still have more stuff to clean. I've projected getting it back on the road by the end of July, so I'll keep looking.

I've already asked Dave if he wants to break down the 12a, and the housings are good, to let me know. He's agreeable if it comes to that.

Thanks for the information as always.

ray green

iTrader: (14)

Well I dunno Tim, the way medicine is going these days, you might be driving just fine in 30 years.

Especially if you do most of it between now and then in the FB.

If pairing your front rotor housing is an option, I'll check the local 12A housing bank, they may have one for shipping costs.

Can you post a really sharp photo of the worst part(s) of your front housing so we know what to match?

TimWilbers

iTrader: (1)

Ray,

Thank you.
When I get home after work I'll take some new photos of the front housing.
(The back one scares me as well.)

And how does a dowel pin break? It was locked into the rear iron, but slid right out of the rear housing. (Not really expecting an answer.)

NCross

iTrader: (18)

The pin was cracked? Detonation? Was there a crack in the rear iron?

Those housings are no good, but you could make a mean display out of them! Or coffee table.

ray green

iTrader: (14)

I tend to agree with NCross, unless you're doing a cheap junkyard rebuild just to get something in the car, you're better off finding parts that meet the rebuild specs.

It looks like you already have some leads on housings that might meet specs, so see if you can go that route without breaking the bank.

And while you're at it you should put a micrometer on your iron surfaces to be sure they won't need some work and check your rotors and bearings.

But if you're down for the junkyard rebuild, I'm sure we can find you a used 12A rotor housing that will match your "good" one for cheap, like the price of postage (these aren't hard to find, for some reason).

TimWilbers

iTrader: (1)

The lower rear dowel pin was a little more than cracked.
The short end was stuck in the rear iron.

I'm thinking of a table lamp for one of the housings.

NCross

iTrader: (18)

Factory defect? Usually the iron cracks near the oil filter.

TimWilbers

iTrader: (1)

Ray,
Image of worse areas of the front housing.

I've already got considerable time and resources into this project. So yes, I want this to last awhile, 30K min and 60K would be great. Matching the best of my worst does not seem a sound solution.

I still think I can do this. One step at a time.

TimWilbers

iTrader: (1)

My thought as well.
I'll check the opposite side at the oil cooler as well.

The dowel pin is the only major damage besides the rotor housings. The apex and side seals moved freely in the rotors and no other broken parts.

Thanks for the input.

ray green

iTrader: (14)

Damn, that is such a pretty housing, other than that minor, but significant, chrome flaking.



You're about where I was a year ago, trying to build a 12A out of stuff you hate to throw away.

Like you say, one step at a time. Spec out your irons, rotors and bearings to see what you need. Look for good rotor housings in the mean time, they will come.

PS, the dowel pins and all those other 12A accessories that aren't irons, rotors or housings are generally available for the cost of shipping.

Assuming you meet the OGTA discount criteria, of course.

TimWilbers

iTrader: (1)

I need to get a caliper and dial indicator (& stand).
There are some at Harbor Freight, but the readouts only go to .01" increments.
That does not seem to be fine enough, or am I wrong?

TimWilbers

iTrader: (1)

I need to get a caliper and dial indicator (& stand).
There are some at Harbor Freight, but the readouts only go to .01" increments.
That does not seem to be fine enough, or am I wrong?

Sears has one with display to .001"

NCross

iTrader: (18)

I got my dial indicator on ebay. $30 shipped. Digital calipers are cheap and can be found at any parts store. A set of feeler gauges wouldnt hurt to have either.

wankel=awesome

Ever think about just picking up another running 12A?

NCross

iTrader: (18)

Just rebuild it. I've been burned on so many kegs before. Either theres an unforeseen problem (cracked rear iron), a stuck seal, or it lasts for about 3 months before it starts eating coolant or oil. The problem is theyve been sitting for ages. You can do a DIY rebuild for under $1000 including tools (assuming you dont have a hoist, stand, dial indicator, flywheel socket, etc). The rebuild itself costs $450 buying the right parts from Atkins, Housings run $100 a piece from forum members.

rwatson5651

iTrader: (5)

You definitely want the .001 version of the dial indicator. You will use it to check your side housings and again to set the end play.

