Monro tiller spark plug

[mitzygolf]

Hi, I’ve just received an order for a replacement for lodge MB3 spark plug. The plug they have sent has n 18mm thread but the original plug thread is much smaller than that. on enquiry th e supplier said this is a replacement for the CB3. The hand book says it should be an MB3 can anyone point me in the right direction, are the suppliers correct?

[mitzygolf]

Sorry that should read CB3 spark plug😏

[enginear]

What marking have you got on old plug, the cb3 is an 18mm plug.

[mitzygolf]

The spark plug that I removed is a 14mms thread and I now know the CB3 is an 18mms but I now wonder why the manuals for the engine and tiller state the plug as CB3

[charlie]

What engine is it, Villiers Mk10, 12 or 15 or is it something else, they did have other engine options?
Without going out and checking my machines I can’t remember what plugs I currently use, but NGK A6 rings a bell. I have one at least one machine, a SIMAR, which has had a thread adapter fitted taking size from 18mm to 14mm.

[mitzygolf]

It’s a Mk12 villiers it had an NGK B-4H but I have since been told that plug will run too hot.

[andyfrost]

From memory all Mk12s had a 14mm plug fitting, along with later Mk10s , early Mk10s had 18mm.

Andy.

[charlie]

I have had a look in the workshop manual for the Mk10,12 and 15 and can see where the confusion has arisen. The Mk10 and Mk12 had 18mm plugs, the Mk10/1, Mk10/2, Mk12/1, Mk12/2 had 14mm plugs. See attached copy of relevant page from manual.

Attachments:

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[mitzygolf]

Thanks for that Charlie. Does anyone know the equivalent gr8 the Lodge BN?

[charlie]

The Green Spark Plug Company is a good pace to look, see Lodge BN

[mitzygolf]

Thanks Charlie

[mitzygolf]

Now I have another problem. I not getting a spark at the plug. Connected the spark tester from plug cap to earth and the light flashers beautifully. Plug cap to body of spark plug light flashers as should. Plug cap to plug terminal no light. It’s as if the spark isn’t strong enough to go through the plug. Before you ask I have used two brand new plugs. Any ideas?

[john-e-w]

I assume you have a good earth on the outer of the plug and also not earthed the inner of the plug. I know it’s stating the obvious, but…….

John

[mitzygolf]

The plug is screwed into the cylinder head

[john-e-w]

If it’s screwed in you will not be able to see if it’s sparking or not and you will have to overcome the engine compression. Try removing it and whilst it is still connected to the HT, rest the plug on a metal part of the engine so that you can see the sparking end whilst you are rotating the engine. If it sparks then it might just be timing that needs looking at. If it doesn’t spark, try rubbing the plug on the metal of the engine to ensure a clean contact.

John

[Author]

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