Glease Man

iTrader: (5)

Ok, so I've had some really weird problems I'm hoping you guys could shed some light on it. I've broken my second front iron this summer, And I am really stumped at why. Let me give you some specs.

Running this stuff: (1991 TII Savanna)

Megasquirt 2 v3.0
Garrett GT4092R
Aeromotive 340
1000cc primaries, 1600cc secondaries
Mallory FPR, fuel system still in series
Meth injection, Comes on at 5psi (50/50 Distilled water and Methyl Hydrate)
Large street port
S5 Irons (Thick Casting)
S5 and S6 Housings
Atkins apex seals
94 octane, premixing 1oz per gallon.
Stock ignition stuff


So here's the thing. I've been tuning the car myself, and it has been going well. I was running 15 pounds wastegate spring pressure for boost, with meth coming on strong and early at 5psi. The car is blazing fast, and has a ton of fuel. Afr's are super safe, deep in the 10s at high rpm full boost, running conservative timing, 12 degrees (at full boost), and stock split timing.

I have not done many full gear pulls in 3rd and 4th, I was tuning very slowly and getting used to it. Suddenly one night I did a short second gear pull and I cracked the front iron right where the oil feed comes put of the block. The piece came right off. There was no bucking at all, and no funny noises. Just broke. NO hint of detonation. Just smooth and hard acceleration then look in the rear view mirror and there's a mega cloud of smoke.

Three weeks later which was this last weekend, I rebuilt the engine again with a new front iron, and after over a doesn't short blips to make sure everything was Ok, I broke the front iron AGAIN in a small 2nd gear pull. Same spot, no signs of detonation again. This time I was on 94 octane too.

So what's causing this?? I read just today about breaking front irons, and it said it can be from severe detonation or from cross fire. Apparently if your spark plug wires all touch each other is can cause crossfire? It will cause an ignition even to happen 180* when it's not supposed to. I have mine zip tied together to keep them tidy, so could that be it?

Just to reiterate, i'm still getting familiar with tuning, but I know more than enough to know I was in a good safe zone. Correct me if i'm wrong on my specs though. if there was detonation present I really believe I would be breaking the weaker atkins apex seals I'm running. Really want to figure this out before it goes together again shortly.

Sorry this is so long, I'm just trying to be thorough.

Here's a link to the article on cross firing.

Cracked rear iron S4 - Page 2 - NoPistons -Mazda Rx7 & Rx8 Rotary Forum

Pics:

Ignore the CAS position, it was moved when I was diagnosing the problem and pulling it apart. Timing was spot on, with a trusted front hub and pulley combo.

ultimatejay

iTrader: (1)

If your not detonating or running lean than this is caused by the engine twisting. That's why you must add extra dowels or install an oversized stud kit.

Glease Man

iTrader: (5)

I thought that too, but the article I listed said that under high hp load, the front iron has little load on it. It's the rear that takes the abuse. There seems to be a lot more people than me at my power level with no twisting problems. I'm only at 15 psi as well...

ultimatejay

iTrader: (1)

There's only two things that can crack the iron like that
1. Engine twisting
2. Detonation- too much timing/ lean

Glease Man

iTrader: (5)

But could that detonation be from cross firing randomly? I know it's not leaning out fuel wise. Timing is the only thing but 12* at full boost seems quite conservative to me.

sleeper7

what type of fitting are you using for the turbo feed on the front plate? one that uses a washer to seal.

Have you ever checked you timing accuracy above 5000rpms? to see how much it moves around.

Glease Man

iTrader: (5)

I'm using a banjo bolt style that converts to - 4 AN line. Seals with copper crush washers.

I've never done that, that's interesting. What would be the procedure?

sleeper7

I like to enable locked timing (15 deg adv. ) and hold the revs up in the higher rpm range and see if the timing wonders around. just something to think about.

Seen guys use the wrong fitting for the turbo feed on the front plate. It puts to much pressure in that area and cracks the plate.

