smart51
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| posted on 2/3/24 at 01:34 PM |
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Have I got this wrong? Helicoil sizes
I've taken the head of my engine and seen that the spark plug threads are not the best, so I bought a helicoil kit to fix it. The spark plugs
are M12 x 1.25 and I bought an M12 x 1.25 kit. When it arrived, the tap is M12 x 1.25 and the coils are 12mm OD. I used the tap to clean up the
existing threads.
Have I got it wrong? I thought the quoted size of a helicoil is the inside thread of the coil, not the outside thread.
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Dingz
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| posted on 2/3/24 at 04:24 PM |
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The ones I have bought were always the finished sizes, ie M8 but they were not genuine Helicoil.
Phoned the local ramblers club today, but the bloke who answered just
went on and on.
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Mr Whippy
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| posted on 2/3/24 at 05:35 PM |
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The ones I've used are just the size of the bolt going into them, you should be able to screw it into the helicoil. They probably sent you the
wrong ones. A quick google gives the proper drill size for M12 as 31/64" or 12.3mm. There's tons of tables on the web.
Tbh for all the trivial cost I'd just give it to a machine shop to do as they'll have done thousands and a mistake with the head, well it
could get expensive. Mind to use copper slip on the spark plug threads to prevent future issues and improve plug cooling (so many people leave that
out!).
Fame is when your old car is plastered all over the internet
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perksy
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| posted on 3/3/24 at 04:38 PM |
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Just my 2p but I'd be very careful with copperslip on the threads as you can overtigten if not careful, particularly on taper thread plugs
From the NGK Website:
"1. Anti-seize
NGK spark plugs feature trivalent plating. This silver or chrome-colored finish on the threads is designed to provide corrosion resistance against
moisture and chemicals. The coating also acts as a release agent during spark plug removal. NGK spark plugs are installed at the factory dry, without
lubrication or anti-seize.
Anti-seize can act as a lubricant, altering torque values up to 20 percent, increasing the risk of spark plug thread breakage and/or metal shell
stretch. Thread breakage can sometimes involve removing the cylinder head for repair. Metal shell stretch changes the heat rating of the spark plug
and can result in serious engine damage caused by pre-ignition. Do not use anti-seize or lubricant on NGK spark plugs. It is completely unnecessary
and can be detrimental."
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rusty nuts
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| posted on 3/3/24 at 07:21 PM |
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I suspect you have maybe a kit for 10x1.25 threads ?
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smart51
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| posted on 3/3/24 at 08:01 PM |
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quote:
Originally posted by rusty nuts
I suspect you have maybe a kit for 10x1.25 threads ?
The tap is marked M12x1.25 so the finished thread is most likely M10x1.25 the seller
doesn't know what they're selling. Amazon will take it back so all is good.
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Mr Whippy
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| posted on 3/3/24 at 11:43 PM |
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quote:
Originally posted by perksy
Just my 2p but I'd be very careful with copperslip on the threads as you can overtigten if not careful, particularly on taper thread plugs
From the NGK Website:
"1. Anti-seize
NGK spark plugs feature trivalent plating. This silver or chrome-colored finish on the threads is designed to provide corrosion resistance against
moisture and chemicals. The coating also acts as a release agent during spark plug removal. NGK spark plugs are installed at the factory dry, without
lubrication or anti-seize.
Anti-seize can act as a lubricant, altering torque values up to 20 percent, increasing the risk of spark plug thread breakage and/or metal shell
stretch. Thread breakage can sometimes involve removing the cylinder head for repair. Metal shell stretch changes the heat rating of the spark plug
and can result in serious engine damage caused by pre-ignition. Do not use anti-seize or lubricant on NGK spark plugs. It is completely unnecessary
and can be detrimental."
Interesting as iirc (was many years ago) about 70% of heat transfer from the plugs is through the thread, so the theory goes that copper slip helps
this and reduces the risk of detonation from the hot plug tip. I suspect that it's one of those subjects you'll get a hundred different
opinions and no clear right or wrong. Just pick the one that seems appropriate for your application.
Fame is when your old car is plastered all over the internet
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rusty nuts
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| posted on 4/3/24 at 11:55 AM |
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quote:
Originally posted by perksy
Just my 2p but I'd be very careful with copperslip on the threads as you can overtigten if not careful, particularly on taper thread plugs
From the NGK Website:
"1. Anti-seize
NGK spark plugs feature trivalent plating. This silver or chrome-colored finish on the threads is designed to provide corrosion resistance against
moisture and chemicals. The coating also acts as a release agent during spark plug removal. NGK spark plugs are installed at the factory dry, without
lubrication or anti-seize.
Anti-seize can act as a lubricant, altering torque values up to 20 percent, increasing the risk of spark plug thread breakage and/or metal shell
stretch. Thread breakage can sometimes involve removing the cylinder head for repair. Metal shell stretch changes the heat rating of the spark plug
and can result in serious engine damage caused by pre-ignition. Do not use anti-seize or lubricant on NGK spark plugs. It is completely unnecessary
and can be detrimental."
VW air cooled engines suffer from seized spark plugs when Champion plugs are installed, never seems to happen with NGK or Bosch
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