More crank problems.

Chucker_Dude

Im absolutly sick to the back teeth of my bike if im honest. Its a GT Chucker. Since ive brought it i havent had 3 weeks in a row without any problems. Im slowely loosing the will to keep MTBing because i cant keep spending so much money on new parts to replace broken ones.

Anyway to the point, a couple of weeks ago i managed to cross thread my bottom bracket. New bottom bracket and new right crank.

So ive got a new bottom bracket and new right crank. After my ride today, on my way home. The crank came loose. I tighten it as much as i could with a normal allen key, but didnt hear the crack. Im going to use a torque wrench tommorow.

But surely i cant have done the same as before? Bearing in mind ive done about 10 hours light/moderate downhilling and about 1 hour of dirt jumping. The biggest drop ive done is about 2 feet.

Surely, surely not again :roll: :roll: :roll:

nicklouse

sounds like you need to improve your spannering skills.

having no idea what went and what your replaced it with i can not comment if it is the same problem again. but i guess you did not fit something correctly.

supersonic

I have to agree with nick, it sounds like you arent quite fitting them properly. As soon as you feel it come loose, stop riding or you'll bugger them further.

Chucker_Dude

supersonic wrote:

I have to agree with nick, it sounds like you arent quite fitting them properly. As soon as you feel it come loose, stop riding or you'll bugger them further.

I did stop riding and walked the rest of the way home grrr

But i follwed the guide from park tools on how to fit a BB correctly. And surely just fitting a crank is simple, you cant really get it wrong? Just putting the allen key bolt in a tightening it until you hear a cracking? Although maybe it needs a tighten with the crank puller?

supersonic

So what crank and BB? Crank puller nothing to do with fitting it! Torque wrench maybe benefecial for you - most mechanics give it torque of between 'a good hoik' and 'a really good hoik', but precision is good...

Chucker_Dude

(unfortuantly) They are SR Suntour Duro cranks. I cant actually remember what the BB was, only that it was £10 :?

How does a BB get cross threaded anyway? As i suspect that may be what is wrong with it.

supersonic

You need to make sure the axle and crank interface are properly prepared as per the instructions. Is it square taper, ISIS? How do you mean cross threaded? Have you cross threaded the BB body into the BB shell, or do you mean you have buggered the crank bolt up? If its the latter, you may never get the correct torque.

Chucker_Dude

supersonic wrote:

You need to make sure the axle and crank interface are properly prepared as per the instructions. Is it square taper, ISIS? How do you mean cross threaded? Have you cross threaded the BB body into the BB shell, or do you mean you have buggered the crank bolt up? If its the latter, you may never get the correct torque.

Square taper yes.

Basically what happend was whenever i inserted the crank bolt. The BB was just muching the threads so they were bald. I got through about 3 bolts before i realised.

supersonic

Are you using steel or alloy bolts? Square taper is not the best sytem for a jump bike. Are the tapers and crank perfectly clean, no grease? Has the crank deforemd? You have to be very careful inserting the bolts, ensuring it has engaged the threads correctly.

Chucker_Dude

supersonic wrote:

Are you using steel or alloy bolts? Square taper is not the best sytem for a jump bike. Are the tapers and crank perfectly clean, no grease? Has the crank deforemd? You have to be very careful inserting the bolts, ensuring it has engaged the threads correctly.

Erm? I dont know about the bolts they look steel though.

I think the tapers and crank may have a bit (if any) dust and dirt in them.

As i havent taken the crank off yet, i dont know 100% if it has deformed or not. Although i have inspected it pretty closely with it still on the bike and it looks fine. I havent ridden it while it was loose so it shouldnt be.

Now i think, they only seem to come loose when i am doing dirt jumps. Yeah it happend at my dirt jumps last time aswell. It doesnt help that the jumps have flat landings. Maybe that is it. Would you advise another 'system'?

supersonic

Yes, I think something llke a Shimano Octalink as a minimum. But for the time being, remove cranks, clean the axle and taper hole, dry, reinstall, clean bolt and threads, add loctite and tighten. Torque wrench good, if not bloody hard with a long allen key!

Chucker_Dude

ok i will go and sort that out tommorow.

Thanks for all your help.