atlas engine compatible parts with 750 commando

74ok · Mar 26, 2018

just trying to put all major available info in one spot, i'll add more as it may come,

what i understand for cranks is rebalance is required for commando use and the end keyway offset is not the same which gets into some 'setting the timing' issues, but, other than that, good to go

not quite clear on barrels & heads, or cases,

on barrels, prior threads
https://www.accessnorton.com/search/814776/?q=atlas+barrels&t=post&o=relevance

with this jumping out
https://www.accessnorton.com/NortonCommando/atlas-barrels.13115/

1965 was the last year that all heavy production got the spigotted cylinder, 500cc, 650cc and 750cc.

I have heard of re-drilling and tapping the Atlas cylinders with the 5/16 head bolts to take the 3/8" Commando head bolts, but if you look between the fins on both an Atlas and 750cc Commando cylinder you will see that the Commando cylinder had a lot of material added in there for the bigger head bolts to anchor in, the Atlas was pretty skimpy in this area.

The 500cc and 650cc engines had the 3/8" bolts just like the Commando, it was just the Atlas that had the small diameter head bolts.

so, given the above, altho perhaps doable, a main issue being small margins scenario for sealing & head gasket issues(?), i also haven't found any solid info on atlas barrel use in commando engines?

atlas cyl heads are oiled from the top vs commando heads from the sides, haven't come across further info getting around that? or use with commando barrels?

dunno about atlas engine cases, whether they can be mounted at the forward angle commando position, or adapted for the commando primary drive covers setup? the ignition & tach drive is also similar to the fastback setup

i'm sticking to 750 here, from what i understand, the 750 head isn't a bolt on to an 850 engine due to fastener spacing diffs

comnoz · Mar 26, 2018

Early Atlases used 5/16 head bolts and spigotted barrels and head.

Late models used 3/8 bolts and are similar to 750 Commando barrels.

Atlas cases are the same as early Commando cases.

texasSlick · Mar 26, 2018

I'll add:

Atlas and early Commando oil pumps can be crossed over.

Commando rotor, and stator mount, while different, can be made to fit an Atlas.

Pistons are interchangeable.

The crank pinion and half time gears are the same profile and ratio, but the Atlas has the magneto drive sprocket in addition to the cam drive sprocket. If someone wanted to fit a magneto to a Commando, the Atlas setup should work.

I would GUESS, main and big end bearings, cam bearings, camshaft (tach, or point drive different?), main seal, and rods are interchangeable.

From my experience, Comnoz's hydraulic cam chain tensioner CANNOT be fitted to an Atlas, but the Comnoz sump plug breather can.

Command valves can be fitted to an Atlas provided Commando pushrods are also fitted.

The Atlas can be reworked to use the Commando top end oiling system. Anyone contemplating this should do more research ..... not simply a question of tapping the oil supply from a different place.

Slick

acotrel · Mar 26, 2018

If the Atlas barrels fit the Commando crankcases, wouldn't it smarter to keep the Atlas head with the Atlas barrels, and the Commando head with the Commando barrels, rather than trying to mix and match ?

comnoz · Mar 26, 2018

texasSlick said:
I'll add:

Atlas and early Commando oil pumps can be crossed over.

Commando rotor, and stator mount, while different, can be made to fit an Atlas.

Pistons are interchangeable.

The crank pinion and half time gears are the same profile and ratio, but the Atlas has the magneto drive sprocket in addition to the cam drive sprocket. If someone wanted to fit a magneto to a Commando, the Atlas setup should work.

I would GUESS, main and big end bearings, cam bearings, camshaft (tach, or point drive different?), main seal, and rods are interchangeable.

From my experience, Comnoz's hydraulic cam chain tensioner CANNOT be fitted to an Atlas, but the Comnoz sump plug breather can.

Command valves can be fitted to an Atlas provided Commando pushrods are also fitted.

The Atlas can be reworked to use the Commando top end oiling system. Anyone contemplating this should do more research ..... not simply a question of tapping the oil supply from a different place.

Slick

Pistons are interchangable but Atlas pistons are cupped for low compression.

Atlas con rods are not as strong near the small end as Commando rods are.

The timing gears would fit in a later Commando if the camshaft and sprocket, spindle and cover were changed also.

