Bit of a weird one; I bought some nice used XT cranks off here to replace the non-series Shimano OEM ones on one of my bikes. A like for like swap, I thought. Except the XTs' axle is 120mm and the non-series OEM ones are 115mm. I've got 4mm of spacers I can use (It's going into a King press fit BB I also got off here, with a #4 Fit Kit), but I wondered if anyone else had run into that at all. FWIW, King's instructions say to fit them to the drive side, so I'll be checking chainline, but I've not run into this before with any Shimano HTII cranks I've owned.
Which model XT?
M8120, and it's going into a 148 boost frame, so it should be the correct chainline. The non-series ones came with the bike and are MT601-1s. They fit the new (and old) BB perfectly fine.
(I should add - the first thing I did was check for spacer washers - no dice. The LBS who did a bang up job of fitting the BB with the correct tools are closed today)
Some Shimano now use spacers on the BB axle as well as spacers behind the BB cup to get the spacing correct.
M8120 is not boost, well its labelled as such but a lot of the time the standard M8100 is better and M8130 is labeled super boost.
As mert hints...it's probably an M8120.
https://singletrackmag.com/forum/bike-forum/bb-spacers-needed-for-xt-12s-chainset-and-chainline/
my wide chainline trek came with a a deore crank that had 2x 2.5mm spacers on it i would say.
so yer id say you have a wide chainline crank that should incorporate those spacer, note, they are part of the crank not BB, at least on the deore setup
Sounds like you need the M8100 not M8120 version.
M8100 gives a 52mm chainline, the M8120 gives you 55mm chainline and has 2 spacers for the axle to make up the difference or should have, I run m8100 with 148mm rear end, some newer bikes are pushing the 55mm chainline, some actually need it due to clearance, some people swear 55mm is better, I think 52mm is right for 148mm rear, I guess both are acceptable if they have clearance.
Thanks all! I could see alerts that people were responding, but couldn't actually see the responses in the new forum, so I gave up and went for a ride on a bike that had working cranks instead. It was a good ride.e
Thank you for the advice. I'll check with the seller to see if he still has the spacers, but it might have to be a case of asking my bike shop nicely if they can bail me out. Checking with a straight edge between the 6th and 7th sprocket on my 12s cassette suggests the chainline is quite wonky with 3mm of spacers in the drive side, which is quite annoying. I don't need the clearance, Clarence, but I'll have to make good and run with it for now I think. Quite annoying, but thank you for the explanations - I really do appreciate it.
Relevant Shimano tech docs for anyone looking in't future:
https://productinfo.shimano.com/en/lineup/deore-xt-m8100-1x12?q=m8100
- it's items 5 and 6, I think - but don't take my word for it
If they are definitely M8120 they should fit a normal width 73mm BB shell and give a 55mm chainline and a wider 174mm Q factor, designed for bikes like the new Scott Scale, Spark etc and also Cannondale Scalpel which utilise the bigger off-set to allow for bigger XC wide style tyres.
I have the Deore (MT512) version on my Scale 930 and it fits straight into the BB shell with no spacers. I tried fitting my XTR M9100 52mm chainline cranks but due to the - also - narrower Q factor the NDS crank was way too close to the chainstay.
Is it definitely not a XT M8130 which is designed for Super boost, 157mm axle width and a 57.5mm chainline with an even wider 181mm Q factor?
Thanks Steve - yes, they have M8120 stamped / laser etched on the back side. What's missing are the spacers that should have come with them to pad out the gap. It's going into a PF92 shell, and a frame that's min 52, max 55 chainline.
you can probably get away with some generic spacers:
Amazon.co.uk : 24mm crank spacer kit
ive got some random spacers on one of mine IIRC
One of my riding buddies recently walked into this but in his case his new cranks had a shorter spindle, so he has struggled.
I also recently fell foul of Shimano chainline embuggerances when buying a used set of HT2 cranks from Ebay. The ones I bought and the ones I was replacing have all of the exact same codes on the inside of the crankarms. But on installation the chainline was different due to the spider itself. Luckily, because I'm still running 4 bolt, this could be sorted with some longer bolts and some washers. Although I have had to file a flat side into every washer so they don't foul the chain outer plates.
Sometimes the pursuit of perfection by manufacturers can create so many options it becomes prohibitive to the average Joe. And seeking perfection in shifting on a MTB, when it will spend much of its life caked in filth, seems OTT.
Thanks Steve - yes, they have M8120 stamped / laser etched on the back side. What's missing are the spacers that should have come with them to pad out the gap. It's going into a PF92 shell, and a frame that's min 52, max 55 chain line.
That seems more odd, as the MT512 I have in my Scott is fitted into a 41x92 BB size (normal press-fit) and there are no spacers on the spindle. It is a tad annoying to be fair with the mixed standards and off-sets, the way Shimano does it.
If it works clearance wise, I'd be very tempted to put the spaces on the NDS to get the chain line as close to 52mm as possible - although that may well the way you do it anyway.