How do I tap a Spark Plug thread?

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jfoldbar
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How do I tap a Spark Plug thread?

Unread post by jfoldbar » July 29th, 2016, 3:19 pm

i have a small petrol motor that i bought new about 6 years ago. i rarely use it and last weekend i decided to drag it out to give it a bit of a run. it wouldnt start so i took the plug out. this is the first time the plug has ever been out of this motor and it turns out when it was put in in the factory, it was shoved in wrong and cross threaded. so now i cant get the plug back in.

i have managed to get a thread tap that matches the plug but i just have 1 concern. after cutting a new thread, should i be trying to get the swarf out of the combustion chamber? and how do i do that?

any thoughs?

V Williamson
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Re: How do I tap a Spark Plug thread?

Unread post by V Williamson » July 29th, 2016, 7:17 pm

Being a small motor, can you lift it and support it with the spark plug hole facing downwards? The idea I have in mind is that the swarf can fall back out the hole instead of falling into the combustion chamber. Or maybe get a grease soaked rag and insert it via the hole into the combustion chamber with the piston close to top dead centre with the idea that any swarf falling into the combustion chamber can land on and stick to the greasy rag. Just thoughts on the matter. I wouldn't like swarf to be free in the combustion chamber.

dom14
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Re: How do I tap a Spark Plug thread?

Unread post by dom14 » July 29th, 2016, 7:32 pm

Put the piston on TDC & use a vacuum cleaner to vacuum the swarf out.
Use vaccum cleaner nozzle attachments, and combine it with a small rubber hose if necessary.
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Peter Aawen
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Re: How do I tap a Spark Plug thread?

Unread post by Peter Aawen » July 29th, 2016, 7:37 pm

Take the head off? It's only a 'small' petrol motor isn't it?? :thumb:
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typhoeus
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Re: How do I tap a Spark Plug thread?

Unread post by typhoeus » July 29th, 2016, 10:19 pm

Ive had the same problem with a lawnmower, I used grease on the tap, and blew compressed air into the plug hole with the exhaust valve open for a bit. It was fine, & is still running years later. I take the trouble to use an anti seize in the plug threads now, as even tho I recut the thread, its not as perfect as a new one

jfoldbar
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Re: How do I tap a Spark Plug thread?

Unread post by jfoldbar » July 30th, 2016, 7:58 am

thanks for the replies.
i dont really like the thought of taking the head off just for swarf.
i didnt wonder if a vacuum cleaner can work. i would have thought that the swarf would kinda stick and be too small to suck up.
i guess if a shove a grease rag in the hole, i could pull it out again with small long nose pliers.
even though its four-stroke i reckon i'll go for tip it over. i could do with an oil change anyway. especially since there could be a bit of swarf in the oil after im done.
i would imagine that the swarf would have to be alloy from the head, making it a soft material(softer than rings and bore). small particles like that would also burn in the chamber wouldnt they?

typhoeus
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Re: How do I tap a Spark Plug thread?

Unread post by typhoeus » July 30th, 2016, 9:13 am

small particles of alloy would probably melt at combustion temps. If you are going to do it up side down, why not get an oil can full of petrol, and flush any swarf out the plug hole that way? You shouldn't get any swarf in the oil as there is only one way to the oil from there and that is by going past the rings!

dom14
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Re: How do I tap a Spark Plug thread?

Unread post by dom14 » August 2nd, 2016, 11:00 pm

jfoldbar

A Vacuum cleaner works fine. Unless you've already flooded combustion chamber with oil, it should suck out any metal dust inside easily. You just need to make sure the attachment is air tight. Most vacuum cleaners come with an attachment that could easily adapt to the spark plug hole entry.
Or as it's pointed out above, you can use high pressure air gun with the piston on exhaust stroke.
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cmar
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Re: How do I tap a Spark Plug thread?

Unread post by cmar » September 4th, 2016, 12:19 pm

Grease on the tap works pretty well too, well has for me anyway. The chips will just be aluminium in any case and any missed by the grease, will just get blown out the exhaust.
Haven't owned a 2WD since 1982.

jfoldbar
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Re: How do I tap a Spark Plug thread?

Unread post by jfoldbar » September 6th, 2016, 5:13 pm

well, i thought id give you guys an update. tapping while upside down worked good. most of the swarf either stuck to the tap or fell out.

Although the silly thing i did was to assume that the sump oil would run out the plug hole as i was tapping, helping to flush out any swarf. but it didnt, it went right through the carby and dripped out the air filter. so it took quite a few pulls to start! So i am probably now partly responsible for global warming, what with all the smoke it blew for a while! but the smoke soon cleared and it seems fine now.

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