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Old 09-06-2013, 02:22 PM   #41
Bob Johnson
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Default Re: What causes deceration vibration

Mike my post #20 08-29-2011 04:41 PM says:

"I just checked the flywheel for wobble. I took out the starter and measured with a dial indicator.

For the front to back wobble I took the measurements on the front face of the flywheel inside of the ring gear (not on the ring gear). I measured every 45 degrees. Before each measurement I made sure that the flywheel/crank was pushed rearward to eliminate the thrust play. The results were 0, 0, 1, 2, 1, 0, 0, 0.5 all in 1/1000th of an inch.

I made a tool to measure the side to side wobble through the starter hole. I measured just in back of the ring gear. I again measured every 45 degrees. The results were 0, 0, 0, 1, 0, 1, 2, 2 all in 1/1000th inch."


I think that means that flywheel run out is not the problem. The flywheel crank and clutch were dynamically balanced.

Mr. Bear;
The valve springs were replaced with new ones at the recent rebuild. I check the spring for proper tension before installing them.

usurs;
The vibration occurs with the card not moving, clutch in or out which means it is not the transmission.

I have driven many Model As and I know that vibration is normal for a 4 cylinder engine. However this one has too much vibration as compared to others.

Thank everyone for the suggestions. Still looking for a solution.
Bob
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Old 09-07-2013, 08:25 AM   #42
Chris in CT
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Default Re: What causes deceration vibration

question:

Is there a way to isolate the source of the vibration WITHOUT removing the engine from the car? Note that all parts were balanced before the engine was assembled. Pistons and rods statically, crank, flywheel and clutch dynamically.


If I had the money and time it would be interesting to take an engine that was running very smooth and experiment with balancing. Adding weights, one at a time, to various parts, flywheel, clutch, crank, pistons, rods ... and see what vibrations show up. Then one could find out what various amounts of imbalances produce vibrations.

Bob[/QUOTE]

Yes, you can do a Fast Fourier Analysis of the vibration in your engine, an expensive, time consuming operation if there ever was one. Two channel, with sine and cosine functions covered would be best, with magnetic trigger that measures the exact position of the crankshaft with the reading of each harmonic peak in the rotating system. If you had the time and money, and could get the assistance of someone who knows how to set up the system, you could in fact determine exactly where the vibration is coming from. Here is the problem: you may find out where it is coming from, but there is no guarantee you could eliminate it. To balance the sine function in an I-4, you could very well unbalance the cosine function at the same time. Its one of physics' little jokes on us all.
Enjoy your Model A!
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Old 09-08-2013, 08:05 PM   #43
amishman
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Smile Re: What causes deceration vibration

Deceleration vibration really bothered me a lot, and a friend says it's a Model A, what do you expect? My first A was a 31 Roadster with a new rebuild from AER in Skokie IL, it had a 5.0 head, and balanced crank. I had my 1930 Townsedan rebuild this last winter with AER also, this one with 5.5 head, Burlington balanced crank, larger intake and exhaust valves, and Stipe .340 cam. The deceleration vibration was about the same. But let me tell you this, because I don't understand all of the physics talked about above, Last weekend I installed the Weber downdraft carb. and First Street electronic ignition and the vibration is gone. Most might not believe this, but it is true I think I'd read something like that in a post before. This weekend weekend we put in the Mitchell overdrive transmission. My wife can't believe it's the same car, she thinks driving from Michigan to Tacoma won't be so bad after all. Hope to meet some of you Fordbarners from the West Coast next summer.
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Old 09-08-2013, 08:56 PM   #44
steve s
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Default Re: What causes deceration vibration

Amishman,
Check out my explanation on post #9. If the Weber setup lets in more fuel during deceleration, that would explain it.

Steve
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Old 09-08-2013, 09:24 PM   #45
Pete
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Default Re: What causes deceration vibration

Posts numbered 5,9,25,32 and 44 pretty well cover it.
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Old 09-09-2013, 11:21 AM   #46
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Default Re: What causes deceration vibration

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So is type of vibration detrimental to the engine?
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Old 09-09-2013, 08:00 PM   #47
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Default Re: What causes deceration vibration

Quote:
Originally Posted by Duffy1 View Post
So is type of vibration detrimental to the engine?
Definitely not.
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Old 12-11-2017, 08:17 PM   #48
markbartlett
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Default Re: What causes deceration vibration

Question how long was the car without engine just sitting in the weather my bet also is the u joint
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Old 12-23-2017, 01:18 PM   #49
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Default Re: What causes deceration vibration

I have a 29 Model A with 600 miles on a rebuilt engine, it also has a substantial engine viberation on decelaration exactly as you described under the same conditions you described. Some years ago I had a stock 30 Model A that vibe rated only slightly under decel. I also have owned 1954 6 cyl Plymouth that vibe rated on decel. My Dad had given it to me because he thought it had a broken crankshaft. Long story short , the flywheel was lose on the crankshaft . Tighten flywheel and viberation was completely gone. Have you been able to lesson or almost elimate your viberation? Do you know if anyone has ever put a harmonic balancer on a Model A engine?
Eddie Condrey
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Old 12-23-2017, 01:56 PM   #50
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Default Re: What causes deceration vibration

Hey Mr Ed, Welcome to the barn.
Do a search for the "harmonic balancer" I believe this has been discussed in the recent past. I think the guys in New Zealand and Australia may have a source for them.
Jeff
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Old 12-24-2017, 10:33 AM   #51
roy green coupe
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Default Re: What causes deceration vibration

While observing my running engine on my 30 coupe, I noticed the belt seemed to be going through a harmonic vibration at certain rpms.I first thought the crankshafts pulley was the problem as the belt seemed to run in and out some.I did notice the belt was rather loose and had been reluctant to tighten it not wanting to put excessive load on the water pump.I was trying to leave well enough alone but I overcame that and decided to order and install the brace for the generator and tightened the belt.I was surprised when the belt now seemed to run smooth and true on the crankshaft pulley .I was also able to notice the engine seemed smoother in high gear at speed.I have read where others have taken the belt completely off for a short test.I think think the high placement of the fan and water pump magnify their vibrations.I have wondered if slowing down the fan speed with different size pulleys would accomplish some of the benefits people talk about with overdrives.
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