Chainline on 70's Flying Scot

lomoUK

Here's the problem:

Just done up a 1972 Flying Scot.

Rear now spaced to 130mm.

LBS put in bottom bracket and Deore chainset.

I built up bike fine but has terrible chainline. On big ring on front chaingrinds on rear sprockets (9speed on shimano 105 wheelset) - perhaps third biggest and thereafter. In small ring at front can get most gears at rear.

I therefore assume the chainset needs to move closer to the frame - shorter bottom bracket. Looking at it I can't see how this would work as the chainset can't physically move closer to the frame than where it is already. The inside of the cranks(by bottom bracket tapers) are only a mm or so away from the frame (where the bottom bracket cups are).

Hmnn.

Thought I'd try another crankset I had lying around. Old late 80s biopace triple. Put it on with same bottom bracket. Doesn't work. Small inner chainring rubs against chainstay.

Hmnnn.

Remove inner chainring. Bingo goes on a treat. Lovely chainline. Gears work lovely and smoothly. Great but I've lost a whole set of lower gears.

My question is?

Can this bike ever have a triple. Is there something in the design that means a triple won't work. I understand bottom brackets come in different sizes but any triple would mean a further out big chainring which would start to cause problems as previously.

Is a road triple what I need? Would it work ?

Help!





lead, follow or get the **** out of the way !

lomoUK

BTW it's a deore triple I had initial problems with.



lead, follow or get the **** out of the way !

Unknown

I assume that it was NOT built for triple - and maybe not even a double. How about a road compact double? I suspect that might be the lowest gearing you can get. Presumably also linked to spreading to 130 : I imagine when new ran a 126 5 speed rear and probably a double clanger up front.

Try copying into Special Interests - the old (sic) bike folk tend to hang out there!

d.j.
"The Angels have my 'phone box."
"Better than The Angels have got your Harley."

monty_dogcp

Suggest you look at sheldonbrown.com and read up on chainline - if you're having problems with a triple i.e. 30 tooth inner grinding the chainstay, then a compact is likely to be worse because of the bigger chainring diameter. Are you sure you've got the right BB length for the chainset?

Unknown

" if you're having problems with a triple i.e. 30 tooth inner grinding the chainstay, then a compact is likely to be worse because of the bigger chainring diameter."

Whoops! True, but would it not mean that could get the outer just a little nearer the stays?

"Are you sure you've got the right BB length for the chainset?"

Well, sounds as if can't go shorter and longer would only worsen the problem?

lomoUK, what IS the measured chainline, front centre to outer ring and rear centre to middle sprocket?

d.j.
"The Angels have my 'phone box."
"Better than The Angels have got your Harley."

lomoUK

Thanks for all your help.

Yep originally it was 126 spacing - 5 speed freewheel and double up front.

I've looked at sheldons stuff on chainline but it doesn't seem to cover this problem.

I'm assuming theres no trick for moving the rear cassette - it's position is fixed so it has to be aligned from the front.

The deore triple(mountainbiketype) when put on couldn't go closer to the frame even with a shorter bottom bracket. Not because of the smallest chainring touching the stays (it's comfortably away from the stays) from but due to the where the chainset slips on the taper of the bottom bracket.

The older 80's shimano triple I tried nexts smallest chainring(26 teeth) did just grate on chainstay. Took small ring off and works fine as above post.

I measured the chainline as sheldon browns side and ended up with 40mm?

It seems most modern chainsets come with a recommended width of bottom bracket.

I'm just hoping someone may have come across this problem before. I'm loathe to go to the bike shop yet as I'll probably get that sort of look of 'yes well we can do that' and then they'll call me later and say oh no! Adapting vintage frames isn't in most mechanics experience.

I already solved the problem of using 700c wheels by using special tektro long reach brakes sent from canada! They needed even longer reach than the shimano long reach calipers. Had to drill out the holes for the allen bolts though.

Anyway it rides like a dream and well worth it - but oh I need a triple!!










lead, follow or get the **** out of the way !

Andrew Christie

You can move the cassette outwards provided you have a decent amount of space between the smallest sprocket and the dropout. It means fiddling with the axle spacers to move the whole hub more to the right. You then have to re-dish the wheel to centre the rim again.
Probably not worth doing unless you have enough room to make an appreciable difference, and if you've re-spaced the rear dropouts from 126 to 130 it's likely things are pretty tight already.

Andy