928: Stripped spark plug threads, previously helicoiled.

Need some help with a technical problem - ask away and let's see if we can all help.

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Burma-Shave
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928: Stripped spark plug threads, previously helicoiled.

Post by Burma-Shave »

Ok, I'm screwed.

Removing the plug it immediately felt wrong, that unmistakeable drag you get through the wrench of threads stripping.

So, the threads are stripped - so I could put in an insert...BUT there is also what I am assuming is a helicoil in there. This is a bodged repair by the PO turkey it seems. Super. If I try to ream it out, I will not only get aluminium chips but also fragments of steel helicoil going everywhere.

What would you do? My Porsche mechanic is 60 miles away.

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1990 964 C4, 1999 Boxster 2.5
'89 BMW E30 325i Touring. '83 Mercedes 280E. '84 Citroen 2CV. '16 BMW i3 REx. '03 BMW R1100S. '99 Yamaha R1. '79 BMW R100 scrambler.

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Ashley James
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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by Ashley James »

I think you’ll have to drop the engine, get the head off and give to a machine shop to make a bronze insert, assuming there’s enough metal to do that. Very sorry.
Burma-Shave
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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by Burma-Shave »

Thanks for the sympathy!

There is quite a bit of helicoil sticking out - I am wondering what the chances are of grabbing it and stripping it all out upwards. That would make the possibility of an insert repair working a little greater.

The heads can come off with the engine in, but is still going to be hours and hours, and then machine shop costs ££££. Dammit. I mean I honestly wouldn't have expected to need to throw money at a totally unknown 40 year old 928 from the middle of nowhere..quel surprise, as they say down there.
1990 964 C4, 1999 Boxster 2.5
'89 BMW E30 325i Touring. '83 Mercedes 280E. '84 Citroen 2CV. '16 BMW i3 REx. '03 BMW R1100S. '99 Yamaha R1. '79 BMW R100 scrambler.

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Burma-Shave
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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by Burma-Shave »

More research suggests that the helicoil can be removed, including use of something similar to this

http://www.engineering-supplies.com/pro ... gKvfPD_BwE

Then, tap and fit insert (with sealant adhesive) and I'm good. PROBABLY.
1990 964 C4, 1999 Boxster 2.5
'89 BMW E30 325i Touring. '83 Mercedes 280E. '84 Citroen 2CV. '16 BMW i3 REx. '03 BMW R1100S. '99 Yamaha R1. '79 BMW R100 scrambler.

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Mike911scrs
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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by Mike911scrs »

HI Johnny

pull the wire out and clean the threads up to fit one of these from the same place as your removal tool

then one of these http://www.engineering-supplies.com/sub ... d-repair-/

regards mike
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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by Burma-Shave »

Thanks Mike, I was pondering sending you an email but secretly hoped you would cast your eyes over this thread. Bet you're glad I don't live in Burton too. :)

Got a big job interview tomorrow but will see how I get on unpicking the wire after that. I am hoping it isn't stuck in there very well and has shifted, causing the problem in the first place.

The tool only goes up to M10 but it looks doable with a pick and some needlenose pliers.
1990 964 C4, 1999 Boxster 2.5
'89 BMW E30 325i Touring. '83 Mercedes 280E. '84 Citroen 2CV. '16 BMW i3 REx. '03 BMW R1100S. '99 Yamaha R1. '79 BMW R100 scrambler.

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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by Jimmy »

I am probably stating the obvious - even if you recover the helicoil, be sure to remove any remnants that may have fallen within the cylinder if not, the problem will be more than a stripped thread. Suggest feeding small a length of flexible tubing into the cylinder and attach to a vacuum cleaner. Good luck.
Burma-Shave
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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by Burma-Shave »

Yes indeed, have been getting various bits of advice about that on rennlist - including attaching a blower to the exhaust so I have a jet of air coming up from the cylinder! The aluminium is apparently not too bad, but bits of helicoil not good.

Have bought one of these too 8) :

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http://www.ebay.co.uk/itm/Video-Snake-T ... 2749.l2649
1990 964 C4, 1999 Boxster 2.5
'89 BMW E30 325i Touring. '83 Mercedes 280E. '84 Citroen 2CV. '16 BMW i3 REx. '03 BMW R1100S. '99 Yamaha R1. '79 BMW R100 scrambler.

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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by bjmullan »

Good luck Johnny hope you get it sorted.
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Burma-Shave
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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by Burma-Shave »

Thanks Brendan..btw, turns out that shocker problem in Yorkshire was the strut gland nut loose and rattling about in the shock body! So the insert was bouncing about and rattling in there, which is exactly what it felt like. Ho hum. Need to tighten it properly this time..big FO pipe wrench apparently. Thanks again for stopping for me :salute:

Anyway - Mike, would you use thread lock on the solid insert? Red or blue?
1990 964 C4, 1999 Boxster 2.5
'89 BMW E30 325i Touring. '83 Mercedes 280E. '84 Citroen 2CV. '16 BMW i3 REx. '03 BMW R1100S. '99 Yamaha R1. '79 BMW R100 scrambler.

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Re: 928: Stripped spark plug threads, previously helicoiled.

Post by fetuhoe »

If you still have good threads you could fit a Timesert -you would need to machine a slight recess for the locating shoulder on the timesert but otherwise they istall with the same STI thread as a Helicoil. The Timsert kit has tool to do this.

You should be able to flush out most of the debris and blow out the rest.
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