67 N15CS Build

Here’s a running summary of my rebuild of a previously clapped out 67 N15CS. I’ve had this bike for 8 years now, tried to sell it for a while but couldn’t get what I needed out of it so put the engine on a stand on my bench about a year or two back for inspiration. Since then I have been casually addressing the head; more recently I bored & painted the cylinder to build some enthusiasm. Then early in October, on a whim I made the active decision to overhaul everything with the goal of racing here in the desert next April. I’ve raced my unit T100 in the same race twice (registered a third time but panicked and flaked).

Chris

I brought this heap home in 2017 along with a collection of crates holding a B50:


October 5:


Boring stuff:


Seat work:

I pulled the engine apart, noticing some odd weld repairs under the grime. Once I got in there I found one likely original con rod and a mismatched new replacement rod. Also a whole bunch of weld under the timing side rod, likely hiding a big scar from a rod nut backing off. Even though the cases mated up and everything spun fine, nothing about the timing side case was straight or square with all that weld. I mated up a matchless case half that was close in serial number… again the crank & cam spun nicely, I just had to dress the cylinder base surface.

Moving forward, I’ve fit a JS1 cam with his BSA followers, skimmed the head .020”, will be omitting the base gasket and with plain ol JCC pistons should be hitting an honest compression ratio north of 9:1.

With a pair of NOS rods, I still need to have the crank ground & balanced. At this point all the reciprocating parts are weight matched.

The head has been a challenge. My goal is always to get a proper 3-angle (or 4 if there’s enough room) valve seat. The stock seat profile on these heads threw me off… no matter, I set out to fit oversize Kibblewhite valves, until the cam instructions made it clear there isn’t enough room in the chamber for that. I compromised with slightly larger, slightly recessed valves, with marginally improved seat profile & throat ratio. I’ve been able to find measureable improvements in flow with the same strategy on a T150 & VH500 head that I’ve built. Beehive springs are in the mail as we speak…

Chris

Nasty case:

Crankcase shuffle:

Fitting the BSA followers. JS Motorsports makes a really nice kit here and not much more costly than a good set of standard followers:

Bringing this up to date -
I had the frame & parts coated and they’ve mostly been sitting around waiting on assembly. Yesterday, the hardware arrived unexpectedly from the plater. Luckily I took the day off and spent the afternoon playing puzzle.

Looking forward, I’ll be fitting a pair of flanged alloy rims to the stock hubs. I’m waiting on fork stanchions and have been working on getting the damper parts correct - I found early teledraulic parts in there, assuming a fork swap after a crash. I’ll be making a few sensible upgrades once I have all the standard parts in hand.

The shocks are Works Performance & will get rebuilt & tuned.

Chris

Hardware arrived like this. I was expecting chaos but not real impressed that it wasn’t also bagged up. Looks like everything is there and I’m extremely pleased with the cost and finish for cad plate (local platers in LA quoted 4x the price):


Loosely assembled:

Chris Johnson said:

..I’ll be making a few sensible upgrades once I have all the standard parts in hand.

​

Click to expand...

A 'sensible upgrade' would be slider extensions.
The stanchions are already an inch longer than Commando ones.
You can make them yourself, or buy from CNN.
They can be hidden inside the chrome shrouds.

That’s on the list, among a few other things.

Chris

Aside from the engine valve train updates, the swing arm pivot sure looks like a vast improvement. It could be stock though, but seems futuristic for the time period and Norton pre-Commandos. I've zero experience with the N15 obviously.

Wow, great stuff, good to see you posting this. Just back from another ride on my 66 (or is it '67 - #119799) and it never fails to bring a smile.

Schwany said:

Aside from the engine valve train updates, the swing arm pivot sure looks like a vast improvement. It could be stock though, but seems futuristic for the time period and Norton pre-Commandos. I've zero experience with the N15 obviously.

Click to expand...

I remember working on that pivot with my typical janky allthread and washers method to push it apart and put back together on the bench, worked out OK. I believe I may even have put new bushings and grease in!

Do you have a centerstand? If so, I'd be interested in seeing pics at some point, if you will. Mine has given me fits, and I'm about to tackle it again to get it right - so far, just a bunch of failures. Mine's orientation, based on witness marks, operation, and angle of the feet, were backward, as if someone had set it up for right-side foot usage with the lever/tang. I spent many hours trying to get it to work, but it always fouled the frame, no matter what I tried. I have the right spring, bolts, you name it. I just haven't cracked this nut yet, last one. In this pic, yellow arrow points to front of the bike as it deployed logically/per witness marks etc. Yet the area I'm pointing to is where the tang was.

