12a rotor housing ?
 

I have a pair of oldschool 12a rotor housings and wondering if they are useable.they have these weird markings on them but I run my finger nail through them and cant feel them.they are smooth all the way around

Another part is by the exhaust port has some edge wear,would that effect compression at all in that area.
Thanks in advance guys.

http://i218.photobucket.com/albums/c...e/null-1-6.jpg

Attachment 646636

I have seen housings like that before . I think mazda experimented with these for some reason. they will be ok to use .I have used many that look the same . the missing chrome is in exhaust area and wont affect your compression that is fine

never seen housings with brush marks like that, doubt mazda put them there either.

someone cleaned those with an abrasive pad..

Weird thing is I cracked open a 79 12a engine and the housings are mint but you can see some markings that are similar to these.
I will post a pic of those in the morning.
These set above were on a running motor but had bad oil seals.
im putting new apex seals.new side seals(clearanced to.002),new Mazda solid coner seals,all new springs,large street port.just want to be sure they will give good compression numbers,if they are not useable I will just use another set I have.but I love the big Mazda logo

the rotary world is relatively small, it's quite possible you wound up with 2 engines that were worked on by the same person/shop.

some people could do something like that for oil permeation for racing engines(premixed), but you'd also recieve some compression losses so i just can't picture it being something mazda would put out. mazda specs are usually pretty anal when it comes to compression.

Weird.
First engine came from a 75 rx3
The 79 engine came from a junkyard motor in San bernandino county
Here's pics of the 79 housings
http://i218.photobucket.com/albums/c...77498C7C4C.jpg

http://i218.photobucket.com/albums/c...B419F7411A.jpg

Oh yeah both were stock engines.

i have seen those cross hashes on some reman engines(before they actually labeled them) but those are machining lines, unlike the ones you posted earlier which are deep and appear to be hand made or done by hand with a machine tool. maybe their tooling was loose but they let them fly...

this appears to be akin to what we do now with resurfacing good used housings for a rebuild. it just has me curious because chrome is very tough to gouge so whatever they were using had some serious power behind it(think housings stacked or prior to being cut apart with a large flapper with diamond tipped honing stones, except the stones were in need of attention). whatever tool they used it must look very mideivel.

back in the '70s a lot of these processes were probably done by hand before automation came into play, so you can see where someone might have manipulated a machine manually. even on the cleaner process you can see the human interaction. it's also a difficult task to accomplish for most without creating a crown to the surface(i have been trying methods but the crown is a undesired side effect for higher mile housings, think less initial compression and compromised edges quicker).


i suppose it's just possible there was some experimenting going on just after the carbon seal debacle was over as mazda struggled to try and push out something that actually worked. the cross hash helps prevent the seals from creating lines, or gouging in the lack of lubrication.



personally i'd just run them, they look better than 90% of the 12a housings you will find.

So your saying run the 79 housings or run the older rx3 housings?
I know the 79 housings I can run and be good.
But I really want to run the older rx3 housings if I can.but I don't want to worry about compression issues.its crazy cause if the chrome is hard like you say I wonder how they made those weird markings and make them to the point that they cant be felt.they are smooth to the touch.