850 Commando won't start, just quit - mid ride.

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NoSkiddoKiddo

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Dec 14, 2023
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my 1975 850 Commando just quit, mid ride. I was accelerating slightly up a slight incline, motor just stopped. Motor seems to turn over, but won't fire.
Before the ride, I'd been waiting for a centre stand bolt that had gone missing to come in the mail, and had noticed the neutral indicator switch had a loose wire, just dangling. After the motor failure, the dangling wire disconnected when I touched it. I reconnected the wire with alligator clips, and neutral light works fine, but motor will not fire up.
I should mention the motor was recently rebuilt by qualified shop, has about 200 miles on it after complete break-in. All motor response has been strong and smooth up to now. I suspect this is an electrical problem, but ... ?
Any thoughts on what to look for, or what steps I can take to track down this problem? I'm pretty good with the wrenches, no Norton experience though. Checked the fuse by the battery, looks good. Also checked the Kill switch, motor won't start with Kill switch in any position.
Thanks, all thoughts appreciated

** UPDATE! ** - I rooted around in the wiring and saw that one ignition coil had a disconnected wire, the other had one looked like it was off too. Reconnected these and she started right up! The clips on these look a little weak to me, I'll be looking for a better way to keep these on tight.

Thanks all for your contributions. Johnm, you were right, just get down (I have to lay down) under the gas tank and start checking those wires.
 
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First check you havnt run out of gas.

Then your right 99.9% chance it's electrical.

First get a wiring diagramme.

What sort of ignition have you got?

Apart from checking for obvious loose or cut wires especially from under the tank to head lamp shell the fastest way to check is to take a jumper wire directly from the negative of battery to the ignition unit feed. Assuming a standard positive earth.

If the bike runs by using this jumper wire then you have a break somewhere in the ignition wiring harness feed, switch unit etc. You will need to check for continuity step by step through the wires using a multimeter to chase it down.

One other weird problem I had once was when the wires down to the trigger unit on the end of the cam got blown around by the wind and melted onto the balance pipe. You can check that in seconds.
 
Hi, Welcome🍻


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S

B

B


1. Check spark. Lay a spark plug on the head, with the lead attached. Turn the engine over.

(and thank you for clearly communicating the difference between "turn over" and "fire")
 
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NoSkiddoKiddo said:
my 1975 850 Commando just quit, mid ride. I was accelerating slightly up a slight incline, motor just stopped. Motor seems to turn over, but won't fire.
Before the ride, I'd been waiting for a centre stand bolt that had gone missing to come in the mail, and had noticed the neutral indicator switch had a loose wire, just dangling. After the motor failure, the dangling wire disconnected when I touched it. I reconnected the wire with alligator clips, and neutral light works fine, but motor will not fire up.
I should mention the motor was recently rebuilt by qualified shop, has about 200 miles on it after complete break-in. All motor response has been strong and smooth up to now. I suspect this is an electrical problem, but ... ?
Any thoughts on what to look for, or what steps I can take to track down this problem? I'm pretty good with the wrenches, no Norton experience though. Checked the fuse by the battery, looks good. Also checked the Kill switch, motor won't start with Kill switch in any position.
Thanks, all thoughts appreciated
Click to expand...
Agree 99% electrical. Other 0.9% is fuel. Then 0.1% mechanical. To rule out fuel....single or dual carbs? If dual, and you have fuel and both taps open, then you can pretty much rule out fuel. If single carb, did it die instantly or splutter and die over a short distance? If instant then electrical. If it spluttered it could be fuel, including a blocked tank vent or crap in the fuel line, etc.

Wouldn't spend cycles initially chasing anything other than electrical unless the mode of failure was other than 100% instant death.
 
Yes , electrical connectors . Replace the whole harness with a modern one . Easy for me to say . As for the MK 111 neutral switch , the whole gearbox has to come apart to fix the problem which is a slot worn into the button , which impedes finding neutral . Back out the switch , until winter when you can get in there .
 
johnm said:
.....
One other weird problem I had once was when the wires down to the trigger unit on the end of the cam got blown around by the wind and melted onto the balance pipe. You can check that in seconds.
Click to expand...
+1 on that. I caught mine just in time. The outer sheath had a nice melt mark, but not yet through. I put a light metal spiral binder around the cable in that area (roll it on without needing to disconnect the wiring) and then cable tied each end to the fame. Looks factory and keeps the wiring out of harms way.