74ok · Mar 26, 2018

acotrel said:
If the Atlas barrels fit the Commando crankcases, wouldn't it smarter to keep the Atlas head with the Atlas barrels, and the Commando head with the Commando barrels, rather than trying to mix and match ?

i haven't run across info for this part, i think oiling went to the sides of the commando head cos of the need to secure it at the top

The Atlas can be reworked to use the Commando top end oiling system. Anyone contemplating this should do more research ..... not simply a question of tapping the oil supply from a different place.

texasSlick · Mar 26, 2018

acotrel said:
If the Atlas barrels fit the Commando crankcases, wouldn't it smarter to keep the Atlas head with the Atlas barrels, and the Commando head with the Commando barrels, rather than trying to mix and match ?

It certainly would make more sense to match, but I think the OP is trying to compile a list of parts than can be crossed over, without major modification, or crossed with a caveat.

Such a list is the solution for the Norton aficionados worst nightmare .... part xyz is now unobtainium, can I substitute the Atlas version, or vice versa? It is also useful to the person who might have one such part in the spares bin, and wants to utilize it, rather than lay out a week's wages for a newly made from AN.

I think such a list (or a single thread) would be valuable. I am glad 840K has started it.

Slick

Hobot · Mar 26, 2018

Atlas pinon gear is wider/more robust than Commando and an Atlas pinion gear from The Swamp venders area, taken off an Atlas saved race day for Kenny Cummings at Barbers a few years ago. Atlas gear box shell saved me $200+ on Peel's bearing size hole blown out in thin AMC shell w/o no issues but tossing in bin the stupid thick hassle wedge washer/spacer. When ya all run out of your knowledge base i remind thee the world wide vintage suppliers are fully up on most all the Atlas to Commando cross overs for many decades of rescue so suggest serious seeker start going down global vendors for more scope. BTW the head steady top fasteners only need a slight drilling to tap into spindle oil flow so not hard to supply oil from Commando that way.

74ok · Mar 27, 2018

from the very first link & a search of - atlas barrels

on the 15th result of the search titled - sleeving down a squish band
https://www.accessnorton.com/NortonCommando/sleeving-down-a-squish-band.23596/

a confirmation of a commando head on (non?) spigot (removed?) atlas barrel
(i thought the ring was for atlas heads that are made to fit a spigot barrel, but that can be modified to fit a flat surface, dunno why a commando head would need a ring)

https://www.accessnorton.com/NortonCommando/sleeving-down-a-squish-band.23596/#post-348093

pommie john said:

I have a Commando head on Atlas barrels. I had a guy insert an aluminium ring into the recess where the spigot of the Atlas barrels used to go. It's been in there a few decades so I'm happy that aluminium works OK.

Click to expand...

this link lndicates
http://atlanticgreen.com/nhth.htm

The BIRCO symbol and 23166 are both easily identified by the positives in the casting of this early ATLAS head. These heads have the late style re-angled degree exhaust ports at 80º included angle or 40º each from straight forward. It has carried over 28.5mm intake ports from the previous heads. The head bolts have been down sized for atlas only to 5/16-26cei.The spigot relief machining is 75mm. Oiling is still top feed.

Click to expand...

https://www.accessnorton.com/NortonCommando/cylinder-head-for-spigotted-barrells.22319/#post-332745

then

The same head with the 25494 steel conversion ring installed. This allows the use of this head on unspigotted flat topped barrels.

Click to expand...

flat barrel head

74ok · Mar 27, 2018

hobot said:
BTW the head steady top fasteners only need a slight drilling to tap into spindle oil flow so not hard to supply oil from Commando that way.

not sure what you mean? "tap into spindle oil flow"

i think it means tapping into an atlas head that flows oil from the top of the head, isn't a big deal

low vs high pressure rocker oil feed
https://www.accessnorton.com/NortonCommando/atlas-commando-head-parts-commonality.7264/#post-90483

L.A.B. said:
I think that will depend on whether the head is early (pre eng. No. 116372) or a later one?

If it is an early low-pressure rocker oil feed Atlas head with scrolled rocker spindles, then you can't use the scrolled spindles with the high-pressure rocker oil feed.

The rocker part numbers are also different on the early heads-so you would have to check for any differences if it is an early head-unless someone else knows the reason for the part number changes?

timing cover info - atlas vs commando diferences
https://www.accessnorton.com/Norton...over-tach-drive-x-commando.18072/#post-268593

new search & threads - atlas cylinder head
https://www.accessnorton.com/search/820571/?q=atlas+cylinder+head&t=post&o=relevance

74ok · Mar 27, 2018

texasSlick said:
The crank pinion and half time gears are the same profile and ratio, but the Atlas has the magneto drive sprocket in addition to the cam drive sprocket. If someone wanted to fit a magneto to a Commando, the Atlas setup should work.

pretty sure that includes going with the joe hunt mag,

points option - Early Commando distributor
https://www.accessnorton.com/NortonCommando/early-commando-distributor.22578/#post-336048

Ron L said:

The early points housing had one bearing and a bushing where the later ones had two bearings and a thrust washer. I'm not sure when the change was made, but the 1967 parts books (P11, N15, Atlas) show the bushing/bearing type, while the 68-70 book shows the double bearing type. Is it possible your breaker housing is from an earlier Atlas or N15?

