Broken 2 front Irons this summer! Full description here, Need Input! (Big turbo 13B)
10-15-14, 09:20 PM
#26
If your planning to by a stud kit just make sure that it requires presicion fit just like the stock dowel, also all you need is 2-4 extra oversized stud depending on your power level. If the studs your planning to buy don't require for you to machine your plates and housing don't waste your money as engine will still twist just like with stock studs.
11-08-14, 07:08 PM
#28
Wow, this thread has grown so much since I last posted. Love the info. A friend of mine just cracked his front iron identically to me, and found this thread. I'm sure he'll post in here soon.
I've abandoned my LS build and bought a rotary again, so this is valuable info to me.
I've abandoned my LS build and bought a rotary again, so this is valuable info to me.
11-18-14, 12:55 PM
#29
Something that might contribute to the front plate cracking.
An aluminum fitting in the front housing turbo oil feed threads.
Both the thermal expansion and the rate of thermal conductivity are MUCH higher for the aluminum fitting right in the upper dowel area for the turbo oil feed than the cast iron side housing.
If we use 316SS fitting instead of aluminum we get the thermal expansion rate much closer to the carbon cast iron of the side housing and the rate of conductivity lower so it shouldn't stress that area.
Malleable iron hydraulic fitting would be a closer match even.
This could fit the failure mode in this thread. Car driven hard, sits and cools some and then driven again moderately and failure happens.
Could the still hot oil heat the aluminum fitting too rapidly in the cast iron front housing causing a spreading force in the threads of the turbo oil feed area that provides a stress riser to the already weak area?
I have cracked the side housings trying to put tapered pipe threads in them before (spreading force)- they are quite brittle. Now I put straight threads in them for the oil mods.
-----------
Carbon cast steel
thermal expansion coefficient ~ 6.0 (microinch/in deg F) 70-212F range
thermal conductivity coefficient ~ 25-55 *varies widely by alloy*
Aluminum alloys
thermal expansion ~ 13.0
thermal conductivity ~ 205 (77F) (215 by 257F)
316 Stainless steel
thermal expansion ~ 8.8
thermal conductivity ~ 14.6
Malleable iron (50005, 60004, 80002)
thermal expansion ~ 7.5
thermal conductivity ~ 59
An aluminum fitting in the front housing turbo oil feed threads.
Both the thermal expansion and the rate of thermal conductivity are MUCH higher for the aluminum fitting right in the upper dowel area for the turbo oil feed than the cast iron side housing.
If we use 316SS fitting instead of aluminum we get the thermal expansion rate much closer to the carbon cast iron of the side housing and the rate of conductivity lower so it shouldn't stress that area.
Malleable iron hydraulic fitting would be a closer match even.
This could fit the failure mode in this thread. Car driven hard, sits and cools some and then driven again moderately and failure happens.
Could the still hot oil heat the aluminum fitting too rapidly in the cast iron front housing causing a spreading force in the threads of the turbo oil feed area that provides a stress riser to the already weak area?
I have cracked the side housings trying to put tapered pipe threads in them before (spreading force)- they are quite brittle. Now I put straight threads in them for the oil mods.
-----------
Carbon cast steel
thermal expansion coefficient ~ 6.0 (microinch/in deg F) 70-212F range
thermal conductivity coefficient ~ 25-55 *varies widely by alloy*
Aluminum alloys
thermal expansion ~ 13.0
thermal conductivity ~ 205 (77F) (215 by 257F)
316 Stainless steel
thermal expansion ~ 8.8
thermal conductivity ~ 14.6
Malleable iron (50005, 60004, 80002)
thermal expansion ~ 7.5
thermal conductivity ~ 59
11-18-14, 05:08 PM
#30
I was convinced my Iron cracked due to my Alum oil turbo feed fitting I had there. It was in fact Tapered. And you can see that only 2 of the threads were really biting. I remember cranking down on it and thinking it was wayyy tooo tight and that I might in fact crack the iron. Add a cold morning to that... and a FULL limitered Burnout onto the track and I think that could have been enough to do it.
