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Lightweight Crank Pulley Check-In

ramsack

Banned Member
3,286
20
Dec 27, 2007
West Lawn, Pennsylvania
Lets put dampers on the camshafts. Without one they will turn to liquid and break or wear the cam castles.

If you're not going to add anything constructive to this topic, get out! What is your logic for that? What forces do the cam shafts see that are anything like the crank? They SMOOTHLY ramp up some lifters and SMOOTHLY shut them. Once you rev high enough to not smoothly shut them anymore and the rockers are just slamming back into it, this is when you will have problems, but I guarantee the valves would be damaged long before camshafts. And BTW the timing belt would act like a damper for the cams ;)
 

dsm-onster

DSM Wiseman
8,593
117
Jul 11, 2004
Bloxom, Virginia
Cams rotate at half engine rpm as well. Nor do they see anywhere near the initial force of peak cylinder applied to the lobes. The recoil of a cam lobe is infinismally small even if they did see the same force. Look how long they are vs. the crank "lobes".
 

tkelly27

Proven Member
1,712
26
Mar 11, 2007
Gresham, Oregon
: / all good technical discussions must come to this for some reason.

Certain volkswagens do not use cam pins, just bolts. So I know the bolts hold the force, was just saying even if we assumed they didn't. Shearing those bolts off sucks, big time.
 

Sp1kE

15+ Year Contributor
375
25
Dec 24, 2005
stratford, ON_Canada
If you are going to be a troll in an otherwise good thread, at least make it less obvious.

Just sucking more discussion from you guys.
I run a Fluidampr and would never run a solid pully.
I will stop now :p
 

dsm-onster

DSM Wiseman
8,593
117
Jul 11, 2004
Bloxom, Virginia
Another arguement for the sake of arguing ???? :confused:

At any rate. . . tkelly, that is a great example of proving that bolts transfer the forces we're discussing. Tell that to unorthodox. Fitting name for their company considering the subject matter BTW :)
 

300dollarGSX

Proven Member
107
3
Feb 28, 2003
Milton, Florida
The problem with our stock pulley is that it was designed to reduce vibration at a specific frequency. The size/stiffness of the elastomer and the weight of the inertia ring were "tuned" to counteract vibration at the point the crankshaft experienced its worst oscillation in a stock engine. Changing weight of the crankshaft or other parts of the rotating assembly will change the crankshafts own resonant frequency. Of course, weakening of the elastomer in our factory pulley should change which frequency it can effectively counteract as well, so I will guess that it doesn't need to be perfect, just close enough to keep the crank from staying at its resonant frequency for too long.

Longer crankshafts will, obviously, tend to oscillate more. Four cylinder cranks are typically single plane which makes them easily balanced and reduces the number of rpm points that create major harmonics. Our crank has another advantage in that it is hardened from the factory, so it is very stiff and relatively short. Most smaller four cylinder engines don't create the torque necessary to make those resonant frequencies for any length of time, so the engineers don't feel a damper is necessary.

I know the tuning fork analogy has been used before, but it's a good one. Attach one to an immovable object (my car) and tap it. Equate this to a typical low power four cylinder. Now tap the fork and play the same sound it makes through that giant amplifier/speaker thing from Back to The Future. The fork will go nuts, probably break into pieces, and you will loose the ability to hear (How Marty didn't have blood flowing from his ears, I will never know). Equate this to a modified DSM that makes real torque.

Personally, I think the Fluidampr is the better choice. It can reduce oscillations at more frequencies than an elastomer based damper. It converts the energy to heat, though, so I would assume that if you did some sort of endurance racing or anything that kept your engine at a point that created one of your cranks resonant frequencies that you would need to cool it somehow.
 

ramsack

Banned Member
3,286
20
Dec 27, 2007
West Lawn, Pennsylvania
I don't believe changing to lighter components will change the resonant frequency, nor will knife-edging the crank or modding it in any way. The torsional "sound waves" still take the same amount of time to travel through the crank because it is the same material, and same stroke. Go with a stroker crank, a shorter crank, or a crank made of different material and its resonant frequency will be different. The rubber part of the crank is not the only part that's tuned for the frequency, but also the outer shell's weight. Things like the fluidampr are the best out there because they absorb a VERY wide range of frequencies around the engine they're built for. I believe the fluidampr would be cooled enough sufficiently just from spinning and air moving under the car.
 

