VW Spark plug - can i trust a helicoil? | Technical matters | Back Room Forum

Sat 23 Jun 2007 15:05

VW Spark plug - can i trust a helicoil? - steveo3002

about 2 years i had spark plug spat out on my vw polo...not sure why it did it , but it cleaned the thread bare

so i found a engineering shop to fit a helicoil repair kit to the plug hole and its been fine sinse, but now the time has come for a plug change . im in two minds if i should leave that plug and do the others in case i disturb the thread repair, then again if i leave the plug to get caked up in soot/carbon there's a even better chance it might get ruined

so... should i fear swapping the plug or are they really safe as houses

and would it be better to change the plug with a warm engine or stone cold

Slight subject re-vamp -PU

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Sat 23 Jun 2007 15:13

can i trust a helicoil? spark plug - bell boy

if you havent changed the plugs for 2 years then its a difficult one to answer
my opinion?
just do it
its only an old vw afterall
if it goes wrong you could always buy something decent like a ford ;o)

by the way the reason the plug probably "flew out" was because it will have been loose in its holding, so check the plugs at least once a year is reasonable.
Ngk replacements come in well under a £10 a set at a factors

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Sat 23 Jun 2007 16:49

VW Spark plug - can i trust a helicoil? - piston power

i do them cold just be gentle if it snaps then it does but if it comes out put some copper slip on the thread of the new plugs which makes it much easier next time, put them in and nip up DON'T OVERTIGHTEN. good luck.

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Sat 23 Jun 2007 17:48

VW Spark plug - can i trust a helicoil? - steveo3002

ok just done em ...cold engine and it all went ok

out of intrest ..whats to stop a helicoil winding out when you unscrew something?

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Sat 23 Jun 2007 17:58

VW Spark plug - can i trust a helicoil? - Hamsafar

They shouldn't wind out due to them being bigger than the hole, so when the insert protrudes out the other end of the hole, it expands, also the fact it is bigger makes it press on the inside of the hole.
You should do what you did, always a cold engine, especially if aluminium head..

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Sat 23 Jun 2007 18:11

VW Spark plug - can i trust a helicoil? - Number_Cruncher

>>out of intrest ..whats to stop a helicoil winding out when you unscrew something?

Not a lot. During some commissioning work I did on some friction welding tooling with M16 inserts (compared with the M14 spark plug threads), I was having terrible trouble with inserts coming out. In practice, if an insert does come out, you can just thread a new one in, it's a 2 minute job. However, the way I solved the problem was to use loctite between the insert and the outer thread, making sure I only used the bare minimum, and none whatever got onto the inside of the thread. This allowed me to use the M16 as designed for pressing out the part after the weld - i.e., repetitive use, without any further problem. These inserts have since been used hundreds of times without a problem.

The most likely cause of the initial problem was someone overtightening the spark plugs, and weakening the whole thread in shear.

Number_Cruncher

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Sat 23 Jun 2007 20:34

VW Spark plug - can i trust a helicoil? - Lud

And if it does wind out, if you're very, very careful you can put it on the plug and wind it back in... Had a VW 411 with one once.

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