Don't over tighten it.

Glease Man

iTrader: (5)

By wrong fitting do you mean some sort of pipe thread, or the banjo bolt they were using was sitting funny or something?

sleeper7

Yes.
should be able to snug the fitting all the way down by hand. then just a bit more with a wrench.

Glease Man

iTrader: (5)

I double checked tonight it wasnt bottoming out or anything. All good, goes in nicely. (into uncracked iron)

bumpstart

im thinking it may be several factors piling up..
i would like you to check the timing error through the rev range ( and log it )
,, compare the real against the map lookup numbers to rule out several potential things
( timing drift inherent in Vr systems .. spark crossfire.. timing signal colouration .. potential polarity issue that drift one Vr pickup the wrong way giving phantom and missing tooth events )

i would also look closely at the material used for the banjo bolt
.. it may have incompatible expansion rate and be adding to the stress there

really only see this issue on dowelled engines or on 12at ones
.. as usually with s4/5 engines the rear plate will let go first with twisting duress and the connection to chassis in the middle plate doesnt load up the front plate
( unlike some 12at installs )

i found in that situ .. leaving out the gearbox bolt behind the oil pressure sender ( and adjacent the oil dowel ) fixed my incidence of broken rear plates
[ i changes a few things,, and a lot more since .. but i always leave that bugger out now .. and in an rx2 it was a real pain to reach at ]

TRRAPLN

Wow, that is a great piece of information! I haven't broken a rear plate yet, but fear it happening some day.

Care to expand on the theory behind that?

Glease Man

iTrader: (5)

Awesome info!

Glease Man

iTrader: (5)

Got the engine apart last night, this is interesting. Both breaks are identical..

bumpstart

move to an oil feed from a spacer under the oil filter

ps.. would think about taking a mm off the dowel length but those things are super hard .. and change the banjo bolt to anything but the one you have

ArmyOfOne

iTrader: (12)

Is it just me or do the first 4 threads on those look abraded?

mannykiller

iTrader: (93)

Whatever ended up being the problem? fix?

diabolical1

iTrader: (3)

+1 (though it's been over a year)

did you pop a front housing, too?

jaaf

iTrader: (3)

now I'm scared...

Howard Coleman

iTrader: (6)

cracked front irons at the dowel pin is an important subject.

while your fitting was incorrect i doubt if it was the primary cause and if my suspicion is correct you may be looking at another cracked iron down the road. i have pasted a lengthy and slightly wandering collage on the subject that should be read very carefully.

most of the heavy lifting is courtesy of my friend Lynn Hanover who posts his thoughts on another board...

Thanks Lynn for all your rotary contributions.

hc

"So here's the thing. I've been tuning the car myself, and it has been going well. I was running 15 pounds wastegate spring pressure for boost, with meth coming on strong and early at 5 psi. The car is blazing fast, and has a ton of fuel. Afr's are super safe, deep in the 10s at high rpm full boost, running conservative timing, 12 degrees (at full boost), and stock split timing.

I have not done many full gear pulls in 3rd and 4th, I was tuning very slowly and getting used to it. Suddenly one night I did a short second gear pull and I cracked the front iron right where the oil feed comes put of the block. The piece came right off. There was no bucking at all, and no funny noises. Just broke. NO hint of detonation. Just smooth and hard acceleration then look in the rear view mirror and there's a mega cloud of smoke.

Three weeks later which was this last weekend, I rebuilt the engine again with a new front iron, and after over a dozen short blips to make sure everything was Ok, I broke the front iron AGAIN in a small 2nd gear pull. Same spot, no signs of detonation again. This time I was on 94 octane too.

So what's causing this?? I read just today about breaking front irons, and it said it can be from severe detonation or from cross fire. Apparently if your spark plug wires all touch each other is can cause crossfire? It will cause an ignition even to happen 180* when it's not supposed to. I have mine zip tied together to keep them tidy, so could that be it?

