Cracked front housing
 

To all who were interested in my engine with the RX-7 rotors I'm pulling the engine as the front rotor housing cracked at the dowel pin on the front right hand side causing an oil leak.

This is a good opportunity to inspect the oil control seals and side seals and if there is evidence of accelerated wear I'll report back.

RG are you listening??

So sas this is not going well for me too right?? :(
Or is there something we can do to make it work to me too?

Can you post any pics later?

Ouch. That sucks. That's not a new problem to rotaries unfortunately. I'll compare Ray's housings to some 13B's to check the casting thickness in those areas as a comparison.

The RX-8 casting is very similar to the FD's.
Cracking housings in the dowel area is a result of abnormal combustion mainly from pre-ignition or detonation. There's no if's or but's about that.

So that problem occured from the use of fd rotors with the renesis housings or it was just a common failure??I am planning to use fd rotors too,will i have the same problem??

It sounds like a tuning error.

Bummer, now you get to drive one the 13 other cars for awhile. :)

make one part stronger and the stress gets passed on to another

I looked at drawings of the housing and I think we might solve the problem by pinning the housing with extra dowel pins to strengthen the housing itself. To allege that it is caused by tuning is really silly. I know that the tuning is spot on.

My guess is that there's a possibility of flexing due to the design of the parts, but that is only a guess. I suspect the engine is not designed for the type of boost we're running and that under heavy engine loads there are stresses which caused the dowel pin to force the casting to twist, causing a crack.

I'm not going to strip the whole motor down, will just clamp the rest in place and remove the front housing. Don't know when I'll have time though, I have to complete my race VW Golf which keeps breaking gearboxes. Too much torque.

Can you elaborate with some substantiative proof please? I am intrigued by this possibility.

The Renesis castings are identical to the REW castings, with the exclusion of the peripheral port, the inclusion of different oil metering bosses and the re-positioned o-rings.

Well, obviously it is not.
Failures of any kind are the result of bad tuning, even if it means detuning to save parts from stress.

I've been building race engines since the 80's and to claim that a crack of this nature is the result of bad tuning is laughable in my experience. I also build in excess of 400 diesel engines a year in our business and have seen a number of stress related failures. Remember:

1. the front housing is a stationery part.
2. the crack is minute and on the outside of the dowel pin location.
3. the location of the crack has nothing to do with any moving part.

If his reply was that I erred when we assembled the engine I could agree. The crack could have been the result of incorrect assembly rather than tuning. I don't know if the housing was dropped, bumped, or forced into position although I think we can ignore the last possibility. There's also the possibility of a manufacturing and/or quality control issue. It is impossible to say if this failure is a result of any of the above. I will send it away for a proper analysis and don't think it's worth while repairing, so I ordered a new part from the local dealer.

Hehehe. I took delivery of a new VW Eos last week. I'll use that one for a while.

If the castings are the same thickness as the last 13B castings, and if the rotors used were the 9.0:1 compression rotors, there should be sufficient strength necessary to hit 700+ hp before breaking a housing. Assuming of course that it is tuned properly.

I'm not saying that it was necessarily poor tuning but if anyone says it can't be improper tuning, they have a lot to learn. I've gotten in arguments with mechanics who've been in the business for years and they've been dead flat wrong about things. Arrogance and over confidence will kill an engine just as fast as inexperience will. It seems there are only 2 possiblities here. OK 3 if you count poor casting quality. This would be a first in decades though so that part is the least likely. The 2 most probably options are that the engine wasn't as tuned as it was assumed it was. The other option is that the housing was in fact dropped in which case it would be careless to assume it was perfectly fine and then use it anyways. Out of the 3 obvious possible causes of the failure, the only one that could be pinned on Mazda is the least likely. You never know though. That's just the way it looks.

I have never seen a housing crack where it wasn't either the engine builder or tuners fault. That's just the way it goes. The older housings from 86-88 cracked at or around the 400 hp mark although some could get them to go higher. They were thinner and people that use those housings know they are weaker. If the Renesis castings are roughly as thick as the 3rd gen 13B was, there is no reason to believe that they couldn't get the insanely high numbers as the 13B before breaking. Assuming tuning was spot on of course.

Your experience must be quite questionable, then.

Hahahahaha!

Sometimes one can only laugh at these "internet" mechanics!

<GRIN>

I really think we can eliminate the tuning factor. Dropping or damaging the housing whilst assembling is more likely in my opinion. I have the motor out and will look a bit closer later today.

The problem is that the crack is so minute it's impossible to spot in position so I'll have to take off the housing and illuminate & magnify the damaged area properly in order to see what really happened.

I'm eager to see what wear we have on the side seals per your previous comment, and if the oil control seals are damaged at all.

APV Valve
 

RG, what's your opinion about leaving the APV valves open?

You'll lose low end power but aside from that it should run fine. It's just less average power over the entire powerband. If it's just a race engine then it shouldn't be much of an issue.

I never owned an rx-7 so my rotary experience is generally confined only to the 8, but I did stay at a holliday inn last night.

How much boost were you running?
When you say right side, do you mean driver's side so toward the combustion end?
Is the alloy of the rx-8 housing the same as the rx-7?

I'm anxious to see pictures.

There is a dowel pin on the driver's side of the engine on top and one on the passenger side at the bottom. He cracked it at the top location on the front housing. All of your oil to the front eccentric shaft bearing flows through this location.

Yes they are the same cast iron as the old housings. I've got each housing type in the shop right now and the welders have verified they are the same material.

Such as yourself, or were you thinking of another example?

^Why do you want to f"ck a thread that is very helpful to others?Just unsubscribe from this...If you have something important to say-say it.

And why i am talking?Cause my project will have many similarities and i want to know if i ll have a same prob.

Then perhaps you will want to know when you are being subjected to incomplete information?
Perhaps you should just put me on your ignore list? Parakalo...

Aren't the housings on both engines different by several cm?