Templeton

iTrader: (10)

I'm looking for some insight as to what could have caused the new engine I built to break an apex seal on the dyno during drivability tuning, before my tuner even brought the engine into boost. My tuner is at a loss as to what would have caused an apex seal to break under the circumstances, fuel and ignition both checked out fine after the apex seal failure. I will be rebuilding the engine and would love to avoid this happening again.

Some background:
I broke the engine in with 500 miles low rpm/no boost on a base map before going in for a tune last year, during which time the car sprung a significant oil leak from the front cover and they weren't able to get past tuning basic drivability. I recently took care of the oil leak and got another ~500 miles on the engine where i hit maybe 5psi/5000rpm and it ran great the entire time. I dropped the car of to get the tuning finished and the above happened.

Setup (I know there is a lot of unrelated stuff listed but i want to cover all of my bases):
13BT 4-port half bridge, small bridge on primary ports, small street ported secondary ports, moderate exhaust ports, all done using pineapple racing templates.
13B-RE(cosmo) rotating assembly
New Mazda 2 piece apex seals/springs(corners away from bridge), new Mazda corner seals/93+ corner seal springs, used Mazda side seals/new springs, did not replace bearings.
new Mazda turbo oil pump, FD oil pressure regulator and spring, Atkins thermal pellet, Castrol 20w-50 oil
NGK BUR9EQP in leading and trailing, MSD 6A Digital on leading coil, MSD super conductor wires
Aeromotive 340 stealth fuel pump, ID 1050x injectors, AEM adjustable FPR, 6AN fuel system run in parallel,93 octane fuel, premixed at 1.5oz/gal
Adaptronic modular ECU for S4 RX7, OEM Engine harness was unwrapped, inspected, unused wires pulled, and rewrapped.
full 3 inch exhaust
Garrett 60 trim T04E turbo, Greddy log manifold, Greddy wastegate to open dump
godspeed FMIC and radiator, properly ducted, dual 11in Spal fans,
FD alternator, relocated optima red top battery in rear bin
Timing properly set but CAS gear was installed backwards(as far as i know this only results in the CAS sitting in a non-typical location)

I'm out of my league on what would cause brand new apex seals to break under such low load conditions. Any insight would be greatly appreciated.

scathcart

What do your plug wires look like? Are they zip tied together?

Templeton

iTrader: (10)

plug wires are a seperated as possible

j9fd3s

iTrader: (3)

+1, ignition is a likely culprit for damage like this. MSD box is on the suspect list too

plug wires have 3 concerns.

1. Flash-over: the energy needed to fire the spark plug goes up more quickly in the rotary than in other engines, and electricity is lazy. there is a point, where the coil will fire and it will leak out of the wire, instead of firing the plug.
2. Inductive Cross-fire: this is a HUGE problem in every engine. when a plug fires, it creates a magnetic field in the wire, and if that wire is parallel to another wire, it can fire that plug. Ford has a couple of bulletins on the issue. if two wires are parallel for more than 50mm, they should cross at 90 degrees, this cancels the magnetic field
3. RFI. Radio Frequency Interference. its electrical noise, and can cause the ECU to do strange things if its bad enough. usually the wires get shielded, common in aircraft

i'm in the research phase so i have no hard numbers/testing, but those are the phenomena

Pete_89T2

iTrader: (4)

No way to know for sure, but I'd suspect intermittent wacky timing issues, since it appears you're still using the CAS and apparently have the Adaptronic ECU setup to run the leading plugs on wasted spark like the stock FC setup. What kind of RPMs was she spinning when it popped? If you were able to collect logs during the session, I'd look closely at the timing for forensic clues.

As is, the CAS has lots of slop built into it by design, and the VR sensor it uses are susceptible to electrical noise/interference issues, especially when used with most aftermarket ECUs.

Templeton

iTrader: (10)

My best guess was some sort of ignition malfunction as well.


