Upgrading square taper BB to Hollowtech 2

nbuuifx

I've currently got a Trek 1000SL which I'm looking at upgrading - I'm in no rush but I'm keeping my eye out for a second hand low mileage entry level groupset to upgrade too.

I've seen a couple of Tiagra sets but they come with an FC-4700 crankset which I believe uses the Hollowtech 2 BB. I currently have a square taper BB - I believe it is a cartridge type - I'm not sure of the thread size etc. Is it possible to upgrade it to make the FC-4700 fit?

Wheelspinner

Yep dead easy. The existing square taper will be an “English” or BSA thread which is standard. The HT2 bottom bracket is available in the same thread.

Only nuisance is it requires two different tools: one to remove the old BB and another to install the new.

Provided your old one is not seized in (it happens) it is a roughly 15 minute job to remove the old cranks/BB and install the new. Maybe 20 minutes allowing for the BB shell threads to be chased/cleaned in between.

nbuuifx

Wheelspinner said:

Yep dead easy. The existing square taper will be an “English” or BSA thread which is standard. The HT2 bottom bracket is available in the same thread.

Only nuisance is it requires two different tools: one to remove the old BB and another to install the new.

Provided your old one is not seized in (it happens) it is a roughly 15 minute job to remove the old cranks/BB and install the new. Maybe 20 minutes allowing for the BB shell threads to be chased/cleaned in between.

Excellent - I believe I have both tools. I certainly have the tool for square taper one. I'm pretty sure my MTB has a HT2 BB so I think I have the tool for that one too.

Do I need to find out the current thread size or is it just a case of measuring it with the calipers?

Wheelspinner

No need to bother. Your Trek will 99.9999999999% guaranteed to use the BSA standard. Other than some exotic Italian frames and weird old French things, pretty much all modern bikes use that thread spec.

The HT2 bottom brackets come to fit road or MTB frames, with three plastic spacers all 2.5mm thick. There’ll be instructions in the BB pack about what to use to fit your frame - just measure the shell width once the old BB is out. Will be 68mm I expect, but check.

nbuuifx

Wheelspinner said:

No need to bother. Your Trek will 99.9999999999% guaranteed to use the BSA standard. Other than some exotic Italian frames and weird old French things, pretty much all modern bikes use that thread spec.

The HT2 bottom brackets come to fit road or MTB frames, with three plastic spacers all 2.5mm thick. There’ll be instructions in the BB pack about what to use to fit your frame - just measure the shell width once the old BB is out. Will be 68mm I expect, but check.

Brilliant thanks - I'll try and pull the BB out tomorrow to measure up.

Currently it has Sora STIs and the left one is sticking, and they are the ones with the lever up on top to go one way with the gears - so I'd like to upgrade them.

The ones I'm looking at have 11-34 cassettes and 34/50 chainrings - which as a double actually gives a lower bottom gear and a higher top gear than my current setup.

If I don't upgrade then realistically as a minimum I need a new BB as mine is making a noise, the chain rings are getting worn as is the cassette and ideally I need to replace the left STI shifter. For the cost of all those parts I'm hoping I can move over to the double tiagra instead.

Fingers crossed it will all fit!

nbuuifx

Right I took it out.

It is a VP-BC82
BC1.37"x24T
68 x 113

Does that all sound correct? It is a bit rusty near the seals so I'm guessing that is why it currently creaks!?

I take it the 68 is the shell width as you suggested. The 113 is the overall axle width. How do I know what able width I'd need of I'm changing to the double cranks instead of triple?

Thanks

Wheelspinner

Yes 68 is the shell width. The thing with Hollowtech BB is you don’t have to worry about axle length - it is fixed on the crank, and the manufacturer has designed it for optimum chainline already.

So, just install the new BB cups (with spacers as defined for a 68mm ROAD bike, if any) and install the new crank. Simple. Only thing you need to pay attention to is: adjust the bearing preload cap on the non-drive side first to the recommended setting (quite low), then do the crank arm fixing bolts up properly. Those bolts are quite high torque. See instructions. Do *not* lose the plastic shim in that gap.

nbuuifx

Is this the correct one? I'm pretty sure it is but it didn't mention hollow tech anywhere. I think it is also the same as the RS500.

https://www.chainreactioncycles.com/mobile/shimano-tiagra-4700-bottom-bracket/rp-prod137762?gs=1&sku=sku499594&istCompanyId=8d42cf00-fc35-44ce-8770-97ae3ffd4c16&istFeedId=c759ee22-6d7f-4501-bd00-f1af47c60490&istItemId=iwxtwamtm&istBid=t&pgrid=60711843258&ptaid=pla-426089234589&utm_source=google&utm_term=&utm_campaign=PLA+All+Products&utm_medium=base&utm_content=mkwid|sgjoF8DZT_dm|pcrid|309840119912|pkw||pmt||prd|499594UK&gclid=CjwKCAjw_-D3BRBIEiwAjVMy7CoOawJ8awXj-bYworvkV0MB1NqkByjhOL0TYlxcZYcXwPYdU13e6hoC_DsQAvD_BwE

Wheelspinner

Yeah that'll work.

Here's the official instructions:

https://si.shimano.com/pdfs/dm/DM-FC0003-07-ENG.pdf

PMark

Just a reminder, if you are going from 9 speed to 10 speed, you might need to get a new spacer for the rear cassette (depending on if the wheels are 11 speed compatible or not).

nbuuifx

markdurdle said:

Just a reminder, if you are going from 9 speed to 10 speed, you might need to get a new spacer for the rear cassette (depending on if the wheels are 11 speed compatible or not).

I'm going from 8 to 10. The drop out is correct. On my last post regarding this someone said as long as I went for the 11-34 cassette it would all fit. Do you know if that is correct?

step83

Cassette will fit, just as mentioned you may need the spacer between the largest sprocket and hub body (goes on before the cassette basically), it will usually come with one anyway.
It'll just be an innocuous looking plastic ring with three thicker bits.
I've managed to get 10 speeds onto some 7 speed hubs in the past so you should be fine.

cq20

I've just done this conversion on an old Giant SCR that I've been using on my trainer. I used an RS500 bottom bracket and a Sora chainset. Given it is on the trainer, I'm not too worried about the weight. Some of the manuals suggest that a spacer(s) will be required between the bb cups and the bb shell. I didn't need any because the chainline is fine without them (just as well because no spacers were supplied with the BB). I have moved from a triple setup and have the front changer switching between the old middle and high positions with the limit screws adjusted to suit. The reason for switching was that the old square bb was getting a bit rough and I wanted to drop down to 165mm cranks to match my road bike setup. All fairly straight forward apart from repositioning and reindexing the front changer which was a bit of a faff.