Sunday 28 April 2019

Countersunk seat bolts

I saw another builder with virtually flush seat mounts on the GBS Zero Owners & Enthusiasts Group, Looked much better than nuts/bolts on the outside and worth copying the approach.

Some Googling and searching on eBay turned up a whole line of undiscovered products designed for Go-kart seat mounting. Kart countersunk seat washers in alloy, nylon and titanium. Perfect.

My mount stack retaining the 50mm square washers inside to spread the load and thick washers above as spacers.


M10x25mm bolts were ok, 30-35mm would have been even better - my new learning for today is countersunk bolts are measured over their entire length including the head. I decided on alloy countersunk washers at about £5 for 10.

On the other side my initial thought was to use T-Nuts in the seat rail, so they cannot rotate when tightening - theres no room for a spanner in here. However - thinking through, not really keen on the robustness of these - I want my seats staying attached to the floor under all circumstances.


The option I decided on - especially since seat attachment strength is critical to safety - known good M10 nyloc flange nuts with flanges ground down so they fit inside the seat rail but cannot rotate. Should have been stainless really but I had none to hand.

Very fiddly to get the nut in place on top of the seat rail and tighten, but overall the finish looks much better to me.


Comparison part way through the job - passenger side closest with say 5mm or so below the floor pans, old style bolts still on the drivers side with at least 12-13mm for the nut alone. Looks tidy enough although the floor pans are not as flat as they used to be.

Hindsight and patience would have avoided my mix of metals - stainless bolt, BZP nut etc.

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