Are the P11 valve springs different than a Commando

Hi Guys,
I am wondering if the Valve spring No.# are the same as the Commando for the Atlas Engine that was built in 69?
My bike is a Ranger about 40 from the end of production and when I took it apart the Valves were shorter than the Commando with longer pushrods.
Atlas Engine.
What A/N number is the proper valve, Exh and Intake and what Springs are used.
Thanks in advance.
Cheers.
Tom

Interesting, a late Ranger, actually all P11s, should have the same valve/pushrod geometry as a Commando, the change happened much earlier. I don’t know the answer to the springs. I’d have to look up the actual change SN. I have a new set of early pushrods on the shelf if you need them.

According to AN, all NHT engines (650 to 850) were equipped with the same springs, which suggests these NHT models from 1961/62 up had this spring set. Different length of stems does not affect springs, as increase in length is above the valve spring collar.


As for valve part numbers corresponding with factory spec, look here:


- Knut

The valve springs were the same for Atlas, P11, P11A, Ranger 750, and Commando. Commando valves and pushrods were used in P11A after engine number 125871 according to Service Bulletin 68/4 FWN. This puts the change somewhere near the middle of P11A production.

Ron L said:

The valve springs were the same for Atlas, P11, P11A, Ranger 750, and Commando. Commando valves and pushrods were used in P11A after engine number 125871 according to Service Bulletin 68/4 FWN. This puts the change somewhere near the middle of P11A production.

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Excuse me Ron, but first Commando was at engine no. 126125 which suggest the alteration was introduced for the P11/G15 series and then propagated to the Commando.

Where can I download the SB you mention?

- Knut

Thanks all who responded. My serial # P11/129XXX It had the shorter valves with the longer pushrods. Atlas type configuration. I understand that you can use Commando valves but need to change the pushrods to Commando length.

mdt-son said:

Excuse me Ron, but first Commando was at engine no. 126125 which suggest the alteration was introduced for the P11/G15 series and then propagated to the Commando.

Where can I download the SB you mention?

- Knut

Click to expand...

The service bulletins are compiled into a booklet which is on the Norton Owners Club website. The Ranger 750 models were built in one batch beginning with 128646 (which resides in my friend's garage) and ends with 129145 which was shipped to Berliner October 17, 1968 (according to Anthony Curzon). Most of these were titled as 1969 models. The Ranger 750 had cylinder heads cast as Commando, but machined like Atlas and N15. The 125871 number would be in the P11A production range which would be a an Atlas style head casting. My P11A had Commando valves and pushrods when I tore it down to rebuild, but could have been replaced, as it had .020 inch oversize Commando pistons and 3/8 inch outer head bolts. My P11 (Cheetah 45) had Atlas valves and pushrods with 5/16 inch head bolts. My Ranger 750 has the correct Commando head casting with Commando valves and pushrods. (but curiously has 5/16 inch head bolts as does my spare Ranger 750 engine!). The fact that the first Commando has a serial number late than the P11A and Ranger 750 is not surprising. The two models were built somewhat simultaneously and likely were given serial numbers in batches.