It may be already on this thread, but with 110psi oil pressure inside the top dowel, the HYDRAULIC pressure could force the housings apart, like spread them, along with some detonaton, could lead to big trouble!! just another idea. Ron

 

opps I effed up, replied to the wrong post....

 

110psi oil pressure over a very small area is nothing compared to the pressure inside the combustion chamber. Compression alone is about 100psi, then it is combusted further increasing its pressure over a much much much larger area than the oil passageway.
The less tension holding the housings together the more each engine housing acts as independent floating part and less like one solid engine. This still wouldn't cause a rear iron to crack directly. It just makes it easier for torsional forces to be transmitted into the points that prevent the housings from shifting (the dowel pins)
Really it comes down to this fang-dangled principal of the conservation of angular momentum (say what?) It basically says every twist has something equally twisting against it. Combusted gas pushes on your rotors (force) on the eccentric shaft (radius) causing it to turn, there is your twist. The opposing twist is the rotor housing well it would twist except it's fixed... through the dowel pins to the rear housing and the rest of the world. The rear iron takes the most abuse because the torque/hp/impulse of both rotors are transmitted into it through those dowel pins.

I've had this picture in my head of how the whole thing works/fails please correct any flaws you see in my logic, if I am "seeing" the scenario correctly I hope I was able to describe it clearly enough that it makes some sense.

 

The last time i dyno it made 780 WHP @35 psi and 520ft/lbs torque,
it takes alot of power to move a 2400lbs Rx3 down 1/4 mile.Best
trap speed so far is 161 mph.Now i have so much tracktion problems
when i turned it up to 45 PSI.I can't launch like i used to.

I haven't had any problems with rotors getting beat up or bearings failing,
i did notice some rotor housing wear with running more boost.Other that that
i have no problem.I plan to take out my motor from my Rx3 next month to see
what it looks like after being in the car for 3+ years.Can't wait to see whats inside.

I am running Methanol fuel with lots of injectors and mechanincal fuel.

 

Rotors don't dent unles you have abnormal combustion like pre-ignition or detonation. I've seen 89 + rotors that dent from stock boost levels as well as live behind 950rwhp motors without denting.
Now on the topic of housings cracking even with a pefect tune abnormal forces for whatever reason will crack them. Rene hit it perfect as everyone experience different levels of output before the plates crack as long as detonation was not responsible. I've also seen the factory holes that were not machined for extra dowels in the front housing experienced small radius cracks in the threaded section. That also happens to the rotor housings.
One lesson I learnt from many years ago racing was to always bypass the oil in the dowel area in the unlikely event a plate/housing cracked and the oil got under the tires and send you for a ride of a lifetime.

 

Would love to hear how much wear there is on those rotors and housings after 3 years of use! Props on the 45+ psi of boost.

 

hello all.

I had an idea that I followed through on a few years ago that I use accasionally on S4 and S5 engines when I actually do build one . Since I don't build many motors anymore I will share it with you.

Since the Late 91 rear iron is rare to get and instead of buying one from mazda for 450 bucks and spending a grand on pinning, I had an idea that works like a champ.

If you look at the rear dowel pin, you will see how far it sits in the rear iron. Its about 3/8" that actually goes into the housing. Since there isn't much dowel going in there, and there isn't any support to hold it when the housings twist, it cracks. What I do is extend the dowel pin further in the housing for more support.

I take 2 dowel pins, butted them together in a piece of angle iron and TIG welded them together. From there you want to add around 1/4"-3/8" to one dowel so you chop the rest off and debur the extended pin. Make sure the 2 pins are strait that way installation will be a breeze. From there you will need a 16mm reamer and center up the rear dowel hole on a good drill press or a mill and you ream the hole further down toward the oil passages for the oil filter mount. Make sure you do not go too far and measure accordingly b/c you dont want to pinch the pin and you don't want the pin to walk around. If all your measurements are correct, you have way more support than ever before and you will not need extra dowels or a stud kit.

Remember, the most important thing with wankels is tuning and if it isn't tuned properly, it will not stay together no matter what seals, dowels or porting you have...

