oil pump compatibility

Anyone know why an early model Cdo oil pump should not be retrofitted to an Atlas? I have a Cdo pump with only 6K miles, and my Atlas has 85K. I cannot see any visual difference between the two pumps. Both have 6 start worm drives.

I know there are people out there who can feel a Norton part in the dark and tell what model it came from and which models it will interchange with.

Slick

I have a Atlas pump on my Commando. The difference is the clearance cut on the 2 o'clock position. The Atlas pump going onto the Commando was no problem. A Commando pump going on an atlas may have clearance issues.

pete.v said:

I have a Atlas pump on my Commando. The difference is the clearance cut on the 2 o'clock position. The Atlas pump going onto the Commando was no problem. A Commando pump going on an atlas may have clearance issues.

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Explain please...clearance cut at 2 o'clock?

First 5 are atlas pumps. The last one is a Commando pump.

Sorry, Pete...at the risk of sounding dense, I fail to see the differences in the pics....I amazed that you could post up pics so quickly! I'll put in the Cdo pump and critically look at 2 O'clock. Anyone else have some caveats?

Slick

See the mount hole on the right side of the pump. You will see that it looks like someone took a slice off it.

I really do not know if it make a difference, all I know is there is one.

A...ha! I'll put it in and see what I see.....Ill let all know what I find. Thanks!

Slick

pete.v said:

First 5 are atlas pumps. The last one is a Commando pump.

Click to expand...

My early Cdo pump has the same slice taken off. This is at the lower mounting stud.

I looked my Atlas over, and I can see no reason why this "sliced off" area is necessary, and no reason why a pump without it can not be fitted. Perhaps it is a carry over from the Dommies, then one day someone realized it was no longer needed. I dunno,...anyone?

Slick

If the only difference is the Atlas pump has the slice off the mounting boss, you should be able to grind the slice off the Commando pump and put in in either a Commando or an Atlas.
Stephen Hill

It looks like that chamfer/slice out of the oil pump is to clear the chain drive to the distributer ?
Early Commandos would have similar, later Commandos wouldn't need it.
Early dommies, with magnetos, don't seem to have it either.
Can't speak for all dommies though.

Interesting. Never seen that mentioned before...

Its always worth comparing the gear widths inside when comparing oil pumps.
The widths varied, a few times, and the outsides don't look too different...

Hi guys....as I said above, this chamfered area is at the LOWER mounting stud, not near the chain. As near as I can tell, it was a work around to fix somebody's boo boo. It looks to me that the oil gallery coming from the sump might at one time on earlier models, been bumping the pump ( or vs versa). The oil gallery on the Atlas is not now in the way, but no one told the pump supplier it had been fixed....at least, that's my thinking.

Here: http://www.centralcoastclassicmc.com/NortonOilPumps.htm. Lotta good stuff including the testing at the end. Also if you ever have a chance to meet or talk to Dave Comeau (Dynodave) at Atlantic Green, do it. He has a built a test rig for oil pumps and says many pumps are still crap even after refacing the pump body sides. (4 ways of leaking). I don't know if he has started testing pumps for others except at rallies. I saw the setup he had at the Empire rally some years back and it was maybe a little kludgy looking but worked great. Ask him.

I had to learn about Norton oil pumps when I had to replace the one in my '66 Matchless G80CS (now sold). You have to watch it. Dominator pumps, which look the same, had thinner feed and return gears so don't pump as much oil. Also there can be different gearing - either a 3-start gear or 6-start. The 6-start gear set works the pump at twice the speed and so twice the volume. I believe they made that change in mid-Atlas production. The driving gear and the gear on the pump have to be a set - ie you can't use a 3-start pump gear with a 6-start crank gear. (Starts refers to the number of individual spirals on the pump gear.)

Russ