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Old 06-16-2016, 10:28 AM   #1
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Default Premature Primary Belt Wear

I had been running an 1/2" 11mm belt (open) on my shovelhead for years with no belt issues. Then I decided I wanted electric start while still keeping the primary drive open. I ended up cutting up a stock primary to support the mainshaft and to house and support the starter components. Because the inner primary now didn't offer enough room to pull the transmission back for proper tension with the 11mm belt and because the open drive does not allow for a tension pulley, I had to switch to a BRAND NEW BDL 8mm setup which offers a belt length I can tension without the primary hitting the gusset on the frame. The 1st year I went through 3 belts. the 1st was due to poor alignment, as the belt was wearing on the starter ring gear and I had shaved roughly a 1/4" plus off it before it gave. The following 2 showed to signs of alignment issues as they still measured 1 1/2" after they ripped in half.

One thing to note is that the 2nd belt was a Primo Rivera and seemed to last longer than any of the other belts, which have all been BDL, but still should have lasted longer than it did. And one ripped right on startup.

My 4th and current belt (installed less than 1000 miles ago) is showing premature wear. here are some photos that are indicating this one too is going to rip anytime soon. What is causing wear like this to happen so quickly?

Last edited by marvintheminnow; 06-16-2016 at 10:34 AM.
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Old 06-16-2016, 11:22 AM   #2
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Default Re: Premature Primary Belt Wear

how tight is it?
i was told by a belt drive producer need to be able to turn belt 90 degrees (like twisting it)
i put 12 years on a belt(primo) on a big twin flathead now got a gates kevlar one.
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Old 06-17-2016, 01:23 PM   #3
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Default Re: Premature Primary Belt Wear

2 things come to mind:

1) Condition of pulley teeth
2) As noted above...belt tension...too tight = excessive heat

Question though...

What size pulleys are you running and what # belt teeth?

The reason I ask is that I was told recently by a BDL tech that one of their 8mm Shovel electric start open belt kits were sent with belts that were improperly marked. The kit Im running needs a 142 tooth belt...BDL said the company that makes their belts sent a small lot of 140tooth belts that were marked improperly with a "-142" fuckin good...and as you could imagine would be a mutherfucker to get on and properly adjusted. So, just a heads up....

Edit: Another you always start this bike with the electric starter or do you kick it as well? Ive had 2 belts snap on an 80" electric start Evo with open belt drive when the ignition timing was off...belt snapped in half both times. Im assuming that your timing is spot on, but if its mag fired and perhaps a tad too advanced, wondering if its snapping back on you a bit???

Last edited by buckman50; 06-17-2016 at 01:36 PM.
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Old 06-17-2016, 01:32 PM   #4
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Default Re: Premature Primary Belt Wear

For primary belt drives, alignment and tension are critical and the key to a long lasting belt. I setup all belt drives (even a 3" belt) so I can actually pull and slip off the belt off by hand when the bike is cold. The pulleys have to be aligned in all planes in order to do this, but it's well worth the time and effort. Tension must set on the loose side when cold because when the parts of the drivetrain heat up the belt tightens up. All of the damaged belts I've replaced and repaired were caused by either mis-alignment, too much tension, or a combination of the two factors.

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