Just to reiterate, i'm still getting familiar with tuning, but I know more than enough to know I was in a good safe zone. Correct me if i'm wrong on my specs though. if there was detonation present I really believe I would be breaking the weaker atkins apex seals I'm running. Really want to figure this out before it goes together again shortly.

I know the S4 rear plates are weak but this just amazes me."

here's another, this time an FC so crack is in rear...


"Let me give you a little detail on the motor and the situation. Car is a 88 10th AE. 1000 miles on the motor. Good sized street port and exhaust port. Turbo is a 60-1 w/ 84. A/R. Full 3inch 304 stainless exhaust. Front mount intercooler. No a/c, p/s, OMP blocked running premix. Engine management is a Haltech E8. Coils are LS1 coils set up direct fire. Injectors are 550 and 1680.

Anyhow we had our Fall BBQ and Track day I ran the car about 12 times around the track. Wish it was more, but since I was organizing it I couldn't run as much. Always shifted by 6200 rpms since the motor is still new. Max water temps wer 209F. Max intake temps at the elbow before the throttle plates was 122F. No issues until the last trip around.


Car had cooled down. I started it up let it reach 190F. Coming out of the first turn, in 2nd gear, I laid into it shifting again around 6000 rpms give or take 100 rpms. Boost was at 16 psi, A/F was 10.9-11.1, leading timing at 13* trailing split at 12*.

I had 1/2 a tank of gas w/ 1/2 101 and 1/2 91. Air intake temps were 105F and water temp was 192F. Turn was a right hand tight turn so no fuel starvation of the pump. Just before shifting into 3rd I saw the oil pressure drop and smoke everywhere. Got it off the track as fast as possible. Car still idled perfectly and the low oil light came. Shut it down as soon as possible while getting of the track. After inspection I had cracked the rear dowell area below the oil filter...

Anyone have any ideas???? I am going to try and upgrade to a later s5 iron. I have a S4 rear plate in the garage and may use it until I brake it. I would like to keep this from happening again. Any help is much appreciated. Pictures are on my other computer and will be uploaded tomorrow."



Lynn Hanover....

"Let me speculate (because I have no experience tuning a turbo engine).

Racing Beat recommends 12 degrees both leading and trailing for turbo engines with timing checked at 6,000 RPM. I would regard this as a hint, and probably the maximum advance used.

They also recommend that torque for case bolts of boosted engines be 32 pounds. Apparently in an effort to develop more clamping power to resist the dowel shearing and iron breaking problem. ..

One of the rotary advantages over the piston engine is extended Dwell time. Dwell time is the period of time when the combustion chamber is at or close to TDC. You can burn more of the charge with less ignition advance, if you have a longer period with the chamber not moving. This is important because if you light the fire well before TDC, then the pressure generated, Brake Mean Effective Pressure (BMEP) must be subtracted from the BMEP from TDC on to exhaust port open point. So it is to reduce the power lost because of ignition advance BTDC.

Simple.

Another advantage is that the length of time the burning charge is heating the combustion chamber is reduced. So, lower charge temperatures, and then you can run higher compression before detonation starts.

The rotary has a very long Dwell time, and therefore requires very little ignition advance.

And that is true of NA rotaries. Boosted rotaries require even less advance than NA rotaries.

Two factors to think about.



When boost is high, effective compression is high. The bits that burn heat each other at a rate inverse to distance. So, in the NA engine the burn rate (Flame front velocity) is low, and a long smooth combustion takes place, and nobody breaks anything. In the boosted engine, the bits that burn are very close together, (the effective compression ratio is higher) and the flame front velocity is very high. So the combustion is quick and peak pressure at the ideal 50 degrees ATDC requires that ignition be retarded compared to the NA engine.

Now review the Detonation definition, and note that the trailing plug igniting starts to look like a detonation event if the time after the leading plug firing is too long. Note Racing Beat says no split timing.

