WackyRotary

HOW is it done?! I really need to do this to my next engine block to avoid cracking the rear endplate I did today. So someone must know how. What are some other measures to prevent this type of cracking to the rear plate besides abstaining from from high boost.

BDC

It's done by machining out the housings to accept several more dowel pins. The idea is to keep the housings (particularly the rotor housings on the combustion side) from being forced away from the end plates. I honestly think that it comes more from spikes in the combustion chamber caused by severe engine knock over anything else (and hence may be a bandaid if that's the only reason why these things stretch and move), but I could be wrong about that.

B

680RWHP12A

too much timing or too lean! i believe you have a small turbo , so its definatly got to do with your tuneup! what kind of gas were you running and with how much boost?

WackyRotary

The crack is at the dowl by the oil filter, I know its cracked there since nothing else is the source of the oil leak. This is at 14-15psi, 92octane, no detonation or knock has occurred. S4 turbo.

Its not running lean, if anything is too rich across the board. I've been meaning to get some smaller main jets and maybe 1-2different air bleed jet sizes larger to lean it out a little more at higher rpm.

Would using shrinkwrap (like from Hayes rotary) on the tension bolts possibly reduce the stress on the dowls by transfering some of the load on the dowls to the tension bolts in the block? As there is a gap between the tension bolts and the holes in the engine. With less gap the flex should be less, correct?

I just don't want to hear that I can't run 14psi once in a while without the fear of cracking the rear dowl by the oil filter because its too weak to support combustion pressures that high in a 12a block.

HN

wheres your timing?

HWO

you are running 14-15psi with a S4 turbo, your HP levels are no where near high enough to begin to stress the plates, it has to be either Detonation, or Pre Ignition that has caused the plate to crack

now

iTrader: (1)

the shrink-wrap thing will do nothing to reduce stress on
the dowel pins. I am about to try to pin a motor,
i have enough old housings to do a few test tries before taking
a chance on good ones
I don't think its that big a deal, and not worth what
a couple rotary shops charge that i know of.
matt

WackyRotary

I could not hear any detonation(yes I know what it sounds like). I have the timing set near stock 12a settings. IF is retarded any from this, it would start backfiring like crazy going past 5psi, then I bumped it up little by little till it smoothed out with higher boost and kept it there, I'm sure the timing gets more and more critical as boost is increased. I was going to set it with a timing light when I got access to one, but it was probably had more retard then it needed to be.

Remember also this is not a S4 block, its a S4 turbo fitted to a 12a, so i assume 12a blocks have less strength in the dowl area. There is no leak into the combustion chamber, it runs great(no oil/coolant loss), its just the rear dowl area has the leak right between the "MAZDA 12A" on the rotor housing and the rear endplate right above the temp sensor were its leaking oil.

So either even a very light amount of detonation caused too much stress on the dowl and cracked, or the o-ring failed, or the endplate was warped and sprung a leak there?

Blake

You mean, this is what happened?



Probably detonation, though you didn't hear it. Even if it did not detonate, per se, at the verge of detonation the cylinder pressures will more than double. One or two degrees of timing can make all the difference, even if you are not lean. I would recommend that you pull the motor apart and thoroughly inspect it for other signs of detonation-related damage -- stationary/internal gears, bearings, etc.

WackyRotary

Man that looks A LOT more severe then what I probably got, I'm sure oil was gushing out of that! OR did the crack spread while untensioning the tension bolts it I suppose?

Either way, I guess i need to re-think the max boost and dial the timing better and ignition improvements to retard timing since I have only a locked distrubuter now.

But from the looks of that, it had to of detonated at a pretty high boost level, Right?

Thats a S4 endplate also, right?

crispeed

How are you controlling timing? Are you using the factory distributor?

crispeed
87 RX-7 TII
9.204@150.47mph
2600lbs
un-tubbed

WackyRotary

Stock yes, locked to max advance.

