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  1. #1
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    Default Primary Belt + rotary top + round swingarm, too loose

    Hi, I'm replacing the primary belt on my 79 shovel. I have the belt that BDL says is correct for my front and rear pulleys. My bike has the stock frame, and a cowpie tranny. I am also running an early shovel/pan round swingarm.

    The belt has always been real loose even at max adjustment back, so I thought I'd figure out why.

    So the tranny is as far back as it can go, and the belt is still loose. The boss on the tranny that the primary/bearing support bracket bolts onto, is hard up against the swingarm. I'm not sure why?

    I've tried the next size down belt (3 teeth smaller), but there's no way it will go on either.

    Only thing I can think is that it's the combination of cowpie and round swingarm? Does anyone know if that primary boss on a cowpie has more meat on it than an older tranny? or if the OD of the round swingarm bigger than the square one, that would prevent the tranny from moving further back?

    I'm thinking I'll have to scallop into that tranny boss with a grinder, but I'd rather not cos it's real close to the studs. Not sure what else to do to get the belt tight though?

    Thanks for any ideas or help, apologies for the long post.
    Attached Thumbnails Attached Thumbnails IMG_3096.jpg   IMG_3094.jpg   Artboard.jpg   Artboard2.jpg  

  2. #2

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    I suspect you simply have the incorrect parts to do the job. I hope I read and understood your description correctly.
    I must assume you have the wrong motor pulley and/or wrong Clutch shell pulley.
    I bet that even if you installed a Stock HD OEM inner primary the components
    would Still Not fit correctly, meaning of course that you have the wrong parts.
    If you have a OEM inner install it and find out However---------
    If appears to my old eyes that it is an 11mm set-up, BDL used to include a Belt Idler with the 11mm.
    I use that same Belt Idler to adjust my 8mm belts when I change both Primary pulleys
    in order to change Gear Ratios. See Picture.

    Perhaps BDL rep assumed you were running a OEM inner rather than an Old-style tin
    that does Not have the stock Primary Chain adjuster. The Belt Idler slips right in the same slot.
    In my experience, if one must resort to Grinding on costly important parts like trans bosses, the
    Parts/components are Not correct.
    Of course, many of us have gone to great lengths to achieve the goal we have but this might be a wee too much.
    Click image for larger version. 

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  3. #3
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    Frisco you’re a genius!

    The original inner on my bike was cracked everywhere. I took it off I put a tin inner on and made it kick only… but I forgot there had been a tensioner on the old one. That’s definitely what’s missing.

    Will see if I can find a way to salvage the tensioner part out of the old f***ed primary and not have to change the pulleys.

    Thanks man.. sometimes you just need someone else to look at it

  4. #4

    Join Date
    May 2015
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    Default

    I had almost the same exact prob Open belt, Panhead motor, Ratchet top, swingarm frame Belts are either too loose or tight. And I wasnt going the pulley route.........

    I took an idler like frisco had, flipped it upside down and the mount I welded on the flat cross over under the primary area. The flat steel stock, closest to the camera in the pic, I drilled a hole thru for the idler, and on the back side cut about 20 small shallow slices with a air tool cutter, so it would engage the mount farthest from the camera: It has teeth so it can be adjusted up/down

    Its easy, but take care in EXACTLY how far inboard or out board the idler sits in relation to the belt. It has to be just about perfect so the belt doesnt creep track over one side or the other on the idler. The idler also has to be at an almost perfect 90 degree angle to the belt as well or the belt will walk right over the side of the idler and get chewed to hell in about 1 second of running

    Also, you are somewhat limited to what width belt you want to run. My 1.5" belt is about as large as I can run on the one I have, but I am sure there are idlers with a larger width for wider belts

    You can find idlers and the mounts on ebay or amazon. I got mine on one or the other, about $20

  5. #5

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    Quote Originally Posted by docmel View Post
    I had almost the same exact prob Open belt, Panhead motor, Ratchet top, swingarm frame Belts are either too loose or tight. And I wasnt going the pulley route.........

