Nuts and Bolts question

[averb]

Are the pinch bolts for the forks anything special or can I replace the damaged units with run of the mill stainless cap screws?
Breva 850
TIA
Steve

[rodekyll]

Almost anything but stainless.  It's not real structural.  Use grade 8 steel metric.  Keep in mind that a pinch bolt *pinches*.  Just a nudge past snug.

[Perazzimx14]

Almost anything but stainless.  It's not real structural.  Use grade 8 steel metric.  Keep in mind that a pinch bolt *pinches*.  Just a nudge past snug.

Metric uses a different grading system. You are looking for bolts with head stamps of 10.9 OR 12.9'S no such thing as a metric grade 8.

 http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CCYQFjAC&url=http%3A%2F%2Fwww.k-tbolt.com%2Fbolt_chart.html&ei=8OcoVd_hNfaIsQTGw4CgAw&usg=AFQjCNGI-QQZC86hdCBZRzQ5BO7Z6csZ8w

[dilligaf]

What would be wrong with stainless?  :BEER:
Matt

[rodekyll]

Metric uses a different grading system. You are looking for bolts with head stamps of 10.9 OR 12.9'S no such thing as a metric grade 8.

 http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=3&cad=rja&uact=8&ved=0CCYQFjAC&url=http%3A%2F%2Fwww.k-tbolt.com%2Fbolt_chart.html&ei=8OcoVd_hNfaIsQTGw4CgAw&usg=AFQjCNGI-QQZC86hdCBZRzQ5BO7Z6csZ8w

Sorry -- I meant grade 8.8 - regular duty metric.  What I was trying to get across is that being pinch bolts they don't need to be super-duty 12.9's, but you do want something more substantial than A2 stainless.

Matt -- the common A2/18-8 stainless fasteners are stretchy and soft.  They're only good for being shiny.  Grade 8.8  steel is roughly 2x the yield strength of stainless.  Even 'mericun grade 2 is stronger.

[John A]

Now I gotta remember stuff. Metric stainless is graded different than ferrous metric . It has a property class of 60, 70, 80 etc. higher number indicates higher tensile strength.if you use 70 or better it is strong enough for general work. For brake discs I ordered 100 or 80 by memory.

[Antietam Classic Cycle]

If I use stainless for pinch bolts, it's A4/80 which is 316 stainless.

[rodekyll]

If I use stainless for pinch bolts, it's A4/80 which is 316 stainless.

But when we run down to tru value hardware for stainless fasteners we're getting A2, which is 18-8 or "grade nothing" ornamental.  That's the stuff your allen wrench chews up.  I just got some 12mm shoulder bolts in A4 (316) stainless to use for brake pedal axles.  Spendy stuff.  Close to twice what they cost in 18-8.

[Antietam Classic Cycle]

But when we run down to tru value hardware for stainless fasteners we're getting A2, which is 18-8 or "grade nothing" ornamental.  That's the stuff your allen wrench chews up.  I just got some 12mm shoulder bolts in A4 (316) stainless to use for brake pedal axles.  Spendy stuff.  Close to twice what they cost in 18-8.

A4 is only a few key strokes and mouse clicks away. I use a lot of A2 and generally find it's actually less likely to be "chewed" by an allen (or any other sort of wrench) than the original plated steel fasteners that came on Guzzi down through the years. 

[rodekyll]

Yes, I get my A4 off the enternet.  We don't have local sources for that sort of stuff. 

But to get back to the op, Charlie -- Are you saying you would or would not use 18-8 stainless for those pinch bolts?

[boatdetective]

The minimum yield figures are:

a2, a4/70 stainless  65KSI
grade 5                 92KSI
grade 8               130KSI
Metric 8.8              93KSI
metric 10.9          136KSI

This seems about right. Austenitic stainless steel cannot be hardened. Still, there are plenty of applications on the engine (valve covers and other non load bearing covers) where yield is not a real issue.

Just out of interest, specialized grades of stainless such as 22/13/5 (aka Nitronic 50 or Aqualloy) or 17-4PH can give very high yield figures comparable to common hardened steels. Upper end 17-4 can give yield of 160-190ksi.  

No- these grades are not commonly available as fasteners. 22/13/5 is available in rod form for those frankenstein types among us who might want some shiny structural material.


  

[Antietam Classic Cycle]

Yes, I get my A4 off the enternet.  We don't have local sources for that sort of stuff. 

But to get back to the op, Charlie -- Are you saying you would or would not use 18-8 stainless for those pinch bolts?

Since they're only an M6 x 40 socket head and get torqued to only slightly more than "snug", I wouldn't hesitate to use regular 18-8. 

[averb]

OK, off to the hardware store. Thanks to all for the swift and erudite answers.

Steve

[Chuck in Indiana]

Since they're only an M6 x 40 socket head and get torqued to only slightly more than "snug", I wouldn't hesitate to use regular 18-8. 

Oh, me either. If you are torqueing them very much at all, you are screwing up..  ;D