Petter A Series II - Wico A Magneto Issues

Hi, if you look at my thread in the New Projects/Restoration Section, under the Scott Generating Set Restoration heading, Pg. 10, the June 18th post, you will see my testing of Wico type A magneto coils. Two units tested open circuit, obviously they had failed internally, although they did still produce weak sparks for a while. The two hopefully "good" ones had values which would seem to be approximately what you were reading, if I understand you correctly. My first good coil tested as 7K ohms, however this may be a rewound unit. The second one read 5.75K ohms, which seems to be very similar to your readings, which I believe translates to 5.24K ohms and 5.47K ohms. This would suggest your secondary coils are in good order. If you are still experiencing poor sparking from these units, I would suggest ensuring the points are cleaned and flattened by using good quality fine grade abrasive paper. If that doesn't improve the sparking, then the next step would be to consider the condenser. I have also covered some of this in my latest posts.

Neil.

Neil,

Thank you for the magneto resistance information and the reference to your 'Scott Generating Set' project which I have now read with great interest.

All really good stuff for someone new to these engines like me.

I have transferred the new set of points to the replacement magneto and carefully gapped them at 0.015" as per the book.

I also have two of the original (brass coloured tin case type) condensers that I suspect are faulty but have been unsure how to check them.

However I have also transferred the brand new X1413 (plastic encapulated type) to the replacement magneto - although brand new I guess this could also be faulty?

I have ordered an analogue multimeter which I am hoping will be a little more sensitive for my needs.

Did the 'EasyCap' solution resolve the issue for you?

David P

David, sounds like you are attempting to eliminate all the potential issues. Sometimes it is difficult to be specific as to what is likely to be the problem, testing by substitution is often the best option, which you are adopting. As you suggest the old metal cased condensers are liable to be well aged and no longer presenting the correct capacitance value as they were designed to do. Worse case is they are not working at all, being either open circuit or short circuit. Unfortunately testing capacitors without a meter designed specifically for that purpose is not really viable. Yes it is feasible to confirm if they are short circuit or even open circuit but it is difficult to ascertain if they are working as a capacitor or what the actual rating is. This is especially so in the case of these components, where the capacitance value is low. Your analogue meter will be useful for the coil testing but is unlikely to be able to help you much in proving the state of the condensers. Unfortunately I have not used any of the replacement X1413 capacitors, so cannot comment on their suitability or quality.

So far I have not fitted the EasyCap devices as I will need to cut them down to size to fit inside the old housings. I have instead identified the best of the old components through testing and put them together into a single magneto. Today I was successful in getting the Scott engine to run again, the first time in a few weeks!

If all else fails you might need to consider the strength of the rotating permanent magnet armature, although I don't believe that is likely to be an issue.

I hope you are successful in sorting your project out, I'm sure you will.

Neil.

Are you expecting a spark every time the impulse spring operates?
I believe the impulse fires every 180 degrees but only sparks every 360 degrees when the points open

Andy,

I was actually expecting to get a spark every time the impulse spring operates.

I am still getting intermittent weak sparks on the bench but my new analogue meter arrived today (with a continuity buzzer that sounds if the resistance in the circuit is less 20 ohms).

So I have just done some quick checks and with cardboard between the points and checking the continuity between the HT coil/condenser/moving breaker connection point and the magneto body the buzzer is sounding.

The isolation strip is correctly in place around the circumference of the contact breaker housing.

I will remove the new X1413 (plastic encapsulated) condenser tomorrow and check the continuity across that - just in case that is the issue.

A process of elimination now I guess.

I think that I have resolved the leakage to the magneto casing issue.

The leakage was from the HT coil/condenser/moving breaker connection to the magneto casing was actually between the HT coil wire in the contact breaker housing and where it connects to the stop switch wiring beneath the HT coil.

I assume the wire insulation had split and was touching the magneto casing as it left the contact breaker housing.

This wire has now been sleeved through to the stop switch wiring beneath the coil and I am now getting zero leakage to the magneto casing (with cardboard between the points) on my new analogue meter.

There is a marginal improvement but still not a strong spark at the plug.

I am still suspicious of the new X1413 condenser and may go down the EasyCap route to see if this improves things.

I’ll give you a bantam coil reading tomorrow.
On my most recent restorations I have done away with the stop button on the blind side and saved the parts for spares as the copper or brass parts are often badly damaged or missing on second hand mags.

Bantam coil is 5.92k ohm

Andy,

Thank you for the Bantam coil resistence - so my two coils at 5.24k and 5.47k ohms seem to be reasonable.

However, on rechecking the leakage from the coil lead in the contact breaker housing to the magneto casing was still an issue (getting the continuity buzzer on the analogue multimeter).

I have now removed both coils and I am getting the continuity buzzer on both coils between the coil leads and the coil earth tags (see photo below).

Any thoughts on this?