    I took an idler like frisco had, flipped it upside down and the mount I welded on the flat cross over under the primary area. The flat steel stock, closest to the camera in the pic, I drilled a hole thru for the idler, and on the back side cut about 20 small shallow slices with a air tool cutter, so it would engage the mount farthest from the camera: It has teeth so it can be adjusted up/down

    Its easy, but take care in EXACTLY how far inboard or out board the idler sits in relation to the belt. It has to be just about perfect so the belt doesnt creep track over one side or the other on the idler. The idler also has to be at an almost perfect 90 degree angle to the belt as well or the belt will walk right over the side of the idler and get chewed to hell in about 1 second of running

    Also, you are somewhat limited to what width belt you want to run. My 1.5" belt is about as large as I can run on the one I have, but I am sure there are idlers with a larger width for wider belts

    You can find idlers and the mounts on ebay or amazon. I got mine on one or the other, about $20
    Shit Forgot my pic
    Attached Thumbnails Attached Thumbnails IMG_20211007_134601992.jpg  

  6. #6

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    Here's a start for your search Key words to use is PRIMARY BELT IDLER BEARING Price seems to have gone up over the years!


    https://www.ebay.com/itm/17368871179...UAAOxyJypTkLdB

  7. #7
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    Thanks Doc, that's a real good idea.

    I have the old cracked inner primary, I was going to cut it up and try to make something similar to this: https://youtu.be/A8bnaZu5nFk

    Keep everything from the front two bolts, back to the two studs on the end of the tranny next to the swingarm.. including the tensioner part, and the mainshaft bearing. Then try to run that and the tin inner as well, so I can put the cover over the whole mess.

    Buuuut... your way seems way simpler, if I can get all the angles correct as you say. Will give it a shot. Cheers
    Last edited by nickfracture; 10-07-2021 at 3:23 PM.

  8. #8
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    Default

    Wish you were closer, I've got an old one that you could have experimented on. But I think the shipping would not make it worth it ;-(

  9. #9
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    Thanks man Yeah shipping everything down here is brutal.. but you gotta pay the cost to be the boss I guess. I think I'll be able to rustle one up here. Will report back on how I go with it

  10. #10
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    Here' my set up: https://www.youtube.com/watch?v=1c6wjiw_BTg

    I ditched the stock inner primary and used a rivera primo motor plate I picked up on ebay per Drag's suggestion a long time ago.
    It's one rad set up!: https://manualmachine.com/riveraprim...0-user-manual/

  11. #11

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    If you still want to run a tin inner, my recommendation prob wont work. But if you go my route, the bearing idler you should be able to find locally. Get away from a specific motorcycle part when you go to search locally. Get a pic of what you needoff the net and go to your local bearing supply store and show and explain what you need. Ill bet your local guy can hook you up. The mount you can make with simple flat stock with just a little ingenuity. My local bearing supply shop takes it as personal challenge to get what I need whne I show up, whetrjer its fork neck bearimgs, wheel bearings, etc. If there arent part numbers on what I need, or I dont have numbers, or if I have an old part or just a pic, they will get what I need. Try a local bearing supply store.

    I have seen a set up simliar to mine, but a guy on a rigid 4 speed (no inner primary) used a serpentine tension belt idler set up off a car from a junk yard which cost him about $5.00 from a pick/pull yard. It was spring loaded so no adjustment set up in the mount was required. He had a wide belt set up, and it worked great. It would work on a 1.5" belt as well

    Ill see if I cant get a number off the bearing I have in my pic: It might simplify a local search

    One last point is that I'm unclear on your tranny set up. If your tranny was from an electric start set up, you need to some sort of bearing support as e start trannies have a longer mainshaft. I have seen guys cut one out of an old aluminum primaries do this, but there are many aftermarket bolt on bearing supports out there for sale for pretty cheap on the used side

    Regardless, you will need some sort of bearing idler to get your belt tension right

  12. #12
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    Thanks Doc. Yes, my tranny was e start and has the long shaft. I have a bearing support on there - it’s the silver thing you can see in my pics.

    If I go your way I’ll keep it on there.

