I came across a problem today I haven't seen before. Maybe I have just been lucky so far. Any way I was putting together a Super Combat lower engine assembly. Everything cleaned up good and went together just fine except for the clutch. Actually the clutch assembled normally but the problem showed up when I rotated the crankshaft with the clutch installed. As I rotated the crank you could see a very noticeable amount of clutch lateral run out / wobble. I checked to see if the clutch was installed properly on the crank and all looked good. Removed the clutch and rotated the crank and it rotated true.....it should I just rebuilt this crank. Thinking a spring might have fallen out of place I measured the clutch assy thickness in several places and it was within a couple thousands of being the same so no problem there. Dis-assembled the clutch and all looked good. I slipped the below pictured clutch hub on the crank and while watching rotated the crank. And there was my problem. The clutch hub had a significant amount of lateral run out / wobble.
I put a straight edge on the flat surface and held it up to the light to find the low spot. Checking with feeler gages the hub was out of true roughly .015 inch. Keep in mind the diameter of the assembled clutch is greater than the hub diameter so the error is greater at the outer clutch edge.
I don't think the clutch hub was bent at some point as it is such a sturdy part. I am thinking it was a manufacturing defect. Two problems at least would be apparent with this condition. Excess engine vibration and poor alignment with the clutch disc. The clutch would be side loaded when applied due to the misalignment and not perform or wear well. So looking for a replacement hub in my stash of parts tomorrow.
It would be interesting to know the machining operation order which was used in the production of the clutch hub. The only way I can imagine to produce a hub with a wobble as described would involve doing all the "facing" operations, then using the freshly machined face as a reference surface to guide the broaching operation to create the splines. In that way, a mis-aligned machine or a bit of contamination between the hub and machine table could cause the splines to be created at a slight angle "off" from the desired 90 degrees to the "face".
Just an up date. Found another clutch hub and it was straight and true. With that I was able assemble the clutch and now it runs true with the crank. I have a couple of projects going right now so I set the bent hub aside and will examine it a little closer later.
Ed, I don't think the hub broached splines are out of square. It appears the flange has the run out. The flange also has the spring seats. I can set it up on my bench center later and find out exactly what is bent or out of alignment.
