Higher RPM Engine vibration?

[29ModelA]

Where should I start looking for a pretty significant engine vibration? I know my crank pulley is slightly bent and I plan to start there, is there a way the flywheel assembly can get out of balance?

[Kurt in NJ]

Have you checked the rear motor mount bolts to see if they are tight?

i have seen other engines that vibrated because they had an xtra 5 quarts of oil in them.

The flywheel won;'t start vibrating when it didn't before --unless it is coming loose on the crank, or something came apart in the clutch and has moved ---but then the clutch probably won't work properly ---or perhaps a big collection of gook is on the inside of the flywheel --and some fell off and made a big lump on 1 side

the rear main can be coming apart ---that usually has other noises along with vibration

the clutch pilot bearing can come apart and then the clutch disc and trans mainshaft can be off center and cause vibration ---but you may have other symptoms like coming out of gear with such failures.

[Geo. H]

There are several ways the flywheel assembly can get out of balance. The car is over 80 years old, isn't it? In that time the clutch has probably been changed, the crank may have been ground off center, the pistons replaced with new ones not weight matched, etc. Henry did a good job of weight and balance. Most of the "mechanics" who've worked on it since hadn't a clue what the original spec's were.

[James Rogers]

I sell the lightened flywheel assemblies that are done in my shop. The only part of the process I don't do is the balance which is done in a race shop. I have watched him balance totally stock and my modified flywheels and I don't even like being in the room with him when it is going on. Almost every flywheel we balance is out some more than others. This is after the flywheels are cleaned and bead blasted to spotless so there is no accumulation of oil and dirt to affect the balance. Many of my customers can't believe how much vibration they eliminate just by adding the balanced flywheel.


Kurt is right about the accumulation of dirt and oil in the front of the flywheel. I have found many that had as much as 1/2" of buildup un the front crevice. The flywheel is like a large centrifuge that throws all the dust and dirt that lands in it to the outer ring and sticks there if there is even a minor leak at the rear main. All rear mains I have looked at leak some even if it is just a very small amount.

[Jim Brierley]

At what RPM? These engines have a natural vibration at several RPM's. 2300 is the worst one, 1800 next down the list. Most are rarely felt but they are there.

[29ModelA]

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Originally Posted by Jim Brierley

At what RPM? These engines have a natural vibration at several RPM's. 2300 is the worst one, 1800 next down the list. Most are rarely felt but they are there.

That is actually about where they are once I hooked a tach up. They felt horrible compared to what I am used to. Then again, I also don't have an interior or anything in it yet to deaden anything.

[Bill Stipe]

Yes Jim Brierly is right on there!
When I dyno test many times we will get a grumbly vibration in the 2000 to 2300 area, say 2100 RPMs as it passes through and then goes away as quick as it comes.
Todays pistons are too heavy which does not help.