Atlas rockers in a Commando head ?.

[Josh Cox]

Can I use Atlas rockers in a Commando head for a 750cc ?.

 

[68&below]

It depends on the specific year of the atlas head, but yes. The rockers and spindles changed a few times over the life of the atlas but you should be safe if you're looking at taking from a later atlas head. My 66 atlas is actually running a commando head with rockers and spindles I took out of a 68 Atlas.

 

[L.A.B.]

Can I use Atlas rockers in a Commando head for a 750cc ?.

Didn't we do this only a couple of weeks ago? post82501.html#p82501

 

[Josh Cox]

LAB,

You are correct, it would appear I have Alzheimers at 37.

Here are a couple of photos, the part numbers I can see:

Head ( old Atlas head the bits are taken from ): 23166
Exhaust rockers: 2070 / ??89
Inlet: 2067 / 2068

The spindle to not appear to be scrolled.

So can I use these in the Commando head I have ?.

The Commando has shorter push rods than the Atlas ?, does that mean the Commando valve stems are longer ?, is it that simple ?, is there a measurement on the valves I can make to tell whether they are for an Atlas or Commando ?. ( just because they were fitted to an Atlas head does not mean they are the correct item ?)

 

[L.A.B.]

Head ( old Atlas head the bits are taken from ): 23166
Exhaust rockers: 2070 / ??89
Inlet: 2067 / 2068

I expect those numbers are casting or forge numbers not part numbers, and I don't have any information on those.

The spindle to not appear to be scrolled.

So can I use these in the Commando head I have ?.

The Commando has shorter push rods than the Atlas ?, does that mean the Commando valve stems are longer ?, is it that simple ?, is there a measurement on the valves I can make to tell whether they are for an Atlas or Commando ?. ( just because they were fitted to an Atlas head does not mean they are the correct item ?)

According to the parts books, Atlas models after 125871 had identical pushrod, guide, rocker and spindle part numbers to the early Commando, the valve part numbers are different however, but that may not be due to any difference in their length?

 

[Josh Cox]

Thanks LAB, in that case would you know how long the push rods should be ?.

 

[68&below]

Per the commando manual; Inlet 8.166/8.130, Exhaust 7.321/7.285.
Atlas are 8.194 & 7.351 respectively.

LAB, if you double check the 66-68 parts manual you'll see that the valve numbers are actually different after 125781. The shorter pushrods went in conjuction with longer valves.

 

[comnoz]

Commando valves are .100 in. longer and the pushrods are .060 to .080 shorter. The length is added to the area above the keeper groove on the valve.

A common Atlas upgrade is to use the longer Commando valves and shorten the pushrods as this improves the valve train geometry and makes the guides last longer. Jim

 

[Josh Cox]

So at worst we are talking about 0.1 of an inch, 100 thou, 2.5 mm, that can easily be taken up with the rocker adjustment.

Thanks Gents.

 

[comnoz]

I am not so sure you could take that much up with the lash adjuster without causing the adjuster to come too close to the edge of the valve. I have never tried it. Jim

 

[Josh Cox]

After a brief wire wheeling to clean off carbon, found the following numbers:

Inlet valve 25501,

Exh valve: 063282 on both,

Here: http://www.alpha-bearings.com/Valve%20cat/norton.htm

Down the bottom confirms I have the correct valves.

The rest must fall in place, either way, 2.5mm can easily be adjusted out.


Thanks for your help.