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2012 Mag Wheel Bonneville. Aprox 1600 miles.

I sat down to lube my chain this afternoon and when I took off the chain guard noticed a grind mark where the chain has risen up and ground down the side of it. It's right where the bend is to allow for shock clearance. No damage to chain noted and it's not a massive amount of grinding, maybe 1mm deep or so. Checked my chain slack and it is just about 1" of slack which, if my calculations are correct, is dead nuts in between the 20-30mm mark the manual states. I don't feel a lot of drive line lash when riding which would indicate a loose chain. It has to have happened in the last 400 miles or so as that's the last time I lubed the chain and did not notice it then. Only thing new on the bike is that I put on some used Hagon shocks. Though I can't imagine that would allow the chain to rise up (stock length).
Any ideas? Should I run the chain tighter? I've checked the chain slack every time I've lubed the chain and with exception of this last one has been every 200 miles. No change in slack at all.
 

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I would not tighten the chain. You could end up with even bigger problems with sprocket and/or seal wear on the front sprocket. Anyway, if I read it right, the wear is on the upper run of the chain, which is where it is, usually, under tension; there could be a rub, I suppose, on deceleration when the upper run is looser. I'd check the chain alignment and the chain guard itself, as it may be slightly bent towards the chain.

Just the opinion of the "village idiot", that's all: Jim
 

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+1 to checking the alignment especially seeing the problem is in one specific spot. Are the has marks lining up on both sides of the guides? You can also take a long screwdriver, pen, thin rod...whatever....and lay it on top of the chain start at the rear sprocket - line it up to the inside collar of the collars and make sure it runs straight down the chain
 

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Discussion Starter #4
I suppose the chain guard could be bent but I purchased the bike brand new and looks normal to me. I've been trying to imagine in my mind if the top side of the chain comes up under high speed conditions or under deceleration as you stated.
When looking at the chain with the guard over it the indentation for the shock on the guard does sit slightly over the chain. Bike runs great so I suppose I could just bend the chain guard slightly outwards but it just seems weird to me that it would do this.
 

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I have the same grind marks my is a 2010 bonneville. I'm not sure where it comes from I took some pics and to me it looks like my guard isn't bent and there would have to be a lot of slack in the chain to rub but what do I know.


 

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Discussion Starter #6
I was just about to post pics but that is exactly what mine looks like. Chain looks good, concerned that it will damage the chain at some point although the guard is much softer metal.
 

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My chain guard has a similar marking. Chain looks fine. I'm at only 1200 miles so far. Using pro motion tool, the alignment is very slightly off (barely noticeable). I plan to adjust when chasing needs to be tightened. Right now, tightest spot measures about 28mm.
 

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Had the same on mine but only noticed it when I tightened the chain and realigned the rear wheel. Even after doing both I was able to pull the chain straight up and see it hit the guard, so I just bent the guard to where the chain is properly under it.
 

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I was just about to post pics but that is exactly what mine looks like. Chain looks good, concerned that it will damage the chain at some point although the guard is much softer metal.
Yeah, the guard is softer than the chain. No way will your chain suffer. Do not tighten it beyond factory specs, or you'll soon be replacing some expensive bearings.
 

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Had the same on mine but only noticed it when I tightened the chain and realigned the rear wheel. Even after doing both I was able to pull the chain straight up and see it hit the guard, so I just bent the guard to where the chain is properly under it.
Is the best way to do it.

Plasma.
 

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Yup, same thing on my 2010 Bonnie.

I hear the chain slapping when I'm pretending it's a Scrambler. Washboard roads seem to be the worst for this. Same grind marks, same place.

Picked up a used aftermarket guard from Stapler, beautifully chromed, and it has the same positioning of the shock indent. I think I'll straighten the rear bracket on the vice and try to move the guard over about a quarter inch - hope I don't bugger up the chrome on the bracket.
 

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This brings back a memory, though only slightly related to the problem.

When the (then) new 1969 Honda CB750 came out, they made a terrible thrashing sound at road speed, noticeable mainly to anyone riding beside them. Turned out that the engine & exhausts were so quiet that the chain "thrash" was the loudest thing about the motorcycle. Of course, ALL bikes made this same thrashing sound, but the motor/exhaust noise covered it up.

Also, it's surprising how many motorcycles over the years have had chain clearance "issues." The old Ducati bevel-drive twins were famous for wearing grooves IN THE CRANKCASES where the chain exited the engine's sidecover. Once it wore down enough for the chain's rollers to touch the center of this "trench," most of the wear stopped. Mine did it, I never liked it, but, I resisted the temptation to tighten the chain because...

...Back in 1974, my buddy (who now lives with me after enjoying a 6-week coma) modified his Bultaco to a "long-travel" rear suspension. First time over a jump, the wide-variance of chain tension hit that "tight" spot where the rear axle/front sprocket/swing arm pivot were all in a straight line. This (yay and verily, I kiddeth thee not) FOLDED the outer length of the gearbox shaft to 30-degree angle. Back to the coyote's ACME Skunk Worx shop (think "Road Runner cartoon") to immerse himself in chain guide technologies.

Proper chain tension is your friend. Chain rubbing stuff is NOT your friend, but it's a much smaller ENEMY. Fix it if you can within the confines of proper chain tension.

BTW: Just yesterday I noticed my Bonnie chain is "shiny" around its perimeter. I'll bet I need to look at my chain guard.

SteveMcK (whom Ali McGraw never calls)
 

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I wonder if the grinding might result from a rear axle out of alignment. The index marks on the frame supposedly are not that accurate. I use a cheap little tool that holds a rod straight along the chain when the axle is aligned. No grindng, anyway.
 
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