Tensioning chain on old Motobecane
08-30-22, 05:15 PM
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Tensioning chain on old Motobecane
I adjusted the two gear screws on the derailer on this mid 70s Motobecane but don't know how to adjust the chain which is a little loose.
08-30-22, 05:31 PM
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Put it on the largest ring & cog.
You should have 1-2" slack. (2-4 half links)
Noticeably more and you need to shorten the chain.
You should have 1-2" slack. (2-4 half links)
Noticeably more and you need to shorten the chain.
08-30-22, 07:44 PM
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I see 3 gear screws in your photo. Which 2 did you attempt to adjust? Not knowing what you are doing can result in unpleasant consequences.
08-30-22, 08:34 PM
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The imaged SunTour der has only a cage (P pivot) spring to help take up or play out chain length (compared to many ders since which also had a B pivot spring, like the Shimano Crane made in the same era as the V-GT). So when the cage pivot is wound up to its limit (determined by a small screw/peg on the cage that contacts the P pivot knuckle's tab) there is no other chain taking up method. One has to balance the total chain length (that hopefully is enough for the big/big combo) with the B screw's rotating the entire der rearwards to increase chain take up. Another issue is having the guide pulley still clear the cog set's undersides (when in the largest cog) but also not ending up with a huge amount of chain spanning the gap between the cog underside (in the smaller cogs) and the guide pulley.
So a rear der has a number of aspects that interrelate and can change how the system works. With so many factors involved it's hard to give a simple and "paint by numbers" answer. Again I suggest The Dancing Chain by Frank Berto for those who want more insight and story about ders and designs. Andy
So a rear der has a number of aspects that interrelate and can change how the system works. With so many factors involved it's hard to give a simple and "paint by numbers" answer. Again I suggest The Dancing Chain by Frank Berto for those who want more insight and story about ders and designs. Andy
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08-31-22, 10:43 AM
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I got the gear adjustment right on, and took out a little of the slack by tightening the tensioner. Not as tight as others I've had. I was just reluctant to go to a bike shop with the high minimums even for the most basic service.
08-31-22, 03:13 PM
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Here's my recently renovated Motobecane Mirage's rear derailleur.
