1970 engine 139xxx

pierodn · Jan 29, 2020

Hi All.
My friend is rebuilding his 1970 engine.
All seemed stock but he has known only now that the cam is a SS.
It is clear that the prevoious owners had changed the cam.
Cases and head are stock and not a Combat.
The question is that this SS cam is in very good condition and he has not a S cam to mount.
I would suggest to him to mount the SS cam and to enlarge the head inlet ports from 30 to 32 fitting a pair of 932 carbs.
Please, what do you think about?.
Thank you.
Piero

cash · Jan 29, 2020

The SS cam is the standard commando cam the 2S is the combat cam. I would keep the engine as is it will be quick enough.
Dave

L.A.B. · Jan 29, 2020

cash said:
The SS cam is the standard commando cam the 2S is the combat cam.

'SS' is the Combat 2S camshaft.
http://atlanticgreen.com/camsurvey.htm
https://www.norvilmotorcycle.co.uk/techtalk21.htm

pierodn · Jan 29, 2020

cash said:
The SS cam is the standard commando cam the 2S is the combat cam. I would keep the engine as is it will be quick enough.
Dave

As far as i know, doesnt exist a stamped "2S" cam.

kommando · Jan 29, 2020

I would fit the cam but leave the head and carbs, check the pushrods length in case the head has been skimmed and the rocker geometry is off.

johntickle · Jan 29, 2020

With the 2S cam and the standard head you can use some 10 to 1 compression pistons in order to improve midrange torque. In the old days they used the Powermax type, today there are other options: Omega, billet pistons from MAP Cycle, JS, ...

pierodn · Jan 29, 2020

johntickle said:
With the 2S cam and the standard head you can use some 10 to 1 compression pistons in order to improve midrange torque. In the old days they used the Powermax type, today there are other options: Omega, billet pistons from MAP Cycle, JS, ...

Hi.
He will use +0,40 New Hepolite pistons with Hasting rings.
Piero

jan nelder · Jan 29, 2020

good ring choice!

dynodave · Jan 30, 2020

Listen up...correct terminology is key if you are to understand.

A 22729 SS (Super Sports) is for a NHT twin chain engine. It started around the manxman (650SS) and 88ss and atlas. It was used until the commando twin chain 20M3 series engine ended. Most all sources state any X1..X2 indicate hardness processing and NOT profile marking.

The 06-1084 "1S"" grind/profile cam is what is in the single chain 20M3S commando until the end.

The "1S" grind/profile is identical to the SS, only the cam blank whether twin chain or single chain is what differs............ besides the two part numbers.

The norton factory combat 2S is originally for a NHT single chain commando engine. 063536 2S was never marked 2S. It was marked with "SS" next to the breather/slinger ring.

1970 engine 139xxx

pierodn

cash

L.A.B.

Moderator

pierodn

kommando

johntickle

pierodn

jan nelder

dynodave

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