Ok, all you engineering savvy people out there...

I was wondering, after looking at the RotaryNews Laguna Seca pictures posted today; why did Mazda move the water seal groove back from the side housings to the rotor housings?

Starting in 1986, Mazda moved the water seal groove from the previous position (in the rotor housings) to the side housings, according to Jack Yamaguchi's book, "...where it is less affected by heat". I think he means, the aluminum, because it has an expansion rate greater than steel, gets crushed if the engine overheats, (after it expands between cast iron side housings held in place by steel studs) yielding a narrower part once it cools, thusly causing coolant leaks. No groove in the aluminum would mean a more difficult surface to crush then, I guess. (more metal)

I noticed the FD also used the above method. (at least early on, shown in a brochure I have) Why the change now?

Below shows the Renesis housings (from the good folks at RotaryNews)

I am not sure why they did it but, I do know that they did is a good thing because it will make rebuilds cheaper and make building a 3 rotor motor easier.

*smacks head so hard i fall out of my chair* MAKES BUILDING 3 ROTORS EASIER, EH????? :D :D :D :D :D :D!!!!!!!
that's SOOOO RIGHT!! OMG!! :cool: :cool: :cool: !!!

what an eye you've got there KKM, i completely missed that... tremendous!!! :D

Damn, wish I had noticed that when we were in the room with the engineer...

But! I have his email address, so I'll send off the question.

--dan

could someone grimace the pics so i know what the rest of you are talking about? what groove?

let me try without photoshop skills...since i don't have photoshop. the top half of the picture is the side housing, there are no grooves in it...like there used to be.

now on the bottom half of the picture, that's the rotor housing, there are 2 grooves on the side of it...the part that would come into contact with the side housing. the seals would fit in those grooves and fit flat against the side housing as opposed to, fitting in a groove on the side housing and going flat against the rotor housing

hows that?

okay i knew which housing was which and now i understand the grooves you are speaking of. why does it make such a big difference as far as rebuilds, putting together 3 rotors etc that they are on the opposite face now?

Aha!

I knew I'd eventually get a rise outta somebody! I'll try to answer my own question, but it's a guess really, I think we'll eventually find out the real answer. Well, here it goes:

Could it be, with the exhaust ports through the side housings now, less heat is transfered to the rotor housings, so they become a safer home for the sealing rings? Hmmm, maybe Dan will find out.

As far as rebuilds, I could see how it would make a difference, (grinding the surface of the side housings flat would reduce groove depth for the seal) but I don't know why the groove in the rotor housing would make a 3-rotor engine easier to build.

I think the reason it would make a 3 Rotor easier to build is because, It would be less to worry about because of the water seal location. If we knew the width of the thicker housing on a 20B. The E. Shaft from a 20B could be used. It would be easier to make a housing From a renesis Side housing to use as a pattern so you can have a center size housing port shape on one side and the Large Port on the other side like in a 20B's Thicker housing. So you would be able to use The 20B E. Shaft , Two Renesis end housing and center housing and the modifed thicker housing, Etc..... Parts that could be used. To make it cheaper to build. Let me know what you think.

Sorry, you lost me. Unless you mean some of the side housings would carry the groove, and some of the rotor housings would carry the groove.

What I was talking about is the inside of the side housings, water passages and intake and exhaust passages, etc..... If a housing was made the right width for use of the 20B Eccentric Shaft and had a correct stationary gear for the use.

Here's the response from the engineer, copied and pasted:

As you mentioned in your mail, water seal groove of RENESIS is in the rotor housing.

Exhaust port is cooled by the water jacket surrounding the port.
Large exhaust port area is required to get high performance, and
some width of water jacket is necessary for casting production.
Moving the seal groove to rotor housing, we could get wider exhaust port and water jacket.

That is the reason of changing the groove location.

Performance, baby... larger exhaust ports ;) :D

Hey, thank you, Rotarynews person!

That explanation makes sense to me! I'm not an engineer, but I can understand the port size / performance relationship.

Now I can catch up on all that sleep I've been losing!

racing beat makes a 3 rotor housing and makes housing for the older rx7 13B housings if they were able to make a housing for a 3 rotor that had side exhaust ports they could use the renesis housing to help them make it. where the water passages and other important passages go. And if they made the housing the same width as the 20B thicker housing we could use a 20B E shaft and modfied stationary gear. what do you guys think

My old 12A motor has the grooves in the rotor housing. According to Mazdatrix, a company that rebuilds engines among other things, states on their website that having the grooves in the end plates means that you can only lap the plates smooth so many times before the grooves dissapear. Therefore, having the grooves in the rotor housing makes the Renesis easier to rebuild, because of the ease of lapping the end plates.