Bryan@BNR
205 640 1193

 

^^ Thanks! I like that idea. Ya know? Those dowels are standard metric swiss (some call hollow) dowels. They can be had in many different lengths. I'm sure you could find one the necessary length or at least longer to cut down. Then being one piece.

 

I demand pictures!

 

OK you asked for it, here it is,This is the IRON i talked about.
You can actually see the iron is like compressed sand in these pictures(so detailed).
enjoy.

 

There are two different types of tension bolts aren't there? I just rebuilt mine and saw it had some really thick bolts with threads right at the intermediate plate as well, compared to the ones that I took out which were crappy looking.

Plus those stud kits can't be used with the stock flywheel, but buying those probably means you have a lighter one.

 

Our stud kits works with the OEM flywheel.

 

\/ \/ \/ Some housing doweling I'm working on. \/ \/ \/
https://www.rx7club.com/showthread.p...45977#poststop

 

Whoopdyfucking doo. They dont do **** to stop housing deflection and are essentaly no better than the stock bolts.

Hope you feel good about whoever you rip off with that junk...... Where do you find these suckers?

 

****... why not just weld the "reinforcement" on yourelf? Or it that making it even worse?

 

Special procedures are required to repair cast iron. Preheating the entire part to 1,800+ °F (Bright yellow) in order to prevent restricted expansion while the repair is made, and then a very slow cool down period (in dry sand or vermiculite) to prevent cracking/warping. Then there are the 100's of welding rods/wires/techniques for all the different types of crappy cast iron out there.(most are not very machinable)

Here's a neat video for anyone interested: http://www.locknstitch.com/expansion_contraction.htm
Its pretty cool what they do to the catepillar engine block in the end.

I'd still be concerned about warpage and softening. It would be fun to do some experimenting on junk housings though.

 

after some experiences i would agree it mainly has to do with tuning/EGT/intake temps.

that night that i first cracked my iron i remembered i was brake boosting before the run which brought the intake temps up a bit, combine that with 18PSI on pump and you have a bad combination. i no longer brake boost and i now have alcohol/water injection to supplement the octane of the fuel for higher boost levels. no matter what your tuning is you are still limited by the octane of the fuel.

i had also thought of doing something similar to what Brian suggested by extending the dowel but getting a reinforced S5 TII casting and lengthening the dowel would be the cheapest/easiest way to see that it doesn't happen again. i had the same issue with oil covering my rear tires after the failure and i also would have to say i am fairly lucky to still be here, had i lost traction at 100+ is a scary thought and i know my rear tires were covered in oil that night and i was running well over 100MPH that run.

 

one of my friends had that happen to him, except he cracked the front housing as well, he was running about 15 PSI on a positive displacement supercharger, it was putting out about 400HP and it died on the dyno.. there is a reason people add dowel pins to boosted engines.. think about it, the oval shape of the housing will want to turn round, the dowel by the exhaust port is useless, and which leaves the oil gallery dowel to do the rest of the work.. since it's not bedded in much iron, it cracks it off.. from what I've heard, it is prudent to dowel pin an engine for over 15 PSI

 

Very good video! Anybody who thinks they are a welder should know these principles. I've never welded on a large part at *1800 but I can tell you that a large (several hundred pound) part at a *1000 sucks ***!


Any precision surface (ferritic) exposed to the atmosphere at *1800 will be ruined by oxidation. The nitriding on an iron would be "burned out" (for lack of better term). I think distortion on an iron would be a serious concern also.

 

Good point. The idea of just lengthening the dowl hole sounds good. For my NA engine some S5 rotor housings are going together with my S4 Irons. Later on it might get some NOS, and it would be nice to have (a little) more strength in that area.

 

i figured it out a long time ago, but everyone likes to jump on the detonation wagon, so no one will believe it.

they crack because the engine mounts allow too much flex, which puts all the stress of the torque reaction force on the rear iron, and since all the torque is produced forward of the rear iron and transmitted through the housings and dowel pins, it causes the housings to flex so much that the dowel pin is twisted out of the side of the iron.

