Crankcases 1967 Atlas vs G15CS?

APRRSV

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Hello all,
Can anyone tell me what the difference (s) are between the 1967 Atlas crankcase and 1967 G15CS crankcase? I see they have differing part #'s: Atlas- 25374 and G15CS-25375.
I am particularly interested in what differences there are on the drive side. Inner primary case mounting hole orientation? Machining to fit inner primary case front hole diameter?

Any info from @dynodave or @pierodn will be appreciated.

Thanks,
Ed
 
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APRRSV said:
Hello all,
Can anyone tell me what the difference (s) are between the 1967 Atlas crankcase and 1967 G15CS crankcase? I see they have differing part #'s: Atlas- 25374 and G15CS-25375.
I am particularly interested in what differences there are on the drive side. Inner primary case mounting hole orientation? Machining to fit inner primary case front hole diameter?

Any info from @dynodave or @pierodn will be appreciated.

Thanks,
Ed
Click to expand...
found some pix on the domi forum. and a little detailed discussion.
I am weak on hybrids but this is what I have so far. Not sure if N15 and P11 are the same
1 the atlas cases are machined for a featherbed sheet metal primary and seperate smaller alternator bracket bolt circle . same for 122 14 (alternator cases only) and all 18 and 20 NHT750 /88 99 650 and atlas bikes
2 The hybrids are very similar to 20M3 commando if not identical
All 3 of them have the larger bolt circle and I doubt they are a different radius and angular positioning, featherbed and commando ARE confirmed same bolt circle.
 
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Atlas and early Commando had the same alternator mounting bracket.
The Matchless alternator was mounted on the outer cover of the chaincase. Which might explain why the Matchless 750 crankcase was not drilled and tapped like the Norton.
Other than that, I think they were both the same.
 
Bernhard said:
Atlas and early Commando had the same alternator mounting bracket.
Click to expand...
Atlas has the seperate alternator casting on a small bolt circle and seperate sheet metal primary.on the outer large bolt circle
Everyone knows that the commando alternator mount is PART OF the primary inner. The commandos all use the outer large bolt circle except the MKIII.

I was aware of one of the hybrids having the stator in the outer cover but I've not had any opportunity to work on both the norton and matchless version. nor had pix of both varieties side by side identified with their name .
 
The G85CS, P11, and I believe G15CS have the stator in the outer primary. N15 I'm not sure about, but maybe. The crank case looks very similar to the early Commandos. 3 small fasteners hold the inner primary cover up against the crank case. That stator in the outer primary of the hybrids is a blessing and a curse. Blessing in that it is real difficult to mount the stator offset and end up with rotor interference. It is an extremely tight fit in the outer primary. Curse in that the stator wire goes through the inner primary and makes removing the outer primary (where the stator is) for clutch service a R&R PITA. You'd have to work with one to feel the joy. All those little bolts around the primary look cool, but it has to be the worst sealing set of primary covers ever created. On the P11 the foot peg is mounted to the center bolt putting additional stress on all those little bolts, which does not help with the seal. Am I still on topic? Probably not.
 
I concur with Bernhard that the early Commando had the same alternator mounting bracket bolt pattern as the Atlas. I bought a wrecked out early Commando for parts that would crossover to the Atlas.

I mounted the Commando clutch in my Atlas. This required the Commando alternator bracket as the Atlas bracket would not pass the wide chain, but the bolt pattern was the same.

I eventually went back to the original type clutch, but the Cdo alternator bracket is still in the primary case.

Slick
 
"Can anyone tell me what the difference (s) are between the 1967 Atlas crankcase and 1967 G15CS crankcase?"