I'm willing to hear how wrong I am on this but I have figured out every other thing about this bike from a box of bits, complete rebuild. This has stumped me.

No center stand on mine… can’t help there.

Chris

Here’s a little progress to report…

Wheels are built, hopefully will have tires mounted this week.

Forks are built, just need to tighten a few things. Improved dampers, extended bushings & chromed stanchions.

Gearbox is built, waiting on kicker & gearchange lever from Toads.

The flow bench finds the limits of the stock ports. I did find a 15% improvement in flow with a few modest changes.

And I have a good start on the exhaust. Bummer that Supertrapp seems to have gone under; their silencers are getting hard to find new.

Chris

Wow, mad skills. You've done this before... That's going to be a great bike, love the upswept pipes on one side.

I just picked up a really nice original 75 Laverda 3C, which is so easy to work on vs. the Norton.

I may have a decent spare monobloc if you need one. I'm sticking with my single Mikuni VM34 as it does fine, loping along with tall gearing - no speedster, but very enjoyable.

gpzkat said:

Do you have a centerstand? If so, I'd be interested in seeing pics at some point, if you will. Mine has given me fits, and I'm about to tackle it again to get it right - so far, just a bunch of failures. Mine's orientation, based on witness marks, operation, and angle of the feet, were backward, as if someone had set it up for right-side foot usage with the lever/tang. I spent many hours trying to get it to work, but it always fouled the frame, no matter what I tried. I have the right spring, bolts, you name it. I just haven't cracked this nut yet, last one. In this pic, yellow arrow points to front of the bike as it deployed logically/per witness marks etc. Yet the area I'm pointing to is where the tang was.

I'm willing to hear how wrong I am on this but I have figured out every other thing about this bike from a box of bits, complete rebuild. This has stumped me.

Click to expand...

Tom,
I believe the tang was fitted correctly, but wear on upper part of the stand fooled you to believe it had to be fitted backwards. Fact is. the mild steel casting and sizing is not up to the job of restraining weight of the heavy G15 when heaving the bike up repeatedly (1000 x ), so it deforms plastically. I am sure you can see whithness marks on your stand's stopping tabs. You need to fabricate or get a new stand. May I remind you that Rob Swift makes (or used to make) improved stands for the G15 series? I can shoot some pictures if you want to replicate it .... or you can order one from him. I haven't fitted mine yet but others claim it fits and works well. Contact details are in a previous posting, do search for Rob Swift.

- Knut

Try Ron Wood Racing (ronwoodracing.com) and see if they have any Supertrapp stuff laying around you could make use of.

mdt-son said:

Tom,
I believe the tang was fitted correctly, but wear on upper part of the stand fooled you to believe it had to be fitted backwards. Fact is. the mild steel casting and sizing is not up to the job of restraining weight of the heavy G15 when heaving the bike up repeatedly (1000 x ), so it deforms plastically. I am sure you can see whithness marks on your stand's stopping tabs. You need to fabricate or get a new stand. May I remind you that Rob Swift makes (or used to make) improved stands for the G15 series? I can shoot some pictures if you want to replicate it .... or you can order one from him. I haven't fitted mine yet but others claim it fits and works well. Contact details are in a previous posting, do search for Rob Swift.

- Knut

Click to expand...

Would they have beveled the back end of the foot? If so, I screwed up royally. My son's pal is a welder/machinist and has offered to fix it, one way or another. Maybe that'll work out.

I do remember the info on Rob Swift - it's a $ thing for me, hope to change that soon.

gpzkat said:

Would they have beveled the back end of the foot? If so, I screwed up royally.

Click to expand...

No bevel at the extension that I can see, but it's difficult to spot this area. Are bevels shown on your stand made this way at the factory or did you make the bevels yourself?



Stoppers at the latter stand have deformed considerably, allowing the stand to rotate too far, so rear wheel is barely off the ground.

- Knut

mdt-son said:

Are bevels shown on your stand made this way at the factory or did you make the bevels yourself?

Click to expand...

This is how I got it. Maybe the bevel is there for the 'at rest' position, not as a 'ramp' as per usual practice. That may explain things, well, except the witness marks on the mounting end.

Chris - are those Fox shocks?

Those are works performance shocks. I have a thing for them and try to buy them up when I find them undervalued.

Chris