Either should work fine on a 20M3 engine.

Click to expand...

prob the electronic stuff also

dynodave · Mar 28, 2018

comnoz said:
snip
Atlas cases are the same as early Commando cases.

My 1966 20M (Atlas) timing side cases have an internal mold # of 20666.
I then have two 1968 20M3 that also have the internal mold # of 20666 but the final overall castings are both different castings from each other and different from the atlas 20M case/part.
Heck even a 650 uses a 20666 mold, but I guarantee you atlas or commando barrels won't fit

74ok · Mar 28, 2018

acotrel said:
If the Atlas barrels fit the Commando crankcases, wouldn't it smarter to keep the Atlas head with the Atlas barrels, and the Commando head with the Commando barrels, rather than trying to mix and match ?

https://www.nortonownersclub.org/

I recently bought a 1970 roadster which needs a lot of work to get back on the road. To speed things up and as the engine needs a complete rebuild.

Could I temporarily fit an early Atlas engine I have, which has been completely refurbished?

https://www.nortonownersclub.org/

It's been done before so not too much of a job,

balance factor tho, also, first info i've seen going this way is doable, info covers adapting an atlas lump to the commando engine forward lean & primary setup along with the top oil feed for the atlas head,

also way better to have the motor apart to do the cdo chaincase fitting mod

There is a danger of swarf entering crankcase doing this so apply grease to tapping drill when nearly through so bits stick.

i'm finding equivalent atlas engine parts on ebay tend to be priced much lower overall than commando stuff & more plentiful

nice to have those additional options tho i find lotsa norton stuff misadvertised, so to go there & get the bargains vs parts that may not even work, the more you know, the better the deals & options

baz · Mar 28, 2018

With regards to the early spigot type atlas barrels
I have heard of people machining the spigot from the top so you can fit a late atlas/750 commando head,
Obviously you need to open the holes up if you fit a commando head

74ok · Mar 28, 2018

https://www.nortonownersclub.org

If the cylinder head and barrel are both from the early spigotted type then you are going to have a problem converting the headbolt holes up to 3/8". If you keep the barrel spigot then you will have to also open out the gasket holes to match the bolts. This will take out gasket material where you need it most and leave the whole area vunerable to leaks. This was one of the reasons that the early Atlas engines had 5/16" headbolts. You could not have a spigotted cylinder head plus 3/8" headbolts. The head gaskets leaked or blew out. Even with the 5/16" bolts many owners found that they got oil leaks through the gasket. Many tried torquing down the head further and promplty snapped a bolt or two.

If you go down the route of having the spigot ground away then you can look at 3/8" headbolt holes. But........if the cylinder head is still the spigotted type then you must get hold of a set of the steel conversion rings (p/n 25494) that sit inside the combustion chamber and help seal the headgasket. Aluminium ones appear to work just as well.

The attached pic shows 3 varieties of later Atlas/Commando cylinder head gaskets plus a 650 type. I could not find an early Atlas gasket for a spigotted head to show how absurdly thin it is in places. But if you look at the top right version and take away the flame ring you will get a reasonable idea.

Like so many other owners, I thought that a solid copper headgasket would solve all my oil drip problems. Not so......both my 650 and 750 motors dripped/blew through the gasket sides despite annealing them carefully. The problem with annealing is that you can over-cook the metal and it actually vaporises away leaving thin parts even thinner. The most vunerable sections are by the pushrod tunnels and the rear head bolts.

https://www.nortonownersclub.org

Gilesy · Mar 29, 2018

Not sure if it's relevant but when I tried a Commando decompression baseplate on my Atlas it semi obscured the oil return hole to the crank case. The base plate for an Atlas is different which might infer that the barrels are not compatible.

74ok · Mar 30, 2018

Could I temporarily fit an early Atlas engine I have
https://www.accessnorton.com/NortonCommando/atlas-engine-compatible-parts-with-750-commando.24881/#post-368793

It's been done before so not too much of a job

Atlas cylinder on Commando
https://www.accessnorton.com/NortonCommando/atlas-cylinder-on-commando.18103/#post-269117

auldblue said:

I spoke to Norman White about this, my atlas barrels are not spiggoted and he said no problem just bore the holes to 3/8 and all will be well. I haven't done it yet but I will be. Obviously taped to take 3/8 head bolts.

