N15CS: question about inner chaincase support stud location

My N15CS inner chaincase (PN 025017) support stud seems to be in a different location than standard. Same PN as several I've seen on eBay and Andover but mine has an extra hole and a stud mounting through it to the engine plate which is below the larger hole which I think is standard.

Pic highlights the larger upper hole which is unused, and the lower which is attached securely to a special stud behind it which lines up perfectly to an existing hole in the engine plate. It's very secure. The upper hole doesn't really line up with a hole in the engine plate , so hmm, has this been modified? I am thinking leave this existing one as it's solid and plug the upper hole. It's strange tho.

Hi gpzkat, we have been through this discussion before. We need to understand the primary cover used on the G/N15 series was an adaption of the primary cover used on the G12, which breathed through the crankshaft shaft, see enclosed link.
AMC designed the upper hole under the oil deflector as breathing hole for the G12 engine. Sure, there is a very small vent at the rear of the chaincase also, it's probably inadequate for the G12 engine. Some venting happens at the sliding disc as well, but pressure pulses through this opening may attract road debris into the chaincase, so a shielded vent was probably considered a better option.

Since there is no need for an engine vent here with the Atlas engine, you may plug the hole. Perhaps the AMC factory fitted a rubber plug when the bike was new, who knows after all these years? As a spare part, the cover was supplied in "assembled" form. The plug may not have been listed separately. I recall a rubber plug was finally listed separately for the P11A -- it should fit your cover as well. Maybe someone can dig out the number - 035xxx I believe.

- Knut

Same 025017 inner is used on a P11, but it is not machined like that. In the P11 inner I have there is a hole left of that upper one in question that the stator wire grommet goes in. The foot peg arrangement on a P11 is not like it is on a N15SC. Different frame, and different gearbox and engine plates. A large stud screwed into the motor/gearbox plate that helps secure the foot peg hardware goes through the hole you have your stator grommet in, and the hole your foot peg hardware attaches to is not there at all. I plugged the original stator grommet hole in mine and use the hole you are wondering about to run my stator wire through. So not typical. I did not add or change location of any holes though.

I would definitely plug every hole in that inner case you are not using. If you don't, as you probably suspect, oil flying around inside the case will find its way to any open hole and down the backside of the inner case.

I have a plug threaded into the hole on my N15.

Thanks all,

Here is a picture off Schwany's thread showing the P11 inner primary cover . By the time the P11 went into production, production of the G12 had stopped. AMC (or NV Matchless Div. as it was named by now) could freely modify the mold for the die casting, so they plugged the hole which served as a vent on the G12.

As for Schwany's theory of a cause for a possible oil leak, it will probably not manifest itself unless the primary cover is overfilled. By using the correct amount of oil, the lower chain run will barely dip into it and subsequentlt the oil will be thrown to the rear of the chaincase where it drains down and flows forward agein. A small fraction will drip on the deflector above the hole in question, but will drain forward and away from it (as can be seen, the factory enlarged the deflector). So, I think the main reason for wanting to plug the hole in your G15 inner cover is to prevent dust and road debris from entering the chaincase.



- Knut

Yuck! I think there are 3 varieties of RTV sealer on that pile of wire. Plus some cloth tape and shrink wrap that gets soft and expands. Terrible patch work over that hole and the solder joints for the short lead connector. It does not leak there though.

Anyway, oil is thrown everywhere in the primary. The primary does not leak as much with exactly 8 ounces of oil or ATF in the primary, because it ends up about .125" below the chain. However, if oil is brought up to where it touches the bottom of the chain it'll find its way out of the primary if it can. Gotta own one to know one.

I have not been able to stop my P11 primary from leaking in 50 years. And frankly don't believe anyone that actually rides their P11 and says they have, unless they have a belt drive in there. The high frequency vibration is not helpful for keeping the primary sealed tight around the perimeter. Only thing I have not tried is a bead of Permatex Right Stuff. Reason is it is too difficult to separate parts sealed with it, and experience tells me I'm not done opening up the primary.

I've read that some forego an oil bath and just use an occasional spray of good chain lube. I've also read that technically the Norton isn't a 'wet' clutch. How tough of a life does the primary chain lead vs. the exposed drive chain? I am leaning that direction unless there's some good reason not to, not sure of the downside, perhaps the clutch bearing.

gpzkat said:

I've read that some forego an oil bath and just use an occasional spray of good chain lube. I've also read that technically the Norton isn't a 'wet' clutch. How tough of a life does the primary chain lead vs. the exposed drive chain? I am leaning that direction unless there's some good reason not to, not sure of the downside, perhaps the clutch bearing.

Click to expand...

The primary has higher RPM and torque loading compared to the drive chain. As a BSA C11 owner, I can commiserate on the sealing vs. keeping it properly lubed issues.

gpzkat said:

I've read that some forego an oil bath and just use an occasional spray of good chain lube. I've also read that technically the Norton isn't a 'wet' clutch. How tough of a life does the primary chain lead vs. the exposed drive chain? I am leaning that direction unless there's some good reason not to, not sure of the downside, perhaps the clutch bearing.

Click to expand...

Ken (lcrken) says don't do it. Oil won't stay on the chain long between manual lube jobs due to the high chain speed. I think he might have told me that in my straight jacket post. He was racing that way, so slightly higher chain speeds than a street bike, but unless you plan to stop every 15-20 miles and lube the chain I wouldn't expect long chain life.

OK thanks I will seal up best I can and use proper stuff and amount etc.