Torque setting for yokes on 750 SF2

Carpenters trick, one palm holding hard down and the other hand turning. Do it too long and you WILL get arm pump.
 
T.C said:
100% correct Thomas.
S/S will strip aluminium threads in a heartbeat.
That last quarter turn to nip it up and buggar....:(
My 3c had all S/S casing bolts when I got it, didn't think anything of it.

They are all zinc plated steel now, as per original.

Cheers
Tom
Click to expand...
Stainless is no stronger than your plated steel bolts, so cannot strip theads any easier. It is the torque you're applying that strips the threads. You might need to re-consider that last quarter-turn! Perhaps the threads were already damaged and close to letting go anyway, I find engines with a dozen or more Timesert or Helicoil and what-not repairs and often need to add some more. Re-dressing gasket surfaces often shows up quite an amount of alloy distortion around the threaded bores, a stress tests on these before assembly show they often give up at very low torque settings. I chase each and every thread on engines I rebuild, the amount of damaged threads and stretched bolts/screws/studs I find is amazing. No rule without exception... the case threads for the cylinder studs were cut to tight and close tolerances by the factory, these should under no circumstances be re-cut if not damaged in any way.

Serrated edges as described by Thomas have nothing to do with it, thread tensile strength is defined by the cross-section of the engaged threads and the material used. Even a rough fastener thread shouldn't pull a sound internal thread, friction at the threads will increase applied torque, but final tension will be greatly reduced. General rule-of-thumb, engaged thread should always be at least Dx1.5, ie, a M8 thread should be at least 12mm deep, the more the better in soft alloys. Stainless fasteners also have rolled threads, if threads show such a serrated condition, I'd re-consider my supplier. If a fastener cannot be wholly inserted without a wrench, there's something fishy with either of the threads. A wrench should only be required for final settling/tightening.

Good idea to use a torque wrench even for such trivial things as engine side covers, 10Nm max for M6, no matter what the fastener material. I often find alloy fasteners used for sidecovers (usually without anti-sieze), these won't allow more than 5-6Nm and cannot even keep the gaskets nipped up so the oil is contained reliably!

piet
 
sfcpiet said:
Stainless is no stronger than your plated steel bolts, so cannot strip theads any easier. It is the torque you're applying that strips the threads. You might need to re-consider that last quarter-turn! Perhaps the threads were already damaged and close to letting go anyway, I find engines with a dozen or more Timesert or Helicoil and what-not repairs and often need to add some more. Re-dressing gasket surfaces often shows up quite an amount of alloy distortion around the threaded bores, a stress tests on these before assembly show they often give up at very low torque settings. I chase each and every thread on engines I rebuild, the amount of damaged threads and stretched bolts/screws/studs I find is amazing. No rule without exception... the case threads for the cylinder studs were cut to tight and close tolerances by the factory, these should under no circumstances be re-cut if not damaged in any way.

Serrated edges as described by Thomas have nothing to do with it, thread tensile strength is defined by the cross-section of the engaged threads and the material used. Even a rough fastener thread shouldn't pull a sound internal thread, friction at the threads will increase applied torque, but final tension will be greatly reduced. General rule-of-thumb, engaged thread should always be at least Dx1.5, ie, a M8 thread should be at least 12mm deep, the more the better in soft alloys. Stainless fasteners also have rolled threads, if threads show such a serrated condition, I'd re-consider my supplier. If a fastener cannot be wholly inserted without a wrench, there's something fishy with either of the threads. A wrench should only be required for final settling/tightening.

Good idea to use a torque wrench even for such trivial things as engine side covers, 10Nm max for M6, no matter what the fastener material. I often find alloy fasteners used for sidecovers (usually without anti-sieze), these won't allow more than 5-6Nm and cannot even keep the gaskets nipped up so the oil is contained reliably!

piet
Click to expand...
Can we have a lead free, ethanol, oil and tyre thread now for a change?

Paul
 
If stainless bolts are a problem, you may want to notify BMW. Apparently they don't know this. On newer BMW bikes, a lot of the bolts and screws are stainless. Looking across the garage at my 2008 R1200RT, the 8mm bolts for the handlebars which screw in to aluminum are stainless.

On my Laverda's, most of the hardware is stainless and after 30 years, no problems. The cost of having the old bolts re-plated these days due to environmental regulations is crazy expensive!
 
Last edited:
You must log in or register to reply here.
Back
Top