One of the airplane guys shuts off his trailing ignition during nitrous injection to eliminate detonation. Mmmmm.......Think about that.

A detonation event in a NA rotary might go unnoticed due to the limited amount of mixture left to burn late in the combustion event. In the boosted engine, a detonation event would include more mixture in the same area, it is likely to be at higher temperature than in the NA engine. It will not go unnoticed as it may result in damage the very first time it happens. The rattle in the muffler is the apex seals.

The detonation events are likely to happen right beside the apex seals...........

Early rotaries used the front case as the engine mounting point. So you end up torque loading the whole stack during hard use. The engine is being twisted in opposition to and in the exact same amount as the torque output.(Newton) So in later years the engines were mounted by the center iron, cutting the load to only half of the stack. Some folks picked up on this fact and mount the engine with only a plate between the rear iron and the bell housing. I figured this out far too late. So all of the torque loads on the stack are just those produced by the torque of the engine. No torque loads from downshifts, upshifts or misfires must use the stack to travel into the chassis. Duh............

So the higher case bolt torque makes more sense. Also the object of the extra dowels and the oversized case bolts is to carry the torsion loads from the housings into the rear iron where it is accepted by the bell housing.

So, 500 HP at 6,000 RPM requires 437.8 foot pounds of torque. That torque is twisting the stack and is prevented from twisting by the dowels and the friction caused by the case bolts squeezing the stack against the rear iron. Like a deck of cards held between your palms, when you twist the stack the pieces end up at slight angles to each other. In the rotary the pieces put the dowels into single shear, and that microscopic angle change puts the same section of dowel in a bending load.

So if the dowel does not shear off, it cracks the hole out of the iron.

When you see a drag racing rotary come off the line with the whole body torqued over in one direction what part of the engine is twisting the whole car that much? Would you mount that engine with the front cover, the center iron, or the rear iron?

So I suggest backing off the ignition advance a bit, shorten the split, spraying water into the intake, spraying water onto the radiator and intercooler, and oil cooler. Run the fans manually.

use all high Octane, use a bit extra ash free synthetic premix (to keep the apex seals cooler).

Use a monster ignition system at least on the leading plugs. Use inductive secondary plug wires.

Keep the wires well away from low voltage wires, and away from each other. No full throttle until the revs are up........

Just a guess though....

Lynn E. Hanover"


Originally Posted by rotaryinspired
Thanks for the informative post Lynn. I appreciate you taking the time to share your knowledge and experiences. After taking the time to review everything I believe I had a misfire due to leading and trailing plug wires touching and not being shielded from each other appropriately. I was also running the car too hard too early without making sure everything was completely ready. I can be impatient, which explains the plug wires. We all spend too much time and money on these cars to let little mistakes side line us. Lesson learned.


"i was gonna suggest that. firing the trailing 180 degrees early will break things

Quite true. If your failure involves the top dowel hole breaking out of the front iron, there has been a cross fire.

Induced by secondary wires from the front housing being too close to rear housing wires, or, early igniters talking to each other. For other than stock operations, most folks discard the igniters (points eliminating SCRs) and use an aftermarket system triggered by the stock pickup coils. Wires from a crank trigger system can also cross talk, as output at speed can exceed 100 volts.

At high boost it takes a huge amount of voltage to get an arc across the plug gap.
Triggering wires need to be run through Dash 4 braided stainless fuel hose. The braid needs to be grounded at both ends.

