Wise guidance required, Mk2 1973 850 commando

Hi there
I bought a basket case of a 1973 850, US import.
Happily working through the mechanical side of things, wheels built, rolling chassis coming together with new vernier isolastics, bottom end new bearings and crank reground, rebore, head sorted and going together with new valves, std cam and twin amals.
I'm starting to look forward with trepidation at the "what to do with ignition and general electrics" bit, there seems to be a bewildering choice from custom looms to +ve and -ve earth, pazon, boyer, etc etc - not my comfort zone really. I have the original loom in a bag with all the rotting bits n bobs attached but wondered if there is a "magic" formula for good reliable performance - not too worried about originality on the out of sight bits if it makes it more reliable .
I want to keep the original switches but want to be able to ride the bike once its done in all weathers -
What would you do..?

I got my 850 '74 MKII in a running. But not road worthy state. First classic bike for me. Didn't want to add more variables to my limited skills so went straight to an EI to replace points. Chose the Vape-Wassell unit which is essentially the same as the original Boyer units which have a huge following. It has some improvements like the stator board being epoxy encapsulated and not worries of wire connection breakages. Its been great for 13k miles now. I also picked up the TriSpark EI which is basically considered top of the line. Have not yet installed as the Wassell unit has been so good. May do it over winter.

For most of that mileage bike was running original wiring after cleaning up all connections and checking all components. New harness now on after some major strip down last winter, really just because it was a good time to do it rather than an issue needing a solution.
I still have the capacitor in place and all the switch gear.

Beefiddler said:

I'm starting to look forward with trepidation at the "what to do with ignition and general electrics" bit, there seems to be a bewildering choice from custom looms to +ve and -ve earth, pazon, boyer, etc etc - not my comfort zone really. I have the original loom in a bag with all the rotting bits n bobs attached but wondered if there is a "magic" formula for good reliable performance

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The magic formula can be as much (or more?) to do with how, and to what standard the work is carried out.

I am using TriSpark EI, coils, and MOSFET rectifier as well and building a custom loom based around these components. You may see the excellent schematic here. It's expensive, but I like the holistic approach of a single manufacturer's solution across several components designed for one another. I will use non-resistor plugs and wiring, and a pair of NGK 5 ohm caps as per TriSpark's advice.

First of all, if the serial number is between 300000 and 307310 it is likely a MkI or MkIA Commando which are the 1973 model 850. These are distinguishable by the silver barrels and RH4 cylinder head with 32 mm intake ports. If the serial number is between 307311 and 32500 it is a MkII or MkIIA which is the 1974 model 850. These are distinguishable by the black barrels and RH10 cylinder head with 30 mm intake ports.

As to making good reliable electrical system. Over the last 49 years I have found electronic ignition (Pazon, TriSpark or even Boyer) is a reliable upgrade. No wear parts to replace. I have one of each and the Boyer has survived over 30+ years with no failures (but I did replace the cheap connectors when I installed it). Pazon and Tri-Spark have also given reliable service. A new harness is a good idea. A factory harness if you are not electrically savvy, but if you understand the basics you can build a custom harness with fewer wires and connections. This is particularly handy if you use a solid state regulator/rectifier (simple and cheap compared to new zener diode and Lucas regulator) and electronic ignition. The old multi wire connector found under the tank is often a source of problems and can be eliminated or replaced with single bullet connectors. Adding more ground wires can also be helpful. Particular in areas such as the turn signals. I tend to go a little overboard and make my harnesses and incorporate a fuse block and lay out separate circuits for ignition, lights, and horn. I like to use relays to insure full voltage to these circuits with a minimal current through the Lucas switchgear.

Converting to negative earth (ground) is really only necessary if you use polarity sensitive devices such as most LED's or USB ports. Nothing wrong with doing the conversion, but why confuse someone trying sort out any problems.

These are my experiences, but others may disagree.

"If the serial number is between 307311 and 32500 it is a MkII or MkIIA which is the 1974 model 850. These are distinguishable by the black barrels and RH10 cylinder head with 30 mm intake ports."

Well, there you go - 307489 its a 1974 black barrel version with 30mm intake ports. Thanks for the taking the time to respond, I'll be mulling it over as I head towards the fiddly bits!

Beefiddler said:

Well, there you go - 307489 its a 1974 black barrel version with 30mm intake ports. Thanks for the taking the time to respond, I'll be mulling it over as I head towards the fiddly bits!

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Whether an 850 MkI, Mk1A (extremely unlikely for a "US import" to be a Mk1A as that model wasn't officially sold in the USA), Mk2 or Mk2A (again unlikely to be a Mk2A with such an early serial number as Mk1A and 2A 'low noise emission' models were intended for sale on the European market although some Mk2As were eventually sold in the USA) makes no difference as far as the electrics are concerned because all had basically the same electrical system (except for the repositioning of the rectifier and flasher relay from the rear to the front of the frame plate to make space for the 'A' model tool tray).

Model year can only be loosely applied to Commandos as there were no official "model years", only 850 Mk1, Mk1A, Mk2, Mk2A, Mk3 etc. so if the documentation has it as "1973" then for registration purposes that's what it was. If the frame has its certification plate with the month/year date stamp then I'd expect the date of manufacture to be approximately 6/73 give or take a month or so.

As mentioned above , I found it much easier to run my own wire loom to keep things simple , my ‘72 had only brake light , horn & head lamp plus charging , ign. system …. Made sense to buy some wire and colour code the circuits , worked fine ….

