Is this a Commando motor?

Commandodave · May 19, 2017

Is this an Atlas or Commando motor?

Somewhere years ago I acquired about 70% of a Norton motor. It is
missing the pistons, con rods, camshaft and most timing chest
internals. The motor identifying marks are rather strange:

20M3S 1521XX

The 20M3S suggests Commando, but where did the "S" come from?

The serial number 1521xx falls in the gap the NOC lists between 1971
numbers 141900 - 150500 and 1972 numbers: 201000 - 216000

The bits I have strongly suggest Atlas. The head and barrels are
Atlas. The timing side of the case is Atlas as it matches the Atlas
timing cover for oil feed. And has the magneto mounts. The left half
looks like it was always attached to the timing half. The crank
bearings are Atlas. The numbers look like factory stampings. Perfectly
lined up and spaced. There are placed on the flat side of the case,
about where my Atlas sports a medallion, not on the curved indent.

Any ideas what I have here? i am trying to sell it this weekend at
British and European Days in Clarksburg, MD. I do not want to
misrepresent what it is.

Regards,
Dave

L.A.B. · May 19, 2017

Commandodave said:
Is this an Atlas or Commando motor?

20M3S 1521XX

The 20M3S suggests Commando, but where did the "S" come from?

1971 Commando. 'S' denotes a camshaft drive points engine (early Commandos with the points housing behind the cylinders were 20M3).
The 20M3S prefix ended with the '15xxxx' series.

Commandodave said:
The serial number 1521xx falls in the gap the NOC lists between 1971
numbers 141900 - 150500 and 1972 numbers: 201000 - 216000

150500 appears to be an error as we know '15' series production continued on past 150500 and I've had a suspicion for some time that 150500 should be 153500.

1972 numbers started at 200001 although I don't believe we've seen any as high as 216xxx so that could be another error.

Commandodave · May 19, 2017

Thanks for the info, I learned something today. Looks like I have a Frankenmotor. It is most definitely an Atlas top end and timing side case. Somebody, somewhere mated the two case halves together.

dennisgb · May 19, 2017

Weren't the Atlas motor cylinders straight up? Commando was the first to slant the cylinders forward. You may have a mix of parts, but the slant of the cylinders would identify the crankcase as being Commando as the numbers already do.

L.A.B. · May 19, 2017

dennisgb said:
Weren't the Atlas motor cylinders straight up? Commando was the first to slant the cylinders forward.

But that was achieved by tipping the complete (Atlas) engine forward in the frame/cradle.

dennisgb · May 20, 2017

L.A.B. said:
dennisgb said:

Weren't the Atlas motor cylinders straight up? Commando was the first to slant the cylinders forward.

Click to expand...

But that was achieved by tipping the complete (Atlas) engine forward in the frame/cradle.

My point was that the slant would identify the crankcase as Commando not Atlas.

L.A.B. · May 20, 2017

dennisgb said:
L.A.B. said:

dennisgb said:

Weren't the Atlas motor cylinders straight up? Commando was the first to slant the cylinders forward.

Click to expand...

But that was achieved by tipping the complete (Atlas) engine forward in the frame/cradle.

Click to expand...

My point was that the slant would identify the crankcase as Commando not Atlas.

How?

dynodave · May 20, 2017

Commandodave said:
It is most definitely an Atlas top end and timing side case. Somebody, somewhere mated the two case halves together.

1. An Atlas is a twin chain motor, which is rear points or magneto, therefore NO ignition on the "end of the cam" (20M3S and up).

2. Atlas drive side has 2 bolt circles, one for the sheet metal primary and second inner bolt circle for alternator mount. A featherbed engine can not be used in commando without engineered and machined interface. I own one of these...

3. A 20M3S case would be machined for aluminum commando primary.

You may be interpreting the failed starter mount as a magneto mount. Very common mistake by folks unfamiliar with norton.