J9FD3S - I had read through threads of crossfire causing broken irons and other weird cases, so i made sure to keep the plug wires separated, however there are several points where they run close to parallel to eachother for a time, I wasn't aware that was an issue.

I've always run MSD boxes on my rx7's and the only time i had trouble with them was when one failed, and even then it was just a straight failure. this one happens to be new with the motor. What problems do the MSD boxes cause?

I guess I will have to look into testing for RFI and look over my ignition wire layout, maybe move to a coil on plug setup.


Pete- I haven't gotten a chance to get logs from my tuner, but I will try to get them today. I would guess that the RPM's were pretty low as boost was coming on early and quickly.

I guess I'll have to look into a trigger wheel instead of the factory CAS, any suggestions on one?

j9fd3s

iTrader: (3)

i'm still in the research phase, so i'm not sure how to quantify some of this stuff, but

the MSD fires multiple times, and that can be bad. you might try running without it, and see what happens

for RFI, i'm not sure its a big problem, but if you were logging data, look hard at the rpm trace, if its a jumping around, that is bad. the old haltechs did this a lot, and if you don't have a good value in the 16,000rpm box = boom

the inductive crossfire is well known, but it was hard to find the name for it! most of the really broken V8 engines are from this, they have two cylinders that are next to each other physically and in the firing order, so its like advancing the timing 90 degrees and the crank falls on the ground... half of Smokey Yunicks book is about this...

Pete_89T2

iTrader: (4)

For a crank trigger, I'd recommend the FFE kit:

https://fullfunctioneng.com/product/...-trigger-hall/

Get it with the hall sensor and the 36-1 wheel option which it says is compatible with the Adaptronic ECU. If your Adaptronic can be configured to support individual coils/COP setup, I'd also chuck the MSD & factory coils and get 4x Mercury Marine/AEM IGN-1A smart coils. You'll have to modify your wiring (since current harness is set up for CAS/waste spark leadings) and build a bracket to mount them, but it's well worth the effort - you'll have a good hot spark, and a very reliable ignition system when it's done.

BTW, the FFE trigger kit website will say you can't use it with factory PS & AC, but it is possible to make it work with PS & AC. You'll need a machinist to mill out some material from the backside of the PS/AC bracket, a spare WP/ALT crank pulley, and some miscellaneous hardware to get the pulleys to line up right.

dguy

iTrader: (8)

Whole lot of conjecture going on without actually looking at the apex seals and their failure mode or how you're diagnosing the breakage (is the engine torn down?), my apologies if you addressed this and I didn't see.

Pete_89T2

iTrader: (4)

The OP didn't say the motor was torn down yet, so I do agree with you. Though he did say he's got about 1000 break-in miles on the build, with some low boost & RPMs up to 5K-ish towards the end, so I would think if something went wrong with the mechanical aspect of the build, the failure would have happened sooner.

scathcart

He asked for possibilities, not a guaranteed diagnosis. Everyone here is trying to help. This is a simple
conversation; a second look at his set up since the professional he hired is baffled.
No one is telling him to buy parts, or that this is the guaranteed failure mode.

Do you have any suggestions to answer the original poster? Its pretty easy to say “tear down the motor and find out”. That’s clearly going to happen regardless.

dguy

iTrader: (8)

Settle down there, turbo.

It's as if you're implying that I was trying to be insulting or something by pointing out that there is too little information being given to give a valid hypothesis as to why it failed.

scathcart

You neglected to answer my, or the original poster’s, questions.

He asked for hypothesis, not diagnosis.

Hypothesis-
A supposition or proposed evaluation based on limited evidence as a starting point for further investigation

dguy

iTrader: (8)

I understand the word quite well, do you? In fact you didn't give one either nor did you ever bring it up so I'm not quite sure what the point of trying to give me a Webster's lesson is other than some sort of weird flex/being a dick.
I'd hypothesize that someone has pissed in your cornflakes and you're taking the age old keyboard cowboy approach as some sort of outlet, not that you actually disagree with me have fun with that? Either way, have fun shitting on this guys thread.

