okay my g/f has just rang up from her sisters house, our mk2 1988 polo has spat out number 1 plug and theres no threads left on the head
im hoping to attempt to helicoil it in situ
can anyone offer any advise, what tools will i need, how long should it take, how should i keep swarf out of plug hole etc
any advise at all, never used or seen a helicol before
what thread do i need?
Edited by Pugugly on 16/06/2009 at 12:14
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It should be possible to helicoil it in situ, but you might find you need to buy quite an expensive kit to get going, so it might be more cost effective to get someone with the kit (and the skills!) to do it for you. Alternatively, I can't see getting the head of one of those engines being all that difficult, so you could whip the head off and take that to your local engineering shop - no chance of swarf getting in the cylinder then!
--
RichardW
Is it illogical? It must be Citroen....
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Look in the Yellow pages-any good engineering firm(usually listed under engine reconditiong) should be able to do it in situ.An amateur would need a bit of practice,you need to drill the head,tap a new thread, fit the helicoil and snap off the inserting tang.
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Going back a bit but I had a Cavalier company car that blew a spark plug out of the head when I was in Malvern (and I live in Chester!) at 4.30PM on a Friday afternoon.
I went to the local Vauxhall dealer and they referred to me to a real 'back street' garage who did it while I waited for a fiver.
The only thing he said is to ensure that whoever works on the car in future knows that it's been helicoiled.
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You can also get a solid insert, which you 'loctite' in place, and doesn't have to carry a health warning like a helicoil does.
El Dingo.
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You can also get a solid insert, which you 'loctite' in place, and doesn't have to carry a health warning like a helicoil does. El Dingo.
Indeed, among them is the "Tappex" insert.
One note of caution (*from bitter practical experience!) when using inserts, whether solid or of wire, is to make absolutley sure that the axis of the new tapped hole remains at right angles to the plane of the seating surface or joint.
* I weighed in and supported their specification in a rail vehicle repair procedure. We didn't specify a tight angular tolerance, and some bolts failed in bending fatigue because they were being bent during assembly because the inserts were skewed. Lesson learnt!
Number_Cruncher
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Why a health warning?
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Why a health warning?
A literal expression that whoever works on the car needs to know the plug hole has been helicoiled to avoid damaging it, not an indication of actual potential damage to health!
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so asumming i can get a helicoil fitted...what precautions do i take next time i wor on that plug?? i was under the impression it will be good as new if done right???
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pardon me for my ignorance but what IS a nelicoil and is it just limited to sparkplug holes?
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so asumming i can get a helicoil fitted...what precautions do i take next time i wor on that plug?? i was under the impression it will be good as new if done right???
I think it just means taking the ordinary sort of care when inserting a plug, the care that might have avoided cross-threading or damage in the first place:
ie clear away muck before undoing, lubricate the threads, use fingers only for several turns before using the wrench, and tighten carefully to the specified torque.
Also possibly being careful in case the plug feels tight when unscrewing, and easing it back and forth with WD40 rather than just forcing it undone.
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I had a helicoil inserted into an outboard motor and thats being running for more than 25 years with no problems.
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I'd steer clear of a helicoil. You need a thread to fit it into.
My method would be to drill out the existing thread enough to fit a threaded bush into place. This bush is then threaded/tapped on the inside. This would allow you to use the standard spark plugs in future. No need for a helicoil. The bush would need to be loctited. Of course this is a head-off job.
Alternatively, try and source a replacement head from a scrap dealer.
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This bush is then threaded/tapped on the inside. This would allow you to use the standard spark plugs in future. No need for a helicoil.
But you can still use a standard spark plug after helicoiling.
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oh well its having a coil at the moment, the guy said it will be as good as new when done, and said theyre used on planes, must be good enough for a mk2 polo
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Heads have to be drilled and tapped for a Helicoil and you then use the std. plug.The advantage is that with the inserting tools it can de done without removing the head.I used them on motor-cycle engines where you have steel studs going into alloy crankcases.
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Plus-gas is a better penetrant than WD-40.
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When I worked on piston aero-engines some years ago, helicoils were accepted as an adequate method of repair for such items as sparkplug bores, so thats a vote of confidence then !
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okay its done..£23.50 and back on the road in less than 24hrs, not sure if im keen on the swarf going in, but in my case its a £200 banger
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When I saw one done they rotated the crank to TDC on compression for that cylinder and stuffed a greasy tack rag down the plug hole. Drilled, tapped and helicoil inserted then rag fished out with all the swarf stuck to it.
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Yes - the Helicoil page above reckons they're a Boeing approved repair method. Makes you think, next time you're on an Easyjet 737...
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>>Makes you think, next time you're on an Easyjet 737...
Not at all!
Inserts are also specified to be fitted in new aerospace parts. If you are specifiying a bolted joint between two aluminium components, the shear strength of the female thread in the aluminium will limit the axial load on the bolt. If you then fit an insert, the area under shear increases as radius squared, and you can allow the bolt to take more of its design strength axial loading. This is beacuse the yield stress in shear of the helicoil material is much higher than that of the aluminium.
In blunt terms, a helicoiled thread into aluminium is stronger than screwing into plain aluminium.
On a project I'm currently working on the design of, I'm specifying a phosphor bronze heliciol between a titanium screw and a titanium housing. This is done as an attempt to prevent cold welding between similar materials (under conditions of high cleanliness and high vacuum).
Number_Cruncher
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Oh, I wasn't implying they were in any way dubious - just surprised, but as you say, an insert can increase strength.
It's just a little amusing that a technique which I think quite a few people probably view as a bodge actually has such engineering integrity!
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we wont mention then that the wings are glued on.
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