Helicoiling a plug thread in-situ

[Slavvy]

Hey guys. I'm a car nut who recently bought a gsx-r250 to see what all this two wheels business is about I'm very capable with diagnosing/repairing cars but bikes are almost completely new to me. It's a great bike and I've had fun learning on it.

Today I went to remove the plugs and, to my dismay, one of them came out with most of the plug thread still attached! That spark plug thread is now thoroughly stuffed, it is just a clean circular hole and there's no chance of re-tapping it to try to salvage it. What are my chances at helicoiling that hole without removing the cylinder head? I'm fairly confident that I can avoid leaving shavings in the bore but I don't know how easy it would be to get a 'coil in there, the threads are tiny and buried deep in the head.

I want to get the bike going ASAP as cost of petrol is kicking my arse (my car is huge, old and...not cheap to run), this plus the intimidating timing chain layout puts me off trying to get the head off, which I realise is the ideal solution.

I'd appreciate any thoughts.

[Drew]

It's been done. I would wet hemp rope in oil, and feed it into the spargplug hole. Do the drilling and cutting of the new thread, fish out the rope and hope the swarf comes out with it. As for getting the coil in there, put it on the plug, and wind it in with that.

Or try turning the bike upside down. Not as dumb as it sounds methinks. Two guys could easily man handle a GSXR250 on it's lid and strap it to the rafters.

[Slavvy]

What about the wee tang on the end of the helicoil? Reckon just snap that off beforehand and wind it onto the plug?

[hayd3n]

take your time
if in doubt get it out

[scumdog]

Some way of having the intake valve shut, the exhaust one open and compressed air being fed into the exhaust port to create a blow-through effect and blowing out any swarf would be another possibility i.m.h.o.

[Slavvy]

Well, I went ahead and cut the thread after work. My extremely knowledgeable boss advised against blowing through the cylinder as it risked the swarf getting stuck somewhere and damaging a valve seat, guide or the bore etc. I slathered a shitton of grease onto the tap and it seems to have caught all the swarf (none visible through the hole, anyway). Went very slowly, took ages but seemed to work.

I'll try to fit the helicoil tommorow, so far my plan is to fit the coil to the plug, apply red loctite, screw them in as a unit. I did a dry run of this after tapping the thread and everything seemed to go smoothly. Fingers crossed!

[imdying]

Vacuum cleaner the spark plug hole to be sure?

[Slavvy]

Ok well I tried to put in a coil today and failed miserably. When i put the coil onto the plug and try to wind them both in, what happens is the coil just stands still while the plug keeps turning and the coil ends up getting sort of bunched up on the plug, thus ruining the helicoil.

I have no way of winding in the helicoil on it's own, and this wouldn't be desirable anyway as the coils are slightly longer than the plug and would stick out too far in the cylinder if I dont trim them. I checked the thread using the tap and it is fine, the coils just aren't going in with the plug in the middle.

I'm completely out of ideas and nearly out of helicoils, does anyone know how I should finish this?

[schrodingers cat]

In my experience you have to use the helicoil installation tool or a homemade version as the (heli) coils as they sit are 'oversize' and need to be compressed to the correct diameter.

Use a pick to count the amount of threads and cut the top of the helicoil off to suit

The greatest danger you'll have in the future is the plug winding the coil out or in.
This is exuberated if the sparkplug thread protrudes through the helicoil into the combustion chamber as it will get carbon build up.

Grind or file off any threads that might protrude.
Use a wire wheel and buff the shit out of the remaining thread to make it just a little bit smaller and use some nickel paste on the threads

Good luck! If it all goes horribly wrong you'll just have to pull the head and get someone to wave a welder at it.

[Flip]

I have a pair of artery clamps that would be brillant for holding the tab, winding in the coil and breaking it off while still retaining it.

[scumdog]

Araldite the helicoil in place?

[Ocean1]

You won't "push" it in, you've got to turn it in from the bottom, with the wee tab. Cutting to top down to the right length is the way to go, make it a half turn or so shorter than you need, it's oversized as supplied and it'll grow in length when you fit it. Dress the cut end before you fit it, or it'll gall the plug.

I have a pair of artery clamps that would be brillant for holding the tab, winding in the coil and breaking it off while still retaining it.

Yup, that orta do it. Although I'd practice on some of the "spare" helicoils you've got first.

Also, I've had more luck with helicoils, rather than recoils, for that sort of job.

[Ocean1]

Araldite the helicoil in place?

Won't take the heat. In fact loctite theoreticaly won't either, but I've pulled a helicoil out of a head before and it had loctite still OK on the upper turns.

[Slavvy]

I have a pair of artery clamps that would be brillant for holding the tab, winding in the coil and breaking it off while still retaining it.

What are these...? I've never heard that term before. I worked out I could probably get the coil wound in if I modify the tool so that it's longer and can actually reach the hole (currently too deep for the tool to reach), and trimming/measuring it should be no problem, but I don't know how i would break off the tang. I read somewhere that tying a length of fishing wire or something to it might work, but im dubious about that.

[Drew]

What are these...? I've never heard that term before. I worked out I could probably get the coil wound in if I modify the tool so that it's longer and can actually reach the hole (currently too deep for the tool to reach), and trimming/measuring it should be no problem, but I don't know how i would break off the tang. I read somewhere that tying a length of fishing wire or something to it might work, but im dubious about that.

Surgery clamps, like, medical type. They would be ideal if they are long enough, and would be easiest methinks.

I would destroy a screw driver to do it myself, but this would work with any piece of rod. Drill a hole sideways through a piece of 4mm rod for the 'tang' to sit in, (this would be a long electrical screw driver in my case, as I don't have a drill press and the flat surface would be easier to drill). Put it through the coil and on to the 'tang', bend the tang so it can't fall back out of the hole ya drilled, and wind it in. Once you've wound it in to the required depth, give it a sharp yank and the tang should break off.

Get it running, and sell the friggin thing before it needs another set of plugs and the coil comes out with it.

ps. Chuck a big blob of grease on the tang and screw driver, to make sure the tang comes out when it snaps.