To the OP: These aren't really questions that I'd suggest trying to answer without at least SOME sort of visual inspection. If you can't/wont/dont have the time/means/whatever to pull the engine at least a mirror and a flashlight to look in the exhaust ports.

Sideways7

iTrader: (7)

Did you ever have what sounded like ignition breakup or misfire? Popped my motor after I swapped to an aftermarket ECU and kept my stock CAS and apparently didn't shield my trigger wire well enough.

scathcart

You’re the only one getting angry. I actually did mention the plug wires as a possible source. You essentially told him he was wasting his time asking for hypothesis.

The technical forums are for asking questions and getting helpful responses, not shutting people down.

Templeton

iTrader: (10)

The engine has not yet been broken down and will not be for a year or so as I will be out of the country. Trying to get pictures with my cellphone of the front rotor through the spark plug hole was not very successful, but I do plan to use a boroscope to get an idea of what condition everything is in.

As much as I would like to know what caused my engine to fail, I am more concerned on how to prevent failures such as this one from happening in the future. I am more than happy to upgrade more systems of my car to improve it's performance and reliability, even if those systems were not at fault.

sideways- I was not present for the engine failure, but my tuner made it sound like all was fine and then began running on one rotor. They didn't notice anything out of the ordinary. Before running a compression check they went through the ignition fuel systems and both checked out fine. I will have a datalog from my tuner shortly to post that everyone can look over.

dguy- I absolutely appreciate you trying to help me get a direct answer to my question on what exactly caused the failure.

pete- The FFE trigger kit looks nice plus it's what my tuner is familiar so thats an easy winner.

Rotary Alkymist

It sounds like a question for your tuner. Could be timing, could be fuel map, could be so many things -things that your tuner/builder should know.

Templeton

iTrader: (10)

As I've said, my tuner is not sure what caused the failure. They have decades of experience with rotaries so I have no reason to doubt them when they say it was an unusual failure, nor do I suspect that their fueling/timing maps were so far off that they managed to pop my motor under such low load conditions. I built the engine, I wired the stand alone, I put the car together, all they did was put the car and attempt to tune it, chances are this failure was on me.

Rotary Alkymist

It's a crappy situation. I'd like to help you but you're so far from stock it's hard to say if anyone will be able to give you any real answer.

If it is mechanical I would suspect the rotor. If/when you rebuild(it's hard to say now because the blown apex seal surely did something to the apex groove) I would inspect the rotor very patiently and carefully, ESPECIALLY if you're gonna use the same rotor. In the event you get another used rotor, take extra time(all the time necessary) to be sure the rotor is within spec.

Again, this is really just a shot in the dark from my end.

j9fd3s

iTrader: (3)

the guys i know who have the best success just test just about everything. they also end to make the car as simple as possible, you want to decrease the points of failure.

fidelity101

iTrader: (11)

the stock CAS is very susceptible to noise which can mask ignition problems or cause ignition problems due a loss of crank position. I had struggled with this on megsquirt and various known good CAS's and eventually threw both of them out and went another route entirely. (FFE trigger kit + Haltech elite) and haven't looked back.

Could be a hardware fault within the ECU that controls the ignition, who knows. all sorts of possibilities but being a refreshed motor always tends to raise some eyebrows.

arghx

iTrader: (3)

There are only two ECU's I trust with the stock crank angle sensor.

The stock ECU, with an Rtek/chipped being in that category, and the Power FC. And even then only with the stock harness.

TRRAPLN

I rerouted the CAS wiring to "Clean it up" only to have the ignition break up bad. Put it back and no problems.

fidelity101

iTrader: (11)

yes and even then you are assuming the 30 year old wiring is intact otherwise its a mootpoint too but I agree.