Crank Pulleys

D

Domino

New member
Anyone have any solid data on the effects/dangers of a lightweight crank pulley? There are so many articles going in both directions. Going from a 6 1/2 lb pulley to a 9 oz is so tempting but not at the expense of the bearings, crank, oil pump etc...

This article from Steve Dinan has been around for a while and I know Larry at Endyn only uses Fluidamper (not available on my D16).

http://www.dinancars.com/whitepapersFile.asp?ID=5
 
There are MANY confirmed reports of turbocharged Miatas grenading the oil pump in short order once a lightweight pulley is installed. I personally do not know of anyone who has had an oil pump failure caused by a pulley on an ITA car.

If you have, speak up!

I'm also very, very tempted...
 
I found the following on Unorthodox Racing's site;

"People are getting their crank pulleys confused with the harmonic dampers found on some V6 / V8 engines. "Harmonic Balancer" is a term used loosely in the automotive industry. Technically, this type of device does not exist. The "balancer" part comes from engines that are externally balanced and have a counterweight cast into the damper, hence the merging of the two terms. None of the applications we offer use a counterweight as part of the pulley, as these engines are all internally balanced.

The pulleys on most of the new import and smaller domestic engines have an elastomer (rubber ring) incorporated into the pulley that makes them look similar to a harmonic damper. The elastomer in the OEM pulley serves as an isolator, which is there to suppress natural vibration and noise from the engine itself, the A/C compressor, P/S pump, and alternator. This is what the manufacturers call NVH (Noise Vibration & Harshness) when referring to noticeable noise and vibration in the passenger compartment. It is important to note in these applications, the elastomer is inadequate in size and durability to act as an effective torsional damper. If you look at the pulleys on some imports there is no rubber to be found at all. We have samples of these, mostly from Acura/Honda, the Nissan Altima, 1.8L Eclipse, 2.3L Fords, Chrysler 2.2L's, and 1.8L VW's, to mention a few. This is not to say with our pulleys you will hear a ton of noise or feel more vibration from your engine compartment. Most owners who have installed our pulleys notice the engine actually feels smoother. This is result of replacing the heavy crank pulley with our crank pulley. NVH is variable and unique to every car. NVH will increase with the installation of an aftermarket intake and/or exhaust, for example. Think of OEM intake systems in newer cars, they use baffles and resonators in the intake to quiet all the intake noise. Aftermarket intakes eliminate these resonators and create dramatic increases in engine noise from the throttle opening and closing. So to most tuners, certain types of NVH can make the driving experience more enjoyable.

The purpose of a traditional harmonic damper is to protect against crank failure from torsional movement. This is not necessary in most modern engines because of the many advances in engine design and materials. Factors such as stroke length, displacement, inline, V configurations, piston dwell time, piston pin off-set, power output, etc., do determine when and how these harmonics and torsional movements occur.

Again, there is a lot of internet hearsay about crank pulleys. When engine problems occur, too often people are quick to blame the pulley first, rather than taking the time to look logically into why there was a problem. We hope that after reading this you will understand the crank pulleys better."

Not that I'm presenting this as fact, just another view, from an obviously biased source. Here is the page it came from, there is more but it's all along the same line of thinking. http://www.unorthodoxracing.com/faq_pulleys.html

EDIT: I will add that my limited experience with these has been positive; I ran the last two events of '06 with a lightweight underdrive pully on my 240, and noticed no ill effects. Of course, we're talking about maybe 2 hours of track time, so it may just be that there wasn't enough time to see any issues.
 
I read the same thing on Unorthodox's site. I also read something quite humorous on AEM's site (see below). I tend to trust OEM thinking to a point, especially Honda. Why would they put a 6.5 lb crank pulley on a 1.6 liter 108 hp motor?! Just to make the ride more comfy? It appears the UR logic is that if the elastomeric/rubber ring is not on the OEM pulley then there is no harmonic dampening taking place but if it is then it's not suffcient enough do anything important therefore it's ok to swap out the whole piece.


