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Old 17-04-17, 09:10 PM   #21
Shifty1962
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So today I thought I'd whip the igniter out and have a look.

Aside from it being totally covered in soot which suggests to me the engine has been running rich the post that holds the fixed electrode (mica washers and all that) was rotated 180 degrees so the flicking contact was using the back face of the post as a contact rather than the proper contact face. Once I cleaned it all up it was obvious the two contact points would never line up as quite a few of the mica washers were broken or missing so the fixed electrode did not protrude enough.

Not having any more mica I saved the existing good ones and used some small steel washers at the tip end to make up the difference. Now the two contact points line up perfectly. They are very worn and pitted but as they only look like they are peened in place I'll turn up some replacements when I get a spare minute.

I tested the igniter off the engine with the coil pack and get a good spark. Does anybody have an idea how big to gap the points? I did it by eye and its about 1.5mm at the moment.

Also is it possible to get mica washers from anywhere or their equivalent?

I've not run the engine yet as my roast dinner was calling and now I'm too full to move.
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Old 17-04-17, 09:33 PM   #22
martinpaff
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The mica washers can be obtained from the States, from places like Starbolt. You can replace them with a PTFE tube, turned from solid. The contacts are made of something exotic (I can't remember what) and again they can be obtained from the States.
The gap doesn't matter as far as I know, as long as it opens. The ignition arc is produced as the points separate.

MP
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Old 18-04-17, 07:49 AM   #23
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Hi
I made a set of contacts for my Powell igniter from stainless steel, that was 20 years ago, no problem since
Ken
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Old 18-04-17, 09:26 AM   #24
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Quote:
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Hi
I made a set of contacts for my Powell igniter from stainless steel, that was 20 years ago, no problem since
Ken
That's exactly what I had in mind as I have some stainless rod kicking around. For the use I'll be giving it I cant see them burning away very quickly. I did think about making some brass or copper contacts but maybe they would not last as long as stainless.
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Old 18-04-17, 09:28 AM   #25
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Quote:
Originally Posted by martinpaff View Post
The mica washers can be obtained from the States, from places like Starbolt. You can replace them with a PTFE tube, turned from solid. The contacts are made of something exotic (I can't remember what) and again they can be obtained from the States.
The gap doesn't matter as far as I know, as long as it opens. The ignition arc is produced as the points separate.

MP
Thanks Martin. Food for thought. I don't need any washers just yet but the PTFE is a good idea. I'm assuming it can take the combustion temps?
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Old 18-04-17, 09:30 AM   #26
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Somewhere, possibly Doc Schuster's Webster book, I have read that soft iron nails are just the thing for LT ignition points.

EDIT; Pure PTFE creeps so you may find that your once tight fixed terminal goes loose and leaky over time. Glass filled PTFE is better but TBH there is no reason not to use mica if you can get it.

NHH

Last edited by nickh; 18-04-17 at 09:36 AM.
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Old 18-04-17, 09:34 AM   #27
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Quote:
Originally Posted by Shifty1962 View Post
...PTFE is a good idea. I'm assuming it can take the combustion temps?
I have never had to do this myself, but I'm assured that it works just fine.

MP
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Old 24-04-17, 04:58 PM   #28
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I've seen PTFE used on igniters with success, but also with no success. No doubt the specific grade is a factor.

For the points I've used soft iron and stainless. Never had a problem with either. As for soot being found on the igniter, I don't think that's a huge issue. You're unlikely to find that lovely grey finish from clean efficient burning on them, especially as it's unleaded petrol that's being burnt.

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Old 25-04-17, 08:43 AM   #29
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Quote:
Originally Posted by Dazzla View Post
I've seen PTFE used on igniters with success, but also with no success. No doubt the specific grade is a factor.

For the points I've used soft iron and stainless. Never had a problem with either. As for soot being found on the igniter, I don't think that's a huge issue. You're unlikely to find that lovely grey finish from clean efficient burning on them, especially as it's unleaded petrol that's being burnt.

Dazzla
Thanks for that. I've not had time to run the engine yet but once I get time I'll knock up some new contacts from iron nails as they are easy to machine. They cant be any worse than what is on there at the moment. If it works then fine but if not I'll try the stainless route and see what happens.
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Old 25-04-17, 09:14 AM   #30
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Quote:
Originally Posted by Dazzla View Post
...As for soot being found on the igniter, I don't think that's a huge issue...
Daz makes an extremely good point!

The ignitor in my FMZ comes out for a clean before every time I run it; a quick wash in petrol removes the thick layer of clag, corruption, volcanic ash and general unpleasantness, and means that when I spin it, the engine might just start! I also take the opportunity, while there's a big hole in the side, to poke some rags into the cylinder to soak up the OPEC oil lake that will have accumulated in there.

These engines are not sophisticated engineering marvels - they're crude and clumsy; just be glad that it runs at all!

MP
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