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Old 12-04-2020, 01:35 PM   #21
Dave in MN
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Default Re: Dynamic dampening front pulley

Changing the belt: While on a long road trip and about 2,400 miles before I made it home, I started to hear a “chirp” every time the alternator started to charge. The belt had worn narrow and would no longer engage with the sides of the pulley on the alternator. Tried my best to get the spare belt past the cross member and u-bolts, the dampener pulley was just too close. I removed the front u-bolt nuts, raised the bolts to allow them to tip sideways from the crank guide. This allowed me to slightly raise the crank guide and push it forward slightly giving me the clearance I needed to get the belt in place. With the weight of the car on the front spring, nothing moved out of position and reassembly was quick.

Vibration:
When I installed the dampener pulley, I estimate the rpm range of the felt vibration narrowed to about half but it did not totally eliminate it.
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Old 12-04-2020, 10:41 PM   #22
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Default Re: Dynamic dampening front pulley

This is my favourite theme, and I can only reiterate that Murray Horne's harmonic dampener worked miracles on our modified engine which had been scrupulously balanced, eliminating a loud timing gear rattle and the vibration periods of the motor.
It made the biggest single improvement to the driveability to our car.
Most modern cars have similar devices of a similar size
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Old 12-05-2020, 12:20 AM   #23
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Default Re: Dynamic dampening front pulley

I also have wrangled a notched B section belt under the pulley. It's not an issue in my mind.
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Old 12-05-2020, 04:41 AM   #24
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Default Re: Dynamic dampening front pulley

I agree with Wensum and Dave in MN. Much of the clatter in my aluminium timing gear was reduced. But not all. As Pete says the balancer could do with being heavier but there is not much room.
In our 31Tudor a belt could possibly be finagled though the gap, but no way would one fit through on our 30 roadster. So I carry a segmented spare belt on this one.
The Tudor had almost subliminal crank torsional wind-up noises to my old ears. Almost gone with the harmonic balancer pulley. Passengers cannot hear anything but years of driving Model A's let me sense the crankshaft vibes as they come and go through certain rev ranges. Or maybe the tinnitus and crickets in my ears is fooling me!!
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Old 12-09-2020, 09:18 AM   #25
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Default Re: Dynamic dampening front pulley

With the engine and radiator in place, and using a front float a motor, are you able to take the old pulley out and replace it with a Murry?

I might have just found my answer from Patrick, YUCK.

"Changing the crank gear in the vehicle can be done with some difficulty. The front of the engine needs to be jacked quite high. The radiator needs to come out, the rear motor mounts need to be loose and the one mount bolt on each side should be removed. The gear is really on the crank and usually takes serious heat and a real puller to get off. When putting the new gear on, do not beat/pound the gear on. Press it on. I use a length of turned pipe closed and drilled at one end so a bolt the same thread size as the crank can be used to press/push the heated gear on."

Last edited by old31; 12-09-2020 at 09:30 AM.
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Old 12-09-2020, 10:30 AM   #26
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Default Re: Dynamic dampening front pulley

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Old31, As you can see in my picture there is not enough room to get the stock pulley off and especially not enough room to install the Murray Pulley.

I had to jack up the engine plus I removed the front spring ubolts to give me more room. I also replaced the broken hand crank guide a this time.



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Old 12-09-2020, 11:03 AM   #27
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Default Re: Dynamic dampening front pulley

Pulley cost?
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Old 12-09-2020, 11:15 AM   #28
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Default Re: Dynamic dampening front pulley

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Pulley cost?
I believe I paid ~$300 including shipping from New Zealand. That was a couple of yeas ago.

One of the features I really like is the reverse scroll on the snout that stops the front seal from weeping oil.

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Old 12-09-2020, 11:43 AM   #29
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Default Re: Dynamic dampening front pulley

Be very careful installing any crankshaft pulley or balancer on an engine with a babbit thrust bearing.
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Old 12-09-2020, 05:47 PM   #30
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Default Re: Dynamic dampening front pulley

Jack, how would you know if you had a babbit thrust bearing and the type of front seal that you have?