Q: Why doesn’t AEM make a crank pulley?
A: Virtually all of the cars we make Tru-Power pulleys for come equipped with a harmonic damper mounted to the crank from the factory. Aftermarket crank pulleys require the removal of this damper, which is required for engine life. Its removal can cause damage to your engine over time by allowing unnecessary Noise Vibration and Harshness (NVH) to affect engine operation.
 
Ok guys -1988 d16 has a 4lb pully but has a small dia. snout[this is the best crank]1989-91 has the big dia and the 9lb pully.you can remove the 5 lb piece of metal from behind and there will be no problem, the motor likes it so no need to worry.ITA it is a gray area. inline motors a always in balance hona annyway
Fastist12 89 CRX-Si
WCS Motorsports/Stormpower Race Engines :eclipsee_steering:
 
I don't want to cause confusion here but I felt that I had something to offer. I used to work in the Design Department of a company that supplied accessory drive and timing drive components to the OEM automotive industry and spent some time reviewing and overseeing a number of OEM Design projects for a variety of motors from small bore I4's, through OHC V-8's to big bore slow revving diesels.

The answer to this question is that there is no hard and fast rule as to whether you can "safely" remove the balancer from the front of your motor. All motors are internally balanced to some degree. If the OEM can provide enough counterweighting inside the motor to negate the 1st, 2nd and 3rd range crankshaft harmonics then they will do it internally. Sometimes they can't and they are required to add sophisticated harmonic dampers to the front of a motor. This could be to dampen torsional crankshaft whip from setting up accessory drive or timing drive harmonics, it could be to minimize crankshaft whip to increase the service life of the bottom end bearings or it could be to dampen power pulse spikes from setting up operational range driveline harmonics.

I have seen some very scary harmonic effects from not fully balanced crankshaft harmonics. From accessory drive brackets moving almost an inch in vibratory motion which can lead to brackets cracking and failing, to belts jumping off pulleys, to timing drive belts setting up a standing wave which moves up and down the untensioned side of the belt (rpm dependent) till it ultimately causes a belt/tooth jump. I have also seen driveshafts in RWD cars start to whip under loads using unbalanced engines.

Now that I have caused all kinds of confusion I will try to give you a rule of thumb that I would use. Every extra part on a motor adds weight, cost, assembly complexity and reduces mileage. This is especially true in a rotating assembly. If there is an external dampening device on your crankshaft, the original OE designers felt it was absolutely needed to prevent something not very good from happening in the normal duty cycle of your motor and car. You can take it off, but expect bearing life to be reduced. Unless the engine is rebalanced to the new counterweight situation you can expect your peak power to be diminished, but your acceleration to that point to improve. Talk to your engine builder about having the motor rebalanced or accept the possible upsides and downsides to removing the external damper. These things may not apply to your situation in a race application, but I expect that they will so look into it a bit before taking an uninformed chance.

Eric
 
Great post Eric, thanks! Can you explain for me why changing the balancer can have such an impact yet swapping out a heavy 18lb flywheel with a 7lb one doesn't seem to have the same problems? I've always wondered....
 
You can add a lighter flywheel if your stock flywheel is dynamically balanced as an individual component. If the engine relies on a counterweighted flywheel to provide balancing the replacement flywheel needs to be counterweighted as well.

For an example, my S5 13b RX7 uses an 8 lb Guru balanced flywheel. To be able to use it on my engine, I need to bolt it on the Auto transmission counterweighted flexplate mounting flange.

As a side note if you add the 8lbs from the flywheel to the 8 lbs from the counterweighted flange the savings versus the stock flywheel are only 5 lbs, not the 13 lbs you would assume.

Eric
 
These things may not apply to your situation in a race application, but I expect that they will so look into it a bit before taking an uninformed chance.

