Upgrade to Front Mech

beardytwo

Hi all, New here and have been following your excellent site for a few weeks and it has inspired me to get out more regularly on my old MTB. I'm planning on building a bike next year (I like to think I am reasonably capable) but in the meantime I have been upspeccing a few bits on my current ride. Anyway I have a Diamondback Topanga which I thought was ok at the time! and has Shimano STX Mechs (21 speed). I planned on upgrading both to Deore with the view of using these again next year.
I have now installed the front mech (Top pull to replace the same) but it will not change to the largest cog if it is set at the correct height to the teeth. It appears that the inner face of the chain guide on the Deore is catching the inner face of the middle cog stopping it from moving over sufficiently. The cogs are all rivetted (Think its an Alivio) and has some pressings in the face which probably help the chain to move from one to the other? If I move the mech up higher it will change but is not ideal as the chain rubs.
Is there anything I've neglected to do or is it just incompatible with my current setup I know the Deore is 8/9 speed compatible but I thought it would be ok if I just restricted its travel. Its not the end of the world as I will keep it for future use (looking at hopefully using a Kinesis frame next year)

Any help would be appreciated Thanks...
?

supersonic

You may have to move the mech a little higher.

beardytwo

I think your right supersonic, I've got the old one on at the moment and went for a ride last night and it is a bit unpredictable in its changing. The rear one is slick after a service but the front is a bit to hesitant although most of my changes are with the rear and I leave the front on the middle cog. I guess thats typical? I might give it another go at the weekend if it doesn't workl I'll keep it in the parts store. Thanks for the response.

stumpyjon

You might find that the mech won't fit a new frame. I built a hardtail up from scratch earlier this year and had a top swing mech to put on. Unfortunately due to the positioning of the bolts for a bottle cage the band on the top swing mech wouldn't fit so I had to swap the mech I had for a bottom swing mech which works fine. Also remeber to keep the shims from the new mech as the seat tube on your new frame may be a different size to your exisiting frame.

I've also had the same problems with setting up front mechs. Don't get too worried if it seems too high etc. as long as it's shifting Ok and not fouling anything it's fine. Use the installation instructions as a guide on the initial position and work from there.

Good luck with build, I thoroughly enjoyed doing mine.

beardytwo

Thanks for the advice Stumpyjon. I must admit now you mention it my bottle cage fittings are very close on this bike. The cage fits over the top of the mech ie: one bolt is either side. As I said if I've got time I'm going to have another bash this weekend.
I'm always prepared to have a go. Built my own computer last year and it hasn't blown up yet! :? Plenty of work on cars and houses over the years. I like the idea of building my own then its personnal and its the best way to learn.

What did you build and do you still use it? Was there anything you didn't do and handed over to your LBS. I was wondering about the headset and maybe the bottom bracket.