11-18-14, 05:26 PM
#31
Hmmn, mine was straight thread sealed with an aluminum crush washer- that is why I was just going off the theory that thermal expansion of the fitting helped weaken the area.
In your case it does sounds like thermal expansion could have been compounded by tapered threads spreading force.
In your case it does sounds like thermal expansion could have been compounded by tapered threads spreading force.
11-20-14, 11:09 AM
#33
I went with the Turblown Stud Kit.. no need to Pin it when there's a direct replacement that doesn't require machining... Check it out
13B Engine Stud Kit - Turblown Engineering
13B Engine Stud Kit - Turblown Engineering
11-20-14, 12:00 PM
#34
If the stud isn't a machined close fit tolerance to the side housings and rotor housings I don't see what it accomplishes besides providing a little more tension on the stack.
I am hesitant to do a machined fit stud kit for a couple reasons-
More machining to do when replacing parts
During the development of the rotary they tried close fit studs and found it caused cracking due to excessive thermal expansion.
pin the motor and be done with it..
sounds like a reasonable compromise.
I am hesitant to do a machined fit stud kit for a couple reasons-
More machining to do when replacing parts
During the development of the rotary they tried close fit studs and found it caused cracking due to excessive thermal expansion.
pin the motor and be done with it..
sounds like a reasonable compromise.
11-20-14, 12:36 PM
#35
Maybe so.... But the tolerances give room for thermal expansion.... the tension bolts are just made from a much higher quality metal...which prevents any movement/twisting...at the same Specified OEM TQ spec as OEM bolts... Win/Win.. and a hell of a lot cheaper than maching...+ time.
08-25-15, 03:23 PM
#39
this may be dumb but just throwing some ideas up.. is it possible the trailing plug is prematurely igniting the next cycle due to too timing too retarded or too much split?
For example, say you are running 10 degrees advanced, with 15 degrees split (trailing plug firing at 5 deg after TDC), then add however many millisec of spark duration, is it possible by the time the apex seal crosses the trailing plug for the next cycle, that the trailing plug is still lit and ignites the mixture?
i was looking at the stock S4 TII timing maps, and the leading timing is 30+ degrees advanced at redline, with split timing at 16 degrees, so the trailing plug doesnt fire after TDC until RPMs get down to below 4000 RPM. Maybe the problem is running flat timing past 4000 RPM, which a lot of us do, maybe a better way to do it would be continue to advance timing all the way to redline to keep the trailing from firing too late
For example, say you are running 10 degrees advanced, with 15 degrees split (trailing plug firing at 5 deg after TDC), then add however many millisec of spark duration, is it possible by the time the apex seal crosses the trailing plug for the next cycle, that the trailing plug is still lit and ignites the mixture?
i was looking at the stock S4 TII timing maps, and the leading timing is 30+ degrees advanced at redline, with split timing at 16 degrees, so the trailing plug doesnt fire after TDC until RPMs get down to below 4000 RPM. Maybe the problem is running flat timing past 4000 RPM, which a lot of us do, maybe a better way to do it would be continue to advance timing all the way to redline to keep the trailing from firing too late
Last edited by gxl90rx7; 08-25-15 at 03:37 PM.
11-13-15, 08:08 AM
#41
i think this is an interesting discussion.. just throwing more ideas out there
i still believe it is tuning related, not really to torque on the engine, else you would see the problem in higher gears, usually problem happens in low load, 2nd gear, high rpm pulls.
on map based ems, at least from what ive noticed tuning mine, is that it takes more fuel in high load areas given the same boost to maintain an AFR.. it seems to run richer in 2nd gear pulls than in 4th or 5th gear pulls. but usually the tune is optimized for worst case, which is wot and higher gears. so it ends up running slightly too rich in lower gears, and under part throttle, which is where this problem happens
i think running too rich can be just as harmful as too lean. in a rotary, there is no separation between combustion events, so any type of misfire can affect several following events and can cause detonation.
