Fitting 9 speed chainset to old BB plus chainline problem.

sturmey Posts: 964
edited March 2009 in Workshop
I have a couple of problems which I would like to try and fix but I won't lose too much sleep if I don't ,as the bike rides well within its current limitations and I have another bike ,but here goes:

I have got a handbuilt Reynolds frame in exc.condition which currently has fitted a 68/119 square taper adjustable bottom bracket. Fitted to that is an early 80's Campag Strada 53/42 chainset. I have measured the chainline and it appears to be roughly 43mm which seems to be about right. The rear chainstay spacing is 126mm and it has a 14-24 6 speed freewheel.

With the current set up there are two issues:

1) When the chain is on the small chainring and either of the two smallest(outermost) rear sprockets, the chain rubs on the inside face of the large chainring, obviously with the deflection of the chain in these gears. I would never use small front to smallest rear,I admit ,as this goes against common practice and common sense,but being able to use at least 5th gear would be nice.
2)When the chain is on the outer chainring and the smallest rear sprocket (top gear) the outside of the chain rubs on the inside of the right crankarm, albeit very slightly.

I have tried a 3mm spacer behind the bottom bracket fixed cup to try and 'gain' some more clearance on the drive side but this was no good as when the adjustable cup was then re-fitted and adjusted correctly there wasn't enough thread still showing on the cup to be able to thread the lockring back on.Makes sense I suppose. So i had to dispense with that idea.

So my theory is ,if I fitted a new chainset (current gearing is too high)which according to the manufacturer ,required a shorter BB axle, but I left the existing BB in situ, am I likely to gain some extra clearance?

Could I fit a modern 9 speed 53/39 square taper chainset or indeed a 50/34 compact with the current bottom bracket?

I have stripped down the BB and it is in perfect condition with no wear whatsoever as I expected,as I knew the history of the bike.

The reason I ask is because I am looking at the following as an option to replace the current chainset: ... 0179878147

I note that this supposedly needs a 111mm BB.

Regardless of chainline, are there any issues in fitting this as it is made for a 9 speed bike? does that just mean the teeth are narrower?
Apologies for asking so many questions.

Any thoughts gratefully received.


  • rickhotrod
    rickhotrod Posts: 181
    Run the correct length bottom bracket for the crankset. Use a 9-speed chain as this is slightly narrower than 6/7/8 speed chains.

    I agree with you, that a 42/24 bottom gear is too high. A 52/39 should be ok. Running a 50 chainring will lower the top gear, so fit a triple 52/39/30 if you need a lower bottom gear.

    Are you planning to fit a Compag or Shimano crankset as the taper on the bottom bracket is different. Shimano use a JIS (Japanese Industrial Standard) taper.

    The chainrings on your current crankset may be too close to each other, and the outer chainring may be too close to the crank. In any case, changing to a 9-speed chain will help both these problems.
  • sturmey
    sturmey Posts: 964
    Are you planning to fit a Compag or Shimano crankset as the taper on the bottom bracket is different. Shimano use a JIS (Japanese Industrial Standard) taper.
    Well I was planning on fitting the chainset shown in the link. I assume this is compatible with the bottom bracket already fitted which I am fairly sure is European(ISO) taper and not JIS as the cranks are a snug fit with no problems tightening them all the way on.

    I have noticed though that ISO taper bottom brackets don't seem as easy to get hold of (?) so perhaps if I am going to replace the chainset I should forget Campag and get a JIS bottom bracket of the right length (as you suggest) to suit a new non-Campag chainset?
    Thanks for the 9 speed chain suggestion.
    I have got one of these spare so will give it a try.
  • rickhotrod
    rickhotrod Posts: 181
    Another thought has occurred to your crankset on square? This could make the chain rub as you have described. You can check this by turning the crank round by hand and looking at the outer chainring to see if there is any lateral (sideways) movement compared to the front mech. This of course, assumes that the chainring isn't bent!

    I read on Ebay, that Campag cranks made before 1994 use a different taper. I don't know if this is correct or not, but if so, then a different taper on cranks compared to the bottom bracket might cause the cranks to not sit squarely on the bottom bracket taper.

    After further consideration, a compact would probably be ok. 50/34 or 50/36 being the usual choices. 36 is my preference over 34, as i don't like tiny inner chainrings!