Voltage drop

Information relating to the Matchless G3 or AJS Model 16 350cc Heavyweight
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Re: Voltage drop

Postby mikeydpippin » Mon Nov 27, 2017 8:42 pm

Thanks so far for your help.
Waiting for new switch so did resistance check on coil ( noticed alternator wires joined to make 12v hence a 12v coil I guess)
Lucas Ma12
Low tension 3.4 High tension 7.5 (7500) so coil looking good?.
Will report back when switch fitted, don’t go away.....👍
Mike

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Re: Voltage drop

Postby aobp11 » Mon Nov 27, 2017 9:12 pm

noticed alternator wires joined to make 12v
Whille you have a 6 V battery? Or is that 6 V battery not the one you normally use on this G3LS? The MA12 is for 12 V indeed, and MA6 for 6V. At 6 V battery the MA12 might give a sufficient spark in a low CR engine (I just don't know), but officially your bike has MA6 and 6 V battery.
Albert

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Re: Voltage drop

Postby mikeydpippin » Mon Nov 27, 2017 9:24 pm

Thanks Albert, I will separate alternator wires replace coil with 6v and get bike back to basics as well as fit replacement switch.Thanks...
Mike

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Re: Voltage drop

Postby Mick D » Tue Nov 28, 2017 8:51 am

Hi

Whilst you wait for the switch to arrive you can confirm the serviceability of the coil, to do this:

Remove the connections to the LT terminals.

Remove the spark plug from the head and re-fit it to the HT lead - lay the plug on the head so as it earths.

Bare the ends of a couple of lengths of wire, anything will do in this case, household mains etc.

Attach one wire to the battery -ve and the coil -ve.

Attach the other to the coil +ve.

Now strike the bare free end on the cylinder head - you will see a spark at the plug if the coil / HT lead and plug are functioning correctly.

If you don't see a spark at the plug, look closely at the end of the wire as you strike it on the head, if you see small sparks it indicates the HT side of the coil or the lead / plug are faulty.

If you don't see any sparks, check there is voltage on the free wire, (put a meter set to dc volts between the wire and the head), if not it is indicative of the coil LT being fried.

Before deciding to revert to a six volt system I suggest you check on the specification of other items in your system, lights, horn, rectifier etc. - it may be more economical to go 12v.

Regards Mick

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Re: Voltage drop

Postby aobp11 » Tue Nov 28, 2017 10:27 am

noticed alternator wires joined to make 12v
I will separate alternator wires
Mike, with Lucas alternators like RM15 (model for 1958) you can't join wires to obtain 12 V. You probably mean the dark-green and the green-yellow wire. When joined the 6 V windings of the alternator are connected in parallel, so you keep 6 V but at higher amperage. Normally these wires are joined together by the lightning switch when you switch on the headlight.
Please find out exactly what is going on here before you order new stuff.

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Re: Voltage drop

Postby mikeydpippin » Wed Dec 06, 2017 8:36 pm

Hi again Mick,
Switch arrived and fitted all lights working well with fully charged battery.
No spark at plug when kicked over or spark at points when flicked with points in closed position ( yes ignition is on)
I did as you suggested above.

If I do exactly as described above I get no spark from plug or voltage from loose cable.
If I do exactly as described plus connect the positive lead (positive earth) to the battery I get a good spark at the plug.

I have also replaced the points.

Thanks again.
Mike

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Re: Voltage drop

Postby Mick D » Thu Dec 07, 2017 9:27 am

Hi Mike

I see my response could be misinterpreted :oops: - (the battery +ve needs to be connected to earth for the diagnostics to work)

From your post you have proven the coil LT and HT circuits to be in order.

Not getting a spark when you exercise the points is indicative of a fault with them.

Remove the wire from the points, (the one at the isolation washers in the image I posted earlier), and place it on an earth for a couple of seconds then remove it - you should see a spark at the plug which confirms the wire between the coil and CB to be good.

With your meter on 'continuity' place one probe on the cable connector post of the CB and the other to an earth - with the points closed there should be continuity - with the points open the circuit should also be open - if this is not the case you need to investigate the isolating washer and sleeve and ensure they are isolating the moving point assembly from earth.

Have you tried removing the capacitor from the system and seeing if you get the spark back? Worth a go

Regards Mick

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Re: Voltage drop

Postby mikeydpippin » Thu Dec 07, 2017 8:28 pm

To update this post.

I had the leads the wrong way round, for some unknown reason my head insisted the lead from the coil was the last lead to be fitted on the CB post as this had a forked terminal fitted, and the condensor/ capacitor lead with the large circular terminal, fitted over the top hat.

WRONG
I changed the terminal and crimped the circular terminal on the coil to CB lead and fitted over the top hat and replaced the Condensor terminal with the forked type and fitted this last next to the fixing nut and away she went.

Mick, Alan and Albert Many Thanks for your help, would still be scratching my head if not for your help.
Mike

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