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Old 08-11-2017, 03:24 PM   #21
Dave in MN
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Default Re: Noisy metal timing gear cured by torsional damper

Carl, I think it could only help absorb a bit more of the torsional pulse change (torsional vibration) at ignition and compression. It is my opinion that Ron Kelly's flywheel mounted absorber takes a small amount of the torsional stress/pulse from the rotating assembly. The added weight of the dampener/damper also changes the rpm range the pulse or vibration is felt.

I know this due to some experimentation I did between 2012 and 2013. I was trying to tame a vibration in an engine with a very light flywheel, V-8 pressure plate and a counter weighted Burlington crankshaft. The vibration was very bad at a road speed between 52 and 55 mph in high gear. By adding the Ron Kelly like damper to the light flywheel the range of vibration changed to a road speed of 43 to 44 mph. It narrowed the range and decreased the perceived intensity to about half. I machined two more flywheels for a V-8 pressure plate varying from the least amount possible to lighten the flywheel and then prepared one that was half way between the extremes. All three flywheels were drilled to mount a customized Chev. harmonic damper on the front side of the flywheel.

Changing to the heaviest flywheel with the damper mounted, the perceived vibration was barely noticeable. The same heaviest flywheel was installed without the damper and the vibration was more noticeable and what I would say typical of a Model A. I went on to check all combinations of flywheel weight with and without the damper installed.

These tests required lots of work as the varying weight flywheels and damper were first tested on a dyno and then mounted in the same car (mine) and driven.

I believe the addition of weight to the assembly did the most to dampen the felt torsional pulse and harmonic vibration. The addition of the damper to any of the flywheels added weight so it helped reduce the pulse but when the damper was added to a very light flywheel, it dampened the felt vibrations more than the next heavier flywheel without damper. The weight of the damper was close to the weight steps of the prepared flywheels.

So my summary: The addition of a damper to the assembly does more than just the addition of weight to the assembly and the result is that the damper improves the felt vibration. So I think Ron Kelly is on to something here.
All this is just my opinion from tests I completed a few years ago.

If we want to debate something further, let's consider the concept of the "Rattler" torsional damper. There is a company in the UK that builds a light weight Model A/B compatible flywheel with "Sterling Rattlers" installed. They claim the addition of the puck weights to the flywheel helps to reduce the torsional stress on crankshafts.

Check out the Sterling Rattlers: http://vibrationfree.co.uk/our-servi...sport/rattler/

Rattler Model A/B flywheel assembly: http://vibrationfree.co.uk/sterling-...egory=16322086


Good Day!

Last edited by Dave in MN; 08-11-2017 at 03:47 PM.
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Old 08-11-2017, 07:25 PM   #22
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Default Re: Noisy metal timing gear cured by torsional damper

It's interesting to hear what RPMs resonant torsional frequencies occur in a Model A. Eons ago I was involved with torsional vibrations in diesel engines. The resonant (or critical) speeds in which the firing impulse frequencies of the cylinders match the torsional vibrations of the crankshaft and the rest of the drive train is called a critical RPM. These torsional vibrations at a critical RPM usually cannot be felt but they can sometimes be heard – by the “ringing” of the clutch pressure plate springs for example. The crankshaft can sure “feel” them though – in the form of oscillatory stresses (ie – fatigue), particularly in the crankshaft journal fillet radii. This can be quite concerning when crankshafts are ground having a journal fillet radius smaller than it should be. High oscillatory stresses may occur in other drive train components as well (transmission shafting, drive shaft, axles). The values of the critical RPMs depend on the rotating weights (especially the flywheel) and the torsional stiffnesses throughout the vibratory system. Torsional stiffness may be visualized by considering a break over bar wrench with a long extension and trying to turn a stuck nut. You can see the long extension deflecting torsionally. A 3/8 extension would deflect torsionally more than a extension the same length and the same torque. Now imagine this kind of thing going on at the crankshaft rod and main journals, driveshaft, and ect. Counter weights added to a Model A crankshaft would lower the critical RPMs. A lightened flywheel would lower the critical RPMs, probably a lot. Having a larger main and or rod journal (as in a Model B engine) would increase critical RPMs. At a critical speed, or resonant condition, where the firing impulses are nearly the same as the natural torsional vibrating frequency of the drive line, torsional amplitudes (and stresses) with zero damping theoretically reach infinity. Fortunately, there is always some damping such as within the metal of the components and within the rod and main journals due to the oil film. Damping always reduces amplitudes (and stresses). This is why a viscous damper is often added to the front of the crankshaft of an engine. Often this vibration (or harmonic) damper consists a rubber ring whose ID is essentially bonded to the crankshaft and whose OD is bonded to the ID of a floating outer steel ring. The size and weight chosen for this steel ring can also reduce torsional amplitudes (and stresses). As Murray said, his harmonic damper may not be right for your engine. However, if your engine has crankshaft counterweighting and a lightened flywheel similar to his flywheel, I would bet it would help your torsional vibrations. By “similar to his flywheel” I am speaking not only of the lighter weight, but where the weight was removed (more at near the ID, near the OD, uniformly, etc).
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Old 08-12-2017, 04:58 PM   #23
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Default Re: Noisy metal timing gear cured by torsional damper

