Advice on pinch bolt studs please

Further to this thread I have bought new stainless steel studs and bolts on ebay. They are not available from Yamaha.

The studs go here,



when i tried to torque them properly, they sheared before the correct torque, so they have obviously been overtightened and compromised in the past.

The old stud vs the new stud



The old stud has a 10mm thread, the new one has a shorter 7.5mm thread. This is the end of the stainless stud that screws into the alloy forks.

Obviously these coming undone when riding could very easily be fatal.

Is the shorter thread going to be safe enough?

Should I put threadlock on the end of the stud that is going into the fork?

Thanks

[Bibio]

why don't you just do away with the studs and fit bolts?

Originally Posted by Bibio

why don't you just do away with the studs and fit bolts?

I'd imagine the reason Yamaha fitted studs in the first place, was to reduce wear and tear on the alloy threads in the forks, and to avoid wear on the alloy bracket that holds the spindle on, caused by steel threads. The stud shoulder is smooth (though a shouldered bolt would be too) and the only bit that ever turns is the nut on the stud.

The front wheel comes off quite regularly for tyre changes (knobblies don't last long with road use between lanes and winter commuting too) and cleaning/lubrication as the bike is exposed to a lot of mud, water (front spindle often submerged in fords or wet ruts) and grit. I'd prefer not to be turning steel bolts inside those alloy threads on a regular basis.

[timwilky]

I always caution against the use of stainless, it is brittle compared to mild steel studs. The sort of stresses induced on the stud in that location could lead to a sudden brittle fracture.

I have 7 days to send them back for a refund if I need to. Would I be better to get hi-tensile then? There are no markings that I can see on the original stud.

[Bibio]

ahhh hadn't thought of that...

stainless will be fine as there are 4 of them as would high tensile. one thing to note about SS going into ally is that there is an electrolysis type of thing that goes on as the SS reacts to the ally causing it to slightly fuse after a period of time, so when your fitting the studs put a little copper slip on the threads.

Thanks.

No offence to either Bibio or Tim, and I'm very grateful for thier input, but I hope you'll understand what forums are like and you'd have to be mad to bet your life on the advice given in them. I try to read a lot of different posts and draw my own conclusions. SO - One vote for stainless OK, one vote for stainless too brittle. Anyone else got a view?

Your suggesting copper slip Bibio, and I was asking about thread lock! So I take it you think the 7.5mm thread depth will be plenty?

Col, I'd go with high tensile personally, as Tim quite correctly said, stainless can be brittle and I've had more stainless heads wear/ snap on me than any other, not on bikes though I must say.

Careful with torquing up stainless into alloy with coppaslip on the threads as the coppaslip increases the chances of stripping a thread due to it being overtightened. You need the friction in the threads to determine when the fastener is at the correct torque, which is why they always state torque values are for dry threads - add a lubricant like coppaslip and you'll keep tightening way past your intended torque value and chances are the fastener either shears or the threads strip before the torque wrench tells you to stop.

This may also come in handy, it's a tensile strength comparison chart for mild and stainless steel fasteners

http://www.anzor.co.nz/?T=40

[andrewsmith]

Originally Posted by Lozzo

Careful with torquing up stainless into alloy with coppaslip on the threads as the coppaslip increases the chances of stripping a thread due to it being overtightened. You need the friction in the threads to determine when the fastener is at the correct torque, which is why they always state torque values are for dry threads - add a lubricant like coppaslip and you'll keep tightening way past your intended torque value and chances are the fastener either shears or the threads strip before the torque wrench tells you to stop.

This may also come in handy, it's a tensile strength comparison chart for mild and stainless steel fasteners

http://www.anzor.co.nz/?T=40

I'd agree with Lozzo on that. Whats the recommended torque value for the pinch bolts?

If your concerned about failure load, I'd go for hi-tensile items.
Having a lookski again at the set-up of the spindle a hi-tensile would be better (or a Yamaha Cheseium steel item ).