M-Trax problems

Hi all,
Got a 1994 M-Trax 1000 (Reynolds K2 Cromoly frame) and having some troubles. I stripped the bike completely of its standard Alivio kit and have sourced almost all NOS XT from 1994/5. This is all 8speed rather than the alivio 7speed. My problem is that when I'm in the smallest sprocket and biggest chainring, the chain seems to just rub the frame slightly just near the cassette.

I know this isn't to do with me putting 8speed on the bike as I did that when I owned one way back in 94 and had no problems then!?!

Also, I got rid of the grinding bottom bracket and just used another I had in the shed but I don't think its the correct size. Anyone know what size bottom bracket id need to order?? I can get one from chain reaction but they list loads of different sizes! All I know is its a 68mm but then theres another measurement too (length??)

I'm hoping these two problems are linked somehow? Maybe wrong length bb is altering chain angle too much causing it to slightly rub the frame??

HELP so I can get this ride on the road and working sweet!

Thanks for any info!
Mark

Re:

regarding your chain catching a quick fix is to take the rear wheel off and remove the quick release skewer.then find a suitable thinish washer to fit over the outer end of the spindle shaft.refit the skewer and wheel make sure the washer sits against the inside of the rear stay of the frame.this should give you enough clearance for the chain to clear.

Re:

Thanks for that. I was thinking that as its only rubbing very slightly, barely enough to scratch paint on the frame. I just remember not having this problem when I owned another M-Trax when I was younger. Mind you every frame is bound to vary by the odd fraction of a mm I suppose.

Sounds like your bb might be ever so slightly too long, pushing the big ring out and causing the slight rub. Would be worth checking the correct bb length for the chainset against the one you have before plating with spacers imho.

Re:

That's what I need to know. What is the correct BB length for this bike? I threw the original BB away and put one in that I had in the shed which is probably wrong but now I cant remember the length of the original!

Running Shimano XT triple chainset.

Re:

Bottom brackets are matched to cranks so there is no 'correct' BB length for any given frame. On Sheldon Brown's site the correct chain line, the distance between the centre of the middle ring and centre of the seat tube, is given as 47.5-50 mm. If your existing chain line is so large that it falls outwith these parameters then simply subtract DOUBLE the difference to arrive at the correct BB length.

Re:

I'd leave the rear wheel alone, why swap spacers and re-dish if it was right before you changed the BB? According to Sheldon brown, you need a 107-113 bb for the cranks:

http://www.sheldonbrown.com/bbsize.html

Pop your cranks off and measure the axle length. If it's wrong, you can get a bb fairly cheaply (I may have one spare but not plugging a sale). If it's right, time to play with the rear wheel spacing.

Re:

Hi , i have pretty much the same frame and cranks and tried a 68x113 but it was too long and ended up using an m900 68x109 which works fine so i would look at the shorter length axles .
Cheers Paul