by Zack » Fri May 08, 2020 12:57 pm
My plans called for an AN4 bolt through the engine mount and leg. I had clearance issues with the bolt and the firewall. Extra washers gave me clearance, but then I had threads in the hole. I wanted the grip length greater than the hole depth because the shear action would be between the titanium rod and the steel tubing. The mount hole depth was 2.615 inches; two standard washers brings the maximum grip length to 2.739. The AN bolt options were:
AN4 bolt grip lengths
An4-30 2.5625
AN4-31 2.6875
AN4-32 2.8125
The AN4-31 has the correct grip length. The overall length includes .500 thread length and is 2.6875 + .500 = 3.1875 inches. This creates interference with my firewall. I researched options and selected a NAS shear bolt. The NAS6204-42 specs are:
Grip Length: 2.625
Overall Length: 2.950
Thread length: 0.375
I used an AN363-428 metal locking nut and two AN960-416L washers. This left me with two exposed threads.
My research found that the NAS6204 has 160,000 Dsi tensile/ 95,000 psi shear vs AN at 125,000 Dsi tensile / 75,000 Dsi shear. I'm considering replacing the AN bolt at the gear also. Additionally, I used the standard torque value for an AN4 bolt with a shear nut, measured with a torque wrench. The plans called for tightening, then backing off. Thoughts on the substitution and torque?
Zack