Things have been largely quiet on the Fuji front recently, since the bike's mostly as I want it and nothing's dropped off.
I have been keeping an eye out for a 170mm replacement for the 175mm crankset however, since I get quite a lot of toe-overlap with the front mudguard and all the cool kids on the internet tell me that smaller cranks are so hot right now. While I'm extremely skeptical of whatever new trend is helping to prop up the cycling industry this week, the science seems sound and my joints are ruined, my flexibility limited and my belly large... all of which could potentially be better accommodated by a shorter crank.
Further, my Routier has a 165mm crankset and seems fine (maybe nicer in this regard, in an unquantifiable way), so I can be confident that shorter cranks won't be any worse than what's on there currently.
Oddly the crankset fitted to the Fuji (Shimano Deore M591) is only available in 170 and 175mm flavours; leap-frogging the middle-of-the-road / typically-most-common 172.5mm option.
Since I've already bought replacement chainrings and low-geared triples are increasingly thin on the ground, it made sense to buy a replacement M591 crankset with the shorter throw. These seem like hen's teeth so I widenened my search to the ostensibly very similar M590; which upon casual glance looks exactly the same.
After a few months of looking I got hold of something apparently suitable for reasonable money in the form of an M590 in pretty decent nick - as illustrated below after a good clean..
The crankset came with a pair of tatty Shimano PD-M324 pedals and BB51 bottom bracket - which turned out to be scrap; although did donate its inner plastic shield in replacement for the cracked one on the bike.
The first job was to remove the pedals; which is easier on the bike but I wanted to get them off first incase there were any issues. I tried to use my brain for once; reversing the NDS pedal on the axle to make the whole lot more stable and give something to lever against; all sat on blocks of wood to support the axle and a towel to protect everything. Thankfully the pedals have an 8mm hex drive in the back so allow the use of a breaker bar; the NDS pedal coming off fairly obligingly.
The DS pedal on the other hand was another matter; taking as much torque as I dared put through the fairly skinny hex bit and remaining resolutely stuck. This apparently wasn't helped by some abuse with the propane torch or application of paraffin (which I'd actually added some days previous); so I had to consider other options.
I was quite pleased with the end result. I could put my foot on the pedal end of the NDS crank arm to prevent it rotating, load up the breaker bar as much as I dared then give the whole lot an additional incentive by twatting the spanner with a mallet - which worked beautifully first time
Pedals off, next were the chainrings as I wanted to swap over those from my existing M591crankset - partially because the outer has the plastic guard; for which there was no provision on the ring fitted to the replacement M590.
I'd purchased Shimano's TL-FC21 tool for the chainring nuts and thankfully it wasn't really necessary to crack the bolts off thanks to the friction between the nuts and rings... later reassembly was a totally different matter that saw the tool slipping out of the nuts many times, often causing damage.
Ultimately I don't think this tool is intended to react the full tightening torque; just hold the nuts in place while the bolts are being spun up. From that point I had success winding the torque wrench round rapidly which seemed to incentivise the bolts turning on the nuts rather than the nuts in the crankset..
The new crankset was fully stripped and got a good clean with paraffin. I noticed some superficial corrosion inside the axle which was treated with phosphoric acid; with varying results.. it certainly did a great job on the corrosion nearest the DS; removing it almost completely and leaving just a bit of discolouration in the area. I don't think it did so well further into the axle for some reason but it's dried leaving a reasonable protective layer so the rust shouldn't get any worse.
Next the original crankset was removed from the bike, stripped, cleaned and its chainrings waxed in preparation for fitting to the new crank.
Now I had both crank assys bare in front of me I thought it prudent to confirm that they were indeed interchangeable.. which much to my dismay turned out not to be the case
Long story short the deal-breaker was that the axle on the original M591 is 126.5mm; 6.5mm longer than that of the M590 replacement. The DS crank arm assy of the M591 is fitted with a 6.5mm thick plastic spacer and its geometry is such that the M590 crank would go on leaving the (stated 50mm) chainline unchanged, but would position the DS pedal further inboard than that of the M591; and we all know the potential dangers of assymetry across the bike..
