Afternoon boys,
So, i was riding along today and my crank arm fell off… Non-drive side.
Managed to get it kinda on there to get me home.

So, i got home and took it all apart, here’s what i find.

The crank arm is ‘toothed’ inside across it’s length, however about 25% of my length of tooth has worn away. Also the thread on my HT2 retaining bolt is badly worn.

So, lets ignore “can we fix it” because i rekon it’s toast… But the question is… WHY ?

What holds the arm in place ? is it the 2 5mm Allen key bolts, or is it the screw in end cap ? Or maybe even a combination of both ?

My thoughts are that i didn’t tighten either the cap or the bolts enough when i’ve had my arms off previously. This is mostly my own fault i guess as i’m over cautious of tightening due to poor longevity of BB’s in the past…

Cheers boys.

the end cap is just to ‘preload’ the BB bearings and plays no part in holding the arm on.

Use a torque wrench – the clamp bolts are ‘pretty tight’ if you’re doing it by hand.

and use loctite on them.

the plastic end bolt is there to gently pre-load the bearings prior to tightening the clamp bolts – not to hold the arm on under any circumstances and should only be finger tight.

Are you sure the drive side arm was fully pushed through the BB and do you have the correct amount of spacers on the BB?

If your BB shell is 68mm you need 3 spacers, if 73mm you only need 1 spacer.

The plastic end bolt should not be used to pull the drive side arm/shaft through the BB. It should already be pushed through fully before fitting the non-drive arm.

The arm that fell off will indeed be toast. If the splines on the shaft are okay it may be worth trying to find a spare arm. If not the whole lot is fit for the bin.

I have a 73MM shell and 1 spacer (Drive side).

I’ve got no real issues binnin the lot… looking at the splines on the shaft, they’re good enough… but i’ll probably go for a new set all round i guess. The price won’t kill me and i have a paypal fund for that.

Cracking deal on a Merlin crankset with their 10% extra discount… Bit irritated as i didn’t plan on spending money this week lol. But hey ho….

This exact same thing happened to me a couple of weeks ago. Never had it happen before but it happened on both bikes on the same day.

First, I was riding the BFe with a Deore crank up a gentle road climb towing Jr on the tag-a-long. Something felt wobbly I looked down just as the crank fell off. The plastic preload bolt was still pinched in the crank arm. I rolled home had a look and the splines on the NDS Arm were chewed a bit so I filed them down and put it back on the axle, it wouldn’t fit without the filing. The preload cap was chewed so I pinched the metal preload bolt off the Saint cranks on my Enduro and went out again all was fine.

Second, a night ride on the same day on the Enduro with no preload bolt but the pinch bolts done up tight. Something felt odd I looked down and the arm was nearly off the axle. I had no tools so I bashed it back on with my heels either end of the axle and headed home. I kept having to do that every 200m or so.

Previously both sets of cranks were done up tight and I have had no previous problems with them, it was as if somebody had undone the bolts for fun. I don’t get it.

I will be making sure my bolts are nice and tight before heading up Snowdon this weekend. Certainly dont want an arm to fall off coming down there!

always use a torque wrench and blue loctite when working on the twin clamping bolts

clamping torque is 12nm on those twin bolts

most issues with Shimano HT2 are related to either improper set up (spacers are incorrect for BB width), unbalanced torque on the clamp bolts causing movement under heavy load, or unprepared bottom bracket shell (not faced)

Shimano HT2 is incredibly simple and reliable when instructions are followed, its basically an “A-Headset” with splines when you look at it carefully, and then look at your fork and modern headset system, your stem is the non-driveside HT2 crank arm and the plastic bearing preload cap is the same as your stem cap