Triple Chainset Front Derailleur Adjustment Problems

Fivethumbs

Regular
Can anyone help with why my brand new Shimano Altus front derailleur (Shimano FD-M371 Atlus) does not seem to want to adjust out enough to clear the outer chainring on my new Shimano Altus triple chainset (Shimano FC-M311 Altus Square Taper Chainset)? I have tried to follow the Park Tools video to make sure I'm doing it right but after adjusting the inner chainring with just enough clearance when I switch to the outer chainring the adjustment runs out and the chain is still rubbing the outer plate of the cage. I'm using a new Shimano CN-HG40 6/7/8-Speed Chain and the rear cassette is a new 8 speed Shimano CS-HG41 mated to a new Shimano Altus RD-M310 Rear Derailleur. I tried to use all compatible components (I am rebuilding my ancient Giant FCR hybrid) so it must be something I'm doing. Any help with this problem will be very gratefully received.
 

Ajax Bay

Guru
Location
East Devon
why [does] my brand new Shimano Altus front derailleur (Shimano FD-M371 Atlus) does not seem to want to adjust out enough to clear the outer chainring on my new Shimano Altus triple chainset (Shimano FC-M311 Altus Square Taper Chainset)?
:welcome:
Well, I will hazard a guess that you've fitted this chainset onto the current bottom bracket (BB) (ie the one for the previous chainset) and the FC-M311 Altus chainset needs a slightly [edit] shorter BB spindle.
Needs a "123 mm square taper bottom bracket"
https://www.tredz.co.uk/.Shimano-FC-M311-Altus-Square-Taper-Chainset_74973.htm
Like this (but maybe a 73 not a 68mm shell): https://www.tweekscycles.com/uk/shimano-bb-un300-square-tapered-bottom-bracket-2012876/
What was the previous chainset? How long is the BB spindle? How many mm between the inner ring and the chainstay, at its closest point?
 
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OP
Fivethumbs

Fivethumbs

Regular
Thanks for the reply! I used a new bottom bracket (Shimano Bottom Bracket BBUN26) and it all fits well but maybe I need a shorter BB so the chainset sits closer to the frame as a longer one would put the outer chainring even further away. I'll measure it all in the morning and see how long it is and the gaps between the inner ring and chain stay! I bought all the components together and I thought I had got the right ones but it was 3 years ago and I've only just got round to putting it all together :blush:
 

Ajax Bay

Guru
Location
East Devon
Sorry - yes you need a BB with a shorter spindle to bring the large chainring in towards the seat tube/FD. Having said that 123mm is on the long side for BB spindles. I'm surprised that the one fitted is longer.
With the FD limit screws screwed 'out' you can determine the horizontal range of the FD (measured from the seat tube) and the proximity of the inner chainring to the chain stay determines how short a BB spindle you can fit yet avoid interference. This will inform your choice.
 
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OP
Fivethumbs

Fivethumbs

Regular
I went out and looked at the bottom bracket and it is definitely too far out the inner chainring is miles away from the stay. Then I looked a bit closer. It looks like I've put it in the wrong way round! I didn't know you could do that, the only other bottom bracket (on my Raleigh Airlite) I've changed only went in one way. Could it be I have a non standard arrangement on my frame or am I just a bit stupid?
 

Ajax Bay

Guru
Location
East Devon
Though the threads on left and right sides are the same tpi they are reversed. So I don't think you could physically have put the UN-26 cartridge BB in the wrong way round. On the UN-26, the left side is (should be) plastic. In any case the square tapers are symmetrical (their ends are the same distance away from the BB shell centre point).
 

Ming the Merciless

Formerly YukonBoy
Location
Inside my skull
Is the derailleur cage parallel with outer ring?
Is derailleur the correct height?
Is the high limit screw set properly?
With cable detached can you push cage out further than achieving via gear cable?
 
OP
Fivethumbs

Fivethumbs

Regular
Yes, Sheldon Brown's is a mine of information, I will give it a read on BBs, up until now I was thinking it was a derailleur issue.
Have you looked at Shelden Brown's website? lot's of lovely bedtime reading on BB's (and whatever else you always want to know but was scared to ask) :smile:
 
OP
Fivethumbs

Fivethumbs

Regular
Is the derailleur cage parallel with outer ring? Yes
Is derailleur the correct height? Yes
Is the high limit screw set properly? That is the issue, it has run out of adjustment!
With cable detached can you push cage out further than achieving via gear cable? Not sure, I'll try that and see, thanks! Now tried and that's when I discovered the issue with fouling the centre chain ring, so thanks for helping me find the issue!
 
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OP
Fivethumbs

Fivethumbs

Regular
OK, after a pleasant (but cold) Sunday morning in the bike workshop I have discovered the problem. It appears that the middle chainring is fouling the inner plate of the derailleur as it moves towards the outer chainring so preventing it moving to the limit of its adjustment. I think the chainset and the derailleur are not compatible but I will try raising the mounting to see if I can get it to clear without it being too high for the outer chainring. This provided a pleasant diversion from discovering that the explosive puncture I suffered on my road bike (going downhill round a bend 😬) was caused by a 10mm cut that went through the tread and the tube, probably caused by a flint hiding in mud dropped off a tractor.
 
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