Unorthodoxed Racing Crank Pulley=Crankwalk?

[kengsx]

Me....

Can you post some additional photos of that fracture? It almost looks like there is an internal casting defect, but it's hard to tell based on the light and focus. Take a couple pics using light that is shining sideways onto the fracture, as opposed to shining straight down on it. My job is determing how parts fail, and this could be helpful to the dsm community. Thanks,

Ken

 

[gsx951]

Can you post some additional photos of that fracture? It almost looks like there is an internal casting defect, but it's hard to tell based on the light and focus. Take a couple pics using light that is shining sideways onto the fracture, as opposed to shining straight down on it. My job is determing how parts fail, and this could be helpful to the dsm community. Thanks,

Ken

It's not a casting, Mitsu cranks are forged.
Ken this is old ground and there are picks of failed cranks all over the net. It's a fatigue failure that starts at a crappy radius on the #4 big end journal. The rest of the crank has never been magnifluxed but is full of cracks for sure. When it is struck, it makes a sick dead-buzz sound.

 

[dsm_illicious]

I won't hold my breath.

 

[kengsx]

It's not a casting, Mitsu cranks are forged.

I spoke too soon. I checked the ASM metals handbook and this looks like a classic reverse bending fatigue failure. So the upper and lower journal surfaces (as oriented in your picture) have multiple origins, and that oblong dark spot in the center is overload.

I was always under the impression, based on misinformation, that our cranks were cast. At least that if any were cast the 2G cranks were. That parting line is thick enough to be a forging though, so I stand pleasantly corrected. I hope I get a chance to section one up at work and look at the microstructure to really convince myself.

Back to the topic at hand though, that appears to be reverse bending fatigue at low nominal stress but at severe stress concentrations, and no signs of torsional fatigue. Therefore there is no smoking gun towards a bad crank pulley/lack of damper scenario, which would have been excessive torsional vibration.

If this is old ground, why did it fail at 11,000 miles? Sure it failed at the fillet radius, but was the radius not generous enough?

Ken

 

[Tevenor]

I won't touch UD pulleys for 3 reasons

1) Harmonics. Our cranks have enough problems without eliminating one of the control measures.

2) Timeline:

Installed UD pulley
Drive 5 miles
Cranksensor goes out/car crankwalks.
Install 6 bolt w/ UD pulley.
Engine walks after 3000k miles.
Replace bearings and crank.
Remove UD pulley.
Still beating the piss out of it racing every weekend 26k miles later. Still in lateral play specs.

An undampened UD pulley will never touch another one of my cars.

3) Money. For 175 I can put it towards a lot more things than a pulley set and get a LOT more performance for the buck.


But that's just my opinion on the matter.

 

[b17tuner]

Me and my friend have these useless pulleys for the 6(polished) and 7(blue) bolt. If they won't sell I think we are going to just shoot them with shotguns.

 

[dsm_illicious]

I just got an email from a rep @ Fluidampr / Vibratech TVD / Horschel Motorsports:

Hi,

You have excellent timing. We are currently machining parts to build a
Fluidampr for the 4G63 / T engine. The design has been released and we
hope to have these available to the public sometime next month. It will
have the current pulleys integrated into the damper similar to our
current late model Fluidamprs. Look on our website or check back with
usin about a month for the release of the latest Fluidampr. If there is
anything else I can help you with please let me know.
Thanks.

Dan Oddy
Sales Engineer

Now I'll be holding my breath for a bit...

 

[gsx951]

If this is old ground, why did it fail at 11,000 miles? Sure it failed at the fillet radius, but was the radius not generous enough?

Ken

Because fillets are rolled and not ground. Nicks left on the radii of crank journals are more than ample stress risers.
The motor was a built short block and I was unaware that a cut crank had been used. Combining Oliver rods and a reman crank is something I would not do myself.
Add to a bad situation, my choice of buggering crank harmonics with a stupid pulley and what you get can be seen in the photo.

 

[MaNGiNa24]

My pulley is about to shit on me, does anyone know if the stock pulley is dampered?

 

[pianoman]

My cousin, had an unorthodox under drive on his 91. About a week later, the motor failed. We ripped it apart, and on the number 3 bearing were side to side scratch marks. Was it the pully? Maybe, maybe not, but somthing to think about none-the-less.

 

[gsx951]

My pulley is about to shit on me, does anyone know if the stock pulley is dampered?

Yes it is.

 

[dsm_illicious]

...and the moral of the story is to not change the crank pulley with anything other than a pulley that has a dampener/balancer since more problems have been reported other than horsepower...Come to think of it, I have yet to see proof of any HP gain with these non-dampener pulleys.

 

[gsx951]

i still wanted to see some bearing pictures of that broken crank man

Those bearing are here somewhere but have been kicked around quite a bit, their examination now would be misleading.

 

[pianoman]

Hmm,

http://www.bmwplanet.com/phpbb/viewtopic.php?t=25284&sid=fa32aa2045bb4227d82a74a6a3a6a458

 

[oldman]

Hmm,

http://www.bmwplanet.com/phpbb/viewtopic.php?t=25284&sid=fa32aa2045bb4227d82a74a6a3a6a458

Awesome read, book marked.

 

[GPTourer]

Yeah, nice find. Do y'all think this is indicative of just inline engines? Don't V8 guys use them all the time with out any of these issues?

 

[doug]

I can't believe another thread on crank pulleys.

