MK1 ignition schematic
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MK1 ignition schematic
Does anyone have a schematic for the MK1 ignition? The coil appears to have 2 connections. This must mean that the primary and the secondary are connected. The secondary shows an open circuit on my multimeter, between the HT connection and ground as well as the HT and other coil connection. By the way, this time I have read [and tried] all the relevant FAQs, and done the thread searches.
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40TPI
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I've never stripped one but given that there are three connection points logic suggests that it will be independent primary and secondary windings with one leg of each of these windings forming a common connection to chassis rather than an auto transformer configuration.
And this is exactly the arrangement shown on the Villiers "museum page":
http://www.localhistory.scit.wlv.ac.uk/ ... liers9.htm
The unexpected detail in this schematic is the "safety gap" in the HT secondary which, if it was located within the coil body, will make dc continuity checks on the HT secondary from the spark plug end of the lead pointless! ( No pun intended.....) I have never seen a reference to this "safety gap" before.
Having just put a cheap DVM across my 102 spark plug lead to chassis to measure resistance I surprisingly find that it is indicating open circuit but quite capable of a welding quality spark when turned over! So maybe that extra spark gap does exist in our Mark 1s or alternatively I have some crap in my coil to HT lead connection which is breaking down when I spin the magneto and produce volts. Sorry if that is inconclusive but it is a little late...
Some Wipac MK 2s tested at the same time indicated several kilohms to chassis.
As an aside this page also shows my favourite Villiers MK 10 stationary engine which can be found on many an ex GPO charging set and also on my 1953 Little Benford cement mixer. (Although I now have to admit to a larger flock of Gulls than Mk10s!)
Peter
And this is exactly the arrangement shown on the Villiers "museum page":
http://www.localhistory.scit.wlv.ac.uk/ ... liers9.htm
The unexpected detail in this schematic is the "safety gap" in the HT secondary which, if it was located within the coil body, will make dc continuity checks on the HT secondary from the spark plug end of the lead pointless! ( No pun intended.....) I have never seen a reference to this "safety gap" before.
Having just put a cheap DVM across my 102 spark plug lead to chassis to measure resistance I surprisingly find that it is indicating open circuit but quite capable of a welding quality spark when turned over! So maybe that extra spark gap does exist in our Mark 1s or alternatively I have some crap in my coil to HT lead connection which is breaking down when I spin the magneto and produce volts. Sorry if that is inconclusive but it is a little late...
Some Wipac MK 2s tested at the same time indicated several kilohms to chassis.
As an aside this page also shows my favourite Villiers MK 10 stationary engine which can be found on many an ex GPO charging set and also on my 1953 Little Benford cement mixer. (Although I now have to admit to a larger flock of Gulls than Mk10s!)
Peter
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40TPI
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The more I think of it a series safety gap is ludicrous. A safety gap is to prevent internal insulation damage through voltage punch through should the magneto continue to be excited without a spark plug present. This would be placed in parallel not series. That drawing is incorrect. If a single cylinder outboard plug lead drops off then the engine stops. No need for a safety gap. A single cylinder motorbike continuing downhill could be a different story.
I can't shift the HT plug on my 102 to get directly to the magneto coil contact to measure the secondary resistance but information from a reliable third party advises 4Kohm resistance for the secondary and 0.5ohm primary on a MK1 and no safety gap series or parallel!
Hope that helps.
Peter
I can't shift the HT plug on my 102 to get directly to the magneto coil contact to measure the secondary resistance but information from a reliable third party advises 4Kohm resistance for the secondary and 0.5ohm primary on a MK1 and no safety gap series or parallel!
Hope that helps.
Peter
There is no reason to suppose that the drawing is incorrect. It is in agreement with my observations on my lawn mower engine and in agreement with Phil's observations.The more I think of it a series safety gap is ludicrous. A safety gap is to prevent internal insulation damage through voltage punch through should the magneto continue to be excited without a spark plug present. This would be placed in parallel not series. That drawing is incorrect
The later figure of 4k is not far adrift though from my reading for the Wipac system
The same drawing can be found on THIS WEBSITE
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40TPI
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In the general case can you please explain the safety function afforded by a series gap?
In the specific case of your lawn mower is that fitted with a Villiers M1634//M1513/M1514 magneto set?
