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My tandem has two small screws above each bottom bracket, one on each side (so four in total). I've not seen them on any other bike, and I can't figure out what they're for! Suggestions so far have been (a) letting water out (except that they're on the top) and (b) putting oil in (except that I didn't think that was how you're meant to service a bottom bracket - I thought you had to take it apart). I know they're not for an eccentric bracket, as there's other screws elsewhere for that. Picture of screws on rear bracket here: http://s8.postimage.org/z4evs6791/IMG_1950.jpg enter image description here

In case it's any help, original bike spec page is here: http://www.nkilgariff.com/CBcats/Cat_40/CB15.jpg

enter image description here

All help much appreciated!

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    This is a nice bike. Could you post MORE (and sharper) photos of it, here or elsewhere? – heltonbiker Sep 28 '12 at 5:25
  • @heltonbiker Unfortunately it's more accurate to say it was a nice bike - the years and the previous owners have taken their toll somewhat. And I'm pretty sure that the guy I bought it from on ebay ("I was going to do it up for the kids, but didn't get round to it") has re-installed the spindles the wrong way round (it's just about visible in the photos). I'm planning to take some photos and post them - in the meantime, it looks a bit like this but worse. – evsmith Oct 1 '12 at 0:31
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It's hard to tell from your picture because they're out of focus, but they look a bit like grease nipples:

enter image description here

i.e. like the ones in the top left of the picture. Do they have the little ball bearing in the middle?

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  • On closer inspection, they do indeed have the ball bearing - thanks for the pictures! – evsmith Oct 1 '12 at 0:36
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Grease fittings are still to be found on the Big Toys, but just about everything consumer-focused is of a sealed bearing design. @heltonbiker is right... the old stuff is just forced out by the new stuff.

What you've got there is the same head design for a fitting that's show in the Wikipedia article too. Your crank isn't the sealed type and probably could use some new grease at least once a decade.

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I know they're not for an elliptical bracket, as there's other screws elsewhere for that

Elliptical? Do you mean eccentric? Are you sure that's not what they're for? Maybe there's one set of bolts to adjust the orientation, and another to lock it in place.

But there's also this on the spec sheet:

LUBRICATION: "CB" twin force-feed to brackets and head, oilgun and instructions provided.

This would suggest that there are two grease fittings on the bottom bracket. Modern bikes don't have them, but this ain't a modern bike.

The only way to be sure is to take it apart.

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  • force-feeding grease with guns through those nipples looks like something common long time ago, I have already seen it in many types of machinery from the past (when things were intended to last and be serviced many times). The principle is to remove the old grease with new one, or something like that. No wonder they gave up doing this, but apparently it was "the way to go" at the time... – heltonbiker Sep 28 '12 at 5:23
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    Grease zerks are not "from the past". While most automotive bearings are now sealed for "life", lots of heavy equipment, manufacturing equipment, etc, still uses zerks. And the idea of removing the old grease with the new works -- if you'd ever seen it done you'd understand this. – Daniel R Hicks Sep 28 '12 at 11:49
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    Yeah, I once worked at a place that had a lawn tractor/front loader and it had plenty of grease nipples on it. You don't see these on bikes anymore because we have sealed bottom brackets. Before sealed hubs you had to take the bottom bracket out to regrease it. With the grease nipples you could regrease without disassembling the bottom bracket. – Kibbee Sep 28 '12 at 12:32
  • Oops, I did of course mean 'eccentric' - I blame posting too late at night! I've corrected it in the question. – evsmith Sep 30 '12 at 11:36
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Though they sorta look like grease zerks, I doubt that.

They could be used to somehow secure the crank bearings. I would guess that they were used for retaining/adjusting the eccentric, but you indicate that's elsewhere.

Note that what you see may be caps over smaller screws.

Have you tried removing one of them?

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