So, a couple weeks ago, I was driving on the highway around 70mph with the cruise control set, and all of a sudden got a "battery/alternator" warning in the MFD. I thought "that's odd" and cycled through the screens to check coolant temp, which was rising rapidly. "That's odd" went to "WTF?" and I immediately pulled to the shoulder and popped the hood.

First impressions weren't good - serpentine belt was off, and there was a perplexing spray of oil and coolant through the front of the engine bay. Looking around further, I saw that my LET Motorsports idler pulley sheared off of its mounting post, and was laying on the cross member towards the driver's side. I wondered "did the bolt break?" - nope, it's a 10.9 grade bolt (same grade/strength as the lug bolts I just sourced from Renntech, FYI) and it appeared brand new. Then I looked at the mounting post, which is integrated into the water pump housing - it was all chewed up, and the threads stripped (looks to be relatively soft aluminum).

In examining the LET idler pulley itself, the culprit became obvious - the NSK bearing in the pulley seized up. When this happened, the LET idler (for those that aren't aware, the idler is a hefty chunk of solid steel) apparently had more centrifugal force than the mounting post could stand, so much so that it sheared completely off its mount and ricochetted around the front of the motor, causing severe damage to other pulleys and the oil cooler (which, by direct impact, it cracked - causing the oil and coolant spray, plus some oil getting into the coolant system and vice versa).

For those that might not be aware, I have had LET's parts on my car for over 5 months and 8,000 miles - the car ran strong with no major issues, until this one. I was one of the earlier LET customers, and bought every LET part offered back in Feb 2008 (except plug wires). I have shared my positive experiences, and referred like-minded modders to LET. At my own expense (like many of us), I have run unbiased before and after dyno runs, and posted the information here on MBW. I have logged many, many miles of data that I was happy to share with LET if it could improve their tunes in any way.

I contacted Jerry, explained the issue, and simply requested what they (LET Motorsports) would be willing to do for me as their customer, through this difficult experience. I received an apologetic but otherwise curt reply from Jerry stating "our warranty only extends to the part that failed - we'll send you a new idler pulley at no cost to you." It would be insincere for me to say that I wasn't disappointed to essentially be brushed off, after supporting LET through their infancy and spending thousands of dollars on their products.

The situation is straightforward: the LET-supplied NSK bearing in the LET idler failed, and directly damaged another guide pulley, the LET crank pulley, the water pump, and the oil cooler. The total bill of this repair? $1,826.85 - that doesn't include the $393 tow (of course, this type of thing would occur along the highway two hours from home ). I was also without my car for 1.5 weeks, because the oil cooler is an AMG specific part, and when one couldn't be sourced locally it had to be shipped from Germany. FWIW, I've still yet to receive a new idler from LET; so far I've only received a used, rusty ASP idler that my mechanic wasn't comfortable putting on the car.

LET is a great software tuner, and on MBW and elsewhere there are many positive reviews of their products and services (mine included) - however, too often the bad news isn't posted... I feel this info might be worthwhile for those considering their hardware vendor; "you pays your money and you takes your chances..."

Enjoy the pics...

water pump




LET crank pulley damage (thankfully, mostly superficial)

 

Guide pulley




Seized bearing





Oil cooler



New water pump



New oil cooler



ASP idler sent

 

holy crap!!.

Well i hope you guys come to some kind of settlement.

 

Wow, that's terrible. Sorry to hear that. Those pictures make me cry...

 

Yauzer. I am sorry to hear about this mishap.
Surely, LET will step up to the plate and compensate you for any expenses related to this incident.

 

Sorry to hear about your catastrophic failure, particularly since it was caused by such a seemingly straightforward component.

Even more disheartening was LET’s response to the matter. I’ve touted their wares on this forum from the time Erick and Jerry first brought them to market...and they were bolted on my engine.

I’m stunned and saddened by your revelation.

 

Thanks for the words of encouragement, guys.

splinter - indeed, a seemingly straightfoward component. I'd be curious to know the mass of the stock idler, evosport's, ASP's, and LET's for comparison... maybe MRAMG1 could then chime in with his physics skills and let us know how much stored energy each has at a given rpm level...

