Hello there,

I started having problems with my thompson bb on my 80's Enik fixed gear bike.

I am trying to find a modern bb to fit my bike, i did some search but i can not find any fitting.

My frame has a shell width of 70mm and 45mm diameter. Spindle length is 145 mm.

What can i fit there?

Regards.

The shell width implies Italian threading but that's not a certainty. Is there any engraving on the current bb cups that might give us an idea of the threading?

I believe there is no threading. BB cups are pressed fit into the shell.



The bb on my frame looks identical to the above, hence different size.
I am looking to upgrade this bb to a much hassle free system. If I cannot i will have to do with a direct replacement but I cannot find a thompson bb with 45mm shell diameter.

Best Regards.

P.S: I will post some pictures when i get home from work.

that is a One Piece crank adaptor? a euro version ? Cottered crank?

you ready to throw some serious money down on this idea?

$ 200 is a opening bid .. if the cups are American OPC specs [measure and report data] there are adapters for the BMX sector
to adopt common a square taper type BB to use different crankarms.


know where you can find A Local Machine Shop?

I may as well change the crankarms with square taper ones that is no big deal. I am not talking $200 solutions. I am trying to find a mechanical solution and understanding.

I know a few local machine shops.

Thanks.

You will probably not find replacement parts for the Thompson, so will have to convert. This may help:

https://fixedgearbikes.blogspot.com/2...t-adapter.html

https://translate.google.com/transla...%2F&edit-text=

Click on KASETTIKESKIÖT on left pane

try walking into a Bike shop , they may order what you need .. dont get sacked writing here from the Job.

I searched the local bike shops for a solution to no success. They are mostly salesman, no real bike mechanic in my town (at least to my knowledge). Actually, i looked at the solutions from velo-orange for their threadless bb yet, there is no fit for 45 mm.

I believe someone has done it before, I mean convert a similar size threadless bb in to a modern bb system (may be welding or threading involved).

Ok, let me ask like that, what would you do if you destroyed your favorite bike's threads in your 45mm diameter bb?

a.Try to fit a narrower shell (welding)?
b.Get it re-threaded?
c.Look for spare frame with threaded bb shell and integrate it to your frame? (cutting and stuff)
d.Look for an adapter of some sorts that may do the trick?

I am looking into this.

There are two approaches i can think of but neither are particularly cheap:

1. Have bushing rings made up with English threaded interior diameters and an OD matching the bb shell and braze them into the current shell after facing it down to 68 mm width. This is a variation on your options a and d. Don't even consider having a replacement shell welded to the old frame.

2. Buy a new English threaded frame and build it up with a current style bottom bracket and crank and transfer as many parts to it from the old bike as you can.

If you manage to "modernize" you current bb shell, you will need a new bottom bracket and crank in any event.

Anyhow I dont know what is in Shops in Helsinki Finland, or Latvia .. only in my Town ..

bike BB are threaded in 34 to 36 mm so the welding in a sleeve machined to do the job is possible.


then threading it with a Bicycle BB tap set. its a specialty tool..



a pair of sleeves with 3 compression bolts have been machined threaded to adapt American OPC to use a conventional Threaded BB..

You may find a Thompson equivalent.. or maybe the axle has a square taper equivalent ..

got any bike shops that have run in the same location since WW2?

Ok, this thread kindly doesnt need your contribution, mister.

My father was a Machinist.. a skilled Machinist could re machine a substitute spindle with a square taper type ends
and you can keep using the old utility bike BB .

Good luck to you .

Shop I worked at had a solution for a batch of frames wit similar BB. A steel sleeve with OD 45 mm and ID 40 (which you may have to have cuctom machined) was pressed in simply using a big vice. Then a much more common 40 mm press fit BB could be installed, although 145 mm spindle length is long. I believe 136 is the maximum with these BB's (but they are cheap)

Example:Startpagina / Fietsonderdelen Stadsfiets / Trapas / Trapas compleet / Thun Trapas Spieloos 136/40mm Thompson Inslag

After you've been on this forum a while you will learn to appreciate fietsbob. He can be pretty obscure and is a dedicated proselytizer for having everything done by a bike shop but, if you read his postings carefully, there is often useful information buried in them.