rich misfires are pretty much caused by weak ignition, correct? in a rich-misfire, the coils cannot deliver enough energy to the spark plugs to bridge the gap. that energy will have to dissipate somewhere external to the engine.. either in crossfiring onto another plug wire, arcing onto the engine block around the spark plug, or arcing within the coil. all those scenarios cause a lot of EMI that can interfere with CAS reading
non-resistor spark plugs and low resistance wires cause a heck of a lot of EMI. and increases linearly with RPM, the worst is at high rpm
also check your CAS trigger settings. at redline, the CAS is generating a signal that swings +/- 15 volts. check your trigger threshold voltage settings, if set too low, you could be picking up interference caused by resistor-less plugs, low resistance wires, and EMI noise caused by misfires
maybe some steps to prevent future problems would be..
always use resistor spark plugs, reduces EMI
avoid "race" spark plug wire with low resistance, reduces EMI
separate spark plug wire to help prevent crossfire
use strong ignition system, or do not tune to the limit of rich misfire
increase trigger threshold voltage (minimum 2V at idle to 5V at redline). gives you better CAS signal/noise ratio
edit.. also check your rev limiter settings, if it is fuel cut type your injector phasing settings can cause lean msfire as your boucing off the limiter. i believe the FSM has something like 45deg BTDC at idle to 180 BTDC at redline, but not exactly sure if those are optimum
i still believe it is tuning related, not really to torque on the engine, else you would see the problem in higher gears, usually problem happens in low load, 2nd gear, high rpm pulls.
on map based ems, at least from what ive noticed tuning mine, is that it takes more fuel in high load areas given the same boost to maintain an AFR.. it seems to run richer in 2nd gear pulls than in 4th or 5th gear pulls. but usually the tune is optimized for worst case, which is wot and higher gears. so it ends up running slightly too rich in lower gears, and under part throttle, which is where this problem happens
i think running too rich can be just as harmful as too lean. in a rotary, there is no separation between combustion events, so any type of misfire can affect several following events and can cause detonation.
rich misfires are pretty much caused by weak ignition, correct? in a rich-misfire, the coils cannot deliver enough energy to the spark plugs to bridge the gap. that energy will have to dissipate somewhere external to the engine.. either in crossfiring onto another plug wire, arcing onto the engine block around the spark plug, or arcing within the coil. all those scenarios cause a lot of EMI that can interfere with CAS reading
non-resistor spark plugs and low resistance wires cause a heck of a lot of EMI. and increases linearly with RPM, the worst is at high rpm
also check your CAS trigger settings. at redline, the CAS is generating a signal that swings +/- 15 volts. check your trigger threshold voltage settings, if set too low, you could be picking up interference caused by resistor-less plugs, low resistance wires, and EMI noise caused by misfires
maybe some steps to prevent future problems would be..
always use resistor spark plugs, reduces EMI
avoid "race" spark plug wire with low resistance, reduces EMI
separate spark plug wire to help prevent crossfire
use strong ignition system, or do not tune to the limit of rich misfire
increase trigger threshold voltage (minimum 2V at idle to 5V at redline). gives you better CAS signal/noise ratio
edit.. also check your rev limiter settings, if it is fuel cut type your injector phasing settings can cause lean msfire as your boucing off the limiter. i believe the FSM has something like 45deg BTDC at idle to 180 BTDC at redline, but not exactly sure if those are optimum
Last edited by gxl90rx7; 11-13-15 at 08:11 AM.
