Short version - I acquired a merlin road frame from a friend who was too short (it's a 60 cm) and am in the middle of swapping out the DA 8 speed components for SRAM rival/red.

I've never seen a BB like this one though - it was a mavic crank and who knows where this BB came from. The merlin is probably vintage mid-nineties.

There were two lockrings, one on either side, you can see the general orientation from one of the photos. There don't appear to be internal threads (this is where I start saying Uh Oh over and over). There appear to be two little... uh, not sure what they are, on the bottom of the BB shell, but I don't see any sort of place to stick a hex wrench.

Before I start whaling on the BB, thought I'd ask, hope somebody knows.

Bottom of the BB shell


Side view


Side view with the lock ring I removed (one on each side)


No visible threads... what the hey.

That Merlin has pressed in BB bearings. The bearings are pressed in and there where at least 2 different sizes used through the years. As far as I know you are stuck with using a square taper crank. May have to use a vintage 8 speed crank with 10 speed chainrings. You have a limited number of crank/transmissions options.

Maybe someone else has come across this same problem and had different results.

This might help...

https://www.merlinbike.com/bikes/pdf/MBBG_NG.pdf

edited to add: Looks like its gonna be a pain in the tuckus though.

wow. i wouldnt remove the BB, since it looks like you're stuck with square taper if there are no BB shell threads. square taper campy cranks are still widely available from UK vendors. they will be 10-sp. you can use whatever group you want with the 10-sp campy crank, i think you were going to go with RED??

Well, that just SUCKS!

Conveniently, I have a vintage 8 speed crank but I wanted to use my shiny new 10 speed carbon fiber crank (sob). I think I'll take it to the LBS and get them to replace the bearings at least, they feel less than smooth.

Anybody else have any good ideas?

Thanks guys. (walks away cursing)

as i mentioned by PM, a good machine shop should be able to turn some threads in the BB shell for fairly minimal $$.

Your Merlin was made before Merlin learned how to properly thread Ti so they bailed and used a pressed in bottom bracket like you are currently stuck with. I assume the taper is JIS since the original crank was a Dura Ace so fitting any Campy square taper crank (ISO taper) will be probematic at best.

You might contact Litespeed (Merlin is part of them now) and see if they can either thread or replace the bottom bracket shell and at what cost. I expect it won't be cheap. Funny thing is that Litespeed always supplied threaded bottom brackets, even in the time period your Merlin was built.

The BB shell may not be big enough to except any threaded BB cup.

Right, and if that's the case, welding in a new threaded bb shell ($$$$$) is the only way to use a current bottom bracket and crank.

good point, i would have just imagined that the shell would be a standard size, but that might not be correct.

https://www.parktool.com/repair/readhowto.asp?id=178

The Park "Shimano Press Kit" -- BB90 -- may work -- maybe. The first gegeration Merlin frames came with a BB shell that was way too small to fit the kit. The next version may fit because I do not know what the measurements of the shell is. I do know that the BB shell appears to be smaller than a standard shell diameter. If it is the same as a Standard/English BB shell then you might have a soluton. Good luck.

Well, the BB shell is narrower than the new BB, so threading isn't an option.

How does that press kit work? Sounds intriguing!

It's irrelevant. It won't work. It's basically a shimano external bb, without the cups. With the bearings pressed into the frame. BB90 frames were designed specifically for that bearing size.

BB90 = 6805 bearings size 25x37x7
OP's BB = 6903 bearings 17x30x7

Dimensions nowhere close to being compatible.

I guarantee you it's not going to work. Especially with info from the op in his above post. The 6850 bearings that are standard on shimano ext bb's are larger than the english shell. That's the point.

OP: If you can obtain different axle lengths and install them you may find one that will give you the appropriate chainline for a campy crank. The taper is probably not the same either -