SOHC.co.uk Forums > CB500/550
What do we see here?
Bryanj:
ANY lubricant on surface or thread allows the nut to turn easier on the thread and this alters the torque setting when the nut stops turning thereby altering the clamping force applied to the items in question.
You shouls always use the manufacturers setting in which should be specified dry, oiled or grease and if so which type.
Honda do specify molycoate on some of the GL1000 bolt settings
K2-K6:
As Bryan says above.
Fundamental problem is that (for convenience) the assembly uses a torque method to measure rotating resistance (friction is changed with lubricant type) to carry out setting of tensile (stretching the cylinder stud) loading.
There's conversion between the two, controlled by friction, which can be changed with the lubricant used.
Make the nut more slippery and for the SAME torque number, it will pull more tensile load on the stud, clamping the cylinder joint tighter.
Ultimate (and how the original engineering design sets the torque) is to put a dial guage on the end of the stud, measure elongation, and compare that to tensile load specification for material used. Example maybe, you get 0.5mm elongation for 10lb/ft torque.
Think of the stud as a elastic "bungy" cord.
Oddjob:
I wonder how that would affect stainless steel cylinder head studs Nigel. I mean it's not really practical to measure the stretch and as they are stainless you need grease to prevent galling so how would you know the correct torque after using say Nickel grease.
K2-K6:
In reality the stretch and calculations would be done for a representative fixing to give a torque number that's suitable and not by individual stud in situ. So measuring and practicalities involved to give usable working figure, same as any stated torque setting.
There's a more fundamental issue, in that generally available stainless steel has nowhere near the tensile load capability of these std studs. In other words it lacks the ability to clamp the structure to the same force needed to keep the head and barrels on during use.
If the tensile load could be matched, then it would likely be a very similar figure.
The stud is working (the bolts on the engine are steel that's "quenched and tempered" ) with a minimum tensile capability to give the clamping force the designers intended. The effect on changing to ss that didn't match this would be like not doing the bolts up sufficiently, the same rotary torque would likely stretch the ss into yeald and not clamp the structure.
These studs may look ordinary, but there's alot of interesting features in them, probably a topic on it's own.
Oddjob:
I've got an engineer making me some stainless steel studs for the 500/550. I find they rust through the barrels. So I sent him one and asked him to match it, the first bolt failed the stretch test, at 16ftlbs it stretched too much due to the waisted look of the old bolts, he's now reducing the waist to see if he can get one that works whilst sort of keeping the original look. I'll also be fitting stainless steel shouldered head nuts, hence the question re the torque.
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