1948 Iron 4G Coil Ignition

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chris.matthews
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Re: 1948 Iron 4G Coil Ignition

Postby chris.matthews » Mon Aug 26, 2019 11:15 pm

Hello
I have no idea about the origins of the conversion, it was on the bike when I got it.
The conversion might have been done in Japan, but I think its more likely to have been done in UK in Late-Eighties.

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Chris

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Re: 1948 Iron 4G Coil Ignition

Postby john.whiting » Tue Aug 27, 2019 7:50 am

OK,if thats a normal coil ignition system,the plate behind the points should be earthed,and if its able to rotate as an advance /retard,it must be continuously earthed.......so check the continuity there for a start.......a normal/ie not transistor system will have the negative terminal of the coil connected to the breaker points......there will also be a capacitor somewhere in the system connected across the points,close to the points as possible,preferably.

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Re: 1948 Iron 4G Coil Ignition

Postby brenton.roy » Tue Aug 27, 2019 1:25 pm

As you can see a spark, the main ignition problem areas should be that either the spark is occurring at the wrong time, or that the spark is too weak to fire the compressed mixture.
The first is unlikely unless the timing has 'slipped' (Paul's check on the distributor drive). You should be able to get a spark on number one, a centimeter or so before tdc (someone will know the correct distance). This will isolate timing.
If it is ok, you are left with the second issue - weak or intermittent spark.
The main things have already been suggested. You've replaced the coil. As suggested I would bypass the wiring. I had the experience of an ignition power wire work hardening from engine vibration and breaking inside the plastic insulation. Also, earth the motor directly to the battery - not via the frame. From there, it is a matter of checking / replacing the ignition components. With the exception of the capacitor, I would think that the electronics will either work properly or not at all.
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.

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Re: 1948 Iron 4G Coil Ignition

Postby paul.jameson » Wed Aug 28, 2019 9:15 pm

There has to be a condenser (or capacitor) somewhere. If you can't see one anywhere external, it is possible that the system is still using the one in the magneto which might well be life - expired by now. So I suggest a condenser search - it has to be connected to points / coil somewhere. If you cannot find one let me know and I will find the article I did for Cheval on the subject many years ago which will be of help. Fundamentally, it is difficult to isolate the condenser in the magneto and if it is duff, then that will mean that you get misfiring, even with a good external condenser fitted.
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36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

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Re: 1948 Iron 4G Coil Ignition

Postby john.whiting » Wed Aug 28, 2019 11:58 pm

I dont see how the original maggie cap could still be in the circuit......in a car points system,the only live part (points open) is the wiring contact in the housing,arm lead ,and the point arm .......which is insulated from all the rest of the setup.A normal external cap is hooked up to the insulated body contact.............i do know from experience that with some el cheapo point sets the plastic lifter would melt if the ignition was left on for more than a few seconds.........quality points have a brown micarta lifter,cheapies used to have brown plastic ......normal place for the cap is attached to the metal dist body with a metal clip...(.some Lucas have the cap inside in a bulge in the housing.)

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Re: 1948 Iron 4G Coil Ignition

Postby nevhunter » Thu Aug 29, 2019 12:16 am

With a conversion such as that you might need to check that when the points open the rotor is in line with the terminal in the cap for the limits of the advance retard range. Nev

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Re: 1948 Iron 4G Coil Ignition

Postby paul.jameson » Thu Aug 29, 2019 8:51 pm

Many years ago, the Club produced a booklet called Square Forum which consisted essentially of a series of articles reprinted from Cheval. One of these described a conversion to coil ignition from magneto. I carried out this conversion on my 1948 4G but was surprised to find the misfires persisted when hot. We tested it out one day at my good friend John Nelson's garage and were surprised to find that the engine still ran with the new external condenser disconnected. It was then that I found out that to disconnect the internal condenser inside the magneto you have to take it out and remove the earth terminal from it, insulate the remains of the contact then put it back into the magneto as you need it to screw the points plate to. To remove the condenser from the magneto, the easy way is to cut off all the windings from the armature.

Hence my comment that disconnecting the condenser in the magneto is not easy. For that matter, it is also far from obvious. The article I wrote for Cheval at the time - around 1990 - is undoubtedly a better description than the one I have just given above and I know it includes a relevant photo.
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

chris.matthews
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Re: 1948 Iron 4G Coil Ignition

Postby chris.matthews » Fri Aug 30, 2019 12:25 pm

Hello,
I am back in circulation, the issues with the car warning lights are resolved.
I took a long look at the distributor and its drive.
The gears are in good shape.
I found a note in the workshop manual " If the dynamo is ever removed.... take car not to turn the engine, otherwise magneto rotor timing will be altered "
A couple of months back I had the dynamo off whilst I investigated the charging circuit.
I then suspected I had 'lost' the magneto timing. A quick check showed -Yes, I had by about 90 degrees…………
So I reset by lining up the rotor arm with the scribed line on the distributor and the spark set at 8mm BTDC with Full Advance.
A few issues.
1. The rotor brass bit is an arc about 5mm long - do I line it up so the scribed line is aligned with the start of the rotor or maybe with the mid-point of the rotor?
2. There is a screw in the top of the rotor drive shaft - what is it supposed to do, as far as I can see it simply stops grease coming up the shaft.
3. I do not have 464261 Grease Dashpot, which also serves to locate the rotor drive. Its been replaced by a grease nipple, but this does not protrude into the rotor drive The drive is free to float up or down and maybe the lack of location could be significant (John Whiting was involved in some posts on this greaser about five years ago).

I tried to start - bike ran a few seconds and died, this happened a few times - even with Easy Start.

Head Scratching continues...……
With best regards
Chris in Tokyo.

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Re: 1948 Iron 4G Coil Ignition

Postby brenton.roy » Fri Aug 30, 2019 2:15 pm

Hi Chris, it depends on how you set the timing. The 'points plate' moves relative to the distributor cap, so you want the copper end piece or the rotor to line up with the post for number one, across the full range of advance and retard. I.e if you set the timing at mid advance, the centre of the rotor would line up with the post.
The link below is for a description of a condenser removal, which further explains the issue with old condensers.
http://www.britcycle.com/Products/EasyC ... ooklet.pdf - or here - https://www.youtube.com/watch?v=2Nww4FHlBc8
I'm not recommending the product, just the info.
The reason I suggested earthing the motor to the battery is that paint, particularly powder coat, can insulate the motor electrically - and the spark cannot 'go to ground'. This can severely weaken a good spark.
'51,'56 Squares, '48 VH, '27 Model C, R67/2, Mk IV Le Mans, '06 Super Duke and Ariel projects.

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Re: 1948 Iron 4G Coil Ignition

Postby john.whiting » Fri Aug 30, 2019 10:24 pm

I do not see how the original magneto capacitor could be in the circuit..........the end of the mag armature now has a (breaker) cam mounted on it ,with a big cross point screw stuck in the guts.......might even be a self tapper ,and a dab of epoxy.The cam is not part of any circuit,and in any case is insulated from the point arm by the fibre lifter block...........check the disributor rotor for clearance from the lead terminals......if the gap is too great ,you will get flashover inside the dist cap.Should be about 1mm.,but not touching.........how ,precisely ,does the coil HT connect to the distributor.....is there a central plug in ?.......I know the setup has an odd cap,probably not easily replaced if its carbon tracked.........I might add,I had an iron square ,and took the easy way out with a Fairbanks Morse magneto,chucked the whole Lucas bit away....FM mag,and a Zenith carb.......the guy with it now has spent a fortune returning it to original ,with a similar result to yours.


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