Commando head on P11 /Atlas engine

What is needed in order to run a Commando 750 head on P11 /Atlas engine?

At least 2 things need to be addressed.

1 is that the 4 Atlas headbolts near the sparkplugs are small, where the Commando are bigger.
And 2 is that Commando heads come in various RH numbers, with different compression ratios
and port sizes.

Before we delve any further into this, perhaps your reason for asking could be useful ?

I do not know if P11's had spigot barrels, but early Atlas's did...the spigots would have to be ground flush.

Rohan: when were spigots eliminated?

Slick

Spigots on cylinders/heads were gone for all P11.
And Commando never had them.
So no problems there.

Early Atlas, Atlas Scramblers and N15CS may be a different story.

Early ones of those would also have had low pressure oiling. (to the rocker gear).
But again, P11 wouldn't have seen that...

I know the CR and head bolts are different. I am interested in knowing what need to be changed for it to work.

I have access to a good, rebuilt commando head to replace my p11 head which needs everything, that is why.

elefantrider said:

What is needed in order to run a Commando 750 head on P11 /Atlas engine?

Click to expand...

Spigots on cylinders/heads where fitted to about the 1966/7 season, the 1965 model did have them, double speed oil pump were fitted from 1966 on, it was a common mod to fit these oil pump gears to earlier bikes.

What is less well known is that post 1966 the oil block and holes in the crankcase to the oil pump were increased in diameter, meaning that it was twice as likely to wet sump; don’t ask me how I know when I did this mod.

Sounds like carefully machining the spigots off the tops of the barrels will be necessary. Not sure, but you may need to obtain thin sleeves for the 4 main headbolt holes due the difference in diameter, or maybe that's not critical with all of the other hardware lining up?