Insulator under the valve spring seat

Hi.
As you know on Atlas and 1968/70 Commando there was not the insulators under the valve spring seat.
Now i have the head a part: is better to fit the insulators or not?.
Thank you.
Piero

As you know heat insulator 23392 is in every norton twin parts book back at least to 1961, except on the inlet of a 72 combat. There is a different insulator part # in the early 50's.
big guides on 850 might use different # too

Hi and thank you.
Sorry, but i have not found insulators neither in Atlas, P11 and 1968 Commando.
Please, do you think is better to fit?.
Ciao
Piero

Fit the them...They are there to reduce the temperature in the head from reaching the valve springs damaging and weakening them. Only an idiot such as the brain deads who came up with the Combat lumps left them out and that was probably because of the higher lift cams they employed which compressed the springs further so to ensure the springs did not become compressed into the coil bound state at full lift, which would very quickly kill the cam lobes, they left the heat washers out. It is known in Engineering as BODGING the job..... Personally I had different thickness heat washers and with the standard type lift cams and genuine Norton valve springs fitted them so that at full lift on the cam the springs still compressed 0.090-0.100 inch before becoming coil baund. I set them up thus on our short stroke 500 and it revved to 8,000 without the valves hitting the pistons etc!