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Someone Prove It

8K views 42 replies 22 participants last post by  PowerDubs 
#1 ·
I know that Pulleys have a negative rap on here. I know and understand the physics behind the issues that they "cause" but I have yet to see proof on any motor.

So, I challenge everyone here to prove it to me. I don't want to see anything more than bolt-ons on the motor that blew up. Going BT or having added FI does not count because there are so many added variables that could have caused something that the pulleys could not be drawn back to as the main cause.

So, show me any 2.0, VR6, 1.8t, any motor, with just bolt ons that suffered an issue from adding LIGHTENED, not underdrive pulleys please!

The motor needs to be unopened, as in no internal engine work for it to qualify. Thank you.
 
#2 · (Edited)
There is practically no point to a lightened, stock-diameter crank pulley.

The majority of the horsepower "found" through an underdrive crank pulley results from reducing the effort to drive the accessories.

Personally, I've had no issues from years of using underdrive pulleys, but I've only used them on vehicles with unbalanced factory pulleys.
 
#3 ·
There is practically no point to a lightened, stock-diameter crank pulley.

The majority of the horsepower "found" through an underdrive crank pulley results from reducing the effort to drive the accessories.
Reducing the rotating mass of the engine actually does provide improvements. you just arent going to notice much on a stock engine if all you do is replace the pulley.
 
#9 ·
I understand the harmonics of it but I want to see proof that a bolt-on motor with a lightened crank pulley will cause damage to the motor.

Everyone on here screams that they break things and cause issues but i have never once seen any proof. Yes, the physics is sound and I understand that but prove it... its all theory as of now.
 
#10 · (Edited)
http://www.atiracing.com/products/dampers/damper_dinan.htm

Steve Dinan of Dinan BMW said:
The popular method for making power pulleys on E36 engines is by removing the harmonic damper and replacing it with a lightweight alloy assembly. This is a very dangerous product because this damper is essential to the longevity of an engine. The substitution of this part often results in severe engine damage.
It is also important to understand that while the engine in a BMW is designed by a team of qualified engineers, these power pulleys are created and installed by people who do not understand some very important principles of physics. I would first like to give a brief explanation of these principles which are critical to the proper operation of an engine.

1) Elastic Deformation
Though it is common belief that large steel parts such as crankshafts are rigid and inflexible, this is not true. When a force acts on a crank it bends, flexes and twists just as a rubber band would. While this movement is often very small, it can have a significant impact on how an engine functions.

2) Natural Frequency
All objects have a natural frequency that they resonate (vibrate) at when struck with a hammer. An everyday example of this is a tuning fork. The sound that a particular fork makes is directly related to the frequency that it is vibrating at. This is its "natural frequency," that is dictated by the size, shape and material of the instrument. Just like a tuning fork, a crankshaft has a natural frequency that it vibrates at when struck. An important aspect of this principle is that when an object is exposed to a heavily amplified order of its own natural frequency, it will begin to resonate with increasing vigor until it vibrates itself to pieces (fatigue failure).

3) Fatigue Failure
Fatigue failure is when a material, metal in this case, breaks from repeated twisting or bending. A paper clip makes a great example. Take a paper clip and flex it back and forth 90° or so. After about 10 oscillations the paper clip will break of fatigue failure.

The explanation of the destructive nature of power pulleys begins with the two basic balance and vibration modes in an internal combustion engine. It is of great importance that these modes are understood as being separate and distinct.

1) The vibration of the engine and its rigid components caused by the imbalance of the rotating and reciprocating parts. This is why we have counterweights on the crankshaft to offset the mass of the piston and rod as well as the reason for balancing the components in the engine.

2) The vibration of the engine components due to their individual elastic deformations. These deformations are a result of the periodic combustion impulses that create torsional forces on the crankshaft and camshaft. These torques excite the shafts into sequential orders of vibration, and lateral oscillation. Engine vibration of this sort is counteracted by the harmonic damper and is the primary subject of this paper.
-continued-
the gist: remove the harmonic balancer and the engine can potentially tear itself apart. At what point that is, how many miles, rpm, ?? Likely a repeated exposure weaking the part over time.
 
