Fastening Concentric carbs to Atlas head

Sure this has been discussed several times but here goes. When fastening the concentric Amal carbs to the head, the original approach apparently was 5/16 BSW studs in the the head and nuts. Was there a special tool that Norton provided to enable you to actually tighten up those nuts? looks like almost an impossibility to get in there. I would image a 5/16-18 BSW or even a UNF allen bolt would be easier.

I remenber that I had used in that case an allen bolt (but UNC !!) , easier to reach with the allen key !

Or those with 5/16 UNF on the carb side with reduced head ,easier to reach with your socket ?

jms said:

Sure this has been discussed several times but here goes. When fastening the concentric Amal carbs to the head, the original approach apparently was 5/16 BSW studs in the the head and nuts. Was there a special tool that Norton provided to enable you to actually tighten up those nuts? looks like almost an impossibility to get in there. I would image a 5/16-18 BSW or even a UNF allen bolt would be easier.

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You have to cut the short leg on an allen wrench to get it in there if using 5/16-18 UNC stainless (or not) allen bolts. Even then I'm not sure it can be done easily in the limited space. Tightening up the center fasteners is a fiddly setup to say the least. A long rounded head allen wrench designed for going in at a funny angle might work well on the outside bolts. It's been so long since I messed with an Amal carburetor solution, I've forgotten the tricks.

You might even be able to use 5/16-18 UNC stainless cap screws for a little more bolt head clearance in that tight space. Not sure though.

I have a feeling I'll be corrected if I said anything out of bounds.

I replaced center studs and nuts on my dual Monobloc carbs with socket head cap screws. Then to make access to the SHCS easier, I made this tool. I can remove/install the screws from behind the fuel tank, as below.

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View attachment 21318


Slick