Advice on helicoiling a spark plug thread

[dern]

My fire blade spat out a spark plug this morning leaving me with one thread left in the head. What's involved with helicoiling this thread?

I assume that I'll need to take the head off, drill an oversize hole, tap it and then insert the helicoil... what does a helicoil kit come with? Is it just the insert and the tool to wind it in or does it come with a drill and a tap too?

In order to drill the old thread out do I need access to a machine shop to do this or will I be able to use a hand held drill and because the drill is only taking out the thread will it follow the correct path without resorting to using a pillar drill or anything like that?

Thanks,

Mark

[GreenV8S]

You'll need a tap, and if you're lucky you will just be able to use the tap to cut new threads into the existing (now stripped) hole. You should be able to get the tap from the same place that supplies the inserts, you may even find they come bundled together automatically.

[paolow]

dern said:

My fire blade spat out a spark plug this morning leaving me with one thread left in the head. What's involved with helicoiling this thread?

I assume that I'll need to take the head off, drill an oversize hole, tap it and then insert the helicoil... what does a helicoil kit come with? Is it just the insert and the tool to wind it in or does it come with a drill and a tap too?

In order to drill the old thread out do I need access to a machine shop to do this or will I be able to use a hand held drill and because the drill is only taking out the thread will it follow the correct path without resorting to using a pillar drill or anything like that?

Thanks,

Mark

You can give it a go - the trouble is the slightest wobble will screw your head. Theres also the problem of getting a drill be big enough for your pistol drill. Id be more inclined to give the whole head to a machine shop and let the headache be theirs!

erm - or just buy one off ebay? there seems to be a selection at the mo...

Edited by paolow on Tuesday 6th June 18:14

[dern]

Cheers, did some research and measured the thread on the plug and it would appear that helicoil do a kit with a tapered tap which can be inserted without doing any drilling so I suspect I'll go for that.

Regards,

Mark

[paolow]

dern said:

Cheers, did some research and measured the thread on the plug and it would appear that helicoil do a kit with a tapered tap which can be inserted without doing any drilling so I suspect I'll go for that.

Regards,

Mark

thats rather clever - how much just out of interest?

[splatspeed]

are you sure you have the clearences for this on a bike

the fire blade is a bit small and extreme

id prefer to do this as a head off job

as the tolerences on this bike are that much tighter

the spark plug is the centre of the heat area and the space between the valves and the plug is the worst place for heat

this area is suseptiable to melting

take care

[dern]

paolow said:

thats rather clever - how much just out of interest?

£50 quid for 10 inserts, the insertion tool and the tap. It's designed for doing spark plugs (alledgedly). That price is for the M10x1.0 thread that I need and they get more expensive as they get bigger.

Mark

[dern]

splatspeed said:

are you sure you have the clearences for this on a bike

the fire blade is a bit small and extreme

id prefer to do this as a head off job

as the tolerences on this bike are that much tighter

the spark plug is the centre of the heat area and the space between the valves and the plug is the worst place for heat

this area is suseptiable to melting

take care

I'll be taking the head off because the risk of getting metal in the bore is too great even if you grease the tap to catch the bits.

Regards,

Mark

[nighthawk]

I've used helicoils kits on car engine spark plugs, never on a bike though.

Always been a complete and reliable success.
The only thing you need to ensure you do is torque the plug up to the correct figure to prevent damage to the helicoil.

[steve_d]

The helicoil is made of diamond shape section wire. The inside of the coil is the same size as the original thread so the outside in only one thread depth bigger which is why you can just tap the hole without drilling. It's not a special tapered tap they are all that way.

If you are going to have a go at this yourself (and no reason why not) find yourself a piece of pipe the tap just passes through. Machine or file the end perfectly square. When ready to tap the hole place the tube over the tap and hold it hard against the face the spark plug washer would seat. The tube is now going to guide the tap as it starts to cut and ensure the finished thread is square to the seat.

Steve

[GreenV8S]

Taps are cheap, it's the inserts that cost the money. Given that the pitch of the old and new threads is the same (obviously) I think you'd be better of very carefully threading a tapered tap into the old threads and use them as a guide - just make sure you don't pull it sideways while it is cutting.

[F.M]

Sellotape a magnet to the top of the `bit` which would make any debris stick to the bit ...no nasty metal in the chamber..?

Ok it won`t work..silly me!

Edited by F.M on Tuesday 13th June 14:44

[GreenV8S]

F.M said:

Sellotape a magnet to the top of the `bit` which would make any debris stick to the bit ...no nasty metal in the chamber..

Is it an iron head?

[Pigeon]

GreenV8S said:

F.M said:

Sellotape a magnet to the top of the `bit` which would make any debris stick to the bit ...no nasty metal in the chamber..

Is it an iron head?

Not on a Fireplace

[GavinPearson]

IMHO it's a head off job but more critical than that you really want to use a timesert and not a helicoil. Timeserts are less prone to winding out, which could be a real problem with a helicoil when you do a plug change.

[GreenV8S]

Was going to suggest that, but they're a bit trickier to install aren't they? If it goes wrong you can end up with the thing stuck half way in. For a first time, I would have thought helicoils were the easier option?

[leorest]

Plus helicoils are designed to be replaceable so when you've bought a pack of ten, that should keep you going for the foreseeable future. I imagine a touch of threadlock would solve most unwinding problems too.

[dern]

Ooo, blimey, didn't realise this was still alive... basically I decided to farm the job out to a local engineering firm because I didn't fancy trying my very first attempt at this on something so important. The other thing that put me off was that the spark plug hole is right at the bottom of the head (obviously) and down a deep recess so I wouldn't be able to see what I was doing very well so I err'd on the side of caution. I'll learn the skill another time I think.

So, I took the bike apart (so many many parts) and lifted the head off and am having an insert put in for me.

It's an alloy head by the way so a magnet wouldn't work.

Cheers,

Mark

Edited by dern on Tuesday 13th June 14:26

[leorest]

Very wise. If you get the chance to learn how to do helicoils on works time and expense then that's the best way It would be interesting to hear what sort of inserts your machine shop prefer and why?