HWO

In all honesty, need we say anything more?

i would have thought you would have wanted it locked on about 5 degrees before TDC (leading)

crispeed

On all my blow-thru set-ups I would pull the springs and lock the timing at full advance for boosted conditions which would normaly be in the 12-15 deg on the leading and 0-5 deg for the trailing.

crispeed
87 RX-7 TII
9.204@150.47mph
2600lbs
un-tubbed

HWO

is that all they advance to? sheez i was running my extended port standard turbo S4 motor at 15 degrees BTDC at idle

WackyRotary

That is probably about were my timing was at when this failure occured. It was just barely more advanced then stock, since stock is 10degrees with the mechanical advance in stock position, I had about ~12degrees across the board, locked the sameway. That is why I wonder if the boost is too high around 14psi for a 12a. I've heard that S4 endplates are also prone to cracking in the dowl area above 15psi so people use stronger built S5 end plates so they can get more hp without cracking, is that accurate? IF that is so, its logical that a 12a block can't run any more then a S4 so I will be a little disappointed.

Crispeed, what boost level were you running and what engine setup were you running it on? I really would feel disappointed that a 12a n/a has to be below 14psi or fear the rear dowl cracking again. I want a ceiling of 14-15psi since that is what I built the engine for with the setup.

Help me guys!@! What other measures besides dowling the hell out of it to strengthen it or other way to reduce stress on the rear dowl. I don't want to have that happen again, and I still want to run 14psi on occation for timed runs. Normally I will only go up to 8-10psi max from now on. And if I don't get a good answer, I guess I'll have to keep it low for engine longevity/rebuild costs.

madas7

You could sandwich a 6mm aluminium plate between the black and sump. And hold it in place with larger sump bolts, simply machine out the holes and rethread them, and then u kill 2 birds with 1 stone you also get a sump baffle as well.

WackyRotary

Do you have any pic's of this? Also do you have any proof this strenthens the engine rigidity to resist dowl cracking failures?

So this is basically a thick plate with some baffle holes for the oil. So you have special holes drilled into the iron plates to bolt it rigidly to the block along with all the oil pan holes?

Anyone else ever heard of this?

SPOautos

What a/f you running??? mid 11's with 12 degrees total advance some heat range 9 plugs and a ignition amp should have you running great.

Maybe your just running soooo rich that your ignition cant combust it all, that can be just as bad as running lean sometimes

STEPHEN

WackyRotary

I don't know forsure what a/f, but its not turning out white plugs or carbon clogged ones either. A mid to dark brown, which doesn't really tell the whole story but I suspect slightly on the rich side. I aim to get a a/f meter since I do have a downpipe with a 02 sensor fitting on it to try when I have more money.

I am using TII/FD NGK's with the heat range of 9 for both L and T. I do agree I should use a ignition amp/multi spark unit. It however was running great the way it was. Very fast and very smooth power across the board with no simptoms of detonation.

RXTASY1

Water/Methanol injection would help also.

12aTurbo510

OK Here is my 2 Cents.....I have a 12a and I have cracked both the front and rear housings. In fact when I cracked the rear housing not only did it crack a LARGE chunk of the casting was missing I could easily feel the dowl pin from the outside of the motor (that was some real oil gushing) That was at stock timing at 7 lbs yes 7!!! Beacuse I had CHEAP gas in the car. (My turbo is quite large though & I have a Jerico which I believe puts a huge torque strain on the motor)
I have been racing/driving rotaries for 17yrs now and Ive found the ONLY way to insure that you do not have harmful detonation is to use a quality high octane fuel (period) If you want to have a race car choose any two of the following:Cheap, Fast, Reliable. My motor is pinned I made 516hp at 24lbs on 118FNL I have made 100's of passes and driven the car on the street and burned 5-55 gallon drums (so far) and have had not a single problem (except for breaking rear end parts constantly) (PS its getting back-halfed right now) Ill let you all know how it runs when I do! So the moral is use good gas!

RXTASY1

Or cheaper yet, buy a Aquamist system!
You can run pump gas with H20 injection and get all the benefits of running race gas.

Since I have installed mine, I have not had a hint of detonation.

Lasse wankel

Is there anybody who has any pics of a fully dowelled side housing? I am gonna build a streetported 20B for a customer in Norway so i got to have some info/ideas.

WackyRotary

I'd like to see some visuals too. I'm sure there is no trade secret in this since its only for making the engine more durable to withstand higher boost levels.

POST THEM IF YOU GOT 'EM! PLEASE!