No. 51 Flywheel Balance Kit
Fast Eddy Co. is making it much easier to rebuild bottom ends. Our No. 51 Flywheel Balance Kit will de-mistify the art of balancing flywheels. Anybody can do it if they have this kit, a scale, and can weigh parts and write down those values. Download detailed instructions available at the bottom of this page.
Rather than making you buy a big "master balance kit" that might require you to pay for parts you don't need, we've broken this up into 4 total kits.
- No. 51 Balance Kit: This is the base kit that everyone will require.
Included with the No. 51 Balance Kit:
- Balance Stand: Designed similar to an industrial shaft balance stand, the all-steel construction of this balance stand will last for decades. It's large steel rollers and low-drag bearings mean that it's accurate down to about 2 grams. And the self-centering design makes it a lot easier to use, than the c-channel types of balance stands. There's more room for more configurations, and your flywheel won't roll off the balance stand every time you're not looking. A real pleasure to use, and built like a tank.
- Organizer Tray with Balance Shaft and all Adapters: With all parts easy to identify in a convenient organizer, you'll have everything you need to balance any early harley crank. The balance shaft that will pass through any harley flywheel with a center hole, all the taper adapters you'll need to fit different flywheels, as well as an EL adapter that let's you balance early flywheels that have a stepped crank pin (which was not possible with the other kit's out there). The organizer is Gridfinity compatible.
- Rod Weighing Stand: With a sturdy steel base and a 3d-printed adjustable-height rod holder, you can easily weigh both sides of your connecting rods, ensuring the rod is held straight and allowing you to obtain accurate values.
- Bobweight Assembly: Including all the shims you'll ever need, the bobweight assembly is adjustable in weight down to 1 gram increments, and will allow for any possible value you'll need.
- Flywheel Layout Jig & Magnet: This layout jig is very convenient to use. Instead of trying to layout holes as you need them, just put this jig in the initial heavy spot on the flywheel and mark up to 6 holes at once. This allows you to drill as needed, and you won't need to go back and lay out additional holes one at a time. And it makes the spacing and location of the holes correct and consistent. This jig also includes a 12 gram magnet. Once you're within this value (and the magnet changes the heavy spot of the flywheel), you know you're within drilling one more hole that is 3/4" deep. This makes it really easy to get close the final number of holes really fast, and then slow down and get it perfectly balanced at the end.
- Scale not included.
For people that work on Evo Big Twins or Evo Sportsters, additional kits are required. These models have flywheel shafts that are forged-in and cannot be removed. For these flywheels, you'll also need to purchase the Counterweight (No. 51 WEIGHT), as well as either the Evo Big Twin Adapter Kit (No. 51 EVO), or the Evo Sportster Adapter Kit (No. 51 XL).
Product Info
- No. 51 Balance Kit includes:
- Balance Stand
- Organizer with shaft and all adapters
- Rod Weighing Stand
- Layout Jig and Magnet
- Complete Bobweight Assembly with all shims
- Fit's all flywheels 1985-earlier that have a center hole with a removable shaft.
- For 1985-later flywheels that have a forged in shaft, you'll also need our additional Evo Big Twin and/or Evo Sportster kits. You must purchase separately:
- Counterweight (No. 51-WEIGHT)
- Evo Big Twin Flywheel Adapters (No. 51-EVO)
- and/or Evo Sportster Flywheel Adapters (No. 51-XL)
- 100% made in USA
- No. 51 Balance Kit includes:
How to use this balance kit
Fast Eddy Co. is making it easy for you guys to balance and rebuild flywheels. You just need to be able to weigh parts, fill in our balance worksheet, and it will output the specific bobweight for your flywheels. Then balance your flywheels to this weight. That's it! That's all. There are a lot of tricks to learn throughout the rest of the rebuilding process, but with our No. 51 Balance Kit, the balancing part is simple and straightforward.
How to use this kit:
Step 1: Weigh engine parts and fill in our balance worksheet to calculate the bobweight for your engine
Step 2: Put the bobweight on a scale and add and remove shims until the weight is the same as what the worksheet told you
Step 3: Using the shaft and correct adapter, put the flywheel on the rolling balance stand and install the bobweight onto the flywheel
Step 4: Add/remove weight from the flywheel until it's balanced and no longer rotates on the stand.
YOU'RE DONE!
General Notes About Flywheel Rebuilding
There is A LOT to flywheel rebuilding. This is only a simple overview.
Flywheel Disassembly
- Place Flywheel Fixture in vise, mounted to sturdy table
- Place flywheel assembly in fixture
- Remove crank pin keeper screws and keepers
- Loosen crank pin nut
- Flip flywheel assembly over and do the same to the other side
- Use steel wedges to spread flywheels and break bond between crank pin and flywheel halves
- Remove rods, bearings, and crank pin
- Place individual flywheel half in the jig, remove shaft nut keeper and shaft nut. Tap shaft out with rawhide mallet or other soft hammer.
- Repeat for other flywheel half.
Rebuilding process:
- Replace worn parts
- Rebalance flywheel halves for new rod & piston weights
- Reassemble flywheels
Flywheel Assembly (simple overview only):
- Ensure all tapers are clean and dry. Wipe everything with acetone
- Use jig to assemble shafts back into flywheels by torquing nuts to specification
- True pinion shaft to right side flywheel. Check runout of side of the flywheel with the both ends of the center shaft mounted on centers. It's very important that you are able to achieve a runout of less that 0.001". This may require persuading the shaft a bit in a particular direction. You can use a sacrificial pinion nut on the shaft in order to protect it during this process. Repeat this until shaft is true to the flywheel half.
- Repeat with sprocket shaft and left flywheel.
- Install keepers on pinion shaft nut and sprocket shaft nut
- Place RH flywheel in shaft-down orientation on the fixture.
- Install crank pin and key, and snug crank pin nut hand-tight
- Install rod bearings and rods. (forked rod is the rear rod, so if facing the notched side of the jig, this rod should be on your left).
- Place the sprocket shaft flywheel on top of the crank pin
- Use two pieces of steel C-Channel and 1/2-20 all-thread rod to clamp flywheels straight. We like to use 4" wide C-channel (7.25 lbs per foot). Each piece should be cut approximately 4.75" long, and have a hole drilled in the center for the 1/2-20 all thread. Tighten with nuts and washers onto flywheel assembly.
- Snug crank pin nut hand tight
- Flip over flywheel assembly and alternate tightening crank pin nut on each side until final spec is achieved.
- Don't attempt to true flywheels until crank pin is fully tight. You're just wasting your time, because it will go out of whack every time you tighten the crank pin nuts.
- Make sure endplay of rear rod to flywheel thrust washers is acceptable. Anywhere between .010 and .050 is acceptable in our opinion.
- True flywheel assembly. This is a whole other adventure. And the old school outlook is that you only have 15-20 minutes to true a set of flywheels, if using green loctite on the tapers. We like to use a couple drops of Loctite 609 on all the tapers.
- Install crank pin nut keepers
- Install plug in the end of side-oiling pinion shaft, if applicable.
- Build the rest of that motor!
There are a lot of ways to skin a cat!! There are a ton of different ways to do things, and there is no single correct way. People have very strong opinions on how to rebuild flywheels. This is only a simple overview, and expresses our opinions only.
Instructions