How would you remove an old helicoil from a sparkplug hole

[Johnny G Pipe]

This is an M14 spark plug hole in an aluminium Porsche 928 head. There appears to be a mixture of crossed head threads and an old helicoil in there. The hole will not take a plug without chewing it up. I want to try and fix this without removing the head (lots of hours and pounds even with the engine in).

I am planning to use a tap and insert (and have lots of contingency plans for keeping the aluminium chips out of the engine while tapping the hole) - but what is the best way to remove the helicoil first? There are special tools but they seem to only go up to M10. It is hard to show in the pic, but there is a loop of the helicoil clearly visible protruding out of the base of the hole, so there is definitely something to grab..

Any help appreciated, trying extremely hard to make the money pit that is a neglected 78 928 as shallow as possible :-)

]

[stevesingo]

If you can expose the top end of the helicoil (use a pick or scribe) enough to grab it with some good long nose pliers, you can try and wind it back out counterclockwise. In turning it counter clockwise you will also be collapsing it and this will reduce the hold it has on the aluminium threads.

You won't be able to wind it out by grabbing the bottom of the helicoil.

[Super Slo Mo]

Winding it counter clockwise won’t make it ‘collapse’, it will do the opposite, it will drive it harder against the threads.
When you install them thy are wound in clockwise which makes them collapse slightly and allows them to be wound into the thread.

The only way realistically is either brute force, by grabbing the top and pulling, or by continuing to wind it down the thread and into the engine. This is probably not desirable.

[mr.man]

It should be a very simple job. You need a metal working scriber with a sharp point.
You can clearly see the end of the helicoil at the top of the thread. Gently pick the end
of the helicoil out of the top vee of the thread. It will bend inwards towards the centre of the
hole. When you've eased out about 5-6 mm of the wire insert carefully, using long nosed
pliers, pull some more of the insert out of the vee form. Whist rotating the pliers anti-clockwise
you now unwind the wire insert out of the hole. You may need a small screwdriver to help
tease the wire out.
Now that's half the job.
You've still got to re-tap the hole with a helicoil tap, probably M14 x 1.25 , and fit a new helicoil
insert. You may now have cured your problem but I suspect there will be something else.
Good luck!

Edited by mr.man on Sunday 1st October 18:27

[Johnny G Pipe]

Thanks for the help folks. I wasn't sure if that top stepped thread was the beginning of the helicoil but I will have a pick at it to see.

If I can get it all out, the plan would be to use a solid insert kit, either timesert or one of the lookalikes on ebay. Basically a solid threaded brass insert with a top shoulder (so it can't get screwed down into the hole.

Hopefully I can tap enough material to hold the new insert's threads, but I will use some threadlock/adhesive on the insert-to-head part.

[GreenV8S]

Super Slo Mo said:

Winding it counter clockwise won’t make it ‘collapse’, it will do the opposite, it will drive it harder against the threads.
When you install them thy are wound in clockwise which makes them collapse slightly and allows them to be wound into the thread.

They are wound in from the bottom and the comment you quoted was about unwinding from the top, so the effects are reversed. Winding the top counter clockwise will collapse it and pull it away from the wall so that it can be withdrawn.

I would expect to find pieces of damaged thread caught in there and I think this is very likely to end up with debris dropped into the chamber. Is there some cunning plan to block off the bottom of the hole?

[stevesingo]

Super Slo Mo said:

Winding it counter clockwise won’t make it ‘collapse’, it will do the opposite, it will drive it harder against the threads.
When you install them thy are wound in clockwise which makes them collapse slightly and allows them to be wound into the thread.

The only way realistically is either brute force, by grabbing the top and pulling, or by continuing to wind it down the thread and into the engine. This is probably not desirable.

You wind it in clockwise driven from the tang on the leading thread.

Winding it counterclockwise from the top is the same. Duh!

[Johnny G Pipe]

GreenV8S said:

They are wound in from the bottom and the comment you quoted was about unwinding from the top, so the effects are reversed. Winding the top counter clockwise will collapse it and pull it away from the wall so that it can be withdrawn.

I would expect to find pieces of damaged thread caught in there and I think this is very likely to end up with debris dropped into the chamber. Is there some cunning plan to block off the bottom of the hole?

Yep, when working on the coil I'll have a greased rag on a string sitting at the bottom of the hole. There are a few methods apparently of getting rid of the aluminium chips when tapping the new threads(like grease on the tap, repeatedly pulling back after each advance, and even attaching a blower to the exhaust!!), but the ally isn't as dangerous as steel fragments. I really need to watch the coil.

I'll be going around the chamber with a hoover attachment and a then a magnet, and I have bought a cheap boroscope camera off ebay!

http://www.ebay.co.uk/itm/Video-Snake-Tube-Camera-...

We will prevail..

[Super Slo Mo]

stevesingo said:

Super Slo Mo said:

Winding it counter clockwise won’t make it ‘collapse’, it will do the opposite, it will drive it harder against the threads.
When you install them thy are wound in clockwise which makes them collapse slightly and allows them to be wound into the thread.