Hi, it looks like you are testing the primary side of the coil. This will always test as a continuity circuit, causing the buzzer to operate, due to it being a very low resistance value. You will only be able to measure the actual value with a sensitive meter. I don't think you need to worry about this reading, it is unusual for the primary to fail as it is wound from thick wire, hence the low reading.

Hope this helps,

Neil.

Neil,

Thank you - that is reassuring to me as I was starting to think I had two coils with major problems.

The continuity buzzer does seem quite weak between these two connections (the buzzer sounds on my analogue meter if the resistance in the circuit is less 20 ohms).

I have now bought the two Univeral EasyCap and have mounted the 220nF ready for installation (see photo) and hope that might improve things.

David P

David,

Your EasyCap installation looks very neat. It will be interesting to see how well it works, especially as I'm still to undertake the same modification on my magnetos.

Hope you are successful with the magneto rebuild and it helps you to get your Petter to run smoothly.

Neil.

Neil,

I have now transferred the 5.47k ohm coil from the original magneto to the replacement magneto, removed the stop switch arrangement on the blind side (facing the engine) and rewired and sleeved the primary coil wiring to the contact breaker housing.

I have actually had the engine running very briefly using the original magneto (5.47k ohm coil) after the carburettor overhaul so thought this was prudent.

However, with carboard between the points and new 220nF EasyCap condenser fitted I am getting a strong continuity buzzer between the moving contact breaker fixing and the magneto casing (see photo below).

Surely this cannot be correct as it is the same as activating the very crude stop switch?

I have not tried bench testing for a spark yet but suspect there will be none.

Would appreciate your thoughts.

David P

Neil,

An update on this crazy situation as follows.

If I discoonect the condenser and the coil primary leads from the moving breaker connection and test the continuity seperately.

I get no buzzer between the condenser lead and the condenser mounting plate which I already know as it has been tested previously after my modification work.

I get no continuity buzzer between the primary coil lead and the magneto body but get a strong buzzer between the primary coil lead and the stop switch bolt as you would expect.

With the leads both still disconnected if I put the screw and washer back into the moving breaker connection and screw it fully home and test the continuity between the screw head and the magneto body I get no buzzer.

However, if I then reassembly the two leads (coil primary and condenser) to the moving breaker connection and tighten down and then test the continuity between the screw head and the magneto I get a strong buzzer.

I have checked that the tags on both leads (coil primary and condenser) are not touching anything else - a bit of a puzzle but I will try and work it out.

David P

Neil,

Sorry for this extended saga but just writing it down is helpful to me.

By a process of elimination the problem seems to occur only when the coil primary and the condenser leads come together.

If I put the coil primary lead only onto the moving breaker connection, insert the screw and washer, tighten down and then test between the screw head and the magneto casing I get no continuity buzzer.

If I then add the condenser lead, insert the screw, tighten down and then test between the screw head and the magneto casing I get a strong continuity buzzer.

If I then remove the two leads (coil primary and condenser) crocodile clip them together away from the contact breaker housing and then test between the clipped lead tags and the magneto housing I get a strong continuity buzzer (see photo below).

So the problem seems to be related to the EasyCap condenser modification although as stated previously there is no continuity between the condenser lead connector and the mounting plate.

All very strange - next step is to revert to the new X1413 condenser and see what occurs.

David P

Today I discovered what caused the original magneto rotor shaft to fail.

A loose rogue screw had become jammed between the rotor and the magneto casing (see photo below).

I remember that one of the original condenser fixing screws had been replaced with a self-tapping screw and I am guessing that the original screw had migrated to the main housing was resting at the bottom of the magneto casing somewhere.

When I removed the magneto I had spent some time cleaning the external casing, brass plate, oiling instruction plates and flanges and probably had it upside down at one stage.

Anyway it now makes sense why the shaft failed - as you can see the rather battered screw is  firmly wedged and the shaft is locked.

David P

djpeng wrote:Today I discovered what caused the original magneto rotor shaft to fail.

A loose rogue screw had become jammed between the rotor and the magneto casing (see photo below).

Anyway it now makes sense why the shaft failed - as you can see the rather battered screw is  firmly wedged and the shaft is locked.

David P

Root cause located then !

David, it is sometimes difficult to fully assess the situation remotely. However from what I can infer from your testing so far, I wonder if there is a short circuit being presented by the EasyCap installation. Unless you have already ensured that there isn't continuity across the two connections to the device, I would start by testing there. Also ensure that the mounting points are fully isolated, and not making contact when the mounting screws are fitted.

Glad to see you solved the broken shaft question, not good but at least you know why.

Neil.

Neil,

Thank you for your message.

I had already checked that there was no short circuit (continuity) between the EasyCap condenser connection lead and the mounting metalwork after the modification work on the bench and when installed.

However, I have now removed the EasyCap condenser and reinstalled the X1413 condenser and I have excactly the same issue.

With cardboard between the points and the coil primary lead connected I get a strong continuity buzzer signal between the connection screw head and the magneto casing (see photo below).