You would need to show pix to substantiate your theory.
A clever and skilled machinist could make a bitza motor but would be worth almost nothing except to the builder. :?:

L.A.B. · May 20, 2017

dynodave said:
You would need to show pix to substantiate your theory.
A clever and skilled machinist could make a bitza motor but would be worth almost nothing except to the builder. :?:

Perhaps the "Atlas" timing side case is actually 20M3 Commando?

dynodave · May 20, 2017

L.A.B. said:
dynodave said:

You would need to show pix to substantiate your theory.
A clever and skilled machinist could make a bitza motor but would be worth almost nothing except to the builder. :?:

Click to expand...

Perhaps the "Atlas" timing side case is actually 20M3 Commando?

The 20 and 20M3 are very similar and use the 20666 casting mold for the internal part. However the oil return details inside the timing chest are the most noticeable change for commando. Later 20M3 had a second sump drain passage added, which lowered the timing chest oil level.
20M3S used a 06-1517 ? now for single chain engine details and inboard tach drive.

dennisgb · May 20, 2017

L.A.B. said:
But that was achieved by tipping the complete (Atlas) engine forward in the frame/cradle.

My point was that the slant would identify the crankcase as Commando not Atlas.[/quote]

How?[/quote]

I always assumed that the Atlas engine was different crankcase because I've never owned one. After looking at pictures it's the same. The engine was rotated forward to get the slant on the Commando as you said earlier...I wasn't following you L.A.B...my bad.

Commandodave · May 20, 2017

L.A.B. said:
dynodave said:

You would need to show pix to substantiate your theory.
A clever and skilled machinist could make a bitza motor but would be worth almost nothing except to the builder. :?:

Click to expand...

Perhaps the "Atlas" timing side case is actually 20M3 Commando?

I am familiar with the differences in the oil porting between the Atlas and Commando timinc side cases and timing covers. It is most definitely an Atlas timing side crankcase. It also has an Atlas head and Atlas barrels. And Atlas main bearings. The only part identified as being Commando was the primary side crankcase. Which started the whole thread off because I was confused as to why an Atlas motor would have a Commandoish model number. I had never heard of the "S" being added to the model identifier by the factory. And a weird serial number that fell between 71 and 72 as published by the NOC.

Now if only I could identify the crankshaft. Atlas or Commando?

Dave

L.A.B. · May 20, 2017

Commandodave said:
And Atlas main bearings.

Early Commandos had the same main bearings as far as I'm aware (17822 ball & 17824 roller).

dynodave · May 21, 2017

Commandodave said:
Now if only I could identify the crankshaft. Atlas or Commando?

with the crank at TDC an atlas crank 's alternator key slot is up and a commando alternator key slot is down.
They have different PN flywheels too.

Rohan · May 21, 2017

dynodave said:
A clever and skilled machinist could make a bitza motor but would be worth almost nothing except to the builder.

Worth 'almost nothing' - really ??

Some of the best racing engines are made with an assortment of parts.
Can just see the Commando bits on the other side, and the JH maggie.
Ayee thats a big pic, might make it clickable

http://i.ebayimg.com/images/g/07EAAOSwu ... -l1600.jpg

But we diverge. Potential there though...

Bigbossmonty · Aug 5, 2017

Hi Lads.
this thread peeked my interest I have picked up an engine and gearbox complete in cradle.
It has cases 20M3S 1495xx on the camshaft it has a Joe Hunt Mag which is a new thing for me.

But it has a blanking pale where the lucas mag would fit behind the cylinders?

Its for a Seeley type frame from 71' whichhad a Norton engine originaly but has had 4 cb750 engines in it and at present a 64 bonnie engine I am taking it back to 72 spec Norton Dvla have changed V5C to Norton from Honda as I have original details from old council records.

so your thoughts would be appreciated
cheers
BBN

L.A.B. · Aug 5, 2017

Bigbossmonty said:
But it has a blanking pale where the lucas mag would fit behind the cylinders?

The blanking plate covers the hole intended for the original Lucas M3 starter motor that the factory never got around to fitting because it had a tendency to self-destruct. No standard Commando had a magneto although the early 20M3 model Commando had a points housing in that location but the bolt/stud spacing is different. The starter motor hole was eventually filled in around mid-'72 and the cover plate deleted.

Bigbossmonty · Aug 5, 2017

Cheers LAB,

was putting R3 engine in got main parts as Norton engines don't come up but 1 did so will take it back to original

cheers
BBM

Is this a Commando motor?

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