Bob Jackson renovation.

[Colin Jenkins]

I've been given a ca. 1980 Bob Jackson racing bike with no wheels. It originally had 27" wheels; the only 27" ones available now are a quality-mismatch for the frame. A decent new 700c wheelset typically has a freehub with 8,9,10 or 11-speed capacity. The Bob Jackson has downtube retro-friction gear shifters, and I anticipate these will not select nicely over such gear clusters. A freehub with 6 or 7 speeds max would, I think, be a better match to the original spirit of the bike. I'm sure others have trodden this path before me and would appreciate any ideas or recommendations from experience.?

[colin54]

Hi here's a previous thread outlining some of the issues you might come up against.
Good luck
viewtopic.php?f=5&t=44074&hilit=brakes

[thirdcrank]

When you say "racing bike" is it a true racing bike or just a lightweight? In that linked thread, quite a lot is made of the brake braze-ons, which are unlikely on a racing bike. A lot of racing bikes were made to take both sprints (for racing) and 27" for other riding, so 700C wheels - the same nominal diameter as sprints - should be ok. Your big issue will be widening the rear end for wider hubs. The gear lever bosses can be ignored or used to mount cable stops.

(I've a BJ Super Tourist frame frame from 1980 with the canti brake bosses.)

[Ugly]

Another route to go would be to buy some period correct hubs and build a pair of 700c rims on them, 5 and 6 speed blocks, not cassettes, are readily available, not high quality but I have had a couple in use for 3 years or so with no problems. Maybe not ideal for high mileage but fine for a 'sunshine' bike. I have a pair of Campag record small flange hubs 36/36 in good order that you can have for £35 plus postage.

[thirdcrank]

Your first step needs to be measuring the width of the back end of your frame

https://www.sheldonbrown.com/gloss_n-o.html#old

A frame from 1980 is from the era of the transition from 5 to 6 speed and if it's 120mm then it would need widening even for 6 speed. For a while, compact 6 speed freewheels were made to fit the old five-speed OLN but they are surely history now.

This is a better link for what I mean

https://www.sheldonbrown.com/gloss_sp-ss.html#spacing

[slowster]

A decent new 700c wheelset typically has a freehub with 8,9,10 or 11-speed capacity. The Bob Jackson has downtube retro-friction gear shifters, and I anticipate these will not select nicely over such gear clusters. A freehub with 6 or 7 speeds max would, I think, be a better match to the original spirit of the bike.

The problem with Simplex retrofriction levers is the greater length of cable that needs to be pulled for higher speed drivetrains vs the small diameter of the part of the lever around which the cable goes. When this issue came up before in a thread, one sugestion was to slide a piece of electrical insulation over the cable to increase that effective diameter and the resulting amount of cable pulled. Dia Compe make a set of down tube levers with an enlarged barrel for the right hand lever to pull sufficient cable for an 11 speed.

https://www.sjscycles.co.uk/gear-shifte ... -shifters/

In your shoes I would be influenced not only by the availability and cost now of the parts you might need to buy, but also by the likely availability and cost of replacements and spares in future. I still use a bike with a 6 speed freewheel, but I would not be keen on spending much money to replace that wheel with another freewheel hub.

You have not mentioned what the rear axle spacing is (Over Lock Nut), but a bike of that era is likely to have a 120mm OLN (or 126mm at most). 8-11 speed hubs require either 130mm (road hub) or 135mm (MTB hub), so you would need to respace the frame, i.e. either get a framebuilder to do it or DIY, as explained here:

https://www.sheldonbrown.com/frame-spacing.html

If you stick with friction down tube levers it will give you maximum flexibility in what derailleurs and cassettes you can use. If you choose indexed shifters, down tube or otherwise, you will need a compatible cassette and rear derailleur (on the positive side 8, 9 and road 10 speed rear derailleurs all use the same cable pull per shift, but availability of all is limited because they have been discontinued by Shimano).

[Norman H]

How committed are you to a period restoration? How much do you want to spend?

BJ made some very nice frames and if it were mine I would definitely be looking to bring it up to a more modern specification, probably 9 or 10 speed. But I'd want to at least ride it some before I spent too much money.

In my view on a decent frame its worth entrusting cold setting of the rear end to a frame maker as they will properly realign the dropouts. The issue with 700c wheels can only be assessed by fitting wheels and measuring the brake drop. Deep drop brakes may well work and don't discount old style centre pulls, which work remarkably well with modern brake pads.

If you like the bike and at some time in the future you are contemplating a respray then that would be the time to talk to a frame builder about more costly alterations.

[slowster]

If the pads in the current brakes cannot be lowered sufficiently for the smaller diameter 700C wheel, Tektro 559 calipers may be the best option since they both have a long drop (55mm-73mm) and are available in old style nut fitting as well as modern recessed allen nut fitting.

https://www.spacycles.co.uk/m7b0s100p14 ... %28pair%29

[Colin Jenkins]

Many thanks to all for the helpful replies! The rear OLD is 128mm, which is curious; so I guess it started life as a126mm/six speed rear. The kind offer of the vintage hubs on here appeals, so I will PM and plan to work along the vintage 5-speed freewheel/700C route. Thanks all once again. Regards, Colin Jenkins.

[David9694]

That sounds like an easy thing, to get from 128 mm to 130 mm. I have no issues using friction downtube levers with 10s gears. Tektro is your frined when it comes to nutted, long reach brakes.

[Colin Jenkins]

I forgot to clarify why I think it's a racing frame......
The only braze-ons are for the rear gear and two gear cable tunnels on the bottom bracket shell.
The bottom bracket shell has three transverse cut-outs in it to minimize weight.
The Shimano brake-sets are short-reach types, and set almost at the bottom of their slots to reach the original 27" rims. I will need to change these to reach 700C rims.
The handlebar stem forward extension is 100mm.
There is no clearance for mudguards with 27" rims and no mudguard eyelets are fitted on the frame.
The chainset is 54 and 44 teeth.
The existing 108 link chain indicates a small rear cluster with this chainset size.
All things considered, it appears that the original super-fit owner wanted to be first to the tea shop.
Thanks for all the replies.
Regards, Colin Jenkins.