Lynn E. Hanover"

executive summary from Howard:

stock FD makes 184 pound feet Tq
many of us are making 400

our engines are a layered sandwich held together w modest quality thru bolts and 4 tool steel quality dowel pins... anchored in weak cast iron. the rear FD plate is supported by the bellhousing and the dowel pin area is stronger than the front dowel pin anchor well.

twist from detonation, elec crossfire or poorly torqued thru bolts will break the front iron at the upper dowel pin hole.

since our motors are small in displacement but are able to make huge power we need very strong ignition systems. given our split setup it is extremely important to maintain electrical integrity as crossfire can be a front plate breaker.

i suggest a very careful review of all ignition components to eliminate any possibility of crossfire.

howard

BLUE TII

iTrader: (9)

Just broke my S5 TII front housing at the upper dowel area as well.

Weird thing was, it was also pulling away from a stop with Right hand turn as soon as I shifted into 2nd gear with moderate throttle (looked at oil trail).

History-
Engine had ~100 dyno pulls on it with 104 unleaded and some racing time. Current set up was 26psi on EFR 7670 that had ~40-50 dyno pulls on it. 400ft/lb @ 3,500rpm.

Running completely full tank of 110 leaded
720cc pri
1600cc 2nd
running richer than 10s afrs
real Bosch '044 (went through weak Walbros).

Friday I had practiced ~12min total track time or so with no issues- except I noticed some fuel starvation on some tight transitions. I wasn't worried as on the dyno or racing whenever I ran lean on 104 it would just die out in power, never any detonation.

Saturday I topped up the tank 100% with 110 and practiced again ~20mins total track time. No starvation, but it started to accelerate slowly as it was building boost on the last 2 sessions, but ran fine at full boost.

Sunday I topped up the tank with 110 and changed plugs and test drove. It still accelerated slowly building boost and I noticed the boost was wonky (up and down) when spooling.
I turned the boost controller down and it still had the problem.
I checked for boost leaks and found the hose connection right off the turbo did take some tightening. Makes sense that clamp would loosen as turbo was getting really really hot.

I test drove again, pulling away from the stop with light throttle in 1st and then moderate throttle in 2nd and then did a WOT pull in 3rd. Slowing down I saw the smoke plume behind me. Checked oil pressure (ok) and pulled over/shut off engine.

Looking at the oil trail the front iron broke ~ 15ft from the stop sign where I shifted into 2nd and then it really started spraying hard once I went WOT and higher rpm in 3rd.

No hesitation on the run- fixed that problem with the boost leak- lol.

BLUE TII

iTrader: (9)

Anyways, I think it is weird that we are breaking front plates pulling from a stop in 2nd with moderate throttle.

In the last 14 years I broke a S4 and a S5 rear plate with detonation (obvious signs in seals), BUT I always had a solid engine torque brace that went from alternator mount on water pump to the strut tower. Never broke a front plate.

On this build I didn't put the brace on as before my center housing always cracked and bent on the passenger bottom where the engine mount bolted up. It ran fine with the cracked/bent center housing, but I didn't want to break the whole engine mount area off the engine.

Could it be some harmonic or torque fluctuation that causes the front housing to crack?

Note- I haven't taken the motor down to see if there was any detonation damage, but I can't imagine there would be on 110 and moderate throttle in 2nd. I will update when I do.

Could be ignition misfire?

I run my Trailing ignition leads completely separated by 6" to avoid crossfire.

mannykiller

iTrader: (93)

^ hmmmm.......

I've got a hell of a robust Ignition system on my build... Cracked the Iron in the same place two weeks ago.

My ignition system:

Direct Fire configuration
Adaptronic Controlled IGN
AEM Smart coils
Sake Bomb Garage Upgraded custom plug wires
NGK R7420 Race Plugs


Im going to take a wild stab and go with my intuition. I honestly think It may be a combo of our 20year old Plus Production dated Irons/our Low end TQ, and the slight twist our motors see every time we stomp on it. I ordered a Turblown Stud kit to help Eliminate the "micro-twist." Call me unexperienced...but logic tells me it can't Break if it doesn't twist

gxl90rx7

iTrader: (1)

running too conservative can cause problems too.. since in a rotary any misfire (caused by too lean or too rich) can cause misfires in the following cycles as well