Glad you found the problem. I bought mine 3,000 miles after a full engine out rebuild. They did a good job. But subsequent owners did nothing. I found a lot of loose nuts and bolts and the head needed torquing down. Since then I've done 5,000 miles and it's all stayed tight. Suggest you go over it a few times in the next couple of thousand miles, just to check.
 
Mart UK said:
+1 on that. I caught mine just in time. The outer sheath had a nice melt mark, but not yet through. I put a light metal spiral binder around the cable in that area (roll it on without needing to disconnect the wiring) and then cable tied each end to the fame. Looks factory and keeps the wiring out of harms way.

Glad you found the problem. I bought mine 3,000 miles after a full engine out rebuild. They did a good job. But subsequent owners did nothing. I found a lot of loose nuts and bolts and the head needed torquing down. Since then I've done 5,000 miles and it's all stayed tight. Suggest you go over it a few times in the next couple of thousand miles, just to check.
Click to expand...
+1 on 'constant vigilance' for loose fasteners & retorquing head bolts.
The lower rear engine mounting bolt has been a favourite of mine (all pre-Mk 3); they work loose then shear.
I believe the Mk 3 has a bigger bolt than all the prior models.

Also nice to pick up on a story which already has a happy ending :)
 
Spade connectors are used in everything from trains, planes, automobiles to everything else.

They’re perfectly good.

No need to re design anything here. Just ensure they’re the right connectors and in good condition.

Sometimes a gentle nip with pliers is all that’s required. But on 50 year old ones do take extra care as broken spades do not stay in place well !

Also, you’d do yourself a huge favour and get into the habit of using Dielectric grease if you don’t already.
 
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1/4" spade (Lucar) connectors can be brittle, so be careful when nipping them over with pliers.

I have found that petroleum jelly (Vaseline) is perfectly good on connectors. It works well to keep moisture - and hence corrosion - out of the terminal.
 
I now use these clamps - very maintainable and much better than bullets or spades (IMO). No soldering or crimping, just over-centre clamping.
Obviously can't get away from spades on solenoids, etc but for the rest...
Always buy Wago (221) - not imitations.
They are available in 2, 3 and 5 ports.
Cheers
Wago.png
 
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Fast Eddie said:
Spade connectors are used in everything from trains, planes, automobiles to everything else.

They’re perfectly good.

No need to re design anything here. Just ensure they’re the right connectors and in good condition.

Sometimes a gentle nip with pliers is all that’s required. But on 50 year old ones do take extra care as broken spades do not stay in place well !

Also, you’d do yourself a huge favour and get into the habit of using Dielectric grease if you don’t already.
Click to expand...
Whilst I agree they are up to the task or should be I have had those spade connections come loose or fall off so many times I have reverted to ring terminals on the coils
My mk2a also used to shed them
My mates combat also does it
That was enough to convince me but I've never had this happen with vertically mounted coils
 
baz said:
Whilst I agree they are up to the task or should be I have had those spade connections come loose or fall off so many times I have reverted to ring terminals on the coils
My mk2a also used to shed them
My mates combat also does it
That was enough to convince me but I've never had this happen with vertically mounted coils
Click to expand...
I use Thomas & Betts ring terminals on the coils, not because the spades pulled off, because they give extra clearance to the rocker cap nut.

JMWO
 
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When re-wiring I use crimp and solder ring terminals. I cover the solder area and about 1/4" of the wire with heat shrink. There's nothing wrong with spades but by using ring terminals there's four less connections at the coils to be concerned with.

Yes, a clean wire properly crimped into a clean connector makes a "forever" air-tight connection, so solder is not needed. However, the slightest contamination (oil from fingers, etc.) make a connection that will eventually corrode. The crimp then solder connections are the same except that the solder prevents air from getting to the actual connection and therefore no corrosion. Also, you can see your work (not covered in plastic) so you know it was done right. I have seen crimp connectors (spade and ring) where the person was too close to the edge and crimped the plastic only or barely caught the metal - everything seems to work at first but eventually it doesn't and it is a bear to find. BTW, It is important to use rosin core solder and not overheat.
 
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