Author Topic: Spark plugs (8-36 thread)  (Read 8134 times)

Offline Doc

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Re: Spark plugs (8-36 thread)
« Reply #15 on: February 12, 2014, 06:11:13 PM »
That is the way I do my plugs now. I had a terrible time trying  to bend them with lots of fails. I found this works very well.
« Last Edit: February 13, 2014, 03:20:24 AM by Doc »

Offline jerry kieffer

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Re: Spark plugs (8-36 thread)
« Reply #16 on: February 13, 2014, 09:17:56 PM »
George
          If you were to go to a much finer thread such as 56 TPI, you would be able to increase the through hole by about .025"-.030" making the plug much more efficient and dependable.

An example can be seen in the attaches photo.

Jerry Kieffer


Offline ken rector

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Re: Spark plugs (8-36 thread)
« Reply #17 on: August 13, 2014, 07:04:00 AM »
George,

I've made some plugs this size but haven't had a chance to try them yet.  I too had problems bending the side electrode, even using the torch.  Eventually I silver brazed a piece of pre-bent .030 piano wire to the edge of the plug.

Now I can hardly wait to see if the combustion chamber gets hot enough to effect the silver braze (1150 degrees).  What do you think?
Member, So. Cal. Home Shop Machinists
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Offline gbritnell

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Re: Spark plugs (8-36 thread)
« Reply #18 on: August 13, 2014, 12:47:07 PM »
Hi Ken,
I don't think it would but I'm a little skeptical about having it fail and fall off in the cylinder. The problem is you wouldn't know it because the plug would spark from the center electrode to the body of the plug until it was too late. (bent valve, scratched cylinder wall) When I started making plugs many years ago I never used a ground strap, I just let it jump from the center to the side wall of the plug. They worked ok but had a greater tendency to foul.
gbritnell
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Offline Ian S C

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Re: Spark plugs (8-36 thread)
« Reply #19 on: August 13, 2014, 03:13:54 PM »
Rather than a bent electrode, maybe an annular one, just a narrowing of the opening around the centre electrode. :thinking:    Ian S C

Offline IanR

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Re: Spark plugs (8-36 thread)
« Reply #20 on: August 13, 2014, 04:21:31 PM »
Len Mason made plugs as described by Ian S C, down to 2 or 4BA, with epoxy resin as the insulator, and found they worked well and were less prone to fouling than bought plugs.

Offline mnay

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Re: Spark plugs (8-36 thread)
« Reply #21 on: August 22, 2014, 08:28:40 PM »
Guys,
I just read this thread today.  Thanks for all of the great information on making spark plugs.  I have yet to try, but I will know how to tackle it in the future.
Mike Nay

Offline Laurentic

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Re: Spark plugs (8-36 thread)
« Reply #22 on: June 14, 2019, 09:03:26 PM »
Hi gbritnell.  Read this thread with interest.  I know thge last post was something like 5 years ago, but do you have a pic of the clamp/crimp you used to secure the insulator inside the steel body (your post of February 12, 2014, 01:33:32). 

Trying to get my head around this and each time something says no!

Many thanks,


Chris

Offline Art K

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Re: Spark plugs (8-36 thread)
« Reply #23 on: June 15, 2019, 02:40:44 AM »
I have to admit to being one of those who likes to pick my battles, spark plugs not being one of them. For the time being at least. I have been thinking about it though, Steve has been feeding me the idea of how easy it is to make spark plugs....Out of curiosity why not make plugs with the double sided ground strap like in Gray's first photo? does it just add complexity?
Art
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Offline Graham Meek

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Re: Spark plugs (8-36 thread)
« Reply #24 on: June 15, 2019, 10:35:33 AM »
Hi Art,

Making the plugs with a double earth electrode is much easier than a single one. Plus the life of the plug is extended as the spark has twice the number of electrodes to jump to.

Since I first wrote on this post the 4.5 mm plugs have been made and I have attached a few photographs for the forums perusal.

Regards
Gray,

Offline gbritnell

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Re: Spark plugs (8-36 thread)
« Reply #25 on: June 15, 2019, 02:02:36 PM »
Hi Chris,
Here's the tool and procedure for crimping the insulator into the spark plug body.
The first picture shows the components.
On the left is the crimping die. This is made from drill rod and hardened. I have tried to use them without hardening but the edge of the flange on the spark plug digs in and erodes the chamfer.  In the center is the threaded die that matches the spark plug thread. On the right is the guide bushing. The guide bushing size can be anything you like with a standard reamed hole through it. I use a .375 reamed hole that way I can use standard drill rod stock for the crimping die.
In the front is a spark plug body with the crimping flange shown. I make this flange about .006 thick.
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Offline gbritnell

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Re: Spark plugs (8-36 thread)
« Reply #26 on: June 15, 2019, 02:18:14 PM »
The first picture shows the spark plug screwed into the holding bushing. This is then slid into the guide bushing. (Picture 2) Picture 3 is the crimping die. In picture 4 it is slid into the guide bushing. You will notice that the threaded bushing and crimping die bushing are sticking out of the guide sleeve, this is so they can be squeezed together to crimp the flange on the plug. The crimping die needs to have a hole slightly larger than the diameter of the insulator on the spark plug other wise if there is any misalignment with the parts it could break the insulator when crimped. The chamfer angle only needs to be enough to fold over the flange, generally about 30 degrees. The outside diameter of the chamfer is the same as the O.D. of the plug flange.
gbritnell
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Online b.lindsey

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Re: Spark plugs (8-36 thread)
« Reply #27 on: June 15, 2019, 03:02:26 PM »
Nice to see this older thread resurrected and thanks for the additional pictures of the crimping set-up and tools George.

Bill

Offline Laurentic

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Re: Spark plugs (8-36 thread)
« Reply #28 on: June 16, 2019, 02:13:41 PM »
Many thanks for the pictures and description of the crimping device - all is very clear now.  Nice solution, simple and effective.

Cheers,
Chris