Primary Drive Gear, I've stripped 3 now, what am I doing wrong? (photo)

Discussion in 'Frame Mounted Engines' started by Sketch, Feb 27, 2010.

  1. Sketch

    Sketch Member

    Please see attached photo.

    Left to Right:
    (1) lasted 1 week, with other damage to gears in the gearbox, sent me a replacement gearbox.
    (2) lasted 1 week, then I ordered a replacement. Spent some time making sure I understood the gearbox, listening to people here...
    (3) lasted 2 days

    What am I doing wrong. I can't afford to keep going like this, obviously. I was taking it easy, real easy, trying to make sure I didn't push the engine or the gear box. And I was real careful about assembly, lube, nuts and bolts. Checking things as I went to see if there were any emerging problems. But all of a sudden, this third one (at medium speed on a flat stretch) made a crunching sound and I knew it was toast. Pulled over and once again walked 3+ miles home with a broken bike.

    Attached Files:

  2. professor

    professor Active Member

    What gearbox is it out of? How is the mesh when it is together? Is there a lot of slop?
  3. Sketch

    Sketch Member

    I have a stage III. There was a small amount of slop because the inner piece doesn't tighten all the way against the drive gear when I tighten the bolt all the way.
  4. engager

    are you by anychance using the engager? Trying to use the engager like a motorcycle clutch? If you are it can damage the gear box. Most MBer's do away with the engager lever,cable and permanetly engage the engager:detective:
    Just a thought
  5. Sketch

    Sketch Member

    I have it permanently engaged...
  6. Sketch

    Sketch Member

    I noticed today that the outer coating on the clutch is a little beat up. Is the play in the way the housing sits over the clutch the cause of my problems?
  7. Sketch

    Sketch Member

    New primary drive gear I got from had a much tighter fit. Funny thing was, the outside diameter (of the "bell") did not fit inside the inner case opening. I decided to try to remove some of the diameter. I came up with a clever solution using a bunch of fittings to be able to mount the drive gear in the drill press. Then I used the vise that is meant for holding things as you drill them, combined with 4 c-clamps, to mount two metal files. lined everything up and it worked great. The bell spun smoothly and I was able to adjust the files to change the amount of pressure. 3 hours later, I hadn't reduced the size at all. Time for desperate measures. I realized that my setup was a great way to smooth a rough bell. So I made a "rough bell" using the grinder....then used the drill press setup for 20 or 30 minutes to polish the mess. It actually worked. Now that I have the bike assembled....(fighting the usual chain problems...why can't it just work without kinking???)...I am very happy with the new clutch because for once the engagement rpm seems correct. I can actually adjust to a reasonable idle.

    I saw another thread somewhere that was talking about how there are so many variances between parts and sometimes you get lucky. Except for the probably 8 hours of machine shop work I did on this gear, I feel like I got lucky this time. It's weird, the quality of the metal even seems to be better. Maybe a different factory in China...I dunno.
  8. biketec

    biketec Member

  9. Sketch

    Sketch Member

    Yes, when I got the gear I slid it into place to do a test fit, and then tried to place the inner part of the gearbox cover over it, like I normally have done. It wouldn't fit, the bell was just barely too large. I spent some time examining it trying to figure out what was going on. I tried putting the inner part of the cover on first, but when I put the gear on it needs to spin inside the cover I finally reached the conclusion that it really was slightly too large.