What's most troubling is that everything was fine for months and thousands of miles, only to go to hell-in-a-handbasket on a straightforward highway cruising speed. Wasn't like it failed at redline at the track...

Could be a total fluke; maybe just a bad NSK bearing - could potentially be a design flaw in that an idler with this much mass overworks its bearing... hard to say without some extensive R&D and component testing. My hunch is that a lighter pulley (either spec'd with aluminum, or steel but with more material removed) wouldn't pose the same risk - just a theory on my part though.

 

jesus, those pictures looks hope you get it back on the road soon best of luck.

 

HOLY SH$T

 

Those pics are bad! Sorry to hear about this. In Jerry's defense however, he is the software guy, not the hardware. These are problems he inherited now that Erik (hardware guy) is out of the picture. It's not fair to put it all on Jerry as if it's "his" part that failed or caused all of the damage.
I can understand your frustration. I'd be mad as hell as well but it's a sticky situation. All I'm saying is lets not put this all on Jerry.
Aren't those NSK bearings known to go out like that? I have the same bearings on my C3P pulley. Seeing that makes me very nervous. How long are they "supposed" to be good for?
Hopefully you get your car back good as new and a mutual agreement is met.

 

Hey there c32AMG-DTM:

First things first, and that is I am sorry to hear about your situation. Truely disappointing all the way around.

Now a little physics, okay your assumption of no matter what the pulley was made it would have caused the same damage is right on track. In this incident F=MA applies directly. That is Force = Mass times acceleration. The pulley, even if it were lighter would still have a HUGE force applied to it, as it is spinning several time faster than the crank. Most likely happened on your way up the tach. Once the bearing seized, and I had one do this on my supercharged stang, all he__ breaks loose my friend.
Since the water pump is aluminum, aka the weakest link, it had a HUGE force being applied at a 90 degree angle. that is the belt was trying to rip it in two. Once it let go that pulley was sent flying around the engine compartment, and had enough energy to basically smash through anything it hit.
Sorry to say, but it sounds like you wore truely VERY unlucky my friend.
Yes if it was aluminum, it would have done less damage, but probably not very much less. It just dependid on what it hit once it broke loose.

Personaly, I would stay with a steel pulley for the shear strength of it and chalk this up to bad luck.

Again, sorry to hear about my frined, and good luck with the repairs.

See yeah

 

Same thing happened to me with stock pulleys, pulley just explode suddenly.
I was a bit luckier than you because it happened in my garage on idle, so no major damages. I just had to replace belt, one pulley and rebuild the mounting on waterpump...

After checking through damages i came in to conclusion that pulley had started to wobble and then bearing just throw the ***** out and failed.

 

That's true; it is complicated, due to the transition of ownership from Erick to Jerry and Wayne. And, ever since starting the tuning side, Jerry's computer and IT background make him a natural for the ECU tuning. Since "LET Motorsports" has been relatively seemless to the consumer, I was surprised to learn that the company which sold me parts back in Feb. has been completely closed/shut-down, and the current company is brand new but bought the rights to the name, website, etc.

However... LET still offers hardware, in fact they still sell the exact same pulley kit that I have. For awhile they were getting out of that business all together; my understanding is that has changed.

FYI, you're thinking of the S/C's NSK bearing - which apparently does go bad after awhile. I've heard/read that they get noisy - never heard if any have seized up catastrophically. This is an NSK bearing in the idler pulley... completely different bearing.

 

Sorry for your losses. Wasn't there a pulley recall from LET? I can't seem to find the thread.....

Here's the link on the pulley recall...I hope I don't have a bad pulley. Does anybody know if cleaning the bearings with brakleen would prevent bearing failure or at least lubricate the parts and remove debris?

 

Thanks MRAMG1 - knew I could count on you for the quick physics lesson

I see what you're saying - bearing seized up, idler pulley stopped spinning briefly, belt's still going, rips it off and catapults it around the engine bay.

