- Joined
- Oct 28, 2014
- Messages
- 1,996
I pulled apart a 750 Commando crank yesterday for a cleaning and ran into a curious problem. Yes, I marked the direction of rotation. During disassembly the nuts seemed to come off a little easier than 30 ft/lb even though I was driving them past the punch marks. I have a new set of bolts and nuts. The bolts could be pushed out with finger pressure. I also noticed that the flywheel had a lot of balance holes drilled in it. As I tried to install the new bolts and studs I began to have real troubles. the bottom 2 studs went in easily. the next four were going to be impossible to fit with out driving them in with a hammer and punch. First I measured the old bolts and the new bolts. They were the same. I could see that the originals ( 2) had score marks and the threads had been munched a little bit which tells me the factory had driven them in. So began a careful inspection of 4 bolt holes. Yes, I tried flopping the flywheel even though I had marked the direction of rotation. Same problem. Taking the 3 pieces of the crank individually, the bolts would pass through easily. Lining them all up and inserting 2 studs and one bolt, I could see a mismatch of the holes. Slight, but the bolts should be a snug fit for locating purposes. To solve the problem I would have to ream out two holes.
Given the problem of the bolt holes not lining up, with the evidence that the factory had driven in two bolts, coupled with all the balancing holes, my conclusion is that this was a less than optimum crank, the factory banged it together and tried to compensate by drilling many balancing holes. Come to think of it, there was a "B" stamped on the flywheel. If this is a "B" crank I would hate to see a "C" one. There was no evidence of aftermarket balancing. My solution was to sideline the crank and use a different one. It went together easily except for one hole which required a slight sanding to make the bolt fit through. And it had a LOT LESS balancing holes and they were shallower. So what is the story here?
Given the problem of the bolt holes not lining up, with the evidence that the factory had driven in two bolts, coupled with all the balancing holes, my conclusion is that this was a less than optimum crank, the factory banged it together and tried to compensate by drilling many balancing holes. Come to think of it, there was a "B" stamped on the flywheel. If this is a "B" crank I would hate to see a "C" one. There was no evidence of aftermarket balancing. My solution was to sideline the crank and use a different one. It went together easily except for one hole which required a slight sanding to make the bolt fit through. And it had a LOT LESS balancing holes and they were shallower. So what is the story here?
