WackyRotary

Hey all 12a aspiring folks to use a turbo on it. I have a bit of warning for ya.

The long term use of a S4 turbo on mine has resulted in some rotor housing to sideplate movement. I was aready aware this occures before ever starting the project. The main problem is after a while this movement will cause a inner coolant seal to fail. This is the common white smoke at start up with the sweet smell everyone fears. Also the material on both the rotor housing and sideplates were the movement occurred is "pitting", simialer to the mazdatrix website on "results of overboost". This is what happened to me after about 2years of blowthrough(6-12psi boost pressures intercooled) on my streetported 12a. I am using a S4 turbo with wastegate ported, and flapper removed with the twin scroll port matched- to those who have done that mod on there S4's know what this means. On the good side, using 2cycle pre-mix is a very good thing, as rotors are very clean, and apex seals have lost very little material over the last 20,000miles! So if you want your apex seals to last, I recommend going to pre-mixing as that really is smart.

Anyway, I am not super rich, and a cheap *** anyway, so I am going to put it back together and hope for the best. Going to switch the rotor housings around to give each a new surface to slide against to hopefully slow it down for the next time. This is after all the cleaning i have done and such to have a good sealing surface for the inner coolant seals. The best answer is to "dowl" the engine or to have thick tension bolts in the region the rotor housings flex the most.

LONG STORY SHORT: BE forwarned, your stock 12a block (ported or not) fitted with turbo is going to have this issue if its ran long enough with boost!

nevarmore

That doesn't sound too bad to me. 2 years between rebuilds on a rather high performing motor.

Has this been used as a daily driver, weekend warrior, or race machine??

kettlman

iTrader: (2)

20,000 miles is not very long. thanks for the warning. i was thinking of doing that cause i need more speed. but i guess i'll just wait for the right motor.

FB II

lol, anyone planning to do this on a stock 12a should definately know the consequences. i have an s4 turbo on my stock port mazda reman 12a with only 50k on it. if i get 20,000 i'll be thrilled! this is why it's a base setup. gotta build your good motor on the side

evil_motors

iTrader: (3)

are you shure that it happens to all 12a engines?

WackyRotary

Yeap, all three. Gone to the track(several summer events), drag strip(once), driven to work lots, went on plenty of weekend road trips. Point is, I still have practically new apex seals and it runs great before other parts go bad(apart at the moment though). The area that is flexing is also eroding or pitting from the act of sliding against each other. That is not good for supporting the coolant seals in a rebuild-but I am doing it anyway. Basically a side plate lapping + questionable sanding down of the rotor housings to the pitted level. Hence, the reason for dowling a engine or thick tension bolts capible of tolerences that hold high combustion pressures better then the 12a block can do on its own.

Just the high combustion pressure on a 12a in stock form with high boost is not the best thing, but it will be fun for a little while with high boost, probably longer with low boost levels.

Anyone have a "cheap way" to reduce rotor housing flexing on a 12a with boost?

Mr BiG G

drop it in wet cement and let it sit

trochoid

iTrader: (6)

Some of the Aussie guys are making thick aluminum oil pan baffle plates, in hopes of avoiding doweling. I think a 1/2-3/4" plate would stiffen up the stack quite nicely.

WackyRotary

Don't see how this will help? The area is around the spark plugs basically were pressure is highest is moving in and out .... is what I am saying. A way to keep the rotor housings from moving in and out there is the answer I am looking for.

Mschafe

you should replace your rotors with a set of low-compression ones.. I know where you can get a set...

WackyRotary

What about front counterweight and my light steel flywheel balanced for a n/a 12a engine. Also, low compression rotors+shipping probably are not as cheap as I would need to be fiesble for my needs, and will hurt mpg even worse in normal driving.

I'm trying to figure out why low compression 12a rotors are the answer exactly? Pros: Sure they are lower compression, good for more boost. But what about the combustion pressure? To produce the same power as a 12a with n/a compression with a turbo, wouldn't have to make higher boost to get the same combustion pressure to produce the equal power, which would also cause the housings to flex at that point also? Is there some magic that low compression rotors have that cause them to make the same power with lower compression at the same boost as a n/a 12a with the same boost(all other things being equal)? This sideplate movement also happens on 13bT's with higher then stock boost levels.

Any more suggustions?

seanrot

iTrader: (2)

OK ill bite, what is the difference in the 12at engine compaired to the stock 12a in the way that the engines are assembled. I dont believe the 12at has stronger tension bolts. If it does then there is your answer. I wonder if a couple extra foot lbs of torque on the tension bolts would stiffen things up?

Also wacky on your 20,000 mile engine was that a rebuild?

WackyRotary

I don't know if the stock 12at uses thicker tension bolts? I have no idea...