If it is not, and it shows an open circuit to chassis on the HT lead, then I'd suggest that it possibly may have an additional series spark gap but this would then be better termed a spark intensifier. Villiers, as I understand, never incorporated spark intensifiers in their magnetos.
My current conclusion is that the example circuit is :
a) not necessarily fully representative of a Villiers and certainly not a M1634//M1513/M1514 Seagull outboard magneto set although it does show the general scheme of a common connection low resistance primary/high resistance secondary pulse transformer in a magneto application. Mea maxima culpa for the introduction here.
b) has possibly been incorrectly copied and annotated during transcription from the original source
c) published at multiple websites from the same (copied) source
I'm off to the workshop to try and shift that HT connector on the 102 refurb project so I can get to the magneto directly. Given the other sins present it wouldn't surprise me if the previous " custodian" hadn't Araldited the damn thing in. (Amongst other "repairs" the HT lead had been extended by twisting together the stripped ends of two lengths and binding them with Sellotape.......)
Peter
In the specific case of your lawn mower is that fitted with a Villiers M1634//M1513/M1514 magneto set?
If it is not, and it shows an open circuit to chassis on the HT lead, then I'd suggest that it possibly may have an additional series spark gap but this would then be better termed a spark intensifier. Villiers, as I understand, never incorporated spark intensifiers in their magnetos.
My current conclusion is that the example circuit is :
a) not necessarily fully representative of a Villiers and certainly not a M1634//M1513/M1514 Seagull outboard magneto set although it does show the general scheme of a common connection low resistance primary/high resistance secondary pulse transformer in a magneto application. Mea maxima culpa for the introduction here.
b) has possibly been incorrectly copied and annotated during transcription from the original source
c) published at multiple websites from the same (copied) source
I'm off to the workshop to try and shift that HT connector on the 102 refurb project so I can get to the magneto directly. Given the other sins present it wouldn't surprise me if the previous " custodian" hadn't Araldited the damn thing in. (Amongst other "repairs" the HT lead had been extended by twisting together the stripped ends of two lengths and binding them with Sellotape.......)
Peter
No I can't explain it.
The coil is M1634 and the L and R cheeks are M1513 and M1514 respectively.
( It does not now have a M1750 condenser though ..... Ford escort IIRC )
I did not make my measurement on the HT lead I unscrewed the connector and measured direct on on the contact on the side of the coil.
My conclusion is that the circuit agrees with what I have found with that magneto set
Whether it has been correctly or incorrectly labelled is immaterial a gap clearly exists.
(It could easily fool someone into thinking that the coil was defective and it would have fooled me but for the knowledge gained from this thread)
No doubt both drawings have the same source , they are identical.
The coil is M1634 and the L and R cheeks are M1513 and M1514 respectively.
( It does not now have a M1750 condenser though ..... Ford escort IIRC )
I did not make my measurement on the HT lead I unscrewed the connector and measured direct on on the contact on the side of the coil.
My conclusion is that the circuit agrees with what I have found with that magneto set
Whether it has been correctly or incorrectly labelled is immaterial a gap clearly exists.
(It could easily fool someone into thinking that the coil was defective and it would have fooled me but for the knowledge gained from this thread)
No doubt both drawings have the same source , they are identical.
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40TPI
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This thread has been surprisingly quiet in the interim..... Deep breath....get ready to duck back under the parapet........
It's been a busy week but I finally managed to remove the 102 ignition lead pickup plug to get a measurement directly on the coil. Measuring to chassis gave about half a megohm. Measuring to the live side of the primary gave the same result give or take. The second check measurement was made in case the magneto common to chassis contact was dubious. (The primary resistance is negligible compared to the secondary and although I no longer have access to UKAS/NAMAS traceable calibrations on my DVMs I'm pretty confident of their accuracy)
So, I measure a reasonably stable resistance measurement which is way too high to be a copper wire path..... but not high enough to be an open gap.
A worrying and also slightly puzzling result all at once since a professional magneto rewinder has confirmed the 4k Ohm secondary resistance along with no "safety gap" (sic) and I have also noticed that the S.O.S FAQ also has a dc resistance quoted for "go/no go" test purposes.