The bottom line is I blew it, I should have installed the balancer when I installed the engine.
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Old 12-09-2020, 06:06 PM   #31
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Default Re: Dynamic dampening front pulley

I checked with Murray Horn. With shpg to US $336
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Old 12-09-2020, 06:21 PM   #32
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Default Re: Dynamic dampening front pulley

Quote:
Originally Posted by Jack Shaft View Post
Be very careful installing any crankshaft pulley or balancer on an engine with a babbit thrust bearing.
Never heard of this before. Please explain.
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Old 12-10-2020, 08:22 PM   #33
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Default Re: Dynamic dampening front pulley

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Never heard of this before. Please explain.
He is referring to hammering a pulley or damper on instead of using the proper
"puller".
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Old 01-24-2021, 10:43 AM   #34
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Default Re: Dynamic dampening front pulley

Well, the dampening pulley finally came and I installed it a few weeks go. I am going to report on the results in three posts. The first post will be some background theory that I uncovered while waiting for the dampener. The second post will explain how I installed the new pulley, and the last post will be the results.



So here is the first post: Warning: Technical discussion following.



The crankshaft experiences torsional vibration AT ALL ENGINE SPEEDS and the vibration can be several different modes at the same time. At certain rpm’s the vibration can be more extreme due to the exciting pulses matching a resonate frequency of the crankshaft. The resulting torque on the crankshaft can be 6 to 10 times the amount of torque going out the end of the engine to drive the car. For the Model A, the natural resonance of the crankshaft can be within the operating engine rpm depending on how fast the engine is revved, but there is always torsional vibration present.



The flywheel rotates at a more or less constant speed while the front end of the crankshaft can be torqued 1 degree or more. The torsional vibration can lead to a broken crank and can reduce the life of bearings, camshaft gear, cam bearings, and variation in ignition timing. The maximum torque on the crankshaft due to torsional vibration is at the rear bearing.



The stock flywheel rotates as a very constant speed because the node point (where there is no torsional movement of the crank) is right at the flywheel. For a lightened flywheel the node point moves forward so the flywheel now experiences some torsional vibration. A counterbalanced crankshaft will lower the natural frequencies somewhat but will add to the overall torsional deflection at the front of the crankshaft.



The dynamic dampener pulley consists of three parts: The hub which is pressed onto the end of the crankshaft, the inertia disk which is a heavy disk mounted to the outside diameter of the hub, and the rubber that connects the two. The dynamic dampener has its own natural frequency, the rubber acting like a spring. The natural frequency of the dynamic dampener is designed to counteract the natural frequency of the crankshaft. It applies a counter torque at the end of the crankshaft that dampens the crankshaft. There is some energy absorbed by the rubber but the main action is a counter torque due to the resonance of the dampener. The dampener has to be designed to fit the engine. It does not have to be especially large but it does have to have the proper natural resonance. Computer modeling and vibration testing is used to design the dynamic dampener. This is not something that an average Model A owner can do.



The hub of the dynamic dampener has to be a press fit on the end of the crankshaft so that the hub and the end of the crankshaft work in unison. The rubber is molded between the hub and the inertia disk and has to be the right durometer, compound, and configuration. There is a lot of science built into each dynamic dampener. The rubber compound will determine the life of the dampener and is a closely guarded secrete held by the manufacturer.