As for my engine. I've had it apart before. The apex seals have actually probably 70-80k on them? I lost track of the actual! The only reason I took it out this time was syptoms of a blown coolant seal. And, after seeing why enlightens the concerns of a 12a using boost-hence the reason for posting this thread. I am simply putting it back together with a gasket set wary of the same thing happening eventually again. I don't know if tightening the tension bolt will help. I guess I could point out the break-away torque for the tension bolts in the area around the spark plugs were lower from simply comparing to the feel of the rest. Probably due to the material lost from sliding against each other has caused that. I don't know if over torqueing those bolts will do any good.

Any info on this is welcome?

13btnos

iTrader: (1)

12AT tension bolts are not thicker they are the same. On choice of inner water seals I would go with the teflon encapsulated seals http://rotaryresources.com/modules.p...viewitem&id=27 if you have the kit already I'd ditch the stock ones and go with these they are only $40.00 for 4 of them. They are a pain in the *** to put in but seal better than stock and I've seen motors over 220degrees without failing and the good thing about them is you can reuse them. Torque the tension bolts 32-34ft/lbs and make sure the threads are extremely clean both on the bolts and on the front plate that they thread into so you get an accurate reading. But best suggestion to do is get the motor pinned. The cost is well worth it and you won't be opening your motor ever 20,000 miles. Good luck. Oh yeah make sure you have good oil pressure 85psi atleast and the front main bolt torque up to 90-100ft/lbs.

mikey D

just but a 13b turbo engine.......20k miles 12a is a joke and a waste of money.
it isnt that high of performance typically either.


13b turbo motor will make 250-300whp without breaking a sweat and last 100k miles no problem stock.

DAVID GRIMES

Uh Oh ! Pass me a flame suit.

WackyRotary

Yeah, this isn't a discussion a 12a is worse or a 13b is better then topic. The answer is irelivent to me. I'm looking for usable sulutions for low cost on reducing sidehousing/rotor housing movement from boost usage.

Mschafe

Yeah on the 13bt vs 12at thing. Wacky's car is VERY VERY powerful for a 12a. We've gone sideways in 3rd gear down an on-ramp. I know for a fact its making more power than a stock 13bt easily, and has even more potential with the right prep work.

mikey D

doesnt take alot of power to spin tires in a first gen going sideways.



moroso makes a braced oil pan...one that will fit in a stock chassis rx7.
summit sells it. make sure you read the descriptions carefully or youll order the wrong one.

you could make your own brace/baffel plate

you could have extra dowels added but i doubt that would be cheep.

I imagine you could run a bigger turbo at a lower boost.
Same amount of air going in. less heat and less pressure.
60 compressor upgrade on that s4 turbo!!!!

doesnt seem like your rotor housings should flex at lower than 15lbs


anyways the oil pan will help somewhat and would be the cheepest.
the flange that the oil pan bolts to will work as a lever on the rotor housings with a sturdy oil pan resisting movement.
it will help resist flexing.

WackyRotary

Maybe I am not seeing the advantage of a special oil baffle/pan thing. I already use a air/oil seperator, sometimes refered to as a baffle plate in my oil pan. Can you give a pic of what you are talking about that may help?

And when the engine is flexing, its not the whole thing, its the rotor housings moving outward towards the spark plugs in that region(generally from a little above the trailing spark plug down just below the leading of the rotor housings ONLY. I fail to see how a baffle plate below the engine makes it stop do that.

That upgrade compressor is interesting. Only thing is, I do not want to alter it as it has virtually no clearance with the sidedraft manifold I use as is and I am not changing anything at this point on that side of things. I want to stick with something internal that can be done cheaply to help if possible. Any more takers?

trochoid

iTrader: (6)

When running high boost, the motor does 2 things. 1. Because of the way the 1st gens are mounted, ( as compared to the later engines), this allows for more twist in the stack. 2. This is where the boost pushes the housing out as you refered to earlier.

Addressing the 1st issue is fairly simple in a home shop with a few tools. You say are running a baffle plate now, use that as a pattern. Granted, this won't change the housing expansion, but it will reduce the total movement between the plates and housings. This may be just enough to prevent the problem you are having.

If I were to do this, I would look into retapping the pan bolts to the next larger size for added strength. This may not solve your problem and doweling is probably the best way to fix it, however, installing a thicker baffle plate certainly won't hurt and should be fairly inexpensive to do. The only down side I see is reduced clearance between the pan and center link, but there should be enough. On the up side, you have a little more oil capacity.

FB II

hmmm, what would be a good way to make a more solid engine brace? could we do something like what the FD guys can get... as in a link that ties the motor to the frame around the top section or so? hmmm, i'll try and find a pic of what i mean.

trochoid

iTrader: (6)

If you anchor the front of the motor even more, it will twist more through the stack. You would need to put a torque brace at the back of the engine. An engine brace is usually installed to prevent rotation of the motor and tranny, and prevent mounts from breaking. They also transfer the energy used to wind up the drive train, to the wheels, making better use of available hp.

FB II

that's what i meant, a torque brace. would that be pretty hard to fab up?

trochoid

iTrader: (6)

Shouldn't be. Find some picks and have at it. Just keep in mind what I said. You may end up compounding your problem if you brace the front of the motor, which is where most of them are designed to fit.