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Spark plug cross threaded

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Greg65:
Very frustrating as I have just got the bike to MOT status, however had a starting problem so have taken the plugs out. Now I was aware that No. 4 was tricky to replace as the initial damage had been done by a previous owner. Now I can't get the plug back in and more than a half to one turn, so it looks like I've lost the original thread. Are there any suggestions or is it going to be a head off and an insert fix. Suggestions from the wise please.

Thanks
Greg

haynes66:
head off, i'm afraid. any swarf could end up inside and cause more damage. better safe than sorry.

Saisei:
I have known folk to successfully repair tthreads with the head on. Make sure the piston is at TDC on the compression  stroke. Fill the void with carb cleaner before  chasing the thread with one of these. Finally blow out the fluid and any swarf with compressed air, repeat  the cleaning process as many times as necessary.
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Greg65:
Thanks for the replays so far. Just spent a frustrating 30 mins trying to find the original thread start by turning the spark plug backwards and noting the drop and then carefully exploring each "lead". All to no avail. I think the thread chaser may be a lost cause but will give it a go as it may avoid a lot of work, however I think an insert may be the solution. Any recommended suppliers?

Greg

mike the bike:
Try this;
Take the head off and wind a plug in from the wrong side.  It may realign the threads to allow a plug to go in normally.

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