M739 FC requires new middle ring i thnik!

sparkyork

hi everyone,

ive got the above chainset of the 4 arm fixed outer ring variety, after my last three rides to dalby and sherwood, ive been getting chain suck in between middle and inner.

ive got a nine speed chain, cassette, shifters

somethings telling me that the current middle ring doesnt have the chamferred edges like the 9 speeds to push the chain down or up etc, ive looked at a 9 speed chainset and the 9 speed ones defo have a more gubbins to stop chain suck by the looks of it

this is the only time i get chain suck, so im wondering if anyone knows of a good replacement middle ring for this crank set, i believe its 104 bcd too

i know external cranks are all the rage but i like the look of my retro m739's! and they were the brain child of future crank design too!

any help advise appreciated on sourcing a reliable middle ring

never had chainsuck when i was 8 speed on my truvativ cranks only when ive changed to m739 and 9 speed chain

thanks

supersonic

You have thicker 8 speed chainrings, and a 9 speed chain: with Shimano chainrings they often do not work.

You need a new chainset really. You could buy a 9 speed inner and outer, but would need to shim them.

sparkyork

thanks for your reply

do you mean the farthest outer one? if so this four arm spider has the outer ring permenantly attched to the spider, with the middle and inner being removable, do you mean i should just replace the inner and middle or the inner and outer skipping the middle?

the only way i can change the outer is by getting a 5 arm spider giving me full ring replacement, think i can get on of these for £15

but i dont get any problems from outer to middle and vice versa, just middle to inner and back up, so should i just get the middle and inner?

ive just been tinkering in the garage and removed the middle ring, when removed it sits like its bent throughout its middle, what seems odd though is that the inner seems to sit farther away friom the middle ring, unless its just an illusion with the chamfered edges not getting particularly close to the inner ring,

could you go into a bit of detail about shimming out some new chainrings aswell?

many thanks

rich

njee20

That being a very dated chainset, and having that integrated spider on the big ring it'd be easier to just replace the whole thing, cranks, rings and BB. Look at the latest Deore chainsets, be a much better solution for little more money than a new inner and middle.

supersonic

Yes, I'd just replace.

I had an old LX chainset very much like your XT. I got a 9 speed middle ring for it, but it does not sit in the middle as they are thinner, so needed to use 0.75mm chainring shims.

Not really worth the hassle!

sparkyork

Thanks for your input, I know ultimately I'd be better with new chainset etc but if all I need is a middle ring and four shims then that's gonna be a lot cheaper than splashing out on new chainset and bottom bracket

supersonic

I needed 8 shims at a quid each lol!

And the chain may still not work on the outer ring correctly. Worth a go maybe, your call!

sparkyork

A pound each! Good grief!

The chain runs fine on the outer so maybe that won't be n issue for now

Do the 9 speed rings have more of a chamfered edge aswell to aid shifting ?

Well if I can get a 9 speed ring and a few spacers for 30 bucks then it's a lot cheaper than a crank upgrade, do I might just give it a go!

Any decent makes of rung I should go for?

supersonic

Newer rings have been redesigned with shifting shelves, pins and edges. 9 speed chains on some older ones could get stuck in extreme cases.

I'd look for Deore chainrings, are very good.

sparkyork

thanks

ive got a evans cycles near me and they have one of these http://www.evanscycles.com/products/rac ... t-ec005039
they dont have any deore stuff just xt and xtr and the ones they have might not work with mine anyway

thel33ter

CRC do deore chainrings for £12. Or you can get a whole new crankset for £58.

http://www.chainreactioncycles.com/Mode ... elID=40496

Otherwise have a look on www.retrobike.co.uk - You'll almost certainly find a replacement for around £12