The only way realistically is either brute force, by grabbing the top and pulling, or by continuing to wind it down the thread and into the engine. This is probably not desirable.

You wind it in clockwise driven from the tang on the leading thread.

Winding it counterclockwise from the top is the same. Duh!

Having thought about it, I do believe you’re right. Duh indeed.
I’ve not had a day off for nearly a month, that’s my excuse and I’m sticking to it

[paintman]

Having done one or two helicoils on boat, bike & car engines.
Wound in from the top & the tang at the bottom then broken off.

Removal.
Much the same as given by mr.man. Once you've got something to grip will pull out as a length of twisted wire.
I will admit to contemplating having a spare pair of underpants to hand when I removed the first one but have yet to damage the thread & a new one has gone in without issue.

[stevieturbo]

Looking at the photo, the top of the helicoil appears ok, so exactly which bit is damaged ?

If it is helicoiled either that is ok, or it is not, there shouldnt really be any bare alloy at play as far as functional threads go ?

Are you sure it doesnt just need the threads cleaned up ?

These can be handy, you insert and chase the threads from below, rather than from above with a normal tap.

http://www.ebay.co.uk/itm/Sealey-Reverse-Action-Da...

But as others say, if you can grab part of the helicoil, just pull/unwind it out. But once you've unsettled the top of the helicoil, there is no going back, it must come out.

[Turn7]

Remove the work of the devil Helicoil and fit the, IMVHO,correct thread repair - a Timesert......

[stevieturbo]

Not a damn thing wrong with helicoils when done right, and lots of OEM's use them too in important areas on alloy.

And lots dont, which leads to muppets easily damaging threads ! lol

[GreenV8S]

Bear in mind that most of the instructions you'll see for installing a thread insert will be as a repair for a standard thread i.e. assuming you have plenty of material to cut into to tap for the insert. Here, that material has already been removed to fit the helicoil.

[Johnny G Pipe]

Thanks guys.

Having compared with another hole on the other bank, it is definitely a helicoil in there from top to bottom, the top section of the helicoil looks good (but it isn't budging easily when I have at it with a pick) and I really don't know why it is chewing the plugs up..I presumed it had broken or jumped out of a thread somewhere.

Otherwise are you suggesting just grab the bit at the bottom and pull upwards? It is true I guess I am indeed committed as soon as I disturb it significantly. I think chasing it first is a very good idea to see if it can be left alone, will do that first.

With the inserts, which do look more foolproof, the tap is M16 for an M14 insert, so should be enough with some threadlock I hope.

Really appreciate the help.

[GreenV8S]

If you do decide the helicoil has to go, I'd take a look at the exposed bore and see whether it is still good. I'd have thought it should be. If so, refitting a new helicoil the same size would give you a known good thread without any worry of trying to tap for a different insert, and potential issues of dropping swarf into the bore and/or not having enough material left to tap into.

If that was me I'd try my best to visually inspect the helicoil before removing it. For it to chew up threads there would need to be a major problem and that ought to be visually obvious. It would be nice to get that confirmation before you commit to replacing the insert.

[stevieturbo]

Well you would be wise to look at it and find out exactly why it is chewing up plugs, because if it is that bad, it should be really obvious.

You're about to dive feet first into something that could turn into an expensive fk up if you get it wrong.

[paintman]

Johnny G Pipe said:

Thanks guys.
Otherwise are you suggesting just grab the bit at the bottom and pull upwards? It is true I guess I am indeed committed as soon as I disturb it significantly. I think chasing it first is a very good idea to see if it can be left alone, will do that first.

Not the bottom. Use a fine point to bend out a bit at the top, grip then pull & twist as per mr.man. As you say, once you've started you're committed. Take your time & don't rush.

If you DO think it's going wrong then stop & remove the head. More work but better that than a damaged head.

Edited by paintman on Tuesday 3rd October 09:59

[Arnold Cunningham]

What I've done before is use a jewellers screwdriver to lift the edge of the helicoil and then grab it with some good quality needlenose pliers. Then unwind it out of the hole

[Johnny G Pipe]

stevieturbo said:

Well you would be wise to look at it and find out exactly why it is chewing up plugs, because if it is that bad, it should be really obvious.

You'd think! Even though this is a V8 and not a flat 6 thank goodness, getting a really good view of the plug hole is hard. There is nothing obvious with a light and magnifying glass, and my theory is that the helicoil is just sitting in wrong with a badly spaced thread somewhere, installed badly by the PO and the plug just screwed in hard and fingers crossed.

But I am awaiting delivery of my budget ebay boroscope camera before I do anything else, in theory it will give me a good view of the threads. In practice it might be a bit rubbish. :-)

If I can't see anything obvious, the least harmful next step is very careful use of the reverse tap thread chaser I think. You can vary how wide the tap is, perhaps that may just nudge the helicoil back into place if it has shifted.