Middle ring slippage

[Bodhbh]

Getting slipping under high loads on my middle chainring on an otherwise new drivetrain. Under loads just under that which causes slipping they'll be a clicking noise coming from down there somewhich - it thought it was the pedals at first. The middle ring is 2nd hand however looks pretty fresh, inner/outer ring, cassette, chain are all new, although everythings done a couple of hundred miles now.

First question: It's a FC-M752 XT Hollowtech 1 Shimano crankset. Assuming it's worn and I need to replace it, what middle ring would do? I've got a couple of 32T, 104mm PCD middle rings kicking about but they don't fit on the crank. SJS do both 'N' and 'S' rings (whatever that means) -

http://www.sjscycles.co.uk/product-...-mm-PCD-4-Arm-Middle-Chainring-N-32T-3936.htm

http://www.sjscycles.co.uk/product-...mm-PCD-4-Arm-middle-Chainring-S-32T-12570.htm

Other question: Is there anything else I should be sanity checking before spending money? Other relevant point I think of: used the Sheldon method to get the chain length, although this has given me a chain one link longer than the original. Annoying - otherwise the shifting seems better than any I've managed to date with my own fettling.

 

[spence]

Although great shifting and stiff arms, XT chain rings of that era where known to be made of cheese so I would be suspicious of a 2nd hand one.

If you want VFM and some durability go for basic deore rings.

 

[Ivan Ardon]

Can you flip it over and run it "backwards" on the unworn part of the teeth?

 

[Bodhbh]

Cheers for the replies, although seems I misrepresented the problem after having another look at it last night.

Whole drivetrain is shimano XT and either new or as new as dammit. The middle ring is new. I had some problems fitting one previously and remembered incorrectly how it panned out, but the one on is new. The threat of slippage under high loads as indicated by a clicking noise happens on all 3 rings although it's most easily reproduced on the middle one. Also, tending to get autoshifting under loads on the bigger cogs at the back, and since last night a couple of instances of chainsuck and it getting jammed (1 previous, when still adjusting gears, so I didn't think to mention in the initial post).

Is there an easier way to test how gears performing understress than finding a hill? The nearest one I know that needs the granny ring is about 15 miles away. I intend to tour on the bike in late April and will probably be going thru some pretty steep climbs, I don't want a risk a bail out, so what to be 100% sure the problem is fixed (given gears work great on the about town commute, easy to gloss over and ignore atm).

Hrmm very confusing, perhaps I should just post a new thread.

 

[spandex]

The thing is if your drivetrain is set up right and is not worn including the chain it will not slip, jump or 'auto shift' under load or not. The 'auto shifting is down to the mech not being set up right and the slipping as far as I can tell by what you have said it is one of two things. 1st it is a old chain with new kit. 2nd it is the wrong chain for what you are running?. My bet is the 1st one.

 

[byegad]

Agree with spandex. The right new chain on new rings doesn't slip or 'hunt' the rear cassette. Also if the chainrings and cassette are brand new a brand new chain is needed otherwise you will rapidly damage the new rings and cassette.

 

[Mr Pig]

Is the crank on properly, do the gears line up correctly? That could cause both of your problems. Is it the correct length of BB?

 

[Bodhbh]

It's a brand new Ultragra 9-speed chain, I replaced the whole drivetrain at the same time (and dumped most of the old stuff on the hackbike).

As a newbie I suppose I have least confidence in how I've setup the b-tension, everything else seems fairly straightforward (well that's does to, but seems more ambiguous to know if it's set right).

Only old thing in there is the BB, although it worked fine previous (Shimano BB-ES30, was not budging easy so thought it could stay there for time being least I round off the socket).

 

[Bodhbh]

Is the crank on properly, do the gears line up correctly? That could cause both of your problems. Is it the correct length of BB?

Well good question. Cranks seem to be on solid. Chainrings look a bit far out to me, although I'm no judge, with MTB gearing the inner rings tend to be better lined up with the centre of the sprocket anyhow?