Inter vs "cooking" plunger suspension

Possibly to reduce amount of  chain tension on deflection. 

Pure guesswork - maybe they thought the Inter geometry gave better race performance (as per TT's suggestion above) but did not want to spend money on re-jigging for the plebs' machines?

There was a definite policy at Nortons of making sure that the camshaft models were different enough in a number of areas to make sure that the customer would pay the extra. The Inter depended too upon it's sportiness so was closer to the Manx.

A Manx would be less likely to carry an overweight pillion or be attched to a double-adult sidecar. Maybe the difference stemmed from that ?

I read somewhere that the Inter frames with the angled plungers handled better, but have not ridden one to know for sure.  It seems odd that Nortons didn't use up the lugs for the cooking models and adopt the Inter spec for the base models.  More oddly, the plunger Dominator got the more upright plungers, despite having just as much power as an Inter

Paul

Hi all,

   The Inter front down tube is about 1.5 inches longer than the ES2 which drops the cradle that much lower. The top tube is almost straight and the top rear chain stays are 1inch shorter on the Inter. My guess is that with these differences and using the same plunger castings, the angle came about with-out any intention and it was just a case of getting everything to line-up to get the correct wheelbase. Or I could be wrong ?

I'm inclined to agree with Richard. Here are some photos to illustrate his point. Grey primer frame is Inter.

Hi Ian, et al,

   I managed to find these photos after trawling though several SD cards which I took some time ago. This was when I had an opportunity to take my 1939 ES2 frame (the rusty one) over to a friend's place to compare it with his painted 1939 Model 30 Inter frame which has the suspension fitted. These 2 frames are about 600 numbers apart, so probably made within a couple of months of each other. We used lengths of studding to align the cradles, gearbox and front engine lug to try and get a datum, but when the bikes are complete it will be the headstock which will be the same height and the cradle will drop lower on the Inter, the other main point being the rear wheel spindle. The camera angle is a bit deceptive, so you might have to look with that in mind when comparing them.