Ignition coils

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Stan Thomas
Posts: 285
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Ignition coils

Post by Stan Thomas » Tue Jun 06, 2017 9:37 am

I have acquired the C.A.V. coil for my 1931 sleeve valve, albiet not in working order - the intention being to "replace" the inards from a modern oil-filled coil, (which is not an uncommon practice).

However, such is the construction of this C.A.V. coil that it would not be leak-proof, so the question is - can I use one of the modern epoxy resins to refill the coil, and if so, what is the best to use?

Alternatively, is there any other approach I can take?



Regards to all,

Stan.

John Davis
Posts: 37
Joined: Sat Feb 13, 2016 11:48 am
Location: Thetford, Norfolk

Re: Ignition coils

Post by John Davis » Sun Jun 18, 2017 11:40 am

How is the old coil constructed and how do you plan to open it up? What are the original stickers, features etc that need preserving?

Stan Thomas
Posts: 285
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Ignition coils

Post by Stan Thomas » Mon Jun 19, 2017 9:49 am

Hi John, and thank for your interest.

I bought the C.A.V. coil of the Ebay as it is the correct one for my 1931 sleeve valve (but knowing it would probably be faulty) - but it was a start. As predicted I was right, the spark was very very weak - due I'm told to the internal insulation "going down".

Governed by the saying "You can't scrap scrap" I began dismantalling, only to find the actual coil windings etc. were sealed in the main body with pitch - which I soaked away by immersing in white spirit for about two weeks!

Not being able to get any firm advice or confirmation that it could be rewound, I purchased A new Bosch coil and carefully cut away the case - and as we speak, I'm in the process of re-instaling the Bosch internals in the C.A.V. body.

I've been told not to rely upon Araldite or the like to seal it in place within the body, but to use clear silicon sealant which has excellent insulative properties. (I hope that's right)!

That said, it really is a hansome piece of equipment, with a black polished body and large brass dome in which resided a coiled up current limiting resistor on porcelain insulators.

They really made things in those days, although I'm sure the actual efficiency may not have been that great. For instance, the Rotax dynamo is as big as a washing machine drum, but is only rated to produce 12 amps - and the regulator is like something out of Baron Frankenstein's laboratory - but I digress ...........

Regards to all!

JT7196
Posts: 513
Joined: Sat Feb 13, 2016 7:22 am

Re: Ignition coils

Post by JT7196 » Thu Jun 22, 2017 7:07 pm

Whoa, before you go any further, please do contact the company listed below.
I have personally dealt with them a couple of times, and even been shown around their workshops, so contact them and see if they are able to sort out your Ignition Coil:-
CARWOOD REWIND

Address: 12 Buckland Road, Pen Mill Trading Estate, Yeovil, Somerset BA21 5EA
Phone: 01935 476255
Fax: 01935 433627
Email: rewind@carwood.co.uk
Website: www.carwood.co.uk
Services: Specialist winding services including Dynamos, Starter Motors, Wiper Motors, Cut Outs, Armatures.

They offer a superb service, and I thoroughly recommend them.

Best wishes, Al :D :D

Stan Thomas
Posts: 285
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Ignition coils

Post by Stan Thomas » Thu Jun 22, 2017 10:25 pm

All done Big Al - fitted the Bosch internals, filled the casing with the correct RTV silicone - and now I have a spark I could weld with.

All for £60 including the purchase of the original C.A.V. coil.

So - anyone got any cocoa tins so I set about making a set of sleeves ??????????????

Regards to all!

Stan.

John Davis
Posts: 37
Joined: Sat Feb 13, 2016 11:48 am
Location: Thetford, Norfolk

Re: Ignition coils

Post by John Davis » Fri Jun 23, 2017 8:00 pm

Great stuff! I think silicon is a good choice as it's softer, therefore more shock absorbing than Epoxy.

Stan Thomas
Posts: 285
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Ignition coils

Post by Stan Thomas » Sun Jun 25, 2017 9:05 am

Don't use epoxy (Araldite etc.) on electical items of higher voltages like H.T coils and components etc. as it as poor dielectric (non conducting) properties.

I once traced a misfire to an H.T. cap which had been repaired with Araldite - and it was tracking to earth.

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