Here's a simple balance checking fixture I made a few years ago, wanted something to verify flywheel and PP balance at home. My first pass at this was just proof of concept using materials I had on the rack, basically angle iron and some cold rolled shafting. The arbor in the pic below is single purpose, made to duplicate the fit of my crankshaft's flywheel flange/pilot. First the flange was rough turned, then bored to fit the shaft which was then secured in place using red loctite. Then the shaft was set up for zero runout in the lathe, after which the flange itself was finish turned to the exact same size as the crankshaft pilot.
This static flywheel/clutch balancing thing is probably seen as a hillbilly hack at first glance. When a crankshaft is dynamically balanced, most shops balance using the end counterweights, basically balancing each end of the assembly separately. Same for a driveshaft. But when you think about balancing a typical flywheel, dynamic balancing doesn't really bring much to the table as the guy doing the drilling is probably going to drill on the backside of the rim either way. Same for the pressure plate, not really a lot of choices of where to remove or add weight. That coupled to the fact that something dynamically balanced is automatically going to be in static balance as well, static balancing the flywheel first and then balancing the pressure plate bolted to an already balanced flywheel makes practical sense, and gives you the same basic location separation that you get with dynamic balancing.
Turned out it works pretty good for what it is, detects an an out of balance 1 gram on a 6" radius when you set it up on a very rigid surface like a concrete floor. I use it to verify neutral balance of the flywheel first, then add the pressure plate to further balance the assembly. To adjust parallel of the support shafts, i just lay the face of the flywheel across both shafts and check to see if it rocks, then adjust until it doesn't rock. Front to back level I adjust with a digital level, side to side i level by letting the arbor roll on the support shafts until i'm satisfied it has an equal tendency to roll in both directions. Here's some pics with an old cast flywheel i had laying around, here you can see the leveling screws installed in the base...
Here you can see that one end of the support shafts non-adjustable, just holes for the pins that are threaded into the shafts...
Here you see the other end of the support shafts, which go into slotted holes with adjustment screws to allow adjustment for parallel of the support shafts...
Here you can see that the old flywheel, supposedly neutral balanced originally, required 43 grams applied to it's rim to achieve neutral balance...
After verifying that the fixture worked as intended, I then static balanced a 19.3lb steel flywheel that I had been using on my 355. Sorry, forgot to write down exactly how much weight it took before I started drilling. I had taken a little weight out of the backside a while back, i'm guessing it took about 12g to bring it into static balance.
With the flywheel zero'd out, I then bolted a 16.7lb Ram diaphragm pressure plate on to check it's balance. Turns out it needed 22g. I then rotated the PP 180 degrees on the flywheel and checked it again to verify. Took the same 22g on a 5-1/8" radius in the same "6" location. Looks like depending on how the two were bolted up before, balance of this assembly could have been out a minimum of 10g or a maximum of 34g overall. Ram says they balance to .5 ounce inch, that's about 2.5 grams at the radius i'm working with. That has me feeling pretty good about the 1 gram resolution i'm getting from the cold rolled shafts. Since the added weight needs to be added at the "6" location, i'm going to take advantage of the coincidence and install a shouldered stud in the #6 cover bolt position, then make an appropriate balance weight to install on that stud.
This used dual friction disc was only out 1g @ ~ 5". I'm also going to make arbors to check balance of my front hubs and brake rotors as well.
Originally resolution of this fixture was 2 grams, but I soon found that if set up the fixture on the concrete floor instead of the not so rigid bench plate, resolution improved to 1g with the cold rolled shafts. The 65lb bench plate in the pictures plugs into a single 2" square receiver style socket in the bench, turns out it moved a little when the weight of a flywheel/PP were rolled from one side to the other. Setting the fixture up on a concrete floor fixed the problem.
Grant
