Resto advice, specifically Suntour Sprint BB compatibility

[disfocus]

Hi,
After 30 years or more of drooling over it, I've finally got my hands on my Dad's old Abeni Super Record (Reynolds 531, made for him in the late seventies). The frame looks okay--there's a bit of rust, but I'm pretty sure it's only surface. I'm planning to pack it off to Gripsport or similar for a blast and a new paint job. The rear wheel's been rebuilt with a newer hub to accept a 7sp hyperglide cassette, so there shouldn't be any issues there.
My main query regards the crankset. I'm not much of a mechanic, let alone an expert in older gear! The current crankset is a Suntour Sprint from the mid/late eighties. The cranks should clean up nicely, but I'm a little unsure as to the BB. From what I gather, it should be a 108mm JIS. Would a 107mm Shimano UN55 do the trick? To be honest, I'm kind of learning as I go along here...

[rustychisel]

it's all about the frame and how it was built, ie angles and tolerances. A UN55 would be fine, but best to check the BB you have with the drive side crank installed, making sure the spider and inner part of the crank bolts have enough clearance as they go past the chainstay. That's the danger area!!!

[munga]

if you have a sprint bb, you can probably clean it up, or buy new bearings for it, if required.
you could even buy a new spindle.

[disfocus]

Rustychisel: Thanks for that. I haven't stripped it down yet (in fact it won't arrive until tomorrow), so I'll check out the tolerances. So if there's enough room, the only side-effect would be to move the chainline in 1mm, is that right?

Munga: I don't think it's a sprint BB--I seem to remember Dad mentioning he'd swapped to a sealed bearing unit.

[rustychisel]

Sprint is okay, not top quality but okay.

If the BB is a sealed bearing unit then take it out, clean up the threads a bit then regrease and put it back.

Depending on the spinfle alignment you'd expect a 108mm to be 0.5mm in on either side, but it doesn't always work like that.

[funnybike]

I just removed an original Suntour Sprint BB from a bike. The axle actually measures 109.4mm.
Square taper cranks tend to get pushed further on to the spindle each time they are removed and reinstalled as the soft aluminium of the crank compresses against the harder steel spindle. Given the age of your bike the cranks are probably sitting 1mm or so further inboard than when they were new, so you may be better off going slightly wider with the new BB than slightly narrower. The good news though is the original Sprint spindle is symmetrical, so any of the Shimano cartridge BB's will work just fine so long as you get an axle length that is appropriate. Trial and error if you are shopping on the wigglenet. Easy-peasy if you are taking it to your LBS. And remember if you do buy the wrong size on the wigglenet, you can always put it on the swap-meet thread for someone else who has done the same thing and really needs the size that you now have spare.