Click to expand...

Atlas barrels, 750 cases and head.

"Will a 1973 Commando 750 cylinder work on the 67 Atlas?"
https://www.accessnorton.com/NortonCommando/cylinder-sleeving.22899/#post-339953

pierodn said:
Yes, but Commando cylinder barrels has the thread for cilinder head four bolts larger than Atlas one.
So you must drill and enlarge the head for the larger bolts.

https://www.accessnorton.com/NortonCommando/atlas-engine-compatible-parts-with-750-commando.24881/#post-368811

Atlas / Commando head parts commonality ?
https://www.accessnorton.com/NortonCommando/atlas-commando-head-parts-commonality.7264/#post-90483

https://www.accessnorton.com/NortonCommando/atlas-commando-head-parts-commonality.7264/#post-90485

low vs high pressure rocker oil feed
https://www.accessnorton.com/NortonCommando/atlas-commando-head-parts-commonality.7264/#post-90483

Josh Cox said:

Am picking up a head and barrels for my bike, are the rocker arms, spindles and valves in the Atlas head interchangable into the Commando head ?, any differences ?.

Click to expand...

L.A.B. said:

I think that will depend on whether the head is early (pre eng. No. 116372) or a later one?

If it is an early low-pressure rocker oil feed Atlas head with scrolled rocker spindles, then you can't use the scrolled spindles with the high-pressure rocker oil feed.

The rocker part numbers are also different on the early heads-so you would have to check for any differences if it is an early head-unless someone else knows the reason for the part number changes?

Click to expand...

Commando cam on Atlas engine
https://www.accessnorton.com/NortonCommando/commando-cam-on-atlas-engine.24175/

differences between commando and atlas crankshaft
https://www.accessnorton.com/NortonCommando/differences-between-commando-and-atlas-crankshaft.21469/

con rods
https://www.nortonownersclub.org/support/technical-support-commando/conrods

The same con rods were used on all twins from the 1966 650 up to the 850 Commando. They are exceptional rods and give long life. The rod was modified for the 1975 model along with its cap.

Click to expand...

from above info

comnoz said:

Atlas con rods are not as strong near the small end as Commando rods are.

Click to expand...

750 Atlas Tach Timing Cover & Tach Drive x Commando?
https://www.accessnorton.com/NortonCommando/750-atlas-tach-timing-cover-tach-drive-x-commando.18072/

69 Norton Commando timing cover
https://www.accessnorton.com/NortonCommando/69-norton-commando-timing-cover.24903/

points option - Early Commando distributor
https://www.accessnorton.com/NortonCommando/early-commando-distributor.22578/

https://www.accessnorton.com/NortonCommando/early-commando-distributor.22578/#post-336048

The early points housing had one bearing and a bushing where the later ones had two bearings and a thrust washer. I'm not sure when the change was made, but the 1967 parts books (P11, N15, Atlas) show the bushing/bearing type, while the 68-70 book shows the double bearing type. Is it possible your breaker housing is from an earlier Atlas or N15?

Either should work fine on a 20M3 engine.

Click to expand...

new search & threads - atlas cylinder head
https://www.accessnorton.com/search/820571/?q=atlas+cylinder+head&t=post&o=relevance

74ok · Mar 30, 2018

Gilesy said:
Not sure if it's relevant but when I tried a Commando decompression baseplate on my Atlas it semi obscured the oil return hole to the crank case. The base plate for an Atlas is different which might infer that the barrels are not compatible.

year atlas? part # for Commando decompression baseplate maybe? or more info?

Danno · Mar 30, 2018

I once transplanted an Atlas bottom end into a Commando for the rear ignition drive, which I converted to a K2F mag. Went right in.

pommie john · Apr 1, 2018

When I bought the parts to construct my race bike ( from various sources ) I believed I had bought a 750 Commando engine. I always went to the bike shop asking for parts for a 750 Commando and bolted them in and it went fine. It was only in the past few years when I checked the engine number that I realised I had a 1964 Atlas engine ( mainly) but with Commando barrels. maybe I was lucky that the parts I bought happened to fit both models.

I did have a hassle when I bought PW3 camshaft though. The triangular section thrust washer I had always used in the past was too thick and I had to grind it down to get the correct end float.