I was picturing it slightly different - bearing seized up, stored-up momentum in the pulley + force applied by the belt were too much for either the bolt or water pump's threads (WP lost, obviously), pulley spins off and the belt throws it around the engine bay.

Assuming the belt rpm is constant, the force the pulley applies on the other end (i.e. everything it hits) is directly related to how much mass it has... am I saying that right?

 

Thanks pshek - different pulley. LET had problems with some water pump pulleys failing. That pulley doesn't have any bearings; it was simply a structural problem with that pulley. I've kept a close eye on mine since those problems, it appears to be okay at present.

 

Okay, so LET had a recall on a water pump pulley with the 181 mm kit. Now, is Let going to have a recall on the idler pulley?

 

Okay, I remember that others have had idler pulley failures on their cars as well, just not as catastrophic as c32AMG-DTM. I think that c32AMG-DTM's failure was more damaging because of bad luck. Those pictures make me very uneasy.

FrankW and Topgun32 had the same problem with their idler pulley, but less damages. Link to Idler pulley failures on Evosport kit. I think the manufacturer of the pulley is the one at fault here. It's hard to blame LET for a pulley that has a tendency to fail in such a short time. Maybe we should just be replacing these idler pulleys at regular maintance intervals to prevent failures.

 

That is why I was saying that wether it was aluminum or steel, it was still going to break something. Don't forget that you said the bolt stayed with the pulley adding even more mass, aka kentic energry, to break things.

See yeah and good luck with the repairs my friend

 

uh..u havent had that replaced man??? If not...please do....

 

I have called the idler pulley manufacturer and they have confirmed the 15,000 RPM speed limit. He is looking to find a 20k+ rpm bearing that is a direct replacement that we can use. There are a number of options for us, so give him a little time to find the replacement.

One of the NSK 6301's is showing a grease RPM limit of 20,000.

 

OP - LET will replace the failed pulley and the damaged crank pulley (when we spoke you didn't mention the crank pulley was damaged).

I'm still not 100% sure that the bearing was at fault due to over spinning.

Over torqued idlers have been seizing for many, many years.

I have personally put 30,000 miles on my C32 with the same bearing that you had fail with no issues at all. Others have done the same...

Now, take a simple Google search for "Seized idler pulley" and you get tons (7,090) of listings where idlers have seized.

Google Search

There is even MBWorld listings for C32's without our product installed that have had a seized idler.

Link to listing on MBWorld

I understand your frustration and I did everything I could to help get the car on the road. I have taken proper measures and offered to replace the LET parts on the car.

 

Jerry, thank you for your reply.

I agree - we cannot be 100% sure the bearing seized due to overspinning (how often can we be 100% sure of anything?). However, if a bearing is rated to a max rpm of 15K, and the 181mm pulley kit is spinning it to 18K+ ... and it's fine for several months and thousands of miles ... isn't the logical conclusion for premature failure due to the bearing being overspun?

If there are 20K-rpm-spec bearings available in this application, why weren't they spec'd in the first place? It seems like no one bothered to do the math and make sure the spec'd bearing was within its rpm limit (ideally, a comfortable margin of safety under the limit).

 

At the time, I was told that there was a bad batch of water pump pulleys, two of which failed pretty bad. I was informed that mine wasn't one of the affected ones (i.e. not from the same batch), but that I should keep an eye on it; and if it made me more comfortable, I could obtain a replacement to have on hand.

It's bee fine so far... so I replace this too? (is it a ticking time-bomb?)

 

If you take the number of 185 and 181 kits on the market and divide that number by the number of seized idler pulleys, you would get less than 1% failure to date.

I admit that the bearing is being overspun when the car is driven above 5000 RPM's and I have started the process to replace them with new, higher RPM bearings.

However, I would be willing to bet that the torque applied during the install would have provided greater stress on the bearing and it lead to your pulley failure. If it is over torqued, the bearing is squeezed together causing too much heat.

Do I think the bearings will fail because of our design issues? YES

Do I think that was the cause of your failure? NO

How long do you think the bearing actually remained above 15,000 rpm? Were you driving above the max RPM when it failed?