Notice there's four of them on the rotor housing: My guess is they were used to mount the rotor housing up to some machine or device that did more work during the machining process.



Someone mentioned pinning. Those lands aren't as wide as a dowel land (16mm) but a buddy of mine GMON and I had an idea last year to go for using those holes, or similar ones, for something called 'pocket pinning' where a short, thru pin would be used in those or similarly-machined spots. Think of the steel pins that are on the back of your rear iron housing that index into the bellhousing of the transmission.



B

 

I thought i was done substantially BTDC near the upper dowel land?



B

 

Here are some pics of my 3rd gen housing and they have it also I think its from the casting mold or maybe like BDC says formounting purpose for further milling after casting .

 

As you quoted on another thread everyone does it diffrently

 

must be a 13b thing my 20b doesnt have them

 

Thats odd, I thought they were the same as 13b.

 

nar my 20b housing dont have them in it aye, there is some slight differences between 13b-20b, couple of the through bolts are larger etc

 

I believe the old 13b motors actually had a tension bolt there.

 

Not just 13B but all models had an extra tension bolt hole.



If you look at the rear side housing there is probably an undrilled, unfaced boss at that location as well.



Mazda got a lot of life out of their casting forms. Notice that the RX-8 engine has rudimentary exhaust port depressions in the rotor housings.

 

Ah! Now were getting somewhere!



Unused tension bolt hole. But it looks like it will run right through the intake runners...