Mainshaft in and out motion, primary belt splitting

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foundationapps
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Mainshaft in and out motion, primary belt splitting

#1

Post by foundationapps »

Hi all,

This is a weird one to me. Don't find enough info in the manual to diagnose if there is a problem at all.

HISTORY: Rear chain (530) touching off on tire now and then. (180 wide tire on a 5.5 rim). Acceptable wear and tear until I fit a non-oring 520 chain. Then I thought I found a solution. Offset kit from JP, front 22 tooth front sprocket with a .310 offset and a offset spacer for the rear sprocket. That moved the sprockets and chain away from the tire, but very very close to the drive pulley behind the clutch hub.

ISSUE: New BDL belt put on the bike and within a week, that belt was split and shredded. Put on the old belt temporarily, that one split yesterday and was ate up into the front sprocket, (not enough to bind the gear up completely, but it was ugly).

In removing the offset sprocket (to go back to the original 25 tooth PBI sprocket that was on there, I noticed in and out play, BUT NOT OF THE ENTIRE MAINSHAFT, Only the threaded part of the shaft where the sprocket nut goes. When I would hand tighten the nut back up, play went away.

That didn't make any sense. Isn't the shaft one piece? If the threaded portion of the shaft had in and out play (about .200" max"), wouldn't the entire shaft float in and out, and the transmission fail to work at all? It does go, shifts up and down fine.

The offset sprocket setup is coming off, any idea if that offset sprocket was the issue? The drive chain MAY have been touching off on the belt, then grabbed hard enough to destroy the belt. The belt in both failures is a shredded mess. Transmission was aligned using a straight edge, checked over and over. Fixing to put a new spare belt on again with the offsets removed.

Any suggestions please?

Respectfully,

Trig
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Re: Mainshaft in and out motion, primary belt splitting

#2

Post by Bigincher »

To start with, the transmission Main Shaft is the tapered shaft upon which fits the clutch hub.
The drive sprocket (splined) fits on the threaded end of the Main Drive Gear, and is secured with the large special hex nut, left hand threads. (Under the nut is the lock tab ring and oil slinger.) So NO, everything sticking out of the tranny is not "all one piece".
Not being a transmission guy (some here are), I can't speak to the tolerances about which you ask.
I've never used any of that 'offset' stuff, but just by reading your post I have to suspect the rear drive chain is the culprit on the destruction of the primary belt; as you also suspect, sounds like.
I don't know what kind of bike you have, but is changing the rear wheel/tire to a slightly narrower one an option? You don't need that much clearance to the drive chain, 1/4" would be sufficient.
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Re: Mainshaft in and out motion, primary belt splitting

#3

Post by PanPal »

As Big points out, there is a locking washer you bend over the nut after tightening the sprocket. There will be in and out play with this nut loose. Sounds normal, but make sure you have the locking washer that you bend over. I grenaded a case from a loose sprocket nut some years ago.
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Re: Mainshaft in and out motion, primary belt splitting

#4

Post by Andygears »

I think in the mid 70's Harley had a sprocket with a small dish for a 4-speed, then just cut down your spacer for the rear wheel to match.

My two cents
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foundationapps
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Re: Mainshaft in and out motion, primary belt splitting

#5

Post by foundationapps »

Bigincher, how's it going brother? Pics attached. You bought my old rigid pan frame last year. That front spacer sprocket was the problem, after doing the autopsy, I found little tears in the edge of the belt and corresponding polished chain link pins that were rubbing off on the belt, also some nics and rubs from the chain on the back side of the clutch basket. So....

Removed the 22 tooth offset spacer and replaced the original (older, not the real original) 25 tooth PBI sprocket. Now this is going to sound cheesy, but I placed a thin spacer behind the front sprocket. To prevent any possible oil spillage from a seal, I RTV sealed the entire back area, not a lot, but all contact surfaces. This sprocket has a 2 bolt locking plate to prevent the nut from loosing up. Red locktited those two bolts also.

Rear sprocket: New JP 47 tooth to try a different combination to leave me power and have lower RPMs at 75 mph, which works.

Loosened up transmission mounting bolts and the 4 bolts that allow forward and rear adjustment of the primary belt.

Rode the bike to work this morning. So far so good. Belt is aligned well enough to allow shifting out of 1st at the stop. That's been a long time coming. Pics attached.

Bigincher, remember when you mentioned the vertical alignment from the front belt pulley to the clutch and to the rear axle, being in line? Finally go that there too. Handling on this bike is superb. Thank you sir!.

PS, bear spray in rapid deployment mode for those nuts cagers that get too close on the fast roads. Discharge into the airstream. Problem solved.
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