300dollarGSX

Proven Member
107
3
Feb 28, 2003
Milton, Florida
I don't believe changing to lighter components will change the resonant frequency, nor will knife-edging the crank or modding it in any way.

Sure it will! That's exactly how resonance frequencies work. Imagine a nice wine glass with an ounce of pure water in it. When you rub a wet finger across the top, it will vibrate at its resonance frequency and will make a certain sound. If you add another ounce of water to it you will change the resonance frequency and, as everyone knows, you change the sound. The water effectively changes the mass of the wine glass, which changes the frequency of the oscillation.

The torsional "sound waves" still take the same amount of time to travel through the crank because it is the same material, and same stroke. Go with a stroker crank, a shorter crank, or a crank made of different material and its resonant frequency will be different.

Sure, it's the same material, but the mass is no longer the same. The time it takes for the "wave" to travel through the crank is relevant, but it's not what I was talking about. The problem occurs when sufficient torque is applied to the crank in intervals that cause vibrations that match or approach the cranks own resonance frequency.

The rubber part of the crank is not the only part that's tuned for the frequency, but also the outer shell's weight. Things like the fluidampr are the best out there because they absorb a VERY wide range of frequencies around the engine they're built for. I believe the fluidampr would be cooled enough sufficiently just from spinning and air moving under the car.

Yes, the outer shell (I referred to it as an inertia ring) is what actually counteracts the vibrations. The elastomer was to provide the proper timing (back to your comment about timing of the wave) so the inertia ring could counteract the more critical vibrations, but is also thought to provide some damping as well.

I have seen a BMW that was using a Fluidampr that set up some cooling ducts to help cool it down. I assumed they did some sort of endurance racing that kept the engine in a range that produced strong vibrations for long periods of time.
 

pneumo

Proven Member
3,763
58
Oct 19, 2002
Bay Area, California
...at the risk of continuing the arguments...
FROM POST #61
calan said:
But all the engineering and factory testing says that the 4g63 crank needs to be dampened (sic) to prolong bearing life...period.
Could you show your resources for this info...QUESTION MARK :D

IMHO the stock pulley works fine when it's in one piece. The problem is they are known to separate and damage other parts of the engine when they get old. You can reduce the risk of major engine damage by removing this unreliable part. Here's the question: with what should it be replaced?

Fluidampr is excellent at damping, are sfi certified, but they are over one pound heavier than the stock pulley, and are expensive. Adding weight is the easy way to improve vibration damping. Adding weight to the crank will slow acceleration worse than adding weight anywhere else on the car. Is that a good choice for your performance goals?
http://fluidampr.com/DOWNLOADS/CATALOG/SPORT_COMPACT.pdf
Puma Race Engines Technical Guide - Lightening Flywheels

Lightweight solid underdrive pulleys save 4 pounds off the crank and free up a little power by underdriving the accessories and reducing rotational weight. This extra HP is available all the time, not just when in boost. This is a nice benefit when driving off boost and part throttle. It makes the car feel more responsive, and I don't feel like I need to hit boost just to pull away from a stoplight. It might only be a few HP, but at part throttle and low rpm, a few HP can be a 20% increase. Plus they're cheap and the solid design is foolproof reliable.

For comparison, the stock pulley on the Mitsu EVO 8/9 has an aluminum center, rubber ring, and one belt groove. It weighs 4.5 pounds, which is 2 pounds lighter than a stock DSM pulley.

A new stock pulley isn't cheap. Here's a good price: MitsubishiParts.net - Your #1 Source for OEM Parts and Accessories

Some of you guys make it sound like there's a 9.5 earthquake going through the crankshaft and a 2mm thick ring of rotting rubber is going to save everything from shattering into pieces. I think we need to put it into perspective. How severe is the resonance in the crank? How much resonance can the stock pulley absorb? If the stock pulley absorbs as much energy as you say, then why doesn't it get hot on it's own, aside from absorbing heat from the hot engine?