Back to the OP asked question! (not primary configuration)
It is highly likely the crankcases for the hybrids are the eventual version as used on commando. I have heard (hate rumors) they used atlas engines as proto types for commando therefore super early and not realy main stream production. Will a featherbed crankcase run in a commando...absolutely YES. A 650SS (slimline) engine was in a commando. I swapped it for a proper era 20M3S engine. There was a steel ring spacer .215" thick adaptor with the 5" large diameter bolt circle that is used, I'll assume, on all of the NHT family. The featherbed 4" stator mount holes were plugged. The restoration to commando engine was completed with the remaining parts.
The 650SS engine is still sitting in my office with the other 24 NHT. I have 2 of these 650 and they are NOT different configuration.
Bernhard said:
Atlas and early Commando had the same alternator mounting bracket.
The Matchless alternator was mounted on the outer cover of the chaincase. Which might explain why the Matchless 750 crankcase was not drilled and tapped like the Norton.
Other than that, I think they were both the same.
Click to expand...
Other than the first statement that is possibly true for prototype commando, the rest is technically sloppy and Matchless vs. "norton" drilling statement is the exact opposite of the pix shown on facebook domi 49-70. sorry can't copy the pix
Does anyone doubt Ludwig has mounted a shortened commando bolt pattern.primary on his hybrid?

texasSlick said:
I concur with Bernhard that the early Commando had the same alternator mounting bracket bolt pattern as the Atlas. I bought a wrecked out early Commando for parts that would crossover to the Atlas.

I mounted the Commando clutch in my Atlas. This required the Commando alternator bracket as the Atlas bracket would not pass the wide chain, but the bolt pattern was the same.

I eventually went back to the original type clutch, but the Cdo alternator bracket is still in the primary case.

Slick
Click to expand...
the bolt pattern was the same.
How is the 5" commando bolt circle the same as a 4" slimline stator mount bolt pattern? Is the 5" commando stator bracket a special factory product? or was it "carved/cut out"from the conventional commando primary and used the "other"5" sheet metal bolt circle for mounting?.
However confusing, these details are OT from the original question about crankcases!


Top
 
My current thinking is:
2 possible bolt patterns for NHT "alternator" cases
5" bolt circle mount for ALL AMC alternator NHT or "20" matchless primary.... true- yes/no?
4" bolt circle for stator mount "fixture" on slimline engines only.... true-yes/no?

4.375" stator bolt circle... completely irrelevant to crankcase discussion

Any, I guess, I think, responses about "the NHT cases" that conflicts?
 
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Quoting my post, dynodave asked:
"How is the 5" commando bolt circle the same as a 4" slimline stator mount bolt pattern?"
This is relevant to the OP's question since it involves the drilling on the drive side.

All I can say is: I wanted to mount the Cdo clutch in my Atlas because I wanted the two finger pull.
Working with the parts I had from the Atlas and Commando, and with a drill press the full extent of my machining capacity (which, in this case I did not require), I swapped the following parts, Cdo for Atlas: stator mount bracket, rotor, rotor nut, and drive sprocket, and of course the clutch, and I used bulk triplex chain. That was it .... no machining whatsoever.

The Commando was an early bolt up rear wheel model.

Slick
 
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? Is the 5" commando stator bracket a special factory product? or was it "carved/cut out"from the conventional commando primary and used the "other"5" sheet metal bolt circle for mounting?.
I'd assume you did not use both sheet metal and commando primaries. Most know the slimline engine to trans shaft is longer than commando.

It is still not stated but I assume you did NOT use the complete commando casting and instead carved out the commando alternator mount.
1.Did you abandoned the 5" circle mount and modified it to 4" featherbed type mounting?
2. If not then did you partially duplicated the 5" BC commando 650ss abortion I removed.

Unfortunately none of this helps the OP.
This will be the last from me on this topic
PM or phone call OK - contact info on my website
 
dynodave said:
Does anyone doubt Ludwig has mounted a shortened commando bolt pattern.primary on his hybrid?
Click to expand...
He mounted a shortened Commando primary on a Norton engine in his G15 frame. That does not look like a Hybrid drive side crankcase though. Hybrids had the cam breather and did not have that flat serial number pad on the drive side crank case. Whatever crank case he used more than likely had the correct drilled and threaded mounting holes to make what he did possible. That said it could be done on a Hybrid engine if the cases were split and the proper machine work was done.
 
To clear up some confusion regarding the alternator stator mounting bracket.