#11 ·
My situation doesn't meet your "criteria", but I will share anyways.

I put an undampened lightweight pulley on my 92 Eagle Talon. It originally had a harmonic balancer. I got a great deal on it so I threw it on there for the hell of it. I had an upgraded turbo, and a bunch of bolt-ons at the time. Anyways, after about 2000 miles when I was doing a street tune, I heard this nasty knocking\rattling sound so I immediately shut the engine down and towed it home, sounded like a spun bearing :thumbdown:

Upon further inspection, the flywheel bolts had backed out and caused the flywheel to rotate ****-eyed and destroyed the clutch, the input shaft bearing, and cut some nice gashes in my transmission case. I am almost certain it was from running an undampened pulley. I bought an ATI Fluidampr to replace it and I have not had a problem since. People may think, "oh, you didn't torque the flywheel bolts" or something like that, but I have a digital Snap-On torque wrench and used red loc-tite, with ARP Flywheel bolts. YMMV, but I wouldn't run any sort of pulley that isn't of the OE design, or at least maintains the function of the OE unit. Cheers :beer:
 
#12 ·
The last two posts were very good, helpful, and informative.

thank you for posting the physics behind it.

However, MJ your motor was significantly modified it seems, thank you for realizing that. I have little doubt that it was not the pulleys in your case, however, there are too many variables to consider. Your motor had significant work and while the pulleys are an obvious suspect, the amount of work done and other things that could have caused it are also abundant. That is why I am looking for a bolt-on motor at most.

Regards and :beer: for the two previous posts.
 
#16 ·
adding a BT/FI most likely means that you have altered the interior components of the motor. You have changed rods, pistons, taken things apart, looked at it, either way the motor has been opened which means it is very easy for something else to become loosened/not tightened properly/ not torqued, or anything along those lines, that is why I am looking for a strictly bolt-ons at most. I want to minimize the variables present. Adding FI or Cams, or touching the internals adds to many.
 
#19 ·
I didn't know they made them like that. My under drive pulley set, the crank pulley is SFI approved and still functions l like the factory harmonic balancer. I would not put one on a car that was not designed this way though.

I also don't fit any of the other criteria except UDPs are my only engine mod at the moment. Almost 60K miles with no issues.
 
#25 ·
Harmonic balancers are used to balance a cranshaft externally.
Using the wrong weight or just an UD pulley will upset the balance of the crankshaft, unless the crankshaft is internally balanced.

On a ford 302, if you use a pre 79 balancer on a 79+ 302, the crank will be damaged, as the early motor uses a 28oz balance weight and the latter a 50 ox balance weight.

it doesn't sound like a lot, but it will make a huge difference to the rotating parts of the crankline(crank, main bearings, flywheel)
 
#27 ·
The last three posts are good and I understand them execpt for 2 parts.

1) I want proof... Show me a motor that has run pulleys for 100-150k miles and has suffered a failure related to what you speak about and i will believe it. Sure the harmonics are there but maybe they are not enough to make a difference.

2) You mentioned that 1) Lightweight wheels don't make a difference in performance - Wrong. 2) You mentioned lightening the internals - wouldn't that change the harmonics and therefore cause the current damper to be incorrectly weighted? So we can change the weight of internals and there is no issue, but when you change the pulley there is?

Forum physics: applying physics to only the areas you are concerned with and screaming about the negative effects without taking into account the entire system or how great the affects are.

You just did it right there... Internals lightened = fine, Pulley lightened - not fine...

Beyond this, because we are getting away from what I want, I am not looking at a modified engine internals wise... I want a closed engine with bolt-ons at most that blew up from a pulley being added/lightened/changed.

