Bottom bracket length for C Record chainset

[GordonB]

I've just fitted a C Record chainset (the one where one of the 5 spider arms sits behind the crank) to my new Roberts build and the chainline is clearly not correct, chainrings are too far out from the frame. The bb I used is 111mm in length, which I assumed from reading up would be correct for a double chainset.

Anyone any ideas on the theoretical ideal length? My measurements indicate that a 102mm may work but it could be a bit tight for space.

Gordon

 

[foz]

111mm is the correct length for C-record cranks. Do you have a symmetrical one (as it should be)? how much is too far out? what's the distance between the rings and the chainstay?

 

[GordonB]

111mm is the correct length for C-record cranks. Do you have a symmetrical one (as it should be)? how much is too far out? what's the distance between the rings and the chainstay?

Inner ring, which is a 39 tooth is about 11mm from the chainstay but I've done some more detailed measurements using a digital caliper. OLN is exactly 130mm, cassette is 38.5mm wide and there's 4mm from the small chainring to the outer edge of the locknut. This gives a cassette centre chainline of 41.75mm.

Downtube diameter is 28.8mm, from left side of downtube to outside of chainring is 65.3mm, chainring width is 11.3mm. This gives a chainline of 45.3mm, so the chainline is about 3.5mm out, which equates to a 7mm difference in axle length. It looks like ideally I need a 104mm axle but I don't think I've seen one by Campag, the only other one I've seen is 102mm, which may be too short.

Gordon

 

[foz]

I don't know what the chainline should be for C-record cranks, but the 'correct' BB is definitely 111mm. It is a campagnolo BB you are using? are you sure you have the cranks all the way on? Maybe try a bit of grease on the tapers to see if they go on a bit further (without going too far and getting them stuck!). I guess the frame is pretty 'normal'? (No extra long or short stays, straight stays, frame aligned properly, etc)

I have a C-record chainset on my 653 frame with a 111mm record BB and an 8s cassette, and no problems at all. I can take measurements tomorrow, but there is certainly nowhere near 11mm from the inner ring to the stay, probably less than half that.

Andy

 

[GordonB]

I don't know what the chainline should be for C-record cranks, but the 'correct' BB is definitely 111mm. It is a campagnolo BB you are using? are you sure you have the cranks all the way on? Maybe try a bit of grease on the tapers to see if they go on a bit further (without going too far and getting them stuck!). I guess the frame is pretty 'normal'? (No extra long or short stays, straight stays, frame aligned properly, etc)

I have a C-record chainset on my 653 frame with a 111mm record BB and an 8s cassette, and no problems at all. I can take measurements tomorrow, but there is certainly nowhere near 11mm from the inner ring to the stay, probably less than half that.

Andy

It's a Campag bb, definitely installed correctly, I'll whip the cranks off tomorrow and check the tapers.

Gordon

 

[Simplex]

Got to agree with foz, 111mm symmetrical. Centre section should be 48mm with 31.5mm both ends. Campag one should be stamped something like 68-SPc with the winged shield logo.

 

[GordonB]

Took the chainset off, found some crud on the taper, new bb so must have come from inside the chainset, looked like hardened grease. Cleaned all the crap out, re-greased the taper and the chainset now sits 2.5mm further inboard, chainline just about acceptable.

Gordon

 

[rusty bodie]

yup will check mine tomorrow and let you know. i've got c record group with an 8 speed cassette. remember that the axle should be installed so that you could READ the word "CAMPAGNOLO" from sitting in your saddle if the frame was transparent. we used to always get customers putting these things in the wrong way around.

 

[GordonB]

yup will check mine tomorrow and let you know. i've got c record group with an 8 speed cassette. remember that the axle should be installed so that you could READ the word "CAMPAGNOLO" from sitting in your saddle if the frame was transparent. we used to always get customers putting these things in the wrong way around.

It's an English thread Veloce sealed 111mm bb unit, as the right hand side is fixed to the unit and is a left hand thread it's not possible to insert it in reverse. Different for Italian thread of course, perfectly possible to install it the wrong way round, as is also the case with the older style cup, ball race and loose axle units.

Gordon

 

[rusty bodie]

oh sorry - i was thinking it was the cup and axle set of yore!

how embarrassing!