Thinking of going back to Amal

I wouldn't think a highly tuned engine would be much thirstier than any other unless it is on methanol.

acotrel said:

I wouldn't think a highly tuned engine would be much thirstier than any other unless it is on methanol.

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Very true, but all engines (low or high tuned) are much thirstier above 5000 rpm and that is what this modifaction is meant for 8)

Hello Bonwit,
The switch bracket is indeed spot welded to the back of the air filter back plate. The overall length of the bracket is about 4 5/16 inches long. I imagine if you welded the switch bracket back in place it would be at least 1/16 inch shorter than original, so you would probably end up making a whole new bracket. The back plate is originally painted gloss black and is attached to the motorcycle with 3 bolts. The bottom 2 bolts also have a bend tab washer (p/n 060926) so that the bolts would not be able to loosen and be sucked into the intake system. The top bracket mounts to the forward side of the frame plate and there is a 3/16 inch thick spacer (p/n 062170) that goes between the top air filter bracket and the frame plate. The parts book shows the placement of that spacer incorrectly.

The "metal hook" on the back plate is where the oil tank breather hose connects. It is a design feature so that oil from the breather can foul up your air filter (!).

Yes the ignition switch faces directly forward. That was the way it was done in most models of the Norton Commando. On the Mark II/IIA's the ignition switch got a different switch cover (p/n 064892 and p/n 064891) which has a goofy little flap door on the front of it that completely covers over the key as a form of weather protection. Unfortunately it is rather awkward to use especially if you are wearing a glove.

Later you will probably wonder about the routing of the ignition switch wires. I have seen the wires routed on the outside of the frame tube and also on the inside of the frame tube in factory sales brochures. If your motorcycle is an Interstate the obvious choice would be to route it on the outside of the frame. Otherwise I would be inclined to route it between the frame tube and the air filter. On my motorcycle I routed the wires down in front of the frame tube so that there was plenty of clearance for the wires, then routed them on the inside of the frame tube. This is just a matter of personal preference and its your call.

The air filter's front plate originally had some baffles spot welded in it supposedly to help reduce intake noise. If you are a purist, you would want that. If you want to maintain your bike more easily, you don't want it. The front plate is originally painted silver - I am not too sure of the finish, it was probably a gloss finish and through the years they would dull down. However the stainless steel aftermarket air filters look nice.


This is what the forward switch cover looks like - flapper door on the right and slotted hole goes over the switch bracket.


I threw caution to the wind and I made a non weatherproof forward switch cover from aluminum alloy. For me in California foul weather riding is 59 degrees or less on a clear and sunny day. This makes operating the key all around easier. I was going to paint the cover black, but I decided to go with the polished look.

peterjoe that is one slick factory location ram jaming job of aligning and covering and wire routine as I've ever seen, nice effort to view and dread. Its not so much the weather that decays these switches as much as the key fob jerking about hours as a time. My two Combats switches were both upward cocked and also stuck out beyond frame and made wires bend acutely to route in front of cover. I like the bright look of the switch and standard dull grey-sliver paint and cleaned off SS screen. I found trimming off one pleat of the booties made easier install and sealing fit w/o as much distortion and crack forming stress.

PeterJoe said:

Hello Bonwit,
The switch bracket is indeed spot welded to the back of the air filter back plate. The overall length of the bracket is about 4 5/16 inches long. I imagine if you welded the switch bracket back in place it would be at least 1/16 inch shorter than original, so you would probably end up making a whole new bracket. The back plate is originally painted gloss black and is attached to the motorcycle with 3 bolts. The bottom 2 bolts also have a bend tab washer (p/n 060926) so that the bolts would not be able to loosen and be sucked into the intake system. The top bracket mounts to the forward side of the frame plate and there is a 3/16 inch thick spacer (p/n 062170) that goes between the top air filter bracket and the frame plate. The parts book shows the placement of that spacer incorrectly.

The "metal hook" on the back plate is where the oil tank breather hose connects. It is a design feature so that oil from the breather can foul up your air filter (!).

Yes the ignition switch faces directly forward. That was the way it was done in most models of the Norton Commando. On the Mark II/IIA's the ignition switch got a different switch cover (p/n 064892 and p/n 064891) which has a goofy little flap door on the front of it that completely covers over the key as a form of weather protection. Unfortunately it is rather awkward to use especially if you are wearing a glove.

