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Thread: Belt Drive for 47FL Knuckle

  1. #21

    Re: Belt Drive for 47FL Knuckle


    Between the factory repair manual and the instructions with the belt drive kit (most if not all the belt drive manufacturers have installation instructions on the web too), you should have enough info for a basic install. But, the basic instructions don't really go into the issue of proper alignment. If you want a trouble free belt drive you should go further than just considering the basic "in and out" alignment of the the pulleys. I believe its just as important to check that the pulleys are in the same plane both vertically and horizontaly. Another way to look at it is having the motor sprocket shaft and the transmission mainshaft being paralell when observed from both overhead or from the front or rear. Theoretically this is how your bike came from the factory, but in reality you don't often see it especially with parts that have been in service for what, maybe 70 years? This check should be a part of every new primary installation or part of trouble shooting problems with an existing primary wether its belt or chain. All you need to perform the check is a couple of straight edges or a couple of squares, it doesn't have to be a real scientific undertaking. If its off a little, correct it by shimming where needed, it has nothing to do with tapered shafts or bent frames. If its off a lot, check your frame. Sorry for being so dog-gone long winded, I just read what I typed and I sound like the Nutty Professor, but my point is - set it up right and you won't have any problems!


  2. #22
    Join Date
    Mar 2008
    Beautiful Northern NM

    Re: Belt Drive for 47FL Knuckle

    As Geo says, all planes must be in line. That means if you need to slightly rotate the tranny, shim one edge, etc, it all needs to be in line to run true. It is not all about a motor sprocket shim! And as skyrider says, the belt guides are for those not willing to do it right. A properly lined up belt will run true with no drift on either acceleration or deceleration. Ever use a belt sander or bandsaw? The alignment concepts are exactly the same. The length and design of the rear chain will handle any slight misalignment with the rear drum, so it isn't a concern. A well set up belt will last many tens of thousands of miles with no edge fray or wear!

  3. #23
    Join Date
    Nov 2011
    Bothell, Wa.

    Re: Belt Drive for 47FL Knuckle

    Yup, Robbie and others are right, correct alignment and belt tension are the key to long trouble free belt life. A friend of mine introduced me to belts many years ago and my current rider has in excess of 25k since I built it with a belt in the can with no probs what so ever. Mine is a Primo 8mm x 1 1/2''. You should specify a "bulls eye" belt as they are just slightly longer than the standard belt and will preclude having to file the transmission mount slots to get proper belt tension on some bikes. You should also run your belt tension slightly looser than the instructions specify. The clutch and motor pulleys are aluminum and will grow slightly with accumulated heat especially in an enclosed primary, not much, though just enough to tighten the belt slightly which can cause sprocket shaft and transmission seal seepage not to mention accelerated bearing wear if your belt is really, really tight. Be sure to follow the instructions regarding your primary breather, you can't just plug it off like you can a flathead as knucks, and others actually breath through that system and need it for internal pressure relief well as original primary chain lube.


  4. Re: Belt Drive for 47FL Knuckle

    Ok, so do I go for an 8 or 11mm pitched belt and why one over the other?

  5. #25

    Re: Belt Drive for 47FL Knuckle

    I persoall have only run 8's on my own bikes, it makes sense a 11 would be strong, BUT, may generate so much heat, you wouldn;t want it "inside" a closed cover...which is all that ever kept me away from 11mm..... Ask Matt, or Carl Olson......(well, they are at Sturgis, so that will hav to wait)

  6. #26
    Join Date
    Aug 2010
    Twin Cities, MN

    Re: Belt Drive for 47FL Knuckle

    Here's a quote from Carl. "I run 8 MM belt drives on all of my bikes"

    1947 EL
    1948 FL Project
    1947WL Project

    But there's booze in the blender
    And soon it will render
    That frozen concoction that helps me hang on

    You never get just get less awful. "Joe Walsh"

  7. #27

    Re: Belt Drive for 47FL Knuckle

    Ron, what is a "bull's eye belt"? Thanks
    Lonnie C.

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  8. #28
    Join Date
    Jul 2009
    Washington state

    Re: Belt Drive for 47FL Knuckle

    I have always used 13.8 belts and had no issues.

  9. #29
    Join Date
    Nov 2011
    Bothell, Wa.

    Re: Belt Drive for 47FL Knuckle

    The "bulls eye belt" is a minor variation in the length to the long side. The belt has the same number and size teeth as the standard belt that you will find ithe kit. The standard belt will fit most standard setups.
    I have a Primo kit # PE-39-62, 8mmx1 1/2", still have the box, on my '32 that has a '37 ul and later big twin transmission and I traded the standard belt to a friend for his "bulls eye" for the extra length. It is all buttoned up in the primary so I can't easily get the number off the belt. The standard number had a circle with a dot adjacent to the part number hence the "bulls eye" designation. You are in luck though, I haven't put the outer primary cover on my '41 yet and I got the number for you. The belt has part# BDL 30853 with (BE) accompanying the part number. I don't have the box the belt kit came in any more so I can't tell you which company's product it is. I suspect it is a BDL. In that particular model kit both Primo and BDL are about the same. Just choose between them on the basis of price. I can't make any recombination for any other "Names" as I have no experience with them.

    Last edited by ron; 08-10-2012 at 10:50 PM.

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