74 Mk2 - ??? - fuel tank rear mounting and mounting in general

my 74 Mk2 (roadster) has two iso mounts on the rear of the fuel tank, similar to, if not the same as the rear muffler mounts and head steady mounts. the front has a series (5 each) of rubber washers. Old Brits shows a series of rubber washers and 5/16" studs on the rear, so my question, what is the correct configuration? i'm leaning toward the Old Brit illustration. overall, the fuel tank doesn't fit very well - the rear rubber pad is so hard and compressed, that the rear flange of the the tank hits the frame and is digging into the paint. looks like I need to start from ground zero with the tank mounting. second question, approximately, how much clearance should I have between the tank centerline and the main frame tube - OR - should I just let the front/rear rubber mounting pads set the clearance, and shim the hardware mounts with rubber pads as needed? If I go with new mounting rubber pads it looks like I'll need 5 rubber washers (each) on the front mounts and 4 (each) on the rear strap mount. TIA....

follow up question - should there be any type of ground strap associated with the tank and the frame? is there sufficient grounding with the tank mounting hardware, OR am I over-thinking this?

joe czech said:

my Mk2 has two iso mounts, on the rear of the fuel tank, similar to, if not the same as the rear muffler mounts and head steady mounts. the front has a series (5 each) of rubber washers. Old Brits shows a series of rubber washers and 5/16" studs on the rear, so my question, what is the correct configuration?

Click to expand...

You can use either the studs and rubber washers or AV mounts at the rear and by the 850 Mk3 the AV mounts are what's shown on the parts diagram.

https://andover-norton.co.uk/en/shop-drawing/151/fuel-tanks-and-fittings#
Edit: (Note that the Roadster tank uses the curved strap '21' and not the flat strap '23' as marked on the AN diagram)

joe czech said:

overall, the fuel tank doesn't fit very well - the rear rubber pad is so hard and compressed, that the rear flange of the the tank

second question, approximately, how much clearance should I have between the tank and the main frame tube? hits the frame and is digging into the paint. looks like I need to start from ground zero with the tank mounting.

Click to expand...

The tank needs to be securely fastened at the rear or the metal surrounding the front studs can fracture from the tank shaking around so I suggest you fit a new 'thick' rear pad as soon as possible and also a pad at the front to help support the the tank.

The problem with the studs and rubbers over the rubber bonded buffers is that they are not as flexible and so potentially pass more vibration from frame to tank, so the threaded stud insert in the tank can come loose or create a crack in the steel and give you a petrol leak. I have replaced all the studs with rubber bonded buffers after having to repair an Interstate tank where a stud insert had cracked the tank.

My MK II built 8/74 came with the rubber buffers on the rear and rubber pads on the front.

thanks for the replies. pretty much clears up my concerns, questions, and issues with the tank mounting.