Later you will probably wonder about the routing of the ignition switch wires. I have seen the wires routed on the outside of the frame tube and also on the inside of the frame tube in factory sales brochures. If your motorcycle is an Interstate the obvious choice would be to route it on the outside of the frame. Otherwise I would be inclined to route it between the frame tube and the air filter. On my motorcycle I routed the wires down in front of the frame tube so that there was plenty of clearance for the wires, then routed them on the inside of the frame tube. This is just a matter of personal preference and its your call.

The air filter's front plate originally had some baffles spot welded in it supposedly to help reduce intake noise. If you are a purist, you would want that. If you want to maintain your bike more easily, you don't want it. The front plate is originally painted silver - I am not too sure of the finish, it was probably a gloss finish and through the years they would dull down. However the stainless steel aftermarket air filters look nice.

This is what the forward switch cover looks like - flapper door on the right and slotted hole goes over the switch bracket.

I threw caution to the wind and I made a non weatherproof forward switch cover from aluminum alloy. For me in California foul weather riding is 59 degrees or less on a clear and sunny day. This makes operating the key all around easier. I was going to paint the cover black, but I decided to go with the polished look.

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Some great information here. Thanks! Yes, the bracket would be off about the width of the blade kerf. A new plate will run about $50 bucks + shipping, maybe more. Other than the bracket and needing paint, mine's in good shape. I'm wondering if I can't just get a friend to tack-weld the bracket in place and then fill the gap with weld, file it down and paint.

Instead of tabbed washers, I wonder if some blue Locktite would work as well. Even if one backed off, it's hard to imagine it doing much damage.

Thanks for pointing out the spacer on the top bracket. I hadn't noticed that.

My switch has both rubber boots. I wasn't aware it used to have a flap door to keep the rain out. Pretty Micky Mouse. Mine was cut back long ago. Your switch looks fantastic.

So, instead of running the breather to the air filter box (which sounds like an awful idea), where would you run it? I used to run mine to a Taiwanese PCV valve bolted in the battery box, and then exiting to a little catch bottle, also in the battery box. It really kept the bike clean, and maybe I'll use it again.

If you're talking about an automotive pvc valve I don't see how that would work as they depend on manifold vacuum to draw crankcase vapor into the engine to be burnt. On my MK3 I just use a hose off the oil tank running down and secured to the frame as to not get any oil on the rear tire. Truthfully though the only time I see oil from the hose is after coolish ride when the next morning I may see a quarter size drip on the floor made up of an oil and condensation mix.

An ordinary car PCV works quite well. It opens under pressure and creates a vacuum in the crankcases as the pistons rise. I use one out of a Ford Falcon for years, it stopped a lot of oil leaks by sucking the gaskets. It was a matter of welding a tail on the open end of the valve while the body was standing in water to keep the spring cool. Ducatis use to use a rubber flap on the end of a large diameter breather, however it did not work with a catch can. With the PCV you only need a 12mm tube.

acotrel said:

An ordinary car PCV works quite well. It opens under pressure and creates a vacuum in the crankcases as the pistons rise. I use one out of a Ford Falcon for years, it stopped a lot of oil leaks by sucking the gaskets. It was a matter of welding a tail on the open end of the valve while the body was standing in water to keep the spring cool. Ducatis use to use a rubber flap on the end of a large diameter breather, however it did not work with a catch can. With the PCV you only need a 12mm tube.

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But the poster is speaking of venting the oil tank, not the engine. No real pressure there, at least not on the MK3, just kind of a slight back and forth chuff. Crank case venting on earlier models vary though, maybe that's the difference?

Automotive PCV's generally if not universally have too massive internals to act as one valve in Nortons as rpm rise where its needed most. Skin this cat you own way or off the shelf after market variety of options.

Biscuit said:

But the poster is speaking of venting the oil tank, not the engine. No real pressure there, at least not on the MK3, just kind of a slight back and forth chuff. Crank case venting on earlier models vary though, maybe that's the difference?

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The oil pump could be pumping about 1/2 pint per minute of crankcase fumes back into the oil tank.It doesn't just pump oil back from the engine.

X-file said:

Biscuit said:

But the poster is speaking of venting the oil tank, not the engine. No real pressure there, at least not on the MK3, just kind of a slight back and forth chuff. Crank case venting on earlier models vary though, maybe that's the difference?

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The oil pump could be pumping about 1/2 pint per minute of crankcase fumes back into the oil tank.It doesn't just pump oil back from the engine.

