G15-CS/Atlas: primary case oddity

Hi, everyone--

One of the several weird things on my G15-CS is that the inner primary and crank case are drilled for six fixing screws vice the normal three. Didn't seem to be an issue--but now that I'm working with the primary while the bike has fluids, leaking oil signaled that the holes actually reach clear through to the crankcase interior(and that the bike wet sumps tremendously...)

The original and previous owner rode it this way for years it seems, so I'm not thinking it's a tremendous issue, but it did surprise me. Is it normal for these screw holes to penetrate all the way through?? My plan now is to clean the holes and screws with acetone and reassemble with Hylomar or permatex aviation, just to be on the safe side...

Any thoughts? Thanks-

Mike

Yes, the three factory holes are drilled thru, and no doubt the PO did the same for the other three.

Your method to clean and seal the threads should be adequate.

I found a synthetic cork gasket (1/32" thick) sealed the joint between the inner primary cover and the drive side case better than an AN original gasket.

The wet sumping is another issue, well discussed here ..... use the search function for help.

Slick

thanks very much for the insight!

AgentX said:

Hi, everyone--

One of the several weird things on my G15-CS is that the inner primary and crank case are drilled for six fixing screws vice the normal three. < ...>
The original and previous owner rode it this way for years it seems, so I'm not thinking it's a tremendous issue, but it did surprise me. Is it normal for these screw holes to penetrate all the way through??

Click to expand...

Mike, yes they do. Regarding the 6 screws, the history goes like this: AMC were in a state of rush after Norton moved to London early 1963 to get the production of Norton models and engines started as well as launch new models. The first new model was the G15 'N' (markedet "Atlas Scrambler" in the US) and it was shipped in the autumn of 1963 before the last bugs had been ironed out. One of those bugs concerns the primary chaincase, which was held in place by 3 small screws only. This was clearly insufficient and sometime during 1964 or 1965 the primary chaincase support was improved by modification of the inner chaincase and addition of a support bolt. Your 3 additional screws was probably added rather than fitting the later inner primary cover and the support bolt. I suggest you seal the 3 additional bolt holes (one of which is probably at a low spot) and obtain the later parts which will provide a much better chancase support.
030242 -> 032238 chaincase; 032241 Chaincase support stud; 019226 -> 031541 3 screws.
The nearside rear engine plate needs to be drilled for the support stud in the appropriate location - I suggest you obtain a template for this.

-Knut

Hi Knut--my bike does have the bolt and spacer that fastens the inner case to the frame at its mid-point...I think that's what you're discussing, correct? (Original owner said he seems to remember something about drilling the crankcase for the additional screws but can't recall exactly...)

It's a 1965 model by the way.

It's been a few decades but I recall that when I used a G15 bottom end on my Atlas project I had to add three more holes in the casting, maybe to get the alternator mount on. Could your crankcase have spent time on a slimline at some point? It was hard to complete a Norton basket case in the pre-Internet days.

AgentX said:

Hi Knut--my bike does have the bolt and spacer that fastens the inner case to the frame at its mid-point...I think that's what you're discussing, correct? (Original owner said he seems to remember something about drilling the crankcase for the additional screws but can't recall exactly...)
It's a 1965 model by the way.

Click to expand...

OK, so maybe you have a pair of crankcases from a Norton Atlas, which had its chaincase screws in a different position to the G15. There are also the mounting points for the stator carrier - one of which are at 5 o'clock. If this is the case, I suggest you obtain the correct set of crankcases.

-Knut

I have G15-CS crankcases, I'm pretty sure. I bought the bike from the original owner, never been an engine swap...numbers match what's on the owner's registry in all the years of documents he gave me. Seems most likely he drilled them for additional screws.

dculgan, the bike's never been cannibalized far as I know. He had this one bike since 1965 and tinkered with it, but never tore it down till a partial "redneck restoration" (his term) in the early 90s.