The caliper will come in handy but be aware that it is not nearly as accurate as a set of micrometers(waay more accurate, but pricey for good ones). I think you can get by without these if you are willing to put it together without checking the oil clearances between the eccentric journals and rotor/main bearings. Not a big deal if the engine was running prior to teardown and had good oil pressure.

You will also need a good feeler gauge for measuring the clearances on the side seal to corner button and the clearances inbetween the side seals / apex seals and the seal grooves. Preferably one that has a 1.5 thou leaf.

TimWilbers

iTrader: (1)

I considered the unopened box vs. opening mine to see what was going on. It was running fine for 8-9 years then started pooling oil on the 12a markings (dowel pin O-rings). Then it was running just a little rough, not stalling, but seemed a bit off. Then one day about a mile from home going to work when the choke kicked out I thought it was going to throw up. Got it back home. Started it up that evening and clouds of white smoke out the exhaust. I've read here about the intake manifold O-rings failing so I went that route first. (Did the bounce compression test and had 89-90 psi on all faces cold.) The intake manifold gasket was mush and literally falling apart. Replaced the intake manifold gasket, tested, more clouds but had the smell of burning oil this time.

So far, outside of the flaking on the rotor housings, I've found nothing broken, except the lower-rear dowel pin. Apex seals, side seals, corner seals, all moved freely; push in, they pop back out. But, oil was everywhere including on the back of the rear iron and covering the rotors and rotor housings, and the sealant on the oil pan almost looked like it was dripping. (Oil on the front exhaust rubber hanger caused it to smoke and eventually melt.)

Hoist: 2-ton Harbor Freight: $200 (estimated $180 rental for removal and installation)
Engine Stand: Harbor Freight: $65
Mazadatrix stand head and Flywheel lock: $118.
Videos: $65
Flywheel nut removal: Free (our local garage owner thought this was fun)

I've bought other stuff, some wrenches, sockets, but I don't consider those as just for the rebuild.

TimWilbers

iTrader: (1)

Oil pressure always dipped at idle, but about in the middle of the gauge when above 1500rpm.

My old set of feeler gauges were rusted, new ones on the way home. I cleaned and checked the mid iron for warpage on both sides using the straight-edge along the 4 lines as described in the Haynes book. the .0015 would not budge.

I could feel with a bare finger some indentations from the oil and side seals along the lines indicated by the arrows in the attached image. Now I need the dial indicator to see if the irons are still usable.

Jeff20B

iTrader: (13)

Oh please, that iron is awesome. Totally useable from what I can see in the picture. I'd use it as it sits. Well, after a basic clean up and a paint job, that is. Whatever you do, don't damage the factory nitrided surface. Leave it alone. The biggest mistake a newbie can make is treat it like a piston engine and "lap" the surface. The surface of your iron is beautiful. Leave it alone.

Step wear, if any, will be right next to the spark plugs. I'm guessing you have way less than spec of .004".

Man, seeing that nice iron makes me want to hurry up and finish my current jobs to get back into engine building. I'm starting to miss it, you know?

Cookboy

iTrader: (10)

Good plan. I'd like a 74 spec 12a with 84-85 rotating assembly please.

Jeff20B

iTrader: (13)

I could build you one. Got the 3B '74 irons and some perfect 81-82 rotors with the more desireable front counterweight (semi-circle, not half circle like 80 and older) and a high volume oil pump and long tooth stat gears. Even have a rear counterweight for it (fits 74-82). I just need one 81-85 rotor housing to begin the build...

I might have a set of 84-85 rotors and I know I have a stock flywheel for that year spread. But I figured you'd want the rear CW for an aftermarket flywheel. Plus it's more old school. The actual difference is only like 1 pound per rotor. And when you've dealt with old school 13B rotors, any 12A rotor is way lighter.

ray green

iTrader: (14)

That is a decent looking iron Tim and from your description it sounds like you have an excellent candidate for a rebuild, other than the rotor housings. If your irons pass the nail scratch test they're probably alright. There will always be some indentation, especially near that outer lateral edge, but if the indentations are minor they should be OK. I'd still put the step micrometer on them so that you'll know what you have and make sure they are not too far off.



And of course, the chrome flaking on the rotor housings wasn't the cause of your engine malfunctions, so even if you put the engine back together with the "bad" housings it should run as well as it was before your troubles started and be good for at least several tens of thousands of miles. Still, this is a good opportunity to hunt down some better rotor housings and build yourself a high quality 12A.