Engine Drivetrain 1st Gen Cooper S Most liked posts in thread: Lightweight crank pulley?

I'll have to disagree, due to their design, Inline sixes, V12s and flat engines are actually harmonically balanced where 4 cylinders are extremely unbalanced which is why they frequently used balance shafts to counteract this. Still, every flat and inline six engine I've ever seen or worked on (I've never worked on a V12) have had harmonic balancers, including Porsches where you'd think the engineers would've eliminated that to gain a little more HP.

 

There have been reports of the crank pulleys damaging the oil pumps. I would stay away from them.

 

There's many people, including folks who sell them, saying they use them with no issues.

I've seen half a dozen motors with spun bearings due to the oil gears shattering and they all had lightweight crank pulleys.

As they say, your mileage may vary.

I wouldn't run one if you paid me to.

 

There are some that will say "I've had a lightweight cranks pulley for a million miles with no issues" and soem that will say it can be an issue.

No one has had the balls to stand up and say "I had a lightweight crank pulley and I can prove that it did cause and issue". mostly cause people want to validate their purchase or they have no idea why something related has failed. There was no proper postmortem performed most of the time to determine the real cause.

That said...

The cost of vibration dampening crank pulley is significantly higher than one that is not. BMW engineers like saving money. If they could have used a "standard" crank pulley with no adverse effect I would think they would.

I've had a lightweight one on my car. I had issues directly attributed to said pulley. The OEM has been back on the car for some time.

Your mileage, as the saying goes, may vary.

 

It seems every car forum has its heated subject; the MINI's is definitely the undamped crank pulley. Those coming from cross-plane V-8 and inline-6 worlds will practically kill someone over the mere thought of an undamped pulley without even considering physics, and on the other side are shadetree enthusiasts coming from Hondas and other small 4-cylinders that run little to no damping crank pullies with no history of failure but also no history of hard track use. Mix in the group of OEM leg-humpers that swear "BMW knows best" and it's a reciepe for nobody listening to anyone else.

The answer is somewhere in the middle of it all. Big cross-plane V-8s and inline6's do self-destruct without a crank damper to quell the massive crankshaft harmonics, however such self-destruction isn't inherent with tiny inline-4s that have inherently stronger crankshaft design [being flat-plane]. Not only is the MINI's crankshaft extremely short, it's also forged, making it double-strong versus those big floppy crankshafts. BMW certainly isn't going to waste money on frivilous stuff [unless it's under their famous "technology for the sake of technology" mantra, but that's another story]. They implimented a small crank damper on the MINI to quench NVH that would be considered unrefined in a premium small car. NVH gets a huge level of priority during vehicle development so anyone that doesn't think adding a crank damper for anything beyond NVH might be fooling themselves. That said, there may have been a case for adding a crank damper beyond NVH, however I have yet to find any proof for this.

RMW and Jeff H have both claimed to correlate undamped crank pullies with broken oil pump gears. Simply saying so and not being forthright with any helpful data does not help the community and only contributes to the swirl of potential misinformation clogging the internet. As we all know, correlation does not equal causation. It's entirely possible, and likely, that the oil pump gears are a weak fuse in the Tritec engine. SRT-4 owners have run across the problem or broken oil pump gears in their Mopar engines which share similar design philosophy to our Tritec. For now, I can't see any reason to blame broken oil pump gears on an undamped crank pulley because there is no information out there that has been shared. There are much bigger fish to fry regarding developing the MINI in the meantime.

Cheers,
Ryan

 

So in other words..........you take your chances and there is anecdotal evidence that supports that claim.

 

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No disrespect, but you're confusing two separate issues. We're referring specifically to crankshaft harmonic resonances, not overall engine configuration force vectors.

You are correct that inline-6's, V-12's, and all even-cylinder-count horizontally opposed engines are balanced in terms of firing order and cylinder block vibration in 1st, 2nd order harmonics and "end-to-end" vibrations. These system-wide descriptors differ from individual component stresses that this thread is referring to. For the record, Inline-4's are not "extremely unbalanced", they are balanced in the 1st order, and have no "end-to-end" vibration, however they are not balanced in the 2nd order. An example of an engine configuration that is "not very" balanced in all respects is VW's W-8.

The long crankshafts in inline-6's and V-12's [and complex shape of cross-plane V-8 crankshafts], regardless of their overall engine balancing characteristics, present significant stresses on the crankshaft itself, inducing harmonic resonances within the crankshaft itself, independent of the overall engine system. This is why such engine configurations necessitate a harmonic damper on the crankshaft.

This is a good read regarding engine configurations; it's always a good brush-up read for me!

Regards,
Ryan

 

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And what data would you accept? How would anyone actually determine w/o a doubt the cause of these failures? We are talking about stress's that are accumulating over years of use, not just a 1/4 mile run.

Bottom line.....I don't think adding the lighter pulley is worth the marginal gain in responsiveness it may give.

 

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The only damages in evidence have concerned the oil pumps. This in itself would not warrant an engine teardown thus very difficult to quantify. But when some respected tech's have reservations about their use, this is something we can all use to make up our own minds on.

My comment about the 1/4 had to do with assuming your reference to the Camaro was for a drag car.

And it looks like we are actually agreeing in basis again.........:eek6:

 

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Excellent site, I stumbled on it back in '05 while trying to find out how a Torsen Differential worked (check the 4wd section) and wound up reading everything on it. Perhaps I need to give it another going over.

 

The basic engine for the Mini One and the Mini Cooper is fitted with a conventional torsional vibration damper at the front end of the crankshaft. Calculations and measurements showed that the addition of the supercharger with its relatively high moment of inertia was resulting in excessive torsional vibration at about 1600 rpm. This solution was unacceptable both acoustically and in terms of component strength.

The torsional vibration damper used on the Mini Cooper S engine therefore has the belt pulley additionally isolated elastically from the secondary mass, with belt drive vibration damping. Vibration amplitudes are significantly reduced by the isolated belt pulley. However, the decisive factor is that the most marked resonance is shifted into a zone below idle speed and is therefore outside the engine’s operating range.

Hope this clears the LW pulley argument up.

 

...and whom is your source?

Curious how MINI would change the mass of the damper from early years '02-'04 to later years '05-'06 despite no additional change in design to warrant a change in mass damping.

 

I guess this will go on forever. opcorn:

 

The actual weight of the damper doesn't matter as much as the design tho....

 

I knew I'd read that somewhere before, and this is what a quick Google search turned up:

http://www.motoringfile.com/files/MCS_Powertrain.pdf

See section 4.2.1. It's published in a few different places around the internet. ("marked resonance is shifted" - Google Search)