11-13-15, 08:14 AM
#42
better question is, were those who broke the front iron running waste spark or direct fire? The FC CAS also has a tendency to wander on lift(or even light misfires you can't even feel) and not by a small amount, and it advances due to the slack in the gear.
generally i'd guess it is a combination of unfortunate events such as a very abrupt lean condition, accompanied by advanced timing that is almost so quick it can't be logged accurately.
there is obvious steps you can do to prevent it: studding, adjusting the CAS air gaps which puts slightly more load on the CAS gear to help wander, a trigger instead of a CAS, direct fire ignition, lower ICT's, etc.
i haven't personally had a front iron break on an engine i've tuned but i have worked on engines that have had the failure and there was signs of detonation.
generally i'd guess it is a combination of unfortunate events such as a very abrupt lean condition, accompanied by advanced timing that is almost so quick it can't be logged accurately.
there is obvious steps you can do to prevent it: studding, adjusting the CAS air gaps which puts slightly more load on the CAS gear to help wander, a trigger instead of a CAS, direct fire ignition, lower ICT's, etc.
i haven't personally had a front iron break on an engine i've tuned but i have worked on engines that have had the failure and there was signs of detonation.
Last edited by RotaryEvolution; 11-13-15 at 08:22 AM.
11-28-15, 09:41 AM
#44
detonation twisting, studding will save the shell of the engine but may not save the rotors or seals.
however i'd rather eliminate one possible failure in the event the others can manage to handle the misfire. in many cases the rotors will be dented if you run durable seals, but at least the engine will still run, poorly idle but run. my engine is studded and i run S4 rotors which are less prone to caving in.
improved cooling will also reduce the likelihood of it happening even if the tune and setup has minor hiccups.
the FC engines are gimpy cast at the dowels so this is nothing new for me, except i broke about 3 rear irons where the FD tends to eat front irons without reinforcement.
however i'd rather eliminate one possible failure in the event the others can manage to handle the misfire. in many cases the rotors will be dented if you run durable seals, but at least the engine will still run, poorly idle but run. my engine is studded and i run S4 rotors which are less prone to caving in.
improved cooling will also reduce the likelihood of it happening even if the tune and setup has minor hiccups.
the FC engines are gimpy cast at the dowels so this is nothing new for me, except i broke about 3 rear irons where the FD tends to eat front irons without reinforcement.
Last edited by RotaryEvolution; 11-28-15 at 09:47 AM.
11-28-15, 10:08 AM
#45
Old [Sch|F]ool
Misfires will lead to detonation because every chamber brings exhaust residuals around with it since you never get 100% exhaust blowdown.
So you misfire, there's no exhaust residuals really, just raw air and fuel in the chamber coming around for the next rotation. Now instead of being 9 parts air/fuel and 1 part inert exhaust gases, it's maybe 98-99% air/fuel. NOW you have way too much ignition timing...
So you misfire, there's no exhaust residuals really, just raw air and fuel in the chamber coming around for the next rotation. Now instead of being 9 parts air/fuel and 1 part inert exhaust gases, it's maybe 98-99% air/fuel. NOW you have way too much ignition timing...
11-28-15, 11:25 AM
#46
Ohhh almost forgot. WHen I got the engine back together I had some slight intermittent Logging issues. The Log would cut out at higher RPM here and there. A few weeks later I found the issue. And one of my Spark plug wires had a tiny slit in it...past the shielding...all the way to the core. I have no clue how it could've happened as It drove me crazy...and Ilooked around everywhere and still to this day I don't know how the slit happened but the only thing I could think of was maybe in some weird coincidence, i was holding a tool with a small burr on the end of it and it might've caught the wire just right or something as I passed it to change plugs... or any number of small maint things I did routinely. Changed the wire and that was it.... zero logging issues.
Not saying that was the cause...but it could have been a cross fire.. I really don't think the cross-fire issue.....is in fact an issue unless you've got an open cut in a wire as I did. But given that situation... It might've been the culprit
Not saying that was the cause...but it could have been a cross fire.. I really don't think the cross-fire issue.....is in fact an issue unless you've got an open cut in a wire as I did. But given that situation... It might've been the culprit
11-28-15, 04:52 PM
#48
12-02-15, 12:12 PM
#49
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the JDM tuners take pains not to have crossfire, no big secret, although they don't really mention it either.
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