threaded spark plug thread

[davidsonclan5]

Need advice on repairing threaded spark plug thread, its not VMX but dirt track sidecar. (cbr900)
also can it be done with the motor still in.
Cheers Rob

[Curly3]

If the thread is stripped, it'll need to be helicoiled, probably have to remove the head.
If it's just cross threaded you may get away with running a tap back in, but put grease on the tap to catch any swarf and only cut a bit at a time before putting more clean grease on.

[matcho mick]

our shop did helicoils for years ,(local car mechanics useta send them round too  ),no need to strip motor,lots of patience,plenty grease,don't get too ambitious,couple thread cuts at a time,constantly clean tap & regrease,try & use helicoil tap with std size leadin,make sure valves are shut,(i did partially thread an ex valve once ),piston down a little,tricky bits retreiving the coils drive tang,should be magnetic,check 1st,bent spoke with dollop of grease picks it off the piston crown no wukkers,just take it slow,we always used "RECOIL" brand in red boxes,good luck,
ps think we discussed this before on forum

[JAP 454]

Exactly as Matchy says, but try this to recover the drive tang,

After fitting the helicoil, tie a loop , using a slip knot, in some dacron or braid fishing line , loop it over the tang, pull the loop tight on the tang , then , using a pin punch smaller than the plug hole , and leaving some slack in the line,give the tang a sharp tap to break it off, retrieve the tang with the line.

I used to have to do this heaps with two stroke outboards, lose the tang on a vertically stacked twin or 4 cyl motor and you were in trouble.
Foss

[curly001]

I use copper timecerts Specifically designed to replace stripped spark plug threads. They are a solid threaded insert that is locked inplace by the bottom being expanded once in place. Installed basically the same as helicoils.

[davidsonclan5]

Thanks for all the tips, will post how I get on.
Cheers Rob