Eric [/b]
Click to expand...

Eric, great info, thanks. One question remains for me; if we are to consider the race application, where the engine is blueprinted/balanced with the lightweight pully, and will see maybe 25 - 40 hours of running time between rebuilds, is there still cause for concern?
 
In my somewhat informed opinion, I would say as long as your engine was rebalanced as an assembly, you should see no issues.

I am ignoring the fact that your Nissan has Pistons the size of garbage cans and causes about the most torsional stress in the crank that I have ever heard of, LOL.

Seriously, talk to your builder. He knows the rpm the engine is balanced to and the maximum recommended rpm he expects you to go to. You can get away with it for a period of time, as all companies build a safety margin into their motors in strength, but it is a bit like Russian roulette at some point you luck runs out if you exceed designed in operating forces.

Heck last year a co-driver in my car missed a shift and pulled 10,300 RPM. Engine still runs fine, but I expect its life to be much shorter now.

Eric
 
Eric, I agree with what you are saying, but, the whole flywheel, crank and pulley (lightened or OEM) assembly can be balanced outside of the engine. However, when it's installed and utilized it's becomes unbalanced again. The clutch wears down the flywheel somewhat irregularly and the accessory belt(s) when tensioned, apply an uneven amount pressure on the other end.

To your point about 1st, 2nd and 3rd order harmonics, if an OEM manufacturer developed a damper to absorb harmonics that they could not eliminate internally why would we want to remove it even if an engine builder balanced the whole assembly given the caveat mentioned above?
 
To remove extra rotational mass from an engine that is more balanced than it ever was from the factory, is no longer expected to live for 200k miles of all conditions operation, with neglected maintenance schedules.

At least that is why I will do it.
 
Mark, I agree totally with what you are saying. If I had an eccentric damper on my crank snout I would leave it on and look somewhere else for rotational mass reduction. However the other side to this equation is if you had a crankshaft on an externally balanced motor rebalanced using very expensive heavy metals, talented technicians and sophisticated measurement equipment to do the actual measurement, then it should work well in most cases.

I guess that I should temper my statements with the "it all depends" type of claim as even if the rotational mass is balanced, there can be other types of vibrations that can break off a crank snout (i.e. Miata), cause timing chain or belt issues and accessory drive issues. Sometimes even the factory engineers get it wrong when they don't calculate the service life and expected operating conditions correctly. Look at the old DOHC 3.4 Chevy, the Miata, 2.3L Sentra, etc..... I could tell you guys a story about the first versions of the now revered 7.3L Ford turbo diesel that would make you laugh out load.

You can replace the damper with a much lighter pulley just be aware that you may be shortening your engines life, potentially causing other durability issues and potentially reducing peak HP balanced against the potential benefit of quicker acceleration. Thats the equation you have to use.

Eric
 
:dead_horse: Guys ,, You can remove that weight from behind 89-91 D16 motors
Its a 5 lb Gain .
Stormpower Race engines
Passin U
ITA/CRX-Si
 
Three things to add on this topic:

All conventional piston/type engines experience harmonic resonance at some RPMs. How much and at what RPMs depends on material strength, design and other factors including cylinder pressure (which can't be replicated by a static machine shop balancing). Two engines of the same construction could experience different harmonics with different mechanical compression ratios or due to other tuning differences such as fuel mixture flow and ignition timing. The OEM may have felt a need for a damper because at the common 55mph there was a harmonic issue which you won't see in a race application. Or, your normal race RPM may be right at a problem speed.

The bottom line for your engine builder or your own determination is does a harmonic dampener free up horsepower that otherwise would have been lost to vibration and does it make the motor more durable?

The flywheel weight which was questioned is not normally as important for the harmonics because the clutch pressure plate, which is largely a giant spring, absorbs some harmonic vibration on an engine. I have seen only a very few factory motors which include a rubber isolator ring on a flywheel.
 
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