R1pVan

Hi all, I have a Saracen Tufftrax Comp Disc with a knackered bottom bracket. The spindle is marked 113.5mm and the shell width is 70mm (but not Italian).
68mm x 113.5mm bottom brackets seem to be readily available but not 70mm X 113.5mm.
What I'd like to know is, if it's possible to use a 68mm x 113.5mm unit instead?

cxwrench

No.

Steel Charlie

Have the BB refaced to 68mm. That's only 1mm/side and the world will never know

zandoval 

Been there and done that. Of course I am just a Franken Bike builder but the answer is, Yes. And if you must resurface ya really only need to take one mm off of the non-drive side. And that can be done with a Bastard file or a grinder... Ha... Don't be afraid...

79pmooney

Someone correct me if I'm wrong but I see no reason why a Phil Wood wouldn't work just fine. You would have both cups screwed in an extra mm inside the BB shell but neither the bike nor the BB or crankset would care.

With a regular BB, flanged fixed cup and locknutted adjustable cup, the crankset will be pushed a mm too far outboard (not a big deal for most bikes) and the lockring may not see any of the threads on the left hand cup. The appropriate Locktite would likely solve that nicely but I wouldn't do it.

79pmooney

Just thinking at the keyboard - If I did this, I'd file to short of the 1 mm (probably taping the shell before I started at the 1 mm circumference). Then I'd thread on the fixed cup and look where contact is first made. File that with a finer file and repeat. (Perhaps using chalk on the shell lip and filing the spots scraped bare by the cup.) Later I would have a shop face the shell with the proper tool when I had the bike there anyway.

Iride01 

Maybe you could get by with a 68 x 113 UN-300 or such. How important is that extra 0.5 mm to you?

UN-300's are inexpensive enough over here that it won't be a be loss if it doesn't work in the 70mm shell. Don't know what they are where you are. Maybe go by a bike shop and see if they have a used one laying in a scrap bin you can try.

ThermionicScott 

Yes, if the left-side bottom bracket cup does not have a flange on it. Shimano UN300 would work. This will move the whole crankset to the right by 1mm, probably requiring a front derailleur adjustment, but the bike likely has spare clearance for the left-side crank to come inboard by 1mm.

No need to reface the bottom bracket shell to 68mm (professionally, or otherwise) unless you really wanted to.

zandoval 

What ever the case be sure ya try it out first. On one of my conversions I only had to file of about 0.5mm to get a good fit on the loose balls. But then again I don't know what kind of cups I was using because they came out of a parts bin. It very well could fit without any modification at all if ditching the cups and going for a Cartridge Bottom Bracket...

BCRider

That's the trick! A good description.

I'll add a second trick to aid with easily checking how the squaring up is going. Mark the edge of the shell with felt marker. Screw the BB in and lightly pinch tighten, back up and pinch again a few times. This will wear away the marking at the high point(s). File away the silver high marks a little. Re-ink the edge and screw the BB in again. Repeat as needed until things are quite flat and you' are getting at least 5 evenly spaced and fairly broad rub marks around the edge. At that point it'll be as good as if it were a properly reamed short job. If you're doing this for the first time expect to need to file, ink, scuff the ink with the BB, file a little, repeat about 2 dozen or more times. It might take you an hour or more. But going slowly means a more approachable method with a better job.

All in all if they charge you $25 at the LBS to use the proper tool I'd just pay the money. But if no local shops have such a tool or want something crazy to face the shell then you now have a reasonably fool proof self help option.

alcjphil

That bike is a mountain bike. Are you sure the BB width is 70 mm? Most mountain bikes produced in the last 20 years have 73mm wide BB's

cxwrench

I think it's nearly impossible for that bike to actually be 70mm and NOT be Italian. I'm betting it's 68mm or 73mm.

70sSanO

The specs show a Neco brand bottom bracket.

https://www.necoparts.com/en/categor...ets/A0201.html

I would take a look at the BB and see the P/N that is installed. While the website shows 68mm, 70mm, and 73mm, I highly doubt the 70mm is a BSA thread.

John

R1pVan

This is what we're thinking. It's a friends bike he uses as an everyday gad about (he has others). We've ordered this, Suntour BB17XCT Square Taper Sealed Bottom Bracket MTB - BSA 68 x 113.5mm. Cost £14.50 (around 17$us).

R1pVan

I would take a look at the BB and see the P/N that is installed. While the website shows 68mm, 70mm, and 73mm, I highly doubt the 70mm is a BSA thread.

John[/QUOTE]
No PN on the cartridge sleeve just "Neco". As the bearings are completely collapsed the spindle came out separately, so we could see the width stamped on it. Had a look at the Neco site but without a PN it's no help really.

R1pVan

As I understand it, Italian bottom brackets are RH threaded both sides? This is LH thread drive side (fixed cup flanged) and RH thread non drive side. Measured and remeasured the shell width with digital calipers, checking they were properly zeroed and got around 70.6mm on most measures. I don't think there would be 2mm of paint on there but I may scrape the paint off the faces to see what I get.

JohnDThompson 

Yes, Italian (and French) thread bottom brackets are right-hand thread on both sides. Italian cups are 36mm diameter, while English/ISO are 34.8mm diameter (French are 35mm), so an English/ISO cup will fall into an Italian thread shell without engaging any threads, while an Italian thread cup cannot even begin to engage an English/ISO thread shell.

R1pVan

Bottom bracket fitted and working. The shift to the right is unnoticeable when on the bike.

Thanks for all the replies.