If I then remove the coil primary lead and test between the connection tag and the magneto casing I get no continuity buzzer signal (see photo below).

Obviously if I test between the coil primary connection tag and the 'stop switch' bolt instead of the magneto casing I get a strong continuity buzzer signal as you would expect.

So there is no short circuit (continuity) across either of the condensers and there is no hint of a spark on bench testing.

I am at a loss to understand what is occuring here at the moment.

David P

David, I suspect there is an insulating washer or sleeve, either missing, misplaced or being shorted. Unfortunately I don't have my magnetos with me right now to check over, to see what it could be. Unfortunately I'm out tomorrow, so unless anybody else is able to help in the meantime, I will see if I can check on Thursday and get back to you. As always once the issue has been located it will obvious and simple to resolve!

All the best,

Neil.

David, I have now had time to consider your magneto issue. On the face of it doesn't actually make sense as described. Unfortunately I cannot see the rest of the magneto wiring but if it is all connected as it should be then it shouldn't matter if the wire is connected or disconnected, there should still be a low resistance between the wire and case. This is due to the fact that (I believe) the primary and secondary coils are common grounded.




Simplified arrangement, showing how the coil and breaker assembly is connected.




Measuring the primary coil resistance at 1 ohm.




Measuring the secondary coil at 5.6K ohm. (Actually as wired, includes the primary coil resistance, with both ends connected together, for earthing.)


Therefore if the wire you are connected to in the lower picture is the same one as goes to the coil, then there should be no difference between being connected to the condenser top (points moving connection)  or disconnected. As there obviously is a difference, then there must be some other wiring issue which cannot be seen from your pictures. Suggest you ensure that the earth lead to the coil(s) is properly connected to the earth (magneto casing). If it is, then you must see the same resistance in picture 1 and 2, unless the primary coil is open circuit.

Sorry I cannot be more specific but as it stands there must be something else wrong which isn't obvious from the information to hand. Keep at it I'm (fairly) sure you will get there.

Neil.

Neil,

Thank you for taking the time to prepare your very clear response.

Based on your response I have now carried out some further checks as follows:

1) Coil earth is properly connected and checking between the earth lead itself and the magneto casing I am getting a strong continuity buzzer signal.

2) Primary coil resistance berween the disconnected primary coil lead tag and the coil earth tag I am getting a value of 0.5 ohm (on the 200 ohm range).

3) Secondary coil resistance betwen the disconnected primary coil lead tag and the HT tag on the top of the coil itself I am getting a value of 5.45k ohms (on the 20k ohm range).

4) With cardboard between the points and the primary coil lead disconnected and out of the way and the connecting screw and washer at the moving breaker (and condenser) connection point fully tightened I get no continuity buzzer signal between this screw head and the magneto casing.

5) With cardboard between the points as soon as I then connect the primary coil lead to the moving breaker connection (and condenser) connection point I get a strong coninuity buzzer signal between the screw head and the magneto casing.

I have made sure the insulating strip is in place within the magneto housing and that the primary coil lead tag is well clear of the insulating strip anyway.

I am at a real loss to understand what is causing this issue.

David P

Neil,

I do hope at the end of this ongoing magneto saga it may prove helpful to someone else at some point.

Out of interest I substituted the other coil (5.24K ohms) and I had excactly the same issue.

I then removed the X1413 condenser and replaced it with one of the very original brass condenser mountings (with the old condenser removed) and connected the primary coil lead to the moving breaker (and condenser) connection point and fully tightened the screw and washer fixing - I now get no continuity buzzer signal between the screw head and the magneto casing.

So with both the X1413 condenser and the EasyCap condenser removed from the housing the issue has disappeared!!

Just checking both condensers again on the bench I get no continuity buzzer signal across either condenser.

I feel progress is being made here but not sure of my next move!!

David P

Seems crazy but with cardboard between the points and no condenser (of any type) installed (just the original metalwork with isulated plastic mounting), the primary coil lead connected I get no continuity buzzer signal between the connecting screw at the moving breaker (and condenser) connection point and the magneto casing.

Since my previous post I have carried out some further tests reconnecting each of the condensers (X1413 and EasyCap) externally in turn using crocodile test leads back to the connecting screw at the moving breaker connection point in the breaker housing and the magneto casing.

With both of the condensers I then get the dreaded continuity buzzer signal between the connecting screw at the moving breaker connection point and the magneto casing.

As mentioned previously checking both condensers again on the bench I get no continuity buzzer signal across either condenser.

This is a total mystery to me!!

Basic circuit diagram of a single cylinder magneto, including a stop switch which the Wico A has.



Your magneto should be wired like this.
You should not get a buzz from the capacitor on its own (unless it is conducting, in which case it is dead).
If you test between the moving contact and the case (earth) you will get a buzz with points open or closed. This is because the moving contact is wired between the contact, through the primary coil and then to earth (the case).

Edit:
I've just measured the circuit between the moving contact and the case with the points open and I get between 12 and 15 ohms, which will trigger your buzzer.