Replacement 7-speed drivetrain?

[Northwind]

OK, I'll cut a long story short here I'm looking for a suitable replacement 7-speed crankset for an old Carrera mtb, ideally running with a 48 or bigger big cog. The old parts are all Shimano Altus from around 1990, so I'm looking for a fairly direct replacement. Ideally sub £50!

The long story, not cut short:

I've decided to repair/restore my 1991 Carrera Krakatoa, which was my first real mountain bike, bought when I was 15 with my paper-round money (9 months of paper-round money!) I rode it to bits, then I gave it to my brother who rode it into smaller bits for another 5 years, then it landed in the garage and it's not moved since.

I went to throw it away, but I just can't, it's my oldest surviving possesion and we've been through a lot together (it broke a wheel, I broke my wrists, it was a match made in hospital...) I've been looking it over and the spec is surprisingly good, nice (and fairly rust free) Tange cromo frame, Shimano bits all over, bonty wheels. It was the flashest bike in the playground! But there's no denying it's ****ed, not a round bearing in the thing. The BB barely turns

It's not exactly a restoration as I'm not at all bothered about period correctness or even OEM appearance- it had a flex-stem, none of that please! But I want to make it into a comedy occasional offroader (take it to Glentress and make the people on carbon full sussers feel silly- might have to find a set of Smokes for it) and regular commuter. It'll keep a retro style but some bits will be modern (it has an a-head adaptor fitted frinstance, and I imagine I'll use a low riser bar).

So... BB and head bearings were simple, the paint's all coming off (I don't know what the heck it was painted with, but it's tougher than my motorbike tank was...), I've trued the wheels and replaced the hub bearings, etc. (annoyingly, it has one nice Bonty/Weinnman wheel and one horrible halfords special to replace the one I destroyed) But now I have to deal with the drivetrain...

The bike has Shimano Altus gears, combined rapid-fire shifters and canti brakes, and ran 21-speed. The mechs are in decent nick, a few days in a box of paraffin and it all seems to work. The cassette and chain are fairly recent and should be saveable too. But the crankset, hmm. It's intact but it's sooooo worn, 5 years of big-ring commuting with some very worn out chains. I'm amazed it lasted as long as it did.

So... Obviously, Wiggle is a bit short on Altus cranksets, and the chainwheels are rivetted. It was a 48T big ring and I'd like to go to 50T or bigger ideally, as it'll do a lot of commuting. What are my best options for a replacement? For obvious reasons I'd like to keep the original mechs and triggers, since that's a lot of bits to replace.

Cheers!

 

[FluffyChicken]

Well you are in the right place.
Shimano Altus is later than you seem to think (1993 was the first of the Altus brand, there a many different types I believe it was not an MTB group but a Touring/Everyday person group), you should easily be able to pick up anything Deore LX/DX even XT if you want to move to MTB components)
I assume you need a new cassette if you chain has been stretching and destroying it.
They can be had as well, just check if it a freewheel or screw on, picture of everything help lots on this site
7 speed chains can be bough from wiggle or look at ChainReactionCycles they tend to be cheaper (or Merlin cycles who have less choice but even cheaper)

EDIT/
being 7 speed you may have had a 13 tooth smallest sprocket and hence you wanting a 50tooth just for commuting . You will be better looking for a 12 tooth smallest rear cassette and stick with 46 or 48 large ring.

http://www.chainreactioncycles.com/Mode ... odelID=128
7 speed HG50 (even have 11tooth rear but not sure if it will fit the older rear wheels, may do though)
or
http://www.chainreactioncycles.com/Mode ... delID=6387

Been plenty show up in the for sale section though for not a lot.
Same place sells square taper bottom bracket compatible chainsets as well, though you should again put a Wanted in the Wanted section and look through the For Sale section.

 

[Northwind]

Mmm, it was a long time ago, I probably have my dates wrong Cassette and chain might be OK, they were both replaced fairly recently as a "keep it going" measure and from a visual check look not too bad- I'll replace the chain on general principles but they're easy to come by still. The trouble with cranksets is that most shops aren't good at accurately identifying the chain size, from what I've seen.

Cheers!

 

[FluffyChicken]

btw Altus is now a very low end component (probably always was as I never really looked at much lower than Deore LX back in the beginning of the 90's)

I assume you'll be after something like this, but second hand would be cheaper.
http://www.wiggle.co.uk/p/Cycle/7/Truva ... 360021264/


for example
http://www.retrobike.co.uk/forum/viewtopic.php?t=46652
some nice Sugino one's in there.

 

[Northwind]

Yeah, it was just good spec for a kid's bike when everyone else had first-gen SIS Any rapidfire shifters were good for a lot of playground points Still, they've lasted essentially forever despite a lot of neglect, so I'm fairly impressed still. If I'd got that Raleigh Activator...

(oh, it has 11T on the rear cassette, the reason I want very high gears is that my commute to work has a huge descent in it, so even with the 48/11 gearing I still spin out)

Thanks very much for the suggestions! I'd actually looked at the Truvativ cranks but couldn't confirm if they were 9-speed or not.

 

[FluffyChicken]

The difference between a 48 tooth and 50 tooth is only about 1 to 2 mph.

 

[Northwind]

Hmm, yeah, I suspect that I can't run the gearing as high as I'd like without running into othe rissues. So it's kind of a balancing act but I know 48T is slightly lower than my ideal. At the end of the day getting a good reliable crank at a decent price is the goal, slightly higher gearing is just a "nice to have". Certainly not a big enough deal that I'll turn away from that Truvativ crank you mentioned, which is a big tick in every other way.

 

[FluffyChicken]

The only thing I just thought about this morning is
I am assuming you need square taper bottom bracket connections. You bottom bracket is the correct length for that chainset.

You could just buy a new set, but really check the for sale and wanted. The low end stuff is not often posted so wanted may ease it out.

Think about Road chainset and the size you're looking at though.


I use to run 48/11 and now modern MTB set have gone to this compact size (44tooth) unless you buy the trekking version (48tooth)
e.g.
http://www.chainreactioncycles.com/Mode ... elID=11780 think they would call them touring chainsets ?
That's square taper as well.
But if a new bottom bracket is needed then you could get the cheaper and easier to get hold of octalink or even the hollowtech style with built in bottom bracket.


There are lots of choices

 

[Anthony]

Sounds like it's not so much 7-speed that's your limiting factor as the square tapers on the bb, if you plan to re-use it.

You seem to basically need road cranks, and square taper means you need to get retro cranks off eBay. Taking care as Fluffy Chicken says to ensure that what you buy is compatible with the axle length of your bottom bracket. Although tbh you might find it simpler to buy a new bb as well, to suit whatever cranks you choose.

With a bigger big ring, you're likely to need a new chain anyway, unless you kept the spare links when you cut it and you've got a few pins. The cassette sounds no problem.

I don't think the 7-speed aspect matters. A 7/8 or 9-speed chain will run on a 7-speed cassette and either chain will also run on any cranks. There's nothing wrong with 7-speed IMPO.

 

[Northwind]

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?