Hi guys, did the larger, earlier tank have a flat underside like the later tank, or did they have a shaped underside for use with an OHV engine?
Cheers, Mick.

email (option): mick@motorbikemike.org.uk

Hello Mick,

The ones i have seen all had the shaped underside.

Wonder why BSA didn't put a flat bottom in the sidevalve models, should be a lot easier to make and would increase the capacity a lot, which should interest the war department also, I think.

Regards, Michiel

email (option): m.wijbenga@hotmail.com

Hi Mick,
The underside is shaped as an arc,
with the maximum is about 2 inches in, under the middle of tank, as far as I remember.

I once heard that it was shaped so in order to deflect more air flow onto the cylinder head while driving, but I doubt it..


Noam.

email (option): noam10@gmail.com

It was just a case of the tank being used for OHV models as well such as the M24 etc....Ian

email (option): ian@wright52.plus.com

The pre-war Norton tank had clearance for the ohv motors (including the very tall 600cc) but when they went over to the flat-bottomed design for the WD16H with just a small dome above the plug, they retained the same top pressing resulting in a tank with substantially greater capacity than the civilian counterpart.

BSA must have made a concious decision to reduce the size of the tank. Could it have been to do with all up weight ? Did they actually revert to the 1937 style top pressing ?

Early WD16Hs of course broke their front tank mounts. maybe the extra capacity wasn't such a good thing ?

Hi, heres a pic of the underside of my early tank...

email (option): fullerbarry@hotmail.co.uk

barry there is a lot of skirt round the bottom of the tank i think you could easly convert a later tank into this type by just welding an extra skirt along the bottom

Thanks for the pic Barry, that the same as the tank I've just found. And thanks to you all for your comments. Another part for the KM20 project.
Cheers, Mick.

email (option): mick@motorbikemike.org.uk

aargh..i hate you lot...
i'm still searching for one ..4 yrs and counting.

email (option): chris.astinbarker@btinternet.com

I suspect the cutaway isn't deep enough for the ohv engine, it's more for giving clearance for removing head and headbolts easier.I suggest someone try the fit on ohv's before painting!