1974 Roadster Tank Differences?

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Aug 9, 2005
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Is there a difference between Roadster tanks around 1973-74? I have noticed some tanks from this period that have a thin steel flange around the tank, while others do not.

1974 w/flange (look at tank closeup):

1974 w/out flange:

Did these tank designs just change in the middle of 1974, or is there something I am missing here? The reason I am asking is the bike I am looking to buy has the flange and I am trying to figure out what's what. Thanks again!
Like most things Norton this can be debated but I will give my observations.

I was under the assumption the 73 and 74 tanks had the exposed seam with the 75 (Mark III) having the cleaner look.
This thread mentions this bike to be a Mark IIA. So maybe this is another difference in the Mark IIA. It would make sense that the exposed seamed tanks would be used up first, then the transition.
Or maybe the tank was switched.

I believe your tank to be correct for a standard 74, Mark II.
I may have assumed too much by stating that it was a IIA -- the frame number is 305548, which makes it a late '73, so I assume that this would therefore be the correct tank for the bike. I confess, I don't actually know the difference between the II/IIA, though I assume that the latter was a transitional model between the II series and the III series, no?

Thanks again for the clarification -- looks like the tank is correct for the frame. (though I personally think the rounded tanks are more appealing)
The MkIIA had the black cap silencers and an airbox almost like the MkIII (very subtle difference) and retained the right side shift. The left side cover is slightly different as well. It was the first attempt to meet noise restrictions. I believe it was produced only in the 1974 model year although I have seen references to a 1973 manufacture as well.
Mk1A & Mk2A 850s

Hi Ron,

Roy Bacon has pictures of the '73 Mk1A and '74Mk2a in his Norton Twins book. Your comment is the same as his regarding these were made to meet reduced noise requirments. All the John Player Nortons had the Mk2a airbox and annular discharge silencers in 1974 while few Mk2a roadsters or interstates came to the US. I'm not sure if any states required these. The airbox for the Mk2a has the ignition switch bracket bolted on and the left side cover bracketry is different than the Mk3.
The metal tanks have the flange ?

The fibreglass tanks do not ?

That has been my observation.

The seat on your "1974" 850 appears to be from an earlier 750, perhaps an "S" model. It has the pleats on the upholstery & the "banana" shape base, like some of the earlier models had.

Nice looking commando you have.
nortonfan said:
The metal tanks have the flange ?

The fibreglass tanks do not ?

That has been my observation.

The 850 MkIII (metal) Roadster tanks have no flange.
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