Dejected I reassembled everything as I'd found it and resolved to flog the M590 chainset. As the evening wore on I became more defiantly curious and ventured down the shed with various measuring devices. I checked the pedal position of the original M591 setup by measuring from the outside of each crank arm to the opposite side of the down tube with calipers and was shocked to find that the DS crank arm was more than 10mm futher outboard than that on the NDS
A few more measurements confirmed that the fitment of the replacement M590 crankset should actually improve this situation, so this morning it was all back on again with renewed enthusiasm. To avoid wasting more time I fitted the M590 crankset complete and this time found that the DS crank was now only around 1.2mm further out than that on the DS (around 10% of the previous discrepency).. I'll take that!
A quick blast round the village was had to ensure all was well and upon my return everything was stripped again, appropriate bits cleaned a bit more and waxed before being reassembled with the original rings on the new crank.
I also had to polish out an inboard section on the NDS crank arm where it locates on the axle, due to interferance in this area preventing it from seating correctly. I think this was because it had been ridden with the crank arm bolts insufficiently tight in the past which had caused some local damage / a high spot where the material had been displaced by the axle's splines.
Anyway, it's now all back together, on the bike and on the face of it I'm very happy with it. I only have this morning's brief test ride to go by but the shorter cranks do perhaps feel a bit nicer (although I'd probably not have noticed in a blind test) and the overlap is much less if not gone completely (oddly it's fine on the DS, not the NDS - but that's a problem for another day).
The new crankset is in generally better / more presentable nick than the original, and of course actually fits as it should rather than the cranks being spaced differently across the bike. This of course begs the question of how this happened in the first place with an apparently original crank. Was it intentional (to accommodate something I've missed, because of availability issues with the correct items, or perhaps the M591 cranks were cheap..?) or a mistake (crank incorrectly specced at the design stage, the wrong parts supplied). Maybe the M591 I have was fitted as a replacement; although I think this is unlikely given the age of the bike.
Anyway, ultimately it's been a fortuitous if time-consuming rollercoaster - sourcing a crank I thought was essentially the same as the original in the key areas, finding it wasn't and assuming it wouldn't fit but then finding the original was wrong and the new crank is the answer!
While trying to learn about the differences between the M590 and M591 cranks I found precious little on the net, so in the hope of maybe saving someone else from a similar fate the key differences I've found are covered below.
As far as I can tell both cranksets are (or more correctly were, since they now appear discontinued) available in 170 and 175mm crank lengths, with or without the big placcy chainring protector and with one of two gearing options - 48/36/26 or 44/32/22. Both are available in black or silver.
The headline difference is the 6.5mm longer 126.5mm axle on the M591; which, if used with the included 6.5mm spacer places the chainline in the same place as the M590 but puts the pedal position around 6.5mm further out.
I suspect that the M591 may be intended to fit the larger 83mm downhill bottom bracket spec instead of the 73mm MTB standard the M590 appears to be designed to work with; athough I can't be arsed to think about this any more...
EDIT - I think the wonkyness of the M591 and other similar cranksets in the Shimano range is intended for use with chain cases..
I think the two images below nicely illustrate the difference in axle length and crank arm depth / offset between the two (M591 on left). Note that the black plastic spacer is still fitted to the base of the M591's axle:
Difference in axle length illustrated again:
I've also found the shape of the crank arms to be fairly subtly different too; not sure if this is an M590/M591 thing or whether it's due to the different crank arm lengths. M591 at the top..
Tbh I prefer the aesthetic of the outgoing M591; however I don't prefer the prospect of walking in circles because my legs are on the wonk after thousands of miles with effectively mis-matched crank offsets..
NDS arms:
So there we have it; it's been a long and convoluted road but it turned out OK in the end. Thinking I'll hang onto the M591 crankset for a while, then maybe look to move it on if I have no issues with the M590 replacement