I have rebuilt 2 engines that did this so far, both of which had relatively conservative tunes. my car ran fine on the tune it was on for a thousand or so miles of hard 1-2-3 pulls and so forth, but broke on a dry road at 165, and only like 6k rpms. why did it pick that moment to break? because that was the most torque it had ever transmitted for more than a few milliseconds, because every other time i hit peak power, i was getting some tire spin, or accelerating really fast.
the other one was a buddy's car, which broke in a similar fashion.

both engines looked great inside. the apexes were in fine shape, there were no discolored spots on the rotors or chips anywhere or any of the stuff that you find in engines that detonate hard. both cars also had broken engine mounts. coincidence? i think not, but hey, if everyone wants to think that the only thing that can ever blow an engine is detonation, let em.

pat

 

It's about sheer strength, and the only thing that gives sheer strength in the motor are the dowel lands for the four dowels indexing the housings.

The rotor housings don't twist; they deflect laterally.

Raw power levels won't cause it as it's not something that's generated by way of smooth, sequential combustion chamber forces. It happens as a result of shock loads to the sides of the rotor housings on the combustion side (think spark plug side) when a motor is at high power, then is interrupted by any kind of knock or misfiring cause (blown out spart, rev limiter, pre-ignition or auto-ignition, anything else knock-related prior to timed combustion event, etc.) and then immediately sent right back into high power. It's the equivalent of taking a hammer and smashing the inside of the housing. The rotor housing deflects laterally against the adjacent iron housings. The housing holds about 75-80% of the dowel pin and drags it with it when it deflects. The iron lands on each respective, adjacent iron housing takes the jolting shock and stress of this deflection. The thinner ones crack at lower, absolute power levels compared to higher. Normal combustion won't yield this structural failure even though the rotor housings are always trying to deflect away from the irons to some given degree all of the time when the engine is running. Under normal conditions. the dowel lands hold the pins and resulting rotor housings in-place just fine.

It can happen on either the rear or the front iron housing although it appears to be a more predominant failure on the rear. Mine cracked on the front while on the dyno. My car also uses solid aluminum motor mounts (fyi for you to consider, Patman).

I've seen this happen on 300rwhp setups. I've also seen un-pinned, S4 motors with much higher power levels never break.

I am not sure why Mazda changed the cast molds for all of the irons but my guess is maybe because of warranty issues on the then newish turbocharged 13B's in their factory Rx-7's. The cast iron around the latter-made housings' dowel lands is nearly twice as thick in some places. The rear is cast a bit more robust than the front but both are substantially thicker. It's possible to purchase brand-new Series 4 or 5 turbo rear/front irons that have this thicker dowel land casting.

Replacing tension bolts won't do anything for it. Doing a 'stud' kit that doesn't require reaming the housings w/ a fatter stud won't do anything helpful, either. Adding additional dowel pins will transfer the loads out (to what degree, I don't know), but I don't believe it's ultimately the best fix for it. We've got stuff in the works we'll be testing for the older housings in the near future.

Hope this helps guys,

B

 

This can certainly be one of the causes as there's potential there to cause all sorts of knock-related problems in the motor, be it firing the plugs too early due to poor tuning, encountering auto-ignition of the lower octane fuel during the compression stroke, or from running too rich and blowing spark out, causing a rich-type misfire.

That's scary

Some of the Puerto Rican drag racer guys will block that oil passage, through the upper dowel area, at the rear iron housing and run a loop line straight to the front oil galley to the front gear. That way if by chance they have a cracked rear or front dowel land during a run, they won't super-soak oil all over the place and not only ruin the motor potentially but also not spin out of control from having oil get on the meats in back.

B

 

Wouldn't it be possible to use external block reinforcement? I've been thinking about making a block girdle that would use a turnbuckle to pretension rods connecting the rear iron to the brace, distributing the force to other points on the motor, such as the motor mount studs. Has anyone tried anything like this before?

 

Hey Brian, is there any way you can draw a simple picture to show how the dowels like to deflect? I follow you but I am having a hard time visualizing it.

Thanks.

-Maniac