Replacement 7-speed drivetrain?

[Anthony]

Ah, no, no worries there, the BB barely turns now, it is categorically dead. It had a good innings though! BB-LP30, we salute you!
OK, so can I just check something, is there a meaningful difference between a 7-speed and modern 9-speed crank? IIRC the chain is narrower for 9-speed but the link length is identical so presumably a 7-speed chain fits over a 9-speed crank, but just a little looser?

Somebody might correct me, but I don't think there is a difference, no. Nobody has ever made '7/8-speed' or '9-speed' chainrings, the way they do with chains, so I reckon the rings are an identical thickness, and either size of chain fits onto all rings perfectly happily. As you say, the 9-speed chain is narrower, because the 9 sprockets on the cassette fit into the same width as an 8-speed cassette, i.e., they're closer together, so the wider 7/8-speed chain would snag the adjacent sprocket if you used it with a 9-speed cassette.

Personally I think modern road chainsets are too flash-looking to suit an older mtb. I'm also 'careful with my money', and the price of them is a bit :shock: to me. That's why I'd be on eBay looking for something more in my price range. But that's just me, and needn't be you. All a matter of taste obviously.

 

[Northwind]

Thanks for that- I've seen a lot of cranksets advertised as 7/8 or 9 speed, but of course that doesn't mean they don't work with other sizes. And at worst the chain here will be wider, so should still run true even if this isn't right, it's not like the pitch has changed.

Totally agree with what you say re visuals. I'd like to say that the looks of the thing don't matter but it'd be a TOTAL lie :roll: Just spent most of another evening removing paint and scotchbriting the frame up, looking really nice now, I might be able to trick people into thinking it's titanium. At this rate I might get the clearcoat and rust inhibitor on next weekend, that'd be a good start to the year.

Incidentally, did I mention that I love this forum? You guys have been very helpful, much appreciated. I've got a gaping hole in my bike knowledge so I can work fine with the old bits, and likewise I can work fine with modern parts, but it's when I get into teh grey areas that I'm simply clueless.

 

[FluffyChicken]

I'm always learning the modern stuff (to me that would be sometime after ~1995, even then I don't know a lot from the latter parts of 94 and 95 as I just road my bike by that time and was not interested in new stuff).

Oh and I went a looking this morning and you can do no worse than have a good read of this site, just for fun
Things tend to be buried and it's not the easiest site to navigate to that important part you want but here is a good link
http://sheldonbrown.com/speeds.html


If you stay at this site (here at RetroBike) it'll be more then a burning hole in you knowledge that you'll have... watch you pockets...

 

[Northwind]

I'm building a new bike at the same time so don't worry, my pockets are already fully holed. So, either I can't spend any more, or spending more make it any worse, not sure which as yet. That nice Mr Brown told me to spend my way out of the recession

Thanks for the link, I'd been over Sheldon's pages but missed that one somehow :roll:

 

[cce]

Ah, no, no worries there, the BB barely turns now, it is categorically dead. It had a good innings though! BB-LP30, we salute you!

i'm quite surprised at this - i've never had an LP-series BB last more than about 6 weeks of road riding - i once killed one in a single off road ride.

 

[Northwind]

I have no idea how long it's been dead, to be fair, my brother's a bike-killer and probably wouldn't notice So it could have been grinding scrap for most of the last decade.

 

[cce]

they were soooo bad that i stopped taking the bike back under warranty and just bought a proper (UN-52) one. considering i was on paper-round money at the time, that took some doing!

 

[Northwind]

Hmm, at a guess mine did 10000 miles. Between 8 and 10 probably. But not especially high stress for most of that.