Quote:
Originally Posted by CarlG View Post
Well, let's open another can of worms.

What effect, if any, would having one of Murray's dampeners on an engine already fitted with one of the dampers that Ron Kelley puts on the front face of the flywheel?
I have seen a flywheel with a built in dampener and not only does the one I've seen look a complex piece of equipment, but it also means engine out to fit it and possibly re-balancing the engine?
The Murray Horn dampener simply requires the replacement of the pulley and in my experience has been totally effective.
I have a seriously lightened flywheel and a Burlington Counterweighted crankshaft
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Old 08-13-2017, 06:44 AM   #24
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Default Re: Noisy metal timing gear cured by torsional damper

Thank you Dave and Bill for adding very interesting extra information and observations to this thread.
The Rattler dampers are very expensive compared with the $300 rubber dampers Murray Horne makes.
As pointed out, his pulleys may not be perfectly tuned to the two different engines I put them on, whereas the Rattlers, (which act much like dyna beads do in an unbalanced tyre), are specific only to different engine layouts. So i-4 cylinder ones, for instance will work in any vertical in line four engine without special further tuning. So the result will likely be better but at a much higher cost than a rubber damper not specifically tuned to a given flywheel and crank..
The results in my roadster and Wensum's speedster on quelling the aluminum timing gear rattle were dramatic. In my wife's Tudor which had unpleasant lower frequency "noise vibration and harshness" at about 53 mph, the improvement is also gratifying. Our 3 engines are quite different. Tudor has about 6:1 compression, welded on counterwights and a somewhat lightened flywheel with standard clutch. Roadster has heavier pressed and pinned crank bob weights, 6.5 to 1 compression and lighter flywheel with V8 clutch. Wensum's has Burlington crank and even lighter flywheel from what he told me. Plus higher compression again.
The fact that the same type of harmonic balancer pulley produces very noticeable and worthwhile improvements on these 3 very different motors is fortuitous and leads one to wonder what further improvements could result from more thought, analysis, experimentation -and money.
I hope you continue to report your experiments Dave, though I fully realise as a commercial engine rebuilder, you are entitled to retain "trade secrets" to gain commercial advantage over less diligent builders or those with less curiosity and desire to improve this 90 year old engine.
And Bill, I would be interested to hear more of your experiences and more theory. We have not talked much about viscous fluid and steel shot dampers yet. Are their other types too?
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Old 08-13-2017, 09:39 PM   #25
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Default Re: Noisy metal timing gear cured by torsional damper

Ooops. I proofread my writup (#22) but I should have done it twice.
" A lightened flywheel would lower the critical RPMs, probably a lot"
Should read, " A lightened flywheel would RAISE the critical RPMs, probably a lot".
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Old 08-14-2017, 01:48 AM   #26
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Default Re: Noisy metal timing gear cured by torsional damper

Ha ha Bill. Yes noticed that but many are far too picky and love to jump on mistakes. As you said the heavier crank with weights lowers the frequency and in both my cars I suspect this may have moved the resonance into the driving range where it might not be heard at cruising speeds without the weights on.
Both cars have 26% Mitchell o/d s. So 55 mph is about 2000 rpm from memory in the roadster and 2100 rpm in the Tudor with V8 wheels- right on the critical revs for harmonic vibes.
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Old 08-14-2017, 09:48 AM   #27
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Default Re: Noisy metal timing gear cured by torsional damper

[QUOTE=BN;1513066]Ooops. I proofread my writup (#22) but I should have done it twice.
" A lightened flywheel would lower the critical RPMs, probably a lot"
Should read, " A lightened flywheel would RAISE the critical RPMs, probably a lot".[/QUOTE]


That is exactly what I discovered with my dyno and actual driving tests in March of 2013. I had a difficult time detecting the vibrations when the engine and flywheel/damper variations were on the dyno during the tests. In the car, the results were much easier to "feel".
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