Why grind clutch weights

High Life

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Nov 27, 2007
SW Montana
I know this may be a silly question, but I am adding a new set of weights to my '17 Mountain Cat and decided to balance the weights. I've heard of other guys doing this, but never have myself and always been too cheap to run adjustable weights in my primary. After finally getting my hands on a scale that will read to 0.01 gram, I weighed my old weights (0.5 gram difference between 3) and my new weights (0.6 gram difference between 3). This seems like a lot, but is this normal?

I've read a lot of threads about HOW to grind weights, but what about WHY to grind weights? Is some level of performance lost by not matching all weights to the same mass or is it simply to better balance the clutch? Obviously, its not absolutely necessary, but I'm sure there benefits, performance, engine longevity, clutch longevity? What's the theory?
Nov 26, 2007
Elko, NV.
You may want to grind and match your weights in an effort to arrive at a more linear shift curve. I had a sled years ago that would pull a perfect 8,000 Rpm's until about 60 MPH where it would overshift and drop to 7,800. I was able to grind about 1.5 grams off the toe of the weight and arrived at a combination that launched and pulled 8,100 RPM's and evened out the the overshift yielding 8,050 Rpm's all the way through the shift curve. I was able to accomplish a nearly linear shift curve without having to spend any money on different clutch components.
Feb 3, 2017
Grinding mass from the profile will change performance, and that is the biggest reason to grind cam arms in my opinion. Doing it to equalize mass is looking for something to do in my opinion.

The unknown of grinding them to get the same mass overall is where is the variance in weight occurring. Is it in the barrel where it wouldn't have much difference in performance or at the tip of the weight where it would be some effect due to moving the center of gravity. There is variation in manufacturing process for cam arms that causes weight differences.

Without measuring your clutch to a tight tolerance your pin locations for the cam arms and rollers could have variation that is not being tracked either by solely looking at mass of the cam arm.
Mar 6, 2008
Northern Sweden
0.6 grams wont hurt you mechanically, but if you want to fix it for peace of mind take a little off from the underside of the flyweight. Dabbling in grinding/altering the cam curve is for the advanced class =)
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