Here's the problem and a beer voucher to the genius that provides me with a solution that works!

Sanderson Soloist singlespeed with Middleburn RS7 cranks on it – ISIS spline (ISIS and singlespeed together not great I know)….. FSA bottom bracket – cant remember which one but is virtually new. Here's the problem – doesn't matter how tight I do the bloody crank bolts up they always always come lose after 5-10 miles. I've even taken to taking a 10 mil allen key on rides with me!

Is it the cranks, the bolts, the bottom bracket or is it me?

Help please!

Cheers

Tim

I've had this problem with middleburns on a crank bros isis bb on my sons bike. After the second time I gave him my XT's and put the middleburns on my SS.

I've covered the bolt in loctite this time to see if that helps and it's not come loose yet (only done about 60 miles on it though).

Not doubting you manly prowess, but are you deffo tightening it up enough? Get a shop to torque it.

I ran Uno and ISIS no problem.

Sounds to me like the spline on the BB or the inside face of the crank arm may be ever so slightly worn which will allow a tiny bit of play which over time and sometimes a very short period can lead to them loosening. Also have you checked that the bolt is in fact driving all the way home as if not the bolt could seem tight but the cranks wont be fully seated.

You aren't using self-extracing crank bolts are you? From you saying you use a 10mm allen key it makes me think not, but I had a problem with these undoing themselves on my Middleburn cranks… to the extent that one of my cranks fell off the bike while we were driving along the M1! Luckily it landed on the roof, without doing any damage, and stayed there until I could pull over.

Gotta be a crank/bb issue – as the cranks will wear and the bb not, I'd say the cranks (assuming bolts tighten properly)

Thanks chaps

Am using super human heft to tighten them up – and a torque wrench so think I'm off to buy a bucket of loctite and some new crank bolts to see if that does the trick!

Cheers

Who gets the beer token then??

+1 donks as thats happened to me I'd try 10 ton epoxy resin if it is only one side. As you want to be able to remove them. Best solution scrap the isis and get HTII.

On my dodgy bikes, I use a 4 foot steel tube on an allen key to tighten the crank bolts.
Ok maybe not a great solution..
J.

I had the same problem with a different BB/ISIS crank set up. Loctite did the trick, but make sure you give the mating surfaces a good clean first.

I'm not familiar with these components, but would it be possible to employ a star-washer or some other kind of thin retaining washer under the bolt head ?. Such a washer between the underside of the bolt head and the adjacent face on the crank arm, would, I hope, prevent the bolt rotating.

Alternatively, perhaps employ a tab-washer and provide a small flat on the peripheral edge of the bolt head. Wind the bolt in and bend the tab up to prevent the washer unwinding ?. Similar principle to ISO bolts for brake rotors.

Its just an Idea. Surf washer world, see if anything might suit.
(assuming there is space to get a washer under the bolt head, etc)

L

OMG washer world!!…how did that little pearl slip under the radar?