Flywheel Wobble Check

R

Ron/IA

Well-known member
The Mechanics Handbook Vol. 1 illustrates checking the wobble of the flywheel when installing it and the flywheel housing variation measurement; pages 2-22 & 2023

In the service bulletins on page 218, it states to check flywheel eccentricity and wobble; both the rear face of the large diameter and the rear hub of the flywheel.

I have looked up the description of eccentricity, but I am not smart enough to apply it to the flywheel. Would eccentricity and wobble mean the same thing? If so, why do the service bulletins specifically point both out? Also, what part of the flywheel is the rear hub? Or are they trying to refer to the crankshaft flange?

Inquiring minds want to know!
 
Eccentricity is done on the exterior curved surface of the flywheel - a "radial" measure.

Wobble is done on the flywheel surface where the clutch disk is applied. - an "axial" measure. And done at the largest diameter it can be done at.

One does well to check the flange for the crankshaft before even getting to the flywheel. A VERY small amount of wobble here will be magnified in the flywheel. Eccentricity not so much - but still worth checking.

And one would do well to check that the flange rotates true to the rearmost bearing of the crank. Mine did, but the center was not true. Neither was the face. So I trued both of these at home on the lathe.

Then brought both flywheel and crank (and front pulley) back for a re-balance - at their cost.

Some people, even those in the trade, just don't have a clue.

Joe K
 
Joe - Excellent reply; I thought that is what was being implied. I have been going through the engine with a fine tooth comb; weighing connecting rods and pistons within 0.1 grams, and balancing as many rotating components as possible.

Before I had much vibration in my drive train; I am anxious to see what it will be like when I get it back into the car.
 
Hi Ron,
I don't have the handbook in front of me right now, but there are two things you have to watch for. One is just plain old runnout along the OD of the flywheel. One or two thousandths of an inch is OK, but more than that is trouble. The "wobble" is eccentricity, or Z-axis runnout, measured on the face of the flywheel as it is rotated. Again, more than 0.002 is probably more than you want to see.
The wobble could be caused by eccentricity, z-axis, on the flywheel flange of the crankshaft, or it could be caused by distortion of the "hub" of the flywheel itself.
Locating the actual cause can be tricky, and fixing it even more elusive. I had a friend who had both problems in the flange-to-hub connection between the crankshaft and flywheel, and after cleaning of the flywheel hub and tool-post grinding of the crank flywheel flange he had 0.005 runnout and about 0.003 wobble. Being the inventive guy he is, he put the crank/flywheel assembly on his engine lathe and trued the flywheel to the axial center of rotation of the crankshaft. This also required that he bore the pilot bearing out, bush the hole, and reinstall the pilot bearing on center. It was a lot of work, but the engine runs as smooth as cream.
I wish you luck with it...
 
Chris - Thanks for the info. Your run-out dimensions are tighter than the red book and the service bulletin, but I will strive for the closest tolerance I can get.

The + or - of the rod and pistons weights is 2 grams. I was able to get them within + or - 0.1 grams. I am confident I can beat the recommended tolerances for the flywheel wobble.
 
Ron/IA said:
Chris - Thanks for the info. Your run-out dimensions are tighter than the red book and the service bulletin, but I will strive for the closest tolerance I can get.

The + or - of the rod and pistons weights is 2 grams. I was able to get them within + or - 0.1 grams. I am confident I can beat the recommended tolerances for the flywheel wobble.
Click to expand...


Think about it this way, 63 lbs jumping up and down .005 at 2000 rpm. That will make a lot of vibration. I think new the speck was .0005 run out. That is not much. The average human hair is around .003. I would not let it go over .001
 
Here's a couple pictures showing how to do the measurments. I just set this up for the pictures about 10 years ago. I would have the engine in the engine stand, and have the front of the engine pointed down, so the crankshaft end play doesn't mess up the readings. I take the flywheel cover readings at the 9, 12, and 3 o'clock positions and get it .006" or less. I also have the top two bolts tight when I take the readings.

I have another picture showing me checking the flywheel clutch face for runout, but that picture must be on my old computor.
 

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