Listen to your main bearings.

Joined
Oct 19, 2006
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#1
I think my main bearing was bad and that is what took out the flywheel weight on the bike, not the other way around. I put the bike back together with new main bearings and took it for a test ride today. Before, when I chopped the throttle at high speed, the bike would make a little bit of a knock, nothing that bothered me too much. I assumed it was from the pipe. But, with the new main bearings, the knock is gone. I think what happens is that when you chop the throttle at high speed, the cylinder pulls into a vacuum momentarlily and that pulls on the crankshaft. At all other times, there is always a downwards force on the crankshaft. If there is any loosness in the bearing during this pull, it will knock as the load changes from the bottom to the top. After the flywheel weight broke, I could feel some looseness in the bearing. You couldn't actually see the flywheel move when you pulled it, but if you jerked it, it would knock. I split the bearing with a grinder and no races showed any major signs of wear, but it was slightly loose.
 
Joined
Apr 26, 2007
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#2
76GMC1500 said:
...You couldn't actually see the flywheel move when you pulled it, but if you jerked it, it would knock...
That's why it's best to put a dial indicator on the crankshaft and eliminate any doubt. It will easily detect any play in the main bearings that may be inperceptable by other means. As cheap as you can get them from places like Harbor Freight, there's no reason that anyone who plans on working on their own bike shouldn't have one in their toolbox. There are so many uses for one on a bike, it's an excellent return on investment. :cool:

Marc -