Most of this information came from an article in the “Vintage Speed & Sport Secrets Magazine”, volume 23, number 4, April 2014, which in turn is referencing a white paper by William C. Sisco for BHJ Dynamics. (Note: when I tried to visit their website I got a security risk notice.)
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Last edited by nkaminar; 01-24-2021 at 10:49 AM.
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Old 01-24-2021, 10:48 AM   #35
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Default Re: Dynamic dampening front pulley

Installing the dynamic dampener was fairly straight forward. I had to jack up the front of the engine after removing the radiator using a floor jack and a block of wood. I removed the two main bolts from the rear Float-A-Motor mounts and removed the two bolts supporting the front of the engine on the stock front engine mount. I used a puller to pull off the old front pulley after removing the crank nut. I used the correct socket wrench with a breaker bar and put the car in high gear with the overdrive in high. I put the parking brake on and blocked the rear tires.

The dynamic dampener is larger than the old front pulley, see the first picture. This will increase the rpm of the generator or alternator and water pump/fan. I put the fan belt on before lowering the engine. I have not tried to replace the fan belt but it looks like it will be impossible without jacking up the front of the engine.



It is important not to hammer on the dynamic dampener as this will damage the thrust bearing for the crankshaft. I used a series of bolts that fit the thread of the crankshaft (5/8-18), each 1 inch shorter than the last, to push the dynamic dampener onto the crankshaft, see second photo. I carefully lined up the notch in the dynamic dampener with the key on the shaft nose and used a roller bearing underneath the bolts to keep the dampener from turning on the crankshaft and getting out of alignment. I used one then two roller bearings before switching to the shorter bolt.

The dampener went on fairly easily. It is important to have a press fit for the dampener and to tighten the crank nut securely. After getting the dampener on I lowered the engine and put the bolts in for the mounts. The bolts for the Float-A-Motor are just snugged up, not very tight.
Attached Images
File Type: jpg Pulleys.jpg (47.8 KB, 50 views)
File Type: jpg Bolts.jpg (40.4 KB, 41 views)
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.

Last edited by nkaminar; 01-24-2021 at 10:56 AM.
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Old 01-24-2021, 10:48 AM   #36
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Default Re: Dynamic dampening front pulley

Quote:
Originally Posted by nkaminar View Post
which in turn is referencing a white paper by William C. Sisco for BHJ Dynamics. (Note: when I tried to visit their website I got a security risk notice.)
I think this is the white paper in question.
BHJDynamics_Damper_Info.pdf
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Old 01-24-2021, 10:50 AM   #37
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Default Re: Dynamic dampening front pulley

It took me a couple weeks before I could test the dynamic dampener as I has some other issues with the car and had to wait for parts.

Before the dampener I had a torsional vibration issue at about 2,400 rpm. Since installing the dampener I have run the engine up to 3,000 rpm with no torsional vibration issues. I feel that this was a good investment for my engine. It runs nice a smooth now. I have a counterbalanced crankshaft and insert bearings with a high volume oil pump.

If you are running a stock Model A at 45 to 50 mph, you may not feel the need for a dynamic dampener. If you are running a higher performance engine and drive at 60 or so you will definitely want a dynamic dampener. Even the stock engine could benefit from one as the crankshaft has torsional vibration at all engine speeds, even if you don’t feel the vibration. Although stock engines have run for 90 years without a dampener so the choice is yours. The major drawback is the difficulty in changing the fan belt.
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.
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Old 01-24-2021, 10:51 AM   #38
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Default Re: Dynamic dampening front pulley

Alex, Thanks, yeah that is it.
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A is for apple, green as the sky.
Step on the gas, for tomorrow I die.
Forget the brakes, they really don't work.
The clutch always sticks, and starts with a jerk.
My car grows red hair, and flies through the air.
Driving's a blast, a blast from the past.
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Old 01-24-2021, 10:51 AM   #39
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Default Re: Dynamic dampening front pulley

Quote:
Originally Posted by nkaminar View Post
I have not tried to replace the fan belt but it looks like it will be impossible without jacking up the front of the engine.
A lot of folks who use these dampers switch to link belts for this reason.
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Old 01-24-2021, 12:17 PM   #40
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Default Re: Dynamic dampening front pulley

Quote:
Originally Posted by alexiskai View Post
A lot of folks who use these dampers switch to link belts for this reason.


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