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Thread: 64 duo glide belt drive primary drive

  1. #11
    Join Date
    Nov 2018
    Location
    Reno NV
    Posts
    200

    Default

    I have used a number of belt drives over the years, and generally I prefer them over a chain drive.
    However, as with most things, they are not as perfect as the manufactures would have you believe.

    As others have stated, it is important to have the pulley aligned in parallel. This is just the starting point.

    The typical clutch hub is supported by a bearing inboard that is close to the gearbox sprocket. The idea is to have the center of pull from the primary drive as close as possible to a bearing supported shaft. This works fairly well with a relatively narrow single or double row primary chain. Later models with a cast inner primary have an additional bearing to support the main shaft.

    Most belt drives actually have a belt center that is outboard of the clutch hub bearing, depending on the belt width, it can vary a lot. This imparts a bending motion to the main shaft.
    The main shaft flexes as the motor torque is varied, which changes the pulley alignments. During heavy acceleration, the main shaft flexes towards the engine sprocket. This results in the belt tracking trying to track off the front pulley.
    The front sprocket alignment guide is used to hold the belt on the front pulley during these events. Yes, it does wear out the side of the belt, but it doesn't come off. I think some manufactures use a guide that screws on the outside of the pully.

    The engine sprocket shaft can also flex, depending on the design.
    In high HP applications, both the engine output shaft and the transmission output shaft have outboard support bearings to keep any drive system inside supported shafts.

    In practicality, belt drive have been around for many successful years.
    if you are looking for a belt drive for your Duo Glide, an 8mm belt is as much as you need,if it is standard.
    As previously mentioned, make sure your engine shaft seal has it's spring towards the crankshaft, and be aware of wet sumping if it happens.


    Cheers
    Mick

  2. #12
    Join Date
    Aug 2004
    Location
    Beautiful Northern New Mexico
    Posts
    2,772

    Default

    If you have ever adjusted the tracking of a belt sander the drive belt reacts exactly the same. Slightly oversized or slotted transmission plate holes allow the gearbox to swivel slightly getting the belt to run centered in the front pulley negating the need for guide plates to keep it in place. Your '64 won't flex stuff enough to be an issue (strokers and sidecars excepted!) This doesn't work on '65 up bikes with fixed centers. I've run belts for many years on tin primary bikes and never had issues. The original; belt on my '47 Knuckle is still on there from 1990 and I don't go to all the BS of cooling holes, spacers and other nonsense to prevent overheating. They cool just fine, and as Sarge says modern belts are even better.
    Robbie Knight Amca #2736

  3. #13
    Join Date
    Nov 2018
    Location
    Reno NV
    Posts
    200

    Default

    Rubone,

    Belt sander typically have crowned pulleys, hence the need for tracking adjustment. The physics are different to a flat pulley, although some may have a 2 degree pitch that you cannot see.
    I consider a front belt guide as an insurance policy, cheap insurance.
    Last edited by aumick10; 09-17-2019 at 07:26 PM. Reason: change flat pully specifications

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