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Collection, Preservation and Display of Old Lawn Mowers

Allen Scythe contact breakers

Hi to all as i am a new member.

Villiers MK25c Allen Scythe

Electrics not my strong point

On the pot that holds the contact breaker points and condenser there are two wires that are joined together which are then are attached to the bottom half of the points. this seems to be the case in all the searches that I have undertaken and the various pictures seen.

First have a new coil and a new condenser fitted.

Now my testing so far is from the two terminals on the coil one of course is the HT lead and the other is the one that goes to the bottom of the contact breaker plate. here we have a reading of about 5k ohms.

Ht lead to the back plate about 5k ohms

Small terminal of the coil to all other place dead short i.e no resistance.

Nothing I do testing wise makes any difference when I open and close the points, what is wrong here there should I am sure be and off and on when points are opened and closed ???? Help

 

 

Forums

cherami Sat, 30/06/2012

There is an update to my post that in fact when everything was put back I have a spark at the plug and putting the tester from earth to the HT leads produces a on off action. However I am still a little puzzled.

atcocrazy Sun, 01/07/2012

The reason you did not observe an on-off action operating the points is because whether they were open or closed you still had the primary coil in circuit so the current was passing through the negligible resistance of the primary winding to earth instead of through the points to earth, which are in parallel with it!

wristpin Thu, 05/07/2012

Back in the 60s there was a company called Rupert Ledger making ignition testing equipment (very little electronic/solid state around then) and one piece of kit that I still have enabled one to carry out a couple of tests and set the timing without too much hassle and dismantling .

Basically it was a black box (blue actually)  with two wires and an on/off switch (pp9 battery inside)

One wire was connected to the plug lead  and the other to a good earth. Switch on and there  is a continuous tone, turn the flywheel and as the points open and close the tone changes . If the points are nice and clean the tone change is abrupt, dirty points, the tone change is "smeared" . No change of tone and either the points were not opening or were so dirty that although closed there was no contact.. Coil or condenser shorted - different tone.

As well as being useful for diagnostics it is great for setting timing on engines with "unkeyed" flywheels such as the Villiers on Allen Scythes. The exact points opening is an audible signal while the eyes watch the timing marks.

Ledgers also made a very simple spark tester  - a crocodile clip with a length of ht lead and a spark gap. HT lead is long enough that with it connected to the plug lead the  croc can be clipped on to an earth point where the gap can be seen by the person pulling the rope! - simples.

Sometimes it is the simple things that make life easier!

cherami Mon, 25/07/2016

Sorry for the long delay in replying to you. Does this mean that the points are being bypassed as a standard method or have I some sort of wiring problem ?

wristpin Mon, 25/07/2016

If you've got a spark in the right place and right time I'd stop worrying about how it got there !