I never claim to be wise or even smart , so I'm unqualified.
As per electrics , you have some very talented people here to help you.
Myself I know the original connectors on the looms were made of a tin , so best to bin the entire harness and start over again.
Andover realized this and offer a new harness made with better ones.
But yes if you feel like taking on the project go for it by the book with a new harness.
Or (best option) , make your own with help from others , or use the Forum.
Choosing modern electrical components and creating the wiring to them is an idea I recommend .
My bike uses that idea incorporating a :
MK 1V Boyer Ign.
Podtronics Rectifier .
LED tail and LED headlight .
Relays to take the strain off of the Switchgear (s).
RM 23 alternator .
Bigger battery .

It's evolving all the time , it never ends.. Good luck.

Having read all of this including your original post, just a note to say I pretty much did the same stuff being discussed here (electronic points replacement, electronic rectifier/regulator, fresh wiring loom) when I rebuilt my first Commando and STILL encountered problems with the stock and original ignition switch which I eventually discovered was sufficiently corroded internally that it wouldn’t allow full voltage to be delivered to the Boyer and the coils. Once I opened it, cleaned it out and lubed it, it finally ran right. My advice is: If you are going to renew things, renew (or open and clean) everything including the switches.

Replace all female snap connectors. Cheap & easy. Unless the original harness has been butchered, a lot. Do not fall victim to the folklore of alleged unreliable electrics.

I don't know if I can offer wise guidance, but my '74 US import is still on the original harness, and although it's working fine, it really is a bundle of spaghetti under the tank.

I removed the points ignition and installed a Pazon Sure fire. I also dropped Al Osbourne (from the NOC) an email regarding replacing the old harness. He basically knew what I wanted better than I did and rather than a new loom, he sent me a kit (basically a bag of lengths of coloured wire, sheathing, bullet connectors etc.) and also a new reg/rec to remove the Zener diode. The colour of the wiring is the same as original. Without digging out the paperwork, I'm sure it was about £80.


It's a winter project that I'll look at once I've sorted a few other little jobs, but I'm looking forward to tidying up the mess, and bulk, under the tank with the added security of modern electrics - but as Les alludes to above, it's all down to the standard of the work carried out.

Of all the 'new' looms available i would steer clear of the cloth covered variety. Commandos never had cloth/fabric tape covered wiring harnesses, at least not the ones i've had. The problems with the cloth covered harnesses is that they are far too stiff to pack neatly around the bike, they always have wires that are redundant and, being fabric they hold all the oil and shite that the bike attracts. Another problem with purchased new looms is because they are made to be 'original' they have too many block connectors (like the ones under the tank) in them as well, (any connector is a potential source of problems)
I always make my own looms, Quite easy if you set your stall out and get the proper tools and wire/connectors. Get the wiring diagram in the manual photocopied and enlarged and with your choice of components any alteration from 'standard' can be drawn in.
The obvious ones are electronic ignition, means you can do away with the condensers, ballast resistor etc and voltage rectifier/regulator.
A new voltage regulator/rectifier means that the wiring to the standard zenner diode in a 'new original' loom is immediately redundant...
Where are you in the UK?
regards
Peter

That "bundle of spaghetti" under the tank may trigger some OCD response from some, but reality is, it is not problematic to leave it there. Another 50 years.
I have the skills, tools, materials to create a whole new wire harness for my bike. But I won't.
It works reliably. Replacing it would not improve performance.

dobba99 said:

Of all the 'new' looms available i would steer clear of the cloth covered variety. Commandos never had cloth/fabric tape covered wiring harnesses, at least not the ones i've had. The problems with the cloth covered harnesses is that they are far too stiff to pack neatly around the bike, they always have wires that are redundant and, being fabric they hold all the oil and shite that the bike attracts. Another problem with purchased new looms is because they are made to be 'original' they have too many block connectors (like the ones under the tank) in them as well, (any connector is a potential source of problems)
I always make my own looms, Quite easy if you set your stall out and get the proper tools and wire/connectors. Get the wiring diagram in the manual photocopied and enlarged and with your choice of components any alteration from 'standard' can be drawn in.
The obvious ones are electronic ignition, means you can do away with the condensers, ballast resistor etc and voltage rectifier/regulator.
A new voltage regulator/rectifier means that the wiring to the standard zenner diode in a 'new original' loom is immediately redundant...
Where are you in the UK?
regards
Peter

Click to expand...

Hi
I'm near Wantage in Oxfordshire

Torontonian wrote: "Myself I know the original connectors on the looms were made of a tin , so best to bin the entire harness and start over again."

The female connectors are made of plated brass. Perhaps tin plated, but not solid tin. The brass is brittle and breaks easily, leading to unreliable connections. Pretty sure the male ends are plated brass as well.

Here are a couple of electrical items that have worked well for me. I use the voltage monitor in place of an assimilator and it has alerted me to electriclal problems more than once. It is bright enough visible behind a stock jewel in the headlight (amber works best) however dims to half brightness when you are cruising and all is well (steady green).
The other is a non polarized LED H4 bulb, it too works fine with my positive ground system.
The video shows the voltage monitor at "Bootup" and then in a 2 states with the headlight on or off. FWIW I have a '73 850 too.

Stephen Hill said:

The female connectors are made of plated brass. Perhaps tin plated, but not solid tin. The brass is brittle and breaks easily, leading to unreliable connections.

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Some appear to be (Cad.?) plated brass while others seem to be a heavier gauge greyish non-ferrous metal. All need to be replaced regardless.