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1986 RockHopper to 8 / 9spd - chain clearance issue

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1986 RockHopper to 8 / 9spd - chain clearance issue

Old 05-25-21, 09:02 PM
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thundercleese
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1986 RockHopper to 8 / 9spd - chain clearance issue

I've got a weird build that's been dragging on for too long now. It's a 1986 RockHopper frame, pretty beat, that I picked up on the cheap and intended to build up as an around-town errand bike. Most of the drivetrain stuff in my parts bin is 9 speed MTB era so that's what I set out to use. Well, I've hit an odd snag: a chainstay cable guide. Seems like it's not going to allow me to run the 12-32 cassette I'd planned on using, since as you can see, it hits the guide. In front I've got the chain set on a 34t middle ring. The wheel I just built is a 8/9/10 speed Tiagra road hub, 130mm spacing squeezed into the RockHopper's 126mm dropouts. Seems like something that's been done a million times, but... arrgh, there's that cable stop right in my chainline:




Out of curiosity I tried an 8 speed Sora cassette, outer cog 14t, and that just barely cleared the stop, to the point where I bet there'd be rubbing with the slightest bump or pause in pedaling. So that's not ideal.

Looking at the 1986 RockHopper's original spec I see a 14-30 freewheel listed, paired with a Shimano 600 hub. Now I'm not a freewheel expert, having only worked on a couple so far-- but is there something special about the width or spacing of a 6 speed freewheel that would give a 14t cog more clearance than I'd get with my 8 / 9 speed cassette hack jobs?

I've actually got a 600 rear hub laying around, but I'm trying to avoid building a wheel around it and sourcing a cassette & chain unless there's a good chance it'll solve the issue. Any insight?
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Old 05-25-21, 09:36 PM
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I’d suspect your BB spindle is too long on the drive side.
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Old 05-26-21, 01:05 AM
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That 8-speed cassette is wider than the original 6-speed freewheel, so the smallest cog is probably situated further outward, closer to the dropout. This puts the chain closer to the stay. Just looking at where the chain passes the dropout, it looks awfully close. You may have to play with axle spacer location, and then subsequently adjust dish (re-center the rim), to move the cassette away from the dropout.

Odd that yours has the stop on top of the stay. I have an '87, and the stop is on the bottom of the stay. Do you have cable guides brazed onto the seat tube above the BB shell?

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Old 05-26-21, 11:21 AM
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Originally Posted by madpogue View Post
To the OP -- That 8-speed cassette is wider than the original 6-speed freewheel, so the smallest cog is probably situated further outward, closer to the dropout. This puts the chain closer to the stay. Just looking at where the chain passes the dropout, it looks awfully close. You may have to play with axle spacer location, and then subsequently adjust dish (re-center the rim), to move the cassette away from the dropout.

Odd that yours has the stop on top of the stay. I have an '87, and the stop is on the bottom of the stay. Do you have cable guides brazed onto the seat tube above the BB shell?
Yes my frameset has the cable guides brazed onto the seat tube. Kinda cool feature.

Yikes, yeah, I didn't think about re-dishing. Yes the chain is super close to the frame anyway, even if I could get the chain clear the cable stop with a narrower BB spindle, 9spd is probably not going to fly. Right now I'm running a 68 x 113mm square taper BB with a lower-end (sub-Deore but not riveted chainrings level) Shimano MTB triple crankset. MIght try a 109 or 107mm BB that I have lying around.

Starting to think that I'll just rebuild around the 600 hub and go the freewheel route. More cost and delays, but oh well.
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Old 05-26-21, 11:50 AM
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@madpogue nailed it. Your frame was not designed for a 130 spacing. It is luck and good fortune for those frames that can accept the modification.

You also need to be aware that there is enough clearance for the chain to jump from the smallest to the next without hitting the seat stay. It may fit with the chain on the smallest sprocket and then not be able to get by the seat stay. I imagen some will bend or crush the stay to get the clearance/
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Old 05-26-21, 12:29 PM
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Originally Posted by thundercleese View Post
frame, pretty beat, that I picked up on the cheap
But I guess simply hacking the offending stop off, to be replaced by a clamp-on turned 90 degrees to the side, would still be déclassé?
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Old 05-26-21, 12:42 PM
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Before building a new wheel, I'd try that sora 8 speed cassettee with a 14 on the outside and add a 1 mm spacer.
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Old 05-26-21, 01:18 PM
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Originally Posted by thundercleese View Post
Yes my frameset has the cable guides brazed onto the seat tube. Kinda cool feature.

Yikes, yeah, I didn't think about re-dishing. Yes the chain is super close to the frame anyway, even if I could get the chain clear the cable stop with a narrower BB spindle, 9spd is probably not going to fly. Right now I'm running a 68 x 113mm square taper BB with a lower-end (sub-Deore but not riveted chainrings level) Shimano MTB triple crankset. MIght try a 109 or 107mm BB that I have lying around.

Starting to think that I'll just rebuild around the 600 hub and go the freewheel route. More cost and delays, but oh well.
I think that this is probably what you want to do. I had a 1983 Stumpjumper with the same situation and I ended up just using a 6 speed freewheel with friction shifters. This was the only solution that actually worked well and didn't get funky in some way. I was hoping to have a little more modern drive train but the 126mm drop out spacing just wouldn't accommodate anything else.
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Old 05-26-21, 01:29 PM
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Option -- using the pictured 12-32 8-speed cassette, and setting the derailleur high limit so that it can't go to that smallest cog, at least gets you a 13-32 or 14-32 7-speed rear, and the option to use existing bin parts.
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