Joined: Aug 2017 Posts: 3 Threads: 0
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Hi Mark,
How long are your bolts? I may be able to test them for Yield strength.
Bolts with "no coating" are usually supplied with an oxide film, that may be dry, but has usually been oil quenched and possibly washed, this does give them a degree of lubrication. An absolutely dry assembly will give tightening problems due to the torsional "twist" when tightening due to the high thread friction. Best to assemble with Light oil, not with any additives as suggested by Bob Culver.
Clive
Joined: Aug 2017 Posts: 52 Threads: 1
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Location: Aberdeen, Scotland
I thought that's what Bob said. I can only see the suggestion to use oil sparingly.
Joined: Oct 2017 Posts: 1,391 Threads: 44
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For 40 years we had it drummed into us "refer to the relevant engine tightening table and there at the top of each page in big letters oil lubricated threads unless otherwise specified"
Joined: Aug 2017 Posts: 88 Threads: 14
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Location: Fylde Coast
Thank you for all your responses,
The 3 set screws which failed are zinc plated 1/4” and are 3/4” long grade R, one was dry assembled, because I planed to remove it again, the other two I was fitting to stay and had lightly oiled.
All of these fasteners are going into my chassis to replace the unplanted R grade ones used during the build. At the time I assembled the chassis using liberal applications of Wax Oil, indeed all of these original fasteners threads are thick with it, but they took the appropriate ft. lbs. torque without a problem.
You may be wondering why I felt compelled to change them;
Firstly, they have had repeated use during the build, so some stretch and thread wear was inevitable, secondly, I am expecting that as I shake down the car, that either due to vibration or unexpected stresses, some of these fasteners will need tightening, some of them repeatedly, it is amazing how vibration affects track cars, as such I did not want them covered in paint or difficult to inspect. I also did not want any crossion issues with them.
Clive, if you have the facility do a destructive test, that would be very interesting. My concern here is that the fault lies with me, so clarity on the viability of the fasteners would be most enlightening.
Regards, Mark
Joined: Aug 2017 Posts: 60 Threads: 5
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Location: Christchurch NZ
David's and Bob's concerns about the nuts not being BSF appear to be plausible.
As an aside (sorry) I wondered if BSF head sizes were ever different from the head sizes of the corresponding BSW fasteners.
I have seen many spanners marked BSF when I would have thought that BSW or BS would have been the correct designation.
Joined: Aug 2017 Posts: 60 Threads: 5
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Location: Christchurch NZ
Yes thanks Roger, that's what I was getting at.
So when whitworth head sizes changed in 1940 to the BSW sizes, BSF remained unchanged.
I can hear my old teachers: "You fool Wilson!"
