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Old 22 October 2008, 07:25   #1
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Opti Plug X-thread fix

So , having established the plug thread in No1 cyliner is screwed (no pun intended) , options seems to be ;
1) Get a new plug in somehow
2) Take off the head & put an insert in
3) Buy a new head.

Clearly No1 is not ideal , but could work if the correct thread can be picked up somehow ( maybe runa tap/di down ( not sure which is which but you know what I mean) without taking the headoff & 'try & get any bits out' & hope anything left gets burn't up / chuched out of the exhaust .

No2 seems to be the best/ cheapest proper fix

No3 will I guess cause a big cost which I'd rather avoid.

Anyone have any experience of this & then fixing it/ costs ? I'll be paying someone else to do it whatever as I dont the time / ability to do the second option & the first is very 'iffy' and I'm trying not to think about the cost of a new head !
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Old 22 October 2008, 07:43   #2
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Heli Coil

Take the engine to someone who can fit a Heli Coil. They tap the hole and insert a coil which provides the correct size thread. No need to remove the head. Takes a few minutes.

You can easily do it yourself if you are handy.

Good luck.
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Old 22 October 2008, 07:53   #3
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Cheers JABS - its with the local Merc dealer, but I would have thought that runing the TAP down would drop metal chips into the cylinder, & when turning it over they could score the bore to buggery.

I'll give them a bell to get thier view & hopefully they can do it with it without taking the head off. Keen to do a real fix like this than a bodge , ending up with a loud bang & nice plug shaped hole the cowling when I doing 5,000 rpm !
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Old 22 October 2008, 08:16   #4
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They will use a special tap and liberally cover it with grease. There is little metal removed and most of it comes out on the tap.

They then screw in the helicoil with a special tool and off you go!

It is a standard repair used all over the place where threads become galled or stripped.

You probably put as much swarf into the cylinder when you crossed the thread in the first place.

Hope it goes well.
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Old 22 October 2008, 08:26   #5
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Quote:
Originally Posted by JABS View Post
Take the engine to someone who can fit a Heli Coil. They tap the hole and insert a coil which provides the correct size thread. No need to remove the head. Takes a few minutes.

You can easily do it yourself if you are handy.

Good luck.
Not used them for years but don't you have to re drill & tap the hole bigger to fit the Heli coil ?

You can get a thread cleaning tool (looks like a very blunt bottom tap) for spark plug threads we used to use them before doing pressure tests, you may be able to try something with one of those, if not I think it's head off and retap for the Heli Coil
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Old 22 October 2008, 08:28   #6
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Originally Posted by JABS View Post
They will use a special tap and liberally cover it with grease. There is little metal removed and most of it comes out on the tap.

They then screw in the helicoil with a special tool and off you go!

It is a standard repair used all over the place where threads become galled or stripped.

You probably put as much swarf into the cylinder when you crossed the thread in the first place.

Hope it goes well.
Google is my friend

http://www.engineproblem.com.au/helicoil.htm
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Old 22 October 2008, 09:05   #7
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I'll see what they say about if they think they can do it with the head off or not. They will be the ones that will take the wrap if the plug comes out at high speed ! I can only assume it cant be a too big a deal to take the head off . I've done it on cars myself ( years ago ) & thats with all the valves etc sat on top . I'd guess it 'should' just be a case of disconnect everything , undo the bolts - tap the thread , insert insert - new gasket - tighten the bolts up & re-connect the bits & pieces !

Always a trade off between cost / hassle on these things, but if you have all the right tools I've always found it alot easier !
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Old 22 October 2008, 09:11   #8
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It's a good excuse to pop the head off and have a look at the state of your water galleries. After all, it's not got a tonne of valvegear in the way.I'd still helicoil it with it off-or if it's bad then use a timesert (google it) though I'd grease it liberally to stop salt water getting on it if you use a timesert.
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Old 22 October 2008, 09:11   #9
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Tell whoever does the job to be careful, cos a new head is 1,100+, and they'll need to replace the o rings!
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Old 22 October 2008, 09:19   #10
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Holy crap - 1,100 quid !- I think I'll be telling them to take it off & do it very carefuly !

Thanks Nos I'll get on to Google now !
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