After a phone chat with dynodave, it appears that my alternator mount salvaged from an early Commando, was a factory part used to bridge the transition from Featherbeds to Commandos. This stator mount was separate from the inner primary cover, and resembled the Atlas type mount, except having a wider slot to accommodate the wider chain.

Slick
 
What was this transitional bridge stator mount affixed to if not the inner primary cover? The outer cover, the crank case? Anyone have a pic of this unicorn part?

This discussion made me realize I probably just bought a stator I'll never be able to use, dang it.

texasSlick said:
To clear up some confusion regarding the alternator stator mounting bracket.

After a phone chat with dynodave, it appears that my alternator mount salvaged from an early Commando, was a factory part used to bridge the transition from Featherbeds to Commandos. This stator mount was separate from the inner primary cover, and resembled the Atlas type mount, except having a wider slot to accommodate the wider chain.

Slick
Click to expand...
 
Schwany said:
What was this transitional bridge stator mount affixed to if not the inner primary cover? The outer cover, the crank case? Anyone have a pic of this unicorn part?

This discussion made me realize I probably just bought a stator I'll never be able to use, dang it.
Click to expand...

The early Cdo stator mount was separate from the inner primary cover, and resembled the Atlas type mount, except having a wider slot to accommodate the wider chain.
It affixed to the drive side of the crank case exactly as did the Atlas mount, via the 3 screws, hence my earlier post in which I said the bolt pattern was the same as Atlas. The central hole of the stator mount fitted over the raised circular "boss" on the Atlas drive side crankcase.

My stator mount was likely one of very few produced before Norton developed the stator mount integral with the inner primary cover.

Hope this helps clear it up.

Slick
 
Schwany said:
What was this transitional bridge stator mount affixed to if not the inner primary cover? The outer cover, the crank case? Anyone have a pic of this unicorn part?

This discussion made me realize I probably just bought a stator I'll never be able to use, dang it.
Click to expand...
Matchless used an AMC chain cover, this is screwed onto the inner cover by several screws rather than one large nut as seen on the tinware of the Atlas.
Google up images for the 750 Matchless for a picture.
 
texasSlick said:
The early Cdo stator mount was separate from the inner primary cover, and resembled the Atlas type mount, except having a wider slot to accommodate the wider chain.
It affixed to the drive side of the crank case exactly as did the Atlas mount, via the 3 screws, hence my earlier post in which I said the bolt pattern was the same as Atlas. The central hole of the stator mount fitted over the raised circular "boss" on the Atlas drive side crankcase.

My stator mount was likely one of very few produced before Norton developed the stator mount integral with the inner primary cover.

Hope this helps clear it up.

Slick
Click to expand...
Close enough. Things being clear in my mind are few and far between.
 
Bernhard said:
Matchless used an AMC chain cover, this is screwed onto the inner cover by several screws rather than one large nut as seen on the tinware of the Atlas.
Google up images for the 750 Matchless for a picture.
Click to expand...
I was asking Slick about the part he mentioned in regard to his Atlas stator mount, which I am not familiar with.

I own a 1967 P11. It's a 750 Atlas like engine stuffed into a Matchless frame, similar to a Matchless G85CS, but with more balls. After 50 years wrenching on it, I am surprisingly familiar with everything related to it. Mine is a little different from a stock P11 in many ways, but it works well enough.

Look at all those damn primary bolts (14 to be exact) in that AMC outer primary cover. I've had the primary off too many times, and know how it all goes together. I just had the primary off to install a 1/16" cork gasket I made. Hoping for a better seal. I was checking on my stator while I had the outer cover off as well.

Crankcases 1967 Atlas vs G15CS?
 
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Schwany said:
He mounted a shortened Commando primary on a Norton engine in his G15 frame. That does not look like a Hybrid drive side crankcase though. .
Click to expand...
It is an 850 Commando case.
Although I am the original owner of what is probably the last hybrid ever produced (132xxx), the only original parts are
the gearbox shell, fork yoke, oil tank cover and tail light lens.
Over the years, EVERY other part has been modified or changed to make it a practical and reliable touring bike:

Crankcases 1967 Atlas vs G15CS?
 
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