Wyvern Spark plug

Wyvern Spark plug

This topic has 6 replies, 5 voices, and was last updated 23 June 2022 at 21:39 by NR67.

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23 June 2022 at 09:25 #602749
NR67
Participant
@nr67
I am currently machining the cylinder head for my ET Westbury Wyvern. The build notes say to use a M10x1 thread for the spark plug and not the 3/8×24 as per the drawings. I guess thats because modern plugs are metric. I will be running on petrol so my question is are there any recommendations for the plug. I want to leave or remove enough material so the tip is in the correct position. I will want the plug in hand before I continue with that feature. Also what is the correct position for the tip. This is my first IC engine so sorry for the beginner sounding questions.
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23 June 2022 at 09:25 #31409
NR67
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@nr67
23 June 2022 at 09:57 #602753
Andy_G
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@andy_g
The NGK CM-6 plug is often used for engines of that sort of size (it is M10 x 1 thread).

I used one for my little (20mm bore) hit and miss engine:

They are readily available and reasonably inexpensive.

In the absence of any information to the contrary, I'd aim for the end of the plug body to be ~flush with the inside of the head, provided that nothing comes too close to the electrodes in that configuration.

Edited By Andy_G on 23/06/2022 10:05:01
23 June 2022 at 10:08 #602754
Roderick Jenkins
Participant
@roderickjenkins93242
+1 for everything Andy says. That's what I used on my Wyvern it works ok.

Rod
23 June 2022 at 10:21 #602756
JasonB
Moderator
@jasonb
Same here I use the NGK CM-6 on the larger engines.

I've done engines where the plug is a long way removed from the cylinder in separate valve blocks but they still work OK
23 June 2022 at 10:24 #602758
noel shelley
Participant
@noelshelley55608
The main thing is that nothing hits, I once came across an engine that would not run ! The owner had put a long reach plug in and the gap was closed as the piston hit it ! Shorter plug ran fine ! Measure piston height and any head clearance and go from there. Plug position will dictate combustion/flame fromt.. If your near me I could lend you a 10mx1 tap. Good luck. Noel.
23 June 2022 at 21:39 #602828
NR67
Participant
@nr67
Thank you for all the excellent replies. Just what I needed to know. I left the plug entry point a bit high so I can take a bit off to get the plug position right when I get one to install. Coming from steam to IC is challenging so I may have further beginners questions when it come to timing and making a spark. Ordered the tap today. M10x1.

Edited By NR67 on 23/06/2022 21:41:52
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