    If I go the other way, I’ll remove the bearing support and cut up my old aluminium inner primary. I will keep the bearing support part and the tensioner part of the inner primary - basically keep the whole middle section of it, and cut off everything top and bottom.

  13. #13

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    The good thing is if you have a bearing support 90% of the job is already done for you. You dont have to worry if the idler is level with the belt run. The support does it for you. The job of alignment right or left of the belt run will be easy.

  14. #14
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    Here's an update on this. Decided to make my own tensioner and weld it on. Thanks doc for getting me thinking along those lines, it was the way to go.

    I used 6 bearings to make the roller, stacked on a long bolt. I wasn't sure how much pressure the belt puts on the tensioner, so I may have over engineered it a bit.. but it's super solid. I made it out of 5mm mild steel and welded it to the frame with a right angled support, and another supporting piece above the roller.

    I slotted the faces of the sliding piece and the fixed piece by hand. Don't know what I was thinking there.. it took hours and they didn't line up perfect so they don't slot into eachother. It's quite grippy though, so not a total waste of time. If I was doing it over I'd just buy some pre-slotted plate or get it milled.

    I used my old primary as a starting point to position where the tensioner should be, and how tall it should be.

    The only other tricky part was getting the angles perfect.
    - I ran a straight edge from the front face of the front pulley to the front face of the outside bearing to get the 90 degree alignment with the belt
    - For the inboard / outboard angle I used a digital angle finder sitting on top of the front pulley, and then matched that angle with the angle finder sitting across the roller.

    Got it all back together today and started it up... Works like a bought one. I'm stoked. Some pics below.
    Attached Thumbnails Attached Thumbnails 2021-10-10 10.34.48.jpg   2021-10-10 10.37.58.jpg   2021-10-16 18.19.34.jpg   2021-10-17 19.02.16.jpg   2021-10-23 14.46.03.jpg  

    Last edited by nickfracture; 10-27-2021 at 5:15 AM.

  15. #15
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    couple more
    Attached Thumbnails Attached Thumbnails 2021-10-25 11.38.52.jpg   2021-10-26 09.34.35.jpg   2021-10-27 23.31.43-1.jpg   2021-10-27 23.32.09-1.jpg   239E6EBD-491E-4317-A22F-5C0581C933BD.jpg  

    Last edited by nickfracture; 10-27-2021 at 5:24 AM.

  16. #16

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    Quote Originally Posted by nickfracture View Post
    Here's an update on this. Decided to make my own tensioner and weld it on. Thanks doc for getting me thinking along those lines, it was the way to go.

    I used 6 bearings to make the roller, stacked on a long bolt. I wasn't sure how much pressure the belt puts on the tensioner, so I may have over engineered it a bit.. but it's super solid. I made it out of 5mm mild steel and welded it to the frame with a right angled support, and another supporting piece above the roller.

    I slotted the faces of the sliding piece and the fixed piece by hand. Don't know what I was thinking there.. it took hours and they didn't line up perfect so they don't slot into eachother. It's quite grippy though, so not a total waste of time. If I was doing it over I'd just buy some pre-slotted plate or get it milled.

    I used my old primary as a starting point to position where the tensioner should be, and how tall it should be.

    The only other tricky part was getting the angles perfect.
    - I ran a straight edge from the front face of the front pulley to the front face of the outside bearing to get the 90 degree alignment with the belt
    - For the inboard / outboard angle I used a digital angle finder sitting on top of the front pulley, and then matched that angle with the angle finder sitting across the roller.

    Got it all back together today and started it up... Works like a bought one. I'm stoked. Some pics below.
    Nicely done!!: As far as tension goes, go by the top of the belt: You should be able to twist the belt by hand in the middle, by 1/8 turn or slightly more. Folks tend to over tighten belts

    Take the time to be sure the belt doesnt track too far left or right. A little is ok as long as it doesnt come into contact with anything

  17. #17

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    My homemade grippy part (adjuster) is the same way. It doesnt fit together exactly, but does hold. Heck, there isnt that much tension and making the little slots is probably isnt even needed, but a good thing regardless

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