I'll state my opinion again-- if you're going to get a one-piece pulley, don't do it for a HP gain. Do it because it eliminates the possibility of the stock pulley separating on you at some inopportune moment and trashing your engine (bent valves, etc.). There have been many more cases of documented engine damage from a failed stocker than there have been of "unusual" bearing wear/damage from an undampened pulley. Do I have "unusual bearing wear"? I don't know, but I do know that I won't grenade my engine if the stock 2-piece pulley flies apart. It's a matter of "pick your poison" if you ask me-- I chose mine.

 

[sickgsx-316]

Wow. This thread really cracks me up. I thought it was common knowledge that our motors were externally balanced, and were designed to utilize that big dampened/balanced crank pulley that the engineers of this motor put on the car for the very reason of defeating the vibrations that throw the crank off its rotation. Are we smarter than the ones who built this motor? Would they slap on a big expensive crank pulley like that unless it was absolutely necessary? No, they are cheap bastards and looking to cut corners/costs while minimizing the chance of warranty related claims. The only one I know of that makes a lighter crank pulley that will still keep the motor balanced/dampened is Buschur, and it was 300 bucks last I checked, I'd rather spend my cash on other mods.

To everyone that says they have been running an unorthodox crank pulley and say they have "no problems" have you actually pulled the car apart to inspect said bearings? I would highly doubt it.

Like someone said earlier, if you want to lighten your rotation, do it with a fidanza or ultra-lite flywheel. Leave the ricer mods for the honduh's.

 

[oldman]

I think both sides have serious and legitimate concerns, however I do not think going UDP is the only solution. I personally would pay $300 for a more durable aftermarket piece, how about a metal lower timing belt cover?

 

[sickgsx-316]

I've had my car apart many times, and the bearings looked great.

I had my entire rotating assembly balanced, crank w/ flywheel w/ rods and pistons #'d.

As doug says, pick your poison. My stock, was absolutely destroyed, and honestly, I find 300 dollars for a 'buschur' unit a complete insult, when his COP setup is 260.

If anyone is putting underdrive pulleys on their cars for performance, they will get an awakening, but atleast they can sleep at night knowing, it will not grenade after long miles, or extreme heating.

I agree with your last part, and I dont believe with a balanced rotating assembly you would have the need for that balanced dampener pulley.

 

[gsx951]

I agree with your last part, and I dont believe with a balanced rotating assembly you would have the need for that balanced dampener pulley.

None of this has anything to do with the balance of the rotating assy. The damper is not a balancer and has nothing to do with balance.

 

[gsx951]

I can't believe another thread on crank pulleys.

I'll state my opinion again-- if you're going to get a one-piece pulley, don't do it for a HP gain. Do it because it eliminates the possibility of the stock pulley separating on you at some inopportune moment and trashing your engine (bent valves, etc.). There have been many more cases of documented engine damage from a failed stocker than there have been of "unusual" bearing wear/damage from an undampened pulley. Do I have "unusual bearing wear"? I don't know, but I do know that I won't grenade my engine if the stock 2-piece pulley flies apart. It's a matter of "pick your poison" if you ask me-- I chose mine.

How does a pulley delaminating cause bent valves? I've had two or three of the things fail but the only drama was the pulley banging on the subframe and pitching off the belts.
The t-belt is behind the cover. Are you confusing this with a balance shaft belt?

 

[boostedinaz]

Here is a good article on how a Harmonic Dampers work. It is even titled Harmonic Balancers don't Balance. The pics are small because I am not cool enough to have hosting space so I had to upload them here. You will have to save them and blow them up a bit to read the article. If someone wants to host them for all of us that would be cool.

Again this has nothing to do with balancing anything. For those who say they have had an underdrive pulley for X amount of time and nothing has gone wrong, you get a goldstar. People have gone 11's on a 16G does that mean that anyone with a 16G will be able to get an 11 sec timeslip? Not at all. Again some people have better luck than others.

For those who say that the stock ones come apart all the time I call BS. I have owned 3 DSM's and not one has had a problem with the pulley comming apart. All the locals I know, from bone stock to an AWD Spyder with a GT35R, use the stock pulley and have had no problems. The only instance I have seen a pulley fail was with my buddies 92 GSX. When it did fail it didn't turn the car into an atomic bomb like most will have people believe. It just kept tossing the alt. belt and after the second new alt. belt we looked under the car and saw that it was wobbling very badly. We put another pulley on it and it works just fine. Even if the pulley were to have a horrible failure you would know instantly and I HIGHLY doubt it would do anything but fall under the car and beat up the bottom.

 

[oldman]

Michael, when mine separated last year, besides snapping my alternator belt, it also grind out part of my lower timing belt cover exposing my timing belt. I'm not arguing that a UDP is the solution to the problem, I'm just saying 1/4" - 1/2" more, it could have taken out or disrupt the timing belt. If any of the vendors start making metal timing belt covers, I'll be first to buy.

 

[boostedinaz]

Michael, when mine separated last year, besides snapping my alternator belt, it also grind out part of my lower timing belt cover exposing my timing belt. I'm not arguing that a UDP is the solution to the problem, I'm just saying 1/4" - 1/2" more, it could have taken out or disrupt the timing belt. If any of the vendors start making metal timing belt covers, I'll be first to buy.

I guess I could see that but I still find it hard to believe that it would actually cut or distroy the T belt. I have never heard of it in all the time DSM's have been around, but anything is possible.

I would also be in line for a metal timming cover. HHHMMMMM perhaps I should try and see how hard it would be to make.