• Dana

Always Something

This weekend was all about the flywheels. First, balancing. After a lot of research and searching on the Internet I decided to go with a balance factor of 68%. Most everything I read said to use the 'Indian Balance' method. That's where you add both con-rods and one piston to the fly wheels and balance that. But that didn't make sense to me. As the weight of the pistons and con-rods change, the balance factor changes. So if the new aluminum pistons or new modern connecting rods have a different weight then the 90 year old factory pistons and con-rods then the balance factor changes.


I choose 68% for two reasons. I found a 10 year old forum post where someone used 68% and the said the bike was smoother then it ever was before. And, if I change my mind I can lower the factor just by drilling more holes in the flywheel. Adding weight back to the flywheels seemed harder. I really doubt I'll be looking to increase the balance factor above 68%.



Next, I trued the wheel assembly up in my lathe. It went easier then I thought it would. I initially trued the wheels up in my press. I hand tighten the crankshaft nuts and put the entire assembly vertically into the press. Using the press to push down on both wheels at once to square the two wheels up. My first measurements were in the 3 thousands mark. A lot of banging and squeezing later and I'm down to less then 0.001 run out on both the pinion and drive shafts! The whole process took about two hours. The first time!


After I was all done and just about to 'Bag and Tag' them I thought I should test the oil feed passages. I was pretty careful about lining up the crankshaft to match but better safe then sorry. Sure enough the passage was blocked somewhere. I couldn't blow through the oil feed hole. Oil turns out to be pretty important to the crankshaft bearings. So the whole thing had to come apart.


A little bit of searching found the problem. Both my new crankshaft, old crankshaft and old flywheel had the oil feed hole drilled 3/8" from the inside face of the flywheel. But my new flywheels had the oil feed hole drilled 3/8" from the outside face. It was off by about 1/4". So as I tighten the crankshaft up the holes were misaligned and blocked.


Oscar the Bastard strikes again. This time he was in cohorts with my flywheel vendor. Other then returning the flywheel that I had already balanced and lapped true the only fix I could see was to move one the holes. The crankshaft is hardened steel and I really didn't think drilling into that was an option. So I put the flywheel on the mill and made a small 1/4 slot to connect the two holes. I was concerned modifying the taper was going to screw up the truing process but it all seemed to work out.


After milling the slot and testing the oil passages I had to true up the wheels for the second time. It was easier the second time, almost like they knew where to be. Or, I knew how hard to hit them to get them to move.


Moral of the story, trust no one and always check parts as they arrive to make sure they fit and are correct. I could have easily returned the flywheels before I modified them.


Weekends To Race : 62


Truing Details.

Here's the process I used to true the flywheels. I couldn't find the actual detailed process on-line so here's how I did it.


  1. Clean the pinion, pinion nut, and pinion taper in the flywheel with acetone. Lined up the oil feed hole and hand tighten the dry pinion nut. No loctite.

  2. Put the flywheel vertically in the press. You're just using it as a big vice. Tighten the nut up to 60 ft-lbs.

  3. Take the flywheel to the lathe and check the pinion run out. It needs to be less then 0.001. I used an indicator on the inside face of the flywheel.

  4. Mark the high spot on the flwheel. Take it out of the lathe and put the pinion shaft flat on a piece of wood. Hit the flywheel's high spot with a lead hammer, 'Hard' (Well my 'Hard' may be different then your 'Hard'.

  5. Repeat steps 3 and 4 until the run out is less then 0.001.

  6. Take it back to the press and tighten the nut to 80 ft-lbs and repeat steps 3 through 5.

  7. Take it back to the press and remove the pinion nut. Clean with acetone and put red loctite on the threads. Tighten to 100 ft-lbs. Repeat steps 3 through 5. I didn't start with the loctite because it can cure fast and I didn't want to re-torque the nut with cured loctite in it.

  8. Repeat 3 through 7 with the drive side.

  9. Assemble the connecting rod assemble using assembly lube, because this maybe the last time you assemble it. Clean the crankshaft, nuts and crankshaft tapers with acetone. Place the connecting rods on the crankshaft and put the crankshaft in the flywheels. Tight the nuts hand tight.

  10. Put the flywheel assembly vertically in the press with the press pushing equally on both flywheels. Tighten the crankshaft nuts to 60 ft-lbs.

  11. Put the whole assembly in the lathe, I used two dead centers to hold the flywheels. One in the tail stock and one in a mill collet in the head stock. I used the dead centers because I found the live center deflected down from the weight of the flywheels.

  12. Setup an indicator on the driveshaft. Find the high spot. If the crank is opposite the high spot the fly wheels are in a 'V' you will need to squeeze them together with a clamp opposite the crankshaft. If the crank is on the high spot the fly wheels are in a upside down 'V'. You will need to pry them apart with pry bars opposite the crankshaft. If the crank is 90 or 180 degrees from the crankshaft the flywheels are twisted. You will need to rotate on of them back to center. Hold the pinion side flywheel in the press and hit the high spot of the drive side flywheel 'Hard'

  13. Repeat 12 until the runout is less then 0.001.

  14. Repeat 12 and 13 for the pinion side.

  15. Take the assembly back to the press and tighted the crankshaft nuts to 80 ft-lbs. Repeat 12 through 14.

  16. Take the assembly back to the press and remove the pinion side crankshaft nut. Clean with acetone and put red loctite on the threads. Tighten to 100 ft-lbs.

  17. Repeat 16 but with the drive side crankshaft nut.

  18. Repeat steps 12 through 14.

  19. That's it. Easy Peezy.

Build Notes:

Flywheel Balance : 68%

Pinion Run-out : 0.0002

Driveshaft Run-out : 0.0007