And if no one can prove it then the response to the age old question of "Should I get pulleys" is now:

If you do not plan on going BT or Adding FI there is little to no conclusive evidence that says a lightened pulley will damage your motor. However, if you do plan on going FI or adding a BT, the harmonics of the motor become more important and while I have no examples off hand, everything is getting stressed that much more, therefore, you have a greater chance of having those harmonics getting thrown further out of whack. That combined with the significant increase in stress across the engine system could result in a failure.

~~~~

Once again guys, PROVE IT! I dont see any hard examples of a bolt-on motor being destroyed because of a pulley. Hell, Ive seen 2 stories of BT and added FI guys with lightened pulleys having failures related to the pulley, and one posted above. Another was the Mk5 R32, i tracked the thread down and read it some.
 
#28 ·
You just did it right there... Internals lightened = fine, Pulley lightened - not fine...

Internals are balanced. Lightened pulleys are not weighted specifically to balance out harmonics.

I doubt you'll find a motor that has been destroyed, and the failure was traced back specifically to lightweight pulleys. What is indisputable however, is that a lightweight, non-harmonic balancing crank pulley will cause excess wear over the stock unit.
 
#30 · (Edited)
I am merely playing the other side of the argument. And still no one has provided proof.

I am trying to fully understand the physics behind everything and I did mix up the damper verse the balancing aspect. My mistake.

I am not disputing the physics or science behind it. It is completely sound and I stand behind it. Hell I am the first person to shout science at people with regards to almost anything. However, as this discussion (thank god it has remained a discussion and not turned into an argument) has evolved the only thing I am stuck on is the fact that there is no evidence, hard proof, that pulleys on a stock-ish motor will cause issues.

Yes, the science is sound, and definitely true, my argument isn't with the science, but my point is that, on our motors with only bolt-ons (1.8ts, VR6s, ect) the harmonics are not affected enough to cause issues. The magnitude of the affect harmonics and imbalance is not enough to cause failure within the foreseeable lifetime of the motor. Once you start adding the additional stresses of FI or BT, I can see my position being thrown out the window, however, until someone shows me evidence, not just science that a stock-ish motor has had issues, I will not support the pulley bashing.

Guys, just to clarify, I started this thread so we can post it when someone asks about pulleys and have conclusive information regarding the side effects of the pulleys. I am just playing the advocate role. (I will never put a lightened crank pulley on as I track my cars and they see a lot of additional stresses.)
 
#33 ·
so i have lightweight pulleys on my car, its a 2004 gti vr6. ive had them on for probably close to 100,000 miles now. never had a problem. but, there is one thing, the crank pulley i took off, was just that, a pulley. there is no external harmonic balancer to be found on my motor. i think the problem are people removing the balancer for a pulley. there is a reason those balancers are on there. do u think car companies would be putting them on for decades if there wasn't a reason?
 
#38 · (Edited)
Right, on plenty of cars the pulley is just a pulley.

Interestingly, even though Subarus have a pulley that does have a damper built into it, Grimmspeed has this quote from Subaru of America on their website:

SoA said:
Thank you for your patience as I checked with our Technical Services Department regarding your message below. They advised that the crank pulley is a pulley and nothing else. It is not used as a harmonic damper/balancer. Thanks for the opportunity to be of assistance. If you need any future assistance, please feel free to contact us again."

Best wishes, John J. Mergen

Customer Service Department Subaru of America, Inc.
I still wouldn't buy one, as it's $130 that I don't think would actually do anything noticeable on a stock car in a double-blind test. :p

Oddly enough, Subaru published an SAE whitepaper about the EJ22T engine in 1989 which specifically calls out the pulley as a double mass harmonic balancer intended to disperse the torsional vibration of the crankshaft up to 7500rpm.
 
#41 · (Edited)
Spun bearings in the SVT Contour Duratec engine are believed to be because of the crank pulley. A lot of guys install the one from the ST200 in europe. It's a heavier dual mass dampner. I know one I owned had one installed and never had any engine issues. Sold it with 160k on it. It's ok to do power steering and alternator pulleys but I'd never change the main crank pulley.

Here's a pic comparing the 2. Stock is on right obviously. Ford must have redesigned this for a reason.
 
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