I have a custom welded seat mount for a Kirkey aluminum seat that is also attached by brackets to the roll cage. When I replaced the roll bar with a roll cage I had difficulty securing the seat with the OEM (new) seat bolts. Thought I had stripped the thread but finally realized the seat mount frame was not square and the mount was binding the bolt (just barely) from threading. Quick fix was to bore out the hole in the bracket and I was able to make the CR school at RR (thank you guys for a great couple of days).

Have been reading Carroll Smith's handbook on fasteners (they say reading/learning at age 52 prevents the onset of dementia ). The seat bolt is installed loaded in tension but in use (crash) it will be loaded in single shear.

My concern is that widening the bolt hole in the mount I will have weakened the joint strength. Is this concern correct and is it critical enough to demand making a new seat mount frame.

Probably not critical (but yes you are correct that a mishapen hole weakens the mount).

You should ensure that the mounting of your harness is perfect however, that is what will save you and your seat from flying around the cockpit.

You should ensure that the mounting of your harness is perfect however, that is what will save you and your seat from flying around the cockpit.

Hi,

What you say is true most of the time. However, if you spin around, and go rear first into a wall at high speed the harness will not be helping you. The only thing stopping you crunching backwards and hitting your head or spine on the rollcage is your seat and its mountings.

Cheers

Robbo

^Very true, hence the "probably" !

I was assuming the roll bar was fairly close behind the seat to provide additional support, my mistake.

Anyone know if the M10 bolts for the seat mounts are torque to yield bolts?
What would be their maximum allowable single shear load? Any guess on what percentage loss in joint strength by using a wrong size bolt hole?