The pics of the bearings shown in the censored link do not show any unusual wear in the bearing next to the accessory pulley. In fact the bearing next to the pulley looks very good. The 2 worn bearings are shown here-
39019d1096646716-main-bearings-after-50k-

The top bearing is the one next to the torque converter (auto trans). The wear shown is caused by a slightly unbalanced TC or uneven fluid level inside the TC during startup. I've seen similar wear on many engines, both AT and manual. That's why I originally replied saying it shows normal wear, aka no unusual wear for a bearing in that location. The lower bearing in the pic shows wear from dirt contamination which is unrelated to any type of pulley. The bearing next to the pulley shows normal use, and does not appear to be worn out. Please keep track of the location of each bearing.

Overall I think that the main crank bearings are more than large enough to support the given loads without undue wear, assuming the engine is maintained properly. The issue of crank breakage is valid, although how often do we hear of a broken crank? The stroker crank is more likely to break in theory due to longer throws, and reports of actual crank breakage support this theory, although still few.
 

knochgoon24

DSM Wiseman
6,136
89
Jan 29, 2008
Troy, Michigan
After reading through thread, I'm no longer convinced that a damped pulley is completely necessary. At the very least, I'll end up a devil's advocate here.

For starters, I don't see how bearing wear is being brought into the argument. We seem to have gotten off track here. The pulley damps TORSIONAL vibrations, not TRANSLATIONAL vibrations. Torsional stress isn't transferred to the bearings; it goes out the ends of the crankshaft to power the transmission and accessories. Even if you start getting torsional harmonics, you don't get translational movement. Torsional harmonics cause internal shear stresses within the crankshaft. To see damage before catastrophic failure, you'd have to do analysis on several crankshaft to see if there's a difference in the way it's fatigued.

There was mention of the crank becoming unbalanced as it flexes. Maybe that's the source of the bearing wear argument. It would take a lot of flex to throw it far enough out of balance to matter. You'd run into problems with shear stresses first. I would expect to see broken cranks before excessive bearing wear.

But even with undamped pulleys there is still crankshaft damping. The damped pulleys dissipate energy in the rubber layer. Vibrations cause work that heats the rubber which it then radiates. Without that rubber layer, you need to dissipate the energy elsewhere. All the accessories and accessory belts should do some of that. The belts stretch and flex. I can see accessory belts needing changed more frequently when using an undamped pulley. Would the crank pulley be the first thing on our cars that was a bit over engineered for the job?

Now I do understand that the damping has to be tuned for maximum effectiveness. What that frequency is, we don't know. The easiest way might be for someone to take the stock pulley and test it to get a ball park idea.

Our crankshafts are pretty robust. They've held up to 1000whp. And I'm still seeing very few posts by people with broken crankshafts. Just a lot of hot air. ;)

Now I don't like the underdrive pulleys because our alternators are already bad enough. They don't need to spin any slower at idle.

And the argument that it's removing a source of jumped timing belts is a bit of a stretch. That's why we have timing belt covers. :cool:
 

300dollarGSX

Proven Member
107
3
Feb 28, 2003
Milton, Florida
Fluidampr is excellent at damping, are sfi certified, but they are over one pound heavier than the stock pulley, and are expensive. Adding weight is the easy way to improve vibration damping.

You're absolutely right. As mentioned before, they can dampen a wide range of frequencies. The thing is, they aren't 100% effective at any of them. What's the phrase? Jack of all trades, but a master of none. Don't get me wrong, they don't need to be 100% effective to do the job.

Some of you guys make it sound like there's a 9.5 earthquake going through the crankshaft and a 2mm thick ring of rotting rubber is going to save everything from shattering into pieces.

Haha. I hope I wasn't one of them. I actually just finished helping with a project that was supposed to stop some vibration problems with a kit airplane, so I had a little refresher on resonance frequency just as I noticed this thread. In the case of that type of drivetrain, yes, it can make all the difference. They usually use a rebuildable damper, though.

I think we need to put it into perspective. How severe is the resonance in the crank? How much resonance can the stock pulley absorb? If the stock pulley absorbs as much energy as you say, then why doesn't it get hot on it's own, aside from absorbing heat from the hot engine?

1. Honestly, I'm not sure how often we even reach resonance frequency. The crank is relatively short and was factory hardened, so it is very stiff as well. That makes me think that we would need to be at a very high load level (high torque) and at a higher rpm. We also need to take into account that we probably wouldn't stay at any particular rpm for a long period of time. If resonance frequency happened to be at a torque level and rpm that was seen often or maintained for long periods of time (like cruising speed/rpm), I would imagine that there would be more broken crankshafts from those of us using a solid pulley.