My present conclusion is still that there is no series gap on a MK 1 Villiers to prevent a meaningful dc test and the rather likely possibility that I may have a magneto which has a problem on the secondary. I would say it is perfectly possible that my measured half megohm is the local leakage resistance across a break somewhere in the secondary wire that flashes over internally whilst also producing an external spark at the plug. Not good.
At this stage I'd appeal to anybody else with experience on the failure modes of magneto's who is following this thread to share their knowledge!
Peter
It's been a busy week but I finally managed to remove the 102 ignition lead pickup plug to get a measurement directly on the coil. Measuring to chassis gave about half a megohm. Measuring to the live side of the primary gave the same result give or take. The second check measurement was made in case the magneto common to chassis contact was dubious. (The primary resistance is negligible compared to the secondary and although I no longer have access to UKAS/NAMAS traceable calibrations on my DVMs I'm pretty confident of their accuracy)
So, I measure a reasonably stable resistance measurement which is way too high to be a copper wire path..... but not high enough to be an open gap.
A worrying and also slightly puzzling result all at once since a professional magneto rewinder has confirmed the 4k Ohm secondary resistance along with no "safety gap" (sic) and I have also noticed that the S.O.S FAQ also has a dc resistance quoted for "go/no go" test purposes.
My present conclusion is still that there is no series gap on a MK 1 Villiers to prevent a meaningful dc test and the rather likely possibility that I may have a magneto which has a problem on the secondary. I would say it is perfectly possible that my measured half megohm is the local leakage resistance across a break somewhere in the secondary wire that flashes over internally whilst also producing an external spark at the plug. Not good.
At this stage I'd appeal to anybody else with experience on the failure modes of magneto's who is following this thread to share their knowledge!
Peter
we were all waiting for you to report back. Last Friday you said you were off to your workshop but we did not expect you to be gone so long.This thread has been surprisingly quiet in the interim
I'll have another look at my Villiers engine now that we know it has the same coil as fitted to Seagulls but definitely showed open circuit, >2 megohms when I checked it last week.
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pistnbroke
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first post on here but 30 years an auto electrician....It was old technology to have a small gap (in air ) in series with the plug lead...the coil has to develop more HT voltage to jump both gaps so the energy is higher...Its a hang over from poor fuel....in the old days ...you cut the HT lead from coil to distributer on your car beared the ends ( wire in those days) and used the two holes in a shirt button to make a gap pushing one wire thro each and twisting....hence it fired poor plugs/poor fuel...often sold before the trading standars laws a a quartz voltage booster or similar ( crap)
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timberman2004
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Mk1 ignition schematic
Just received a NOS coil for a Mk1 magneto, old coil shows open between HT pickup and ground. Using an inexpensive 20,000 ohm/volt multimeter shows 3500 ohms Ht to ground [coil core] and about 0.5 ohms on the primary winding to ground. Hoping this may be of help to someone checking the coil on their Mk1 magneto. Now I need to try to remove the old coil without turning off the screws. Does anyone have a never fail method?
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40TPI
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Thank you for the resistance value confirmation.
I solved my dodgy magneto replacement problem in a way that doesn't require removing the two countersunk screws you mention. I acquired a complete ignition plate with points, cap etc! In fact I got two so now have a shelf spare too. (Bound to be a flock arrival that needs a new one....)
The tapped holes in the removable soft iron coil cheeks are through holes. I placed my old ignition plate on a shelf and have been dropping the odd squirt of WD40 into the top of each hole every now and then for the last couple of months. With a perfect fit screwdriver in carefully cleaned slots and the usual careful FWD/REV "torqing" neither have moved. I've been reluctant to get the small propane torch out because the capacitor is close by underneath the points and there is the risk of heat conduction through to the coil too.
Peter
I solved my dodgy magneto replacement problem in a way that doesn't require removing the two countersunk screws you mention. I acquired a complete ignition plate with points, cap etc! In fact I got two so now have a shelf spare too. (Bound to be a flock arrival that needs a new one....)
The tapped holes in the removable soft iron coil cheeks are through holes. I placed my old ignition plate on a shelf and have been dropping the odd squirt of WD40 into the top of each hole every now and then for the last couple of months. With a perfect fit screwdriver in carefully cleaned slots and the usual careful FWD/REV "torqing" neither have moved. I've been reluctant to get the small propane torch out because the capacitor is close by underneath the points and there is the risk of heat conduction through to the coil too.
Peter