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Clutch balancing

4.6K views 9 replies 6 participants last post by  LETMGROW  
#1 · (Edited by Moderator)
I mess around with balancing clutches-mainly the P85 on Polaris. For the guys that don't have a $10k dynamic balancing machine, how close can you get it balanced? I usually find about 4-8g out of balance. Does anyone add weight to the clutch-like 4-8g on the light side to make it balanced. Drilling holes in the clutch face doesn't reduce much per hole.

I've seen professionally balanced clutches with a gob load of new holes drillied to lighten up the heavy side. Seems easier to compensate by adding weight on the light side.
The pto side bearing rides on a crankshaft stub I cut off of a junk crank. The cover side is a little harder to get a straight fit. Sometimes I find bushings that I can use on the cover to get the rod straight into the clutch center bolt hole. As for the clutch in the pic. It's a big block 600 poo and a 14mm shaft with a bearing on it .

I have a homemade ******* balancer. Same concept as a tire balancer. After I balance them, they run very true and long when I spin them. Out of balance is easy to see when the rod and bearings are bouncing along. Out of balance run way shorter spinning and always end with the heavy side down.

Just seeing what everyone else does.
 
#3 ·
Pretty simple. Bearings have very very little friction. The clutch will usually start to rotate at 2-4g of added weight to the light side. I keep adding weight until I figure out how much weight is needed to rotate the clutch, making the light side, the heavy side. Then back off the weight until it rolls back to the tight side.
Most of the time , it takes about 4-9g or added weight to balance.

I usually don't post things like this as most people respond with all of the "issues" there are by doing it this way, even though they have never done it themselves. I know there are people with tons more experience than I when it comes to how to balance things. All I can say is they are more balanced after I do it and it makes the engine run smoother.
So that's how I do it without drilling holes in the cover.
 

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#4 ·
Thanks for posting. I think what you are doing is called "single plane static balance". It's the most basic way to balance something. Certainly an improvement over nothing.
I've always wanted to learn more about dynamic balance. I did some balance work on a production line about 30 years ago. It wasn't too complex. The procedure was experimental. A measurement was taken with the item (a disk drive) spinning on a test fixture. The motor was stopped and an experimental weight was added to one of three positions (existing screw holes). Spun up again, measurement taken, spun down. A formula or chart then told what weight to put where. This was a single plane dynamic balance. Only required one single-axis accelerometer. There is probably a name for this type procedure.
Fun stuff, thanks for sharing
 
#5 · (Edited by Moderator)
It looked as if the bottom line price of a dynamic balancer was $10k.

So my question remains, why drill holes to balance? Would adding weight to the light side be the same in principle? Not talking about more than 5-10g atbthe most.

Nobody has ever chimes in to tell me how close they can get it down to on the bench balancer. Not some big expensive machine. You'd have to have a large part of your business setup for balancing in order to pay for itself.

I can tell you that most of the fixed sheave shafts are bent from use. Hardly any of them run true. Lower hp sleds usually have the best chance of spinning true. Like 500cc and less. They balance easier and don't have near the wobble as high hp sleds. When on the bench, you can usually see how it doesn't spin true, kinda like a pto end of a crank out of spec.
 
#9 ·
Since you are talking P-85 clutches, I installed the 911 clutch cover on my XCR. There are tapped holes to add bolts with washers if needed. After I installed the cover, I sent the clutch out for dynamic balance. It came back with one gram of weight added. Probably not really worth the effort, but I will say that triple/triple was smooth as silk, and belt to sheave clearance was very easy to adjust.

The shop that did the balance told me that Doo clutches are all over the place balance-wise.
 
#10 ·
Pretty simple. Bearings have very very little friction.
I like your concept. The bearings can be made to run even more freely. Remove the rubber seals and clean all the grease out of the bearing and lube the bearing with a light lubricating oil. Leave the seals out and when you are done with the bearings after a balance job clean and lube the bearings and store them in a Zip Lock bag.
Lynn
 
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