2. Theoretically, it can absorb most, if not all of the resonance at the frequency it was designed to counteract. It is pretty limited in the range of frequencies it can counteract, though.

3. It does. It counteracts vibrations because the inertia ring is still trying to move in the original direction while the crankshaft is deflecting. By the time the inertia ring changes direction to match the crank, the crank is already moving the other direction again. All that twisting causes plenty of friction and heat.
 

ramsack

Banned Member
3,286
20
Dec 27, 2007
West Lawn, Pennsylvania
The resonant frequency will not change with load, it is speed based because it is a FREQUENCY. The amplitude of all the acoustics will change, however. Has anyone ever seen how a wine glass acts when it is about to shatter from sound waves? How about how solid ROCK of the ground makes waves from earthquakes? Sound can make solids move like liquids. I don't give a damn how hard materials seem. And for the bearing argument...look at the wine glass. It is moving an awful lot more at its resonant frequency than when it is far from it. A crank will do the same and this motion will transfer into any moving part attached to it.

Maybe I'm just overthinking this, but that's what the engineers who design engines do. I don't even study any of this crap, for me it's just common sense from reading and from GOOD science teachers in since junior high school.
 

dsm-onster

DSM Wiseman
8,593
117
Jul 11, 2004
Bloxom, Virginia
Yes, the clearance between the bearing and journal is VERY, VERY small. It's rather silly to think a flexing crank wouldn't distort the journal enough to make contact with the bearing.
 

pneumo

Proven Member
3,763
58
Oct 19, 2002
Bay Area, California
Yes, the clearance between the bearing and journal is VERY, VERY small. It's rather silly to think a flexing crank wouldn't distort the journal enough to make contact with the bearing.

How bad do the vibrations need to be before the crank touches a bearing?
 

donniekak

DSM Wiseman
5,626
977
Mar 23, 2008
Surprise, Arizona
The resonant frequency will not change with load, it is speed based because it is a FREQUENCY. The amplitude of all the acoustics will change, however. Has anyone ever seen how a wine glass acts when it is about to shatter from sound waves? How about how solid ROCK of the ground makes waves from earthquakes? Sound can make solids move like liquids. I don't give a damn how hard materials seem. And for the bearing argument...look at the wine glass. It is moving an awful lot more at its resonant frequency than when it is far from it. A crank will do the same and this motion will transfer into any moving part attached to it.

Maybe I'm just overthinking this, but that's what the engineers who design engines do. I don't even study any of this crap, for me it's just common sense from reading and from GOOD science teachers in since junior high school.

<object width="480" height="385"><param name="movie" value="http://www.youtube.com/v/17tqXgvCN0E&amp;hl=en_US&amp;fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/17tqXgvCN0E&amp;hl=en_US&amp;fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="385"></embed></object>
 

300dollarGSX

Proven Member
107
3
Feb 28, 2003
Milton, Florida
The resonant frequency will not change with load, it is speed based because it is a FREQUENCY.

Right. Did somebody say it would? The resonance frequency will not change at all unless you change something about the rotating assembly (mass, length, etc). Remember, however, that we are talking about a torsional spring. Torsional rigidity plays a part in determining the resonance frequency. We're applying force to the end of a torque arm (the rod journals). I referenced load because 3000 RPM at 10% throttle cruising along the interstate will have minimal torque compared to 3000 RPM at 100% throttle while trying to climb a hill.

Grab a thin crowbar and put it in a vice or something. Pull on it to flex it some and then let go of it quickly. It will oscillate, obviously. Now get a thicker, stiffer crowbar of the same length and do the same thing. It will take more effort to get it to flex at all.

The amplitude of all the acoustics will change, however. Has anyone ever seen how a wine glass acts when it is about to shatter from sound waves? How about how solid ROCK of the ground makes waves from earthquakes? Sound can make solids move like liquids. I don't give a damn how hard materials seem.

Humming quietly beside the glass won't do much (just like not enough torque or effort exerted on a crankshaft). The amplified and directed frequency from the device in the video can do the job, though.

Maybe I'm just overthinking this, but that's what the engineers who design engines do. I don't even study any of this crap, for me it's just common sense from reading and from GOOD science teachers in since junior high school.

No, think away! It keeps things interesting.
 