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Don't know about fumesil ratio but in view of the hose running from the oil tank to atmosphere or the filter housing being about 5/16" I don't see much or any real pressure being built up in that oil tank , and a PCV would only add some. What's the point of adding a PCV at the end of the oil tank vent hose?

Thanks for the kind comments on my switch cover. My next door neighbor actually shamed me into coming up with a different switch cover after he commented that the original switch cover was really ugly. I agree with hobbit, I wouldn't worry too much about weather getting into the switch. I have a BSA 441 with a switch facing into the wind and weather and have had that bike over 20+ years without any problem with the ignition switch.

If you have a friend that can weld the bracket go for it. I am sure I could weld that bracket with a 1/16 inch gap. I wouldn't even bother filing the weld down because once painted and installed you wouldn't even see the weld.

I would say that Locktite would probably work fine for preventing those bolts from backing out. The problem I have with the word 'probably' is that I have worked as an Aircraft Mechanic for over 20 years and the words "probably alright, should be ok (etc.)" are warning phrases that if used would make us reconsider the work before returning the aircraft to service. If it were me I would just use the bend tab washer or drill the heads of the bolts and use safety wire. It is amazing what can get into an intake system. One time while helping someone pull a lower cowling from a P-51 Mustang we saw something fall to the floor. On initial inspection it appeared to be a ball of metal that had been completely hammered. On close examination we determined it was a 1/4-28 stop nut with a threaded portion of a bolt that had broken off still inside the nut. Of course we had to find out where this nut belonged. We figured it out, it was one of the nuts that held the lower intake trunk up to the carburetor. Apparently when the bolt or stud broke while the airplane was in flight the intake trunk dropped down maybe a 1/2 inch on that side. The nut somehow found its way through the small gap between the intake trunk and carburetor. Then that nut was sucked up through the carburetor, found its way through the supercharger section, beat the living hell out of the impeller blades and after finishing that it shot back down through the carburetor. That was not all, the nut magically found its way out through that first gap between the intake trunk and the carburetor then deposited itself on the bottom of the cowling for us to find. Simply amazing!

As far as the breather is concerned, all I have done is route my breather hose from the oil tank down to a low point on the motorcycle and then I also capped off the back of the air filter plate fitting with a vinyl cap (easily found in automotive stores). After parking my motorcycle I get a dollop of white, creamy oil mist on the floor. Right now I am considering using a catch bottle of some kind. The only reason you would want a check valve in your engine breathing system is to keep the crankcase pressure lower than the outside air pressure thus reducing oil leaks from the engine - which sounds like a good idea!

The engine breathing system on the Norton Commando is somewhat unique. On the later 750 and 850's they run a large diameter 1/2 inch hose from the engine close to the oil tank. I guess the reason/theory for the large diameter hose is so that the volume of air coming from the engine would actually slow down and give a chance for the oil mist to separate from the air before draining back into the timing chest. Then of course the oil tank itself would be considered a catch bottle for the oil mist that does return to the tank. The oil tank itself also has a small oil separator built-in the top portion of the oil tank right where the breather outlet is located. After all is said and done oil still finds its way out through the oil tank breather. Its funny that in both the Mark IIA's and Mark III's Norton added yet ANOTHER oil separator mounted externally. However, the Mark II's do not have this extra oil separator. Things that make you go 'hmmmm?'

DONE!

see: http://www.accessnorton.com/new-amals-replace-mikuni-what-difference-t18935.html for a report.

Looks pretty darn nice!

Deciduous as a new lawn mower. Might consider clear coat with gas resistant paint to keep the shine going and easier wash off.

nortonspeed said:

PeterJoe said:

One advantage to returning back to twin carburetors is that you don't have to worry about the allen headed screws inside the intake manifold working loose then taking a walk to the inside of the engine and really screwing things up

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A drop of loctite will solve that problem, however loctite won't stop chipping lower edges of the standard Amal valves (happened twice before I switched to a single Mikuni) :roll:

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That happened to me as well. lost a 6mmx5mm chunk out of l/h carb and it took the spark plug out on the way through. No serious damage, just had to do the rally on the back of a Triumph. [ kerinorton ]

Ugh my 1st Combat lost a thumb nail size piece of slide that peckered the whole chamber and piston surfaces as well as chipped intake and bend exht valve lips but didn't notice a thing operating that way, only found it taking apart to fix a bunch of leaks. Its a brain splitter on which camp to live in, upgrading towards a Honda or keeping the faith pure with its ritual sacrificing.