Does flywheel need to be balanced

O

oldford

Senior Member
My engine seems to vibrate more than it should. I will be removing engine to work on transmission. Since engine is out would it be a good time to balance the flywheel just in case that is the problem. The front engine supports are new and are very soft.
 
Yes, now would be a good time to do that. You should balance both the flywheel and the pressure plate together. There should be marks on each to line up so that they are reassembled with the same orientation as they were when they were balanced.
 
It should not cost too much to have it done. I lived near Edelbrock, so I think mine is about the best I could have.
 
So as an engine rebuilder, my advice is a little different. Unless you have a way to balance the Crankshaft first (-followed by adding the Flywheel and then adding the P/P) you have no assurance you are actually going to improve your excessive vibration situation. In reality, you could potentially worsen your harmonic ranges.
 
I agree with Brent. You should also consider rebuilding your ujoint. This could be where most of your vibration is coming from.
 
something i have never done on a stock flywheel.

there are lots of things that can make it vibrate how bad is it and how deep do you want to dig.
 
I agree with Brent too. Normally the flywheel/pressure plate/crank are done as a "unit."

Be careful the balancer/machinist doesn't "squeeze" too hard between centers and permanently deform the crank.

Joe K
 
BRENT in 10-uh-C said:
So as an engine rebuilder, my advice is a little different. Unless you have a way to balance the Crankshaft first (-followed by adding the Flywheel and then adding the P/P) you have no assurance you are actually going to improve your excessive vibration situation. In reality, you could potentially worsen your harmonic ranges.
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I was under the impression that the crank and the flywheel assembly could be balanced separately.
 
Through the years many crankshafts have been ground a little off center ( possibly even a lot) a flywheel balanced separately is centered by the pilot bearing hole.
If the pilot bearing hole has runout when mounted on the crankshaft it will not be balanced correctly to the crankshaft if it was balanced to the center of the pilot bearing.
 
alexiskai said:
I was under the impression that the crank and the flywheel assembly could be balanced separately.
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Yes, you are correct. I typically balance the Crankshaft first. Then I bolt on the Flywheel to the balanced Crankshaft and use the Crank as my mounting mandrel. Next we balance the Flywheel. While the goal is to balance Crank as close to 0 as possible, if I am at say 2 grams, I might try to get the assembly closer to 0 because of the Flywheel size allows me to get closer. Then when I am there with the Flywheel & Crank as a package, I add the Pressure Plate. (-most of them are horrible.)
 
I am in agreement with balancing every rotating part and also making the pistons all the same weight and the big ends of the rods all the same weight and the little ends of the rods including the wrist pins all the same weight. But even a perfectly balanced Model A engine will vibrate depending on if it has counter balance weights on the crankshaft. Even an engine with counter balance weight will vibrate. This is a characteristic of an inline 4-cylinder reciprocating engine.

Why? At the bottom and top of the piston stroke every mass is changing direction. This include the piston, the small end of the rod, and the large end of the rod. A counter balance would have to be large enough to counteract the momentum off all the parts. But when the piston is about midway down the cylinder the counterweight would only have to counteract the momentum at the big end of the rod. The pistons and the small end of the rods are in a uniform, unchanging motion.

So the counterweights are a compromise between what is needed at the top and bottom of the stroke and what is needed at the mid point. Usually it is 100% of the mass at the large end of the rod and about 67% of the mass at the small end of the rod, including the piston, piston pin, and rings. No inline engine is 100% balanced by the counterweights. A 90 degree V engine can be almost 100% balanced.
 
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If you are trying to eliminate the endemic drive train vibration between 36 and 39 MPH, good luck. No matter what you do to that three-main bearing crankshaft and flywheel/pressure plate, the Model A's four cylinder engine has an inherent vibration between those speeds, give or take one or two MPHs. Those engines have been that way since they left the factory and the vibration is just part of the Model A personality. By careful balancing and matching parts (maybe even adding a harmonic vibration dampener to the pulley), you might be able to lessen the vibration or move the vibration range up or down, but because of the whipping effect of the three-main bearing crankshaft with the center main as the fulcrum point, I doubt you will be able to completely eliminate that RPM vibration.
I wonder if the Burtz five-main bearing crankshaft has eliminated this vibration range? If anything can do it, a five-main bearing crankshaft ought to do the job!
Marshall
 
Thanks everyone. Now I just need to decide how far I want to go. I did remove the oil pan to make sure everything looked OK. It had been rebuilt in the past as the bore and bearings all looked good. Unfortunately, the crank did not have any counter weights on it so I will probably have to live with the vibration. If I can find a shop that will balance flywheel I may just do that. Taking the engine apart to remove crankshaft is way to much work.
 
The right way is as Brent has said above. Balance the Crank, then the flywheel mounted to the crank, then the pressure plate. That said I would check the flywheel balance while you have it out not knowing the history of it. It its out of wack you should see some inprovement as long as someone didn't use it to correct the crankshaft balance.
And who knows how many engines that flywheel has been on in the past.
 
Brent Terry and Marshall V. Daunt are correct.

1)Balance the crankshaft first.
2)Add the flywheel and balance the assembly by only removing weight from the flywheel.
3)Add the pressure plate and balance the assembly by only removing weight from the pressure plate

The new engine crankshaft is made from nodular iron which does not have harmonics (It will not ring like a bell when struck) and the 5 large diameter mains eliminate flexing and spring-back.
 
Aha! So, Terry DID solve the Model A's age-old vibration problem! If one lone guy like Terry working out of his garage (presumably) was able to come up with this solution with his five main bearing crankshaft crammed into the Model A engine block, how's come the entire FoMoCo engineering department couldn't come up with the same answer in 1927 when designing the Model A? How much more money would it have cost the company to have created and installed a five main bearing crankshaft in the cast enblock Model A engine? Terry did it! Maybe if Ford had done this, the Model A could have enjoyed a longer production period, especially if along the way, Model B engine upgrades had been added. A vibrationless four cylinder Ford engine with 50 HP (Model B) might have been competitive until 1933 or 1934! 'Guess we'll never know, though...
Marshall
 
Ford chose to believe not in the engineering when the Model A engine was developed
Harold Hicks alerted Ford that the
crank was not rigid enough to prevent pounding on the center main
He was ignored and the Model B came about in 1932 production

John
PS balancing to "zero" is not necessary
Follow the ISO balancing specifications which take rpm into account
 
Oldford, I must have a warped mind as I find it enjoyable to take things completely apart and rebuild them, including the engine. To me it is not work but a fun part of the hobby.

My stock coupe that I drove all over California in the 1960's would vibrate a lot above 50 mph. Back then the traffic was not going 80 to 100 mph so 50 to 55 mph was OK. I drive at 70 mph with my modern car but got passed the other day by a couple of motorcycles that were going at least twice my speed. Today I stick to the back roads while driving my Model A when I can. My club drives at 45 mph while on tours.
 
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Terry Burtz said:
Brent Terry and Marshall V. Daunt are correct.

1)Balance the crankshaft first.
2)Add the flywheel and balance the assembly by only removing weight from the flywheel.
3)Add the pressure plate and balance the assembly by only removing weight from the pressure plate

The new engine crankshaft is made from nodular iron which does not have harmonics (It will not ring like a bell when struck) and the 5 large diameter mains eliminate flexing and spring-back.
Click to expand...


As I said, balance the entire rotating assembly. You don't need to be a genius to figure this out. Any competent automotive machine shop will do this without question.
 
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