Converted BGF drive box from chain to belt

Discussion in 'General Questions' started by mmachine, Aug 14, 2009.

  1. mmachine

    mmachine Member

    I posted once before about the crummy drive attached to the BGF newest
    4 stroke offer on eBay. After only a little over an hour of use the tiny
    chain was sagging. Also the reduction was only 3:1

    Converted from sprocket/chain to pully/timing belt, see pics.

    Just rode it for a couple miles and it works very well. Thought for sure
    I was screwed on this because the motor has a short tapered shaft and
    won't take other drives. Time will tell about longevity.

    Attached Files:

  2. mmachine

    mmachine Member

    forgot a pic

    Forgot to post the before pic with the chain setup.

    Attached Files:

  3. srdavo

    srdavo Active Member

    I remember your posts. Very cool fix.

    What is your reduction, now.... with the timing belt design??
  4. GearNut

    GearNut Active Member

    Be careful about the bend in the belt where the tensioner pushes against it.
    Idler belt primary drives were very popular in Harley-Davidsons for quite a few years. In time they showed a bad flaw by frequently breaking belts. The cause was found to be that the idler bends the longitudinal (sp?) cords inside the belt backwards from the direction that they bend to go around the pulleys. This constant flexing to one way then the other accelerates the fatigue in the cords considerably.
    All of the belt drive systems nowadays use a fitted belt, no tensioner at all.
    A good compromise is to limit the backwards belt flexing to almost nothing.
  5. motorhedfred

    motorhedfred New Member

    Is this belt designed for Harleys ? If not, I would say the tensioner it might not be an issue. Have you ever seen a passenger car timing belt in use ? Some of them use tensioners, albiet larger diameter ones and get tens of thousands of miles out of them. You might consider some sort of steel wear plate for the spring however.

    Just my $.02

    Last edited: Aug 15, 2009
  6. mmachine

    mmachine Member

    more info

    Knew someone would ask about new ratio but didn't have the info at hand
    when posting. Didn't have much room to work with either 6 1/2" in fact.

    The new ratio is 3.2:1 in the drive.

    12t freewheel output to 56t puts final ratio at 14.93:1 was at 12:1 with
    prior setup. It all adds up nicely. I pedal about 4 times and hit the throttle,
    engages easily and takes off.

    Was clocked by enthusiastic motorist at 30 mph. Think he was asking how
    much I would sell it for but my turn was up ahead : )

    30mph was a blast looking forward to longer ride today. I'll have tools and
    an extra belt with me. This belt is fiberglass reinforced and have steel belt
    on order that should take care of bending.

    Probably open the case after every ride to see what the effects are and
    how it's holding up.
  7. bmc_az

    bmc_az New Member

    Belt drive

    Nice Job !!!

  8. mmachine

    mmachine Member

    important update

    After a 7 mile ride took the cover off and found that the nylon bushing had
    melted, worn through and stuck to underside of it's axel bolt and the belt
    had been riding on the bolt itself.

    Knew the nylon wouldn't last but was forgetting just how hot the drive box
    gets from the clutch and engine.

    The belt itself was burnt and showing heat cracks but continued to work
    without complaint! There was powdered rubber in a thick pile running all the
    way around where it travels, up to an inch thick in some areas.

    Replaced the nylon (once scraped from bolt) with bronze bushing which was
    my original intention but not sure why I didn't follow through.

    Put the original much abused belt back on and took a ride for 24 miles with no
    problems. Those little belts are tough, no question.

    As soon as I arrived took the cover off, had to use gloves it was so hot, and
    all is perfect. Even though the drive housing was blistering hot the belt itself
    was just warm. Needless to say I couldn't be happier.

    Without realizing it got up to 34 mph and noticed the motor seemed to be in
    the zone, smooth and humming a perfect pitch. Then the light changed and
    had to stop in 40' which was easy to do, liking the brakes too.
  9. Rising low

    Rising low New Member

    dude.,you are a freakin genius i have been searching threads for weeks about this,thank the interlocking web..hallelueha!!!If your still out there mmachine text me back on this please.Rising low
  10. mmachine

    mmachine Member

    I'm still here, sorta. Since I subbed to this (old) thread was notified of your response.