DashLaflash

Proven Member
311
7
Jul 4, 2007
Millbury, Massachusetts
So do we have anyone else who can report on the bearing wear in the link posted? One person says it is normal wear and another says it is abnormal wear. Also it seems that having an undamped pulley causes the accessory belts to absorb a lot of the vibrations. Is it possible that Mitsubishi designed the crank pulley to prevent premature belt failure? You guys keep saying that Mitsubishi designed the pulley for a reason. Does anyone know the actual reason and have the test data or are you guys just assuming on its purpose. Maybe Mitsubishi just assumed since all cars in the past have used them they should use them too. Also the wine glass breaks a lot easier than a solid piece of glass. Its shape makes it weaker to resonant effects. We still don't know what fequency the crankshaft vibrates at and what volume it takes for that frequency to break the crankshaft. My guess is its a whole hell of a lot.
 

ramsack

Banned Member
3,286
20
Dec 27, 2007
West Lawn, Pennsylvania
What does belt failure have to do with a crank pulley being dampened or not? Humming beside a wine glass won't do shit because of 2 reasons, not enough amplitude, like we agree on, and the inaccuracies of the sound coming from a human, and not a machine. There could be more than 1 frequency that can be resonant, and it is usually EVEN numbered multiples of the lowest possible resonant frequency. They won't cause as strong of a resonance, but there will still be some. This is also another reason for a damper. A solid pulley really could absorb a certain frequency, because of the crank can resonate and act like a liquid a little, so could something solid bolted to it made to absorb it. Something like metal will only absorb 1 resonant frequency effectively, though, in opposition to something rubber or liquid-filled that can dampen a wide range.
 

Boosted98gsx

Proven Member
2,100
22
Oct 31, 2002
Houston, Texas
So do we have anyone else who can report on the bearing wear in the link posted? One person says it is normal wear and another says it is abnormal wear. Also it seems that having an undamped pulley causes the accessory belts to absorb a lot of the vibrations. Is it possible that Mitsubishi designed the crank pulley to prevent premature belt failure? You guys keep saying that Mitsubishi designed the pulley for a reason. Does anyone know the actual reason and have the test data or are you guys just assuming on its purpose. Maybe Mitsubishi just assumed since all cars in the past have used them they should use them too. Also the wine glass breaks a lot easier than a solid piece of glass. Its shape makes it weaker to resonant effects. We still don't know what fequency the crankshaft vibrates at and what volume it takes for that frequency to break the crankshaft. My guess is its a whole hell of a lot.

VOLUME???

I am going to hope you meant magnitude.
 

ramsack

Banned Member
3,286
20
Dec 27, 2007
West Lawn, Pennsylvania
What would this knowledge of the resonant frequency do for you? Sure you can find out, but you will spend so much time and money to accomplish this, and only be left with a number. Then you would need to design and have something made if you would want to do that, which will cost even more time and money. Much more than buying a Fluidampr, ATI pulley, AND stock pulley COMBINED.
 

blackrosenova40

Proven Member
398
1
Jan 12, 2006
Belle Plaine, Minnesota
Well a harmonic dampner removes crank harmonics in the form of heat. If people think the timing belt removes the crank harmonics when using a lightweight pulley, where do you think the heat goes?

What does belt failure have to do with a crank pulley being dampened or not? Humming beside a wine glass won't do shit because of 2 reasons, not enough amplitude, like we agree on, and the inaccuracies of the sound coming from a human, and not a machine. There could be more than 1 frequency that can be resonant, and it is usually EVEN numbered multiples of the lowest possible resonant frequency. They won't cause as strong of a resonance, but there will still be some. This is also another reason for a damper. A solid pulley really could absorb a certain frequency, because of the crank can resonate and act like a liquid a little, so could something solid bolted to it made to absorb it. Something like metal will only absorb 1 resonant frequency effectively, though, in opposition to something rubber or liquid-filled that can dampen a wide range.
 

KazooGS-T

Proven Member
694
5
Aug 29, 2006
Ridgeland, Mississippi
Removing your balance shafts can also cause oil pump failures, which causes engine bearing damage... There are a lot more people that have had oil pump failures, with a balance shaft removal, than people whom have had a crank break (there's only one I've heard of) yet you do a BSE and preach against a solid pulley.
 
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