Cylinder head spark plug thread

[David orr]

Hi, I have a 3 year old Sym Symphony 125 and the spark plug blew out of the cylinder head as I was riding, I’m unable to screw it back in as it just keeps turning I have a new plug so it has to be the threads in the head is there any other solution for this other than a new head
Many thanks D
David

[Nobby the Bastard]

Helicoil
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[WD Forte]

this kind of thing comes to mind

https://www.ebay.co.uk/itm/393257074532?
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bikers smell of wee

[David orr]

W D Forte,
That’s brilliant and cheap thank you.
I’m assuming the tap cuts the hole for the insert and the inside
thread of the insert is the correct size for the plug.
The head is off now just waiting for the tool.
Thanks again.
David

[om15]

I had the same with a BSA C15, took the head to GCS at Three legged Cross and the damaged thread was machined and a swaged thread was fitted, neater than a helicol.
They did a good job,

Address: 18 Thorne Way, Three Legged Cross, Woolsbridge, Wimborne BH21 6FB
Phone: 01202 826045
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Alcohol doesn't solve problems, but neither does milk

[om15]

Just found this photo,
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Alcohol doesn't solve problems, but neither does milk

[David orr]

Thanks for that the problem is I live in Spain, I’ve got a trip back next month so will certainly consider that.
Thanks again

[WD Forte]

With the right kit and taking your time you can do it as well as any shop will.
Done lots of helicoils but never had to do a plug hole ( yet)

The one I indicated was an example which follows the same procedure, but I can't attest to the quality of that particular product.
I see some products have 'leader' threads to act as a guide
when cutting the new thread (Pic below)

I would advise to take care to follow the axis of the old thread
when tapping out the new one for the insert.
Thoroughly clean and de-grease the new thread and use thread lock when fitting the insert.
Note the inserts have a leading and trailing edge when fitting



https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fcimg0.ibsrv.net%2Fgimg%2Fwww.ford-trucks.com-vbulletin%2F1437x751%2F80-helicoilsavathread_26ba52773ec4c1e368a0e75ba1aac8ded510a590.jpg&f=1&nofb=1
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bikers smell of wee

[Pete.]

Make sure you get the correct insert kit the bike seems to use CR7 plugs which are M10 x 1.0mm thread. The kits listed above are M14 for a B type plug.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[WD Forte]

Ooh! thassa good point.
hadn't considered those modern weeny plugs.
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bikers smell of wee

[David orr]

Yes Pete it is a 10mm x 1.00 mm I will make sure when ordering.
W D Forte I will have a go myself I’ve found a good kit on eBay.es bit more expensive but I think worth it similar to the one you show it has a leading edge the same thread as the existing plug to follow what is left of the old threads then follows up with whatever the insert thread is.
I’ve got Loctite 638 that should do it.
Many thanks everyone you’ve given me the confidence to have a go.
David