I have an “historic” Coker … very heavy, square tapper and I use on it 140mm steel cranks (because it’s my preferred length).
the only problem is that when I fall I often bend cranks! very often!
though I can buy load of cranks … is there a way to “unbend” those? (or not to bend them 
).
thanks for any advice.
May I suggest that you don’t fall?
STM
Not fall is a good idea. But when you fall, dont let your Coker fall too, try to keep your hand on the handle.
Obviously, catching the seat is the first solution. With big wheels/heavy unicycles, let the wheel flop to the side. Just keep the pedal off the ground and it’ll be fine. I learned this long ago with my 45" wheel. Trying to keep it straight up while running out of the dismount can really strain the wrist! Just let it flop to the side and it’ll help you stop. 
Having said that, my old big wheel always seemed to have bent cranks anyway. you might be able to hammer those old cranks straight like I did. These are old-school cottered, steel 6.5" cranks (what’s that, 160mm or so?).
I would take them off the unicycle, lay them down on some strong concrete, and wail away at them with a sledge hammer. The way my cranks were shaped, I’d be hitting on the thickest part, which kind of spread the force out along the crank and helped bend it back without putting too much stress in any one place. It should work with other steel cranks, though shorter ones may be more resistant. Also make sure you’re not doing any damage to the threads where the puller goes!
Good luck.
It’s true, not falling is the best option. I find that, though, when I do UPD riding a coker it’s more likely that you’re doing all you can not to fall and slide on your stomach. You’re either going slow enough that it is easy to run out of it and grab the seat or you are going so fast there is little chance of running out of the UPD.
the sledgehammer is the advice I needed.!
as for not falling it’s a lost cause: bending cranks happens most of the time when I try to save my wrists (both been broken previously :()
If you’re doing it too often, buy new, stronger cranks. The cotterless Nimbus Ventures probably being the best option…
I’ve used a pair of 120 forged Sugino’s for 2 years
AEB had them, down to 127, and the right crank was right threaded and came with no spider. I think some clever person ordered a batch of “left cranks”, to be made with right threads. At the time I was scratching my head wondering why AEB wanted 4 $ more for the right crank.
The Sugino’s are awesome. I always try to catch the seat, but I have pitched down hard a bunch of times. Those cranks will break the hub without bending IMHO.
I don’t know where to find a right Sugino crank now. I looks like your best (only?) bet is to buy 2 left cranks, and put the right side in with loctite. That should work fine, unless you are one of the world’s more persistent backwards 36 riders. If you use Pc pedals, needing 2 pairs is affordable, and you may use the extra rights some day.
The Venture’s look good, but only come in 125 and 150 now. My cynical side wonders if the reason for this is not to cut into the profitable sales of those 67 $ Doteck’s. I have been waiting a year to buy 114’s for my 36, but the only choice seems to be buy the 10 $ benders, or the bank busting Dotecks.
To bad you can’t edit the header
It should have read 140 mm forged Sugino’s. ^
I can’t seem to get stuff right today !
Oh well, at least this screw up is good news. A closer examination of the link I posted ^, shows that they do have two 127 mm left cranks listed, one that comes with right hand threads.
As long as you don’t mind going 127, I highly recomend those cranks as being very good looking and strong.
pedal protectors might help take some of the shock out of the landing reducing the chance of a bent crank.
It might work it might not but it would not be too expensive of an experiment.
it looks like it is fairly hard to find 140mm square tappered cranks!
for sure I could buy a “Kris Holm 36H unicycle hub, 140mm crankset, blk
Kris Holm 36H unicycle hub, 140mm crankset,” but this may be too much an expense for my old Coker (+ won’t probably fit).
would these fit? : http://www.unicycle.uk.com/shop/shopdisplayproduct.asp?catalogid=1010
Hmm…those Schlumpf cranks looked interesting. I have a square taper Nimbus muni with 127mm Prowheel cranks. After trying different lengths (114,127,152,170) I found 152mm to be a little too long, while I am missing some control/torque with the 127mm cranks.
I think about 140mm would be perfect for me, so if those Schlumpf cranks fit my Nimbus hub I will be ordering them as soon as I have the money 
Just got an e-mail from Roger at UDC UK where he said that the Schlumpf cranks should fit my Nimbus
I have 145 mm cranks on my Muni and it’s the perfect length (but it is not a square tapper hub)
The minimum outlay would be £75 (with the Qu-Ax cranks, a Nimbus hub and the 40mm KH bearings), assuming I could use my current spokes. This of course assumes that I am interested in learning how to build a wheel from scratch…which I am, just not now. Compare this with £20 for the cranks which I can bolt on in a couple of minutes and be ready to ride.
I’m mostly into softcore muni (if you catch my drift :p) and the square taper hub has served me fine for almost two years now, so I see no need to upgrade the hub yet.