Loose spark plugs

[Robw]

I have just ran the correct size tap to clean up my spark plug threads, the plugs seem quite loose, although they tighten nicely onto the head. Is this to allow for thermal expansion and am I being over cautious.
Cheers Rob

[Big Fluff]

Oh dear. Fluted taps should never be used to clean threads on spark plug holes. Looks like you've taken a bit of material out there Rob
The best and safest way to clean spark plug threads is with a 'fluteless' tap. Now don't laugh, I'm not winding you up.
Fluteless taps literally have no cutaways, instead they cold form the aluminium to the shape of the thread of the tap. This gives a much stronger hold on whatever is being threaded into them (plugs in this case).
Only ever used on 'soft' metals, use a light lubricating oil and wind in the tap. If I were you I'd try an engineering company to get one for you. If you're lucky, this might even reform what threads you have left.

Good luck - Will

[Mark Stratton]

If all else fails look under "thread repair kits" on ebay. You will be able to pick up a kit for a 14mm plug for about £12 complete with reamer and tap!

[Robw]

Cheers guys, I will get it looked at.

Rob

[cra-z1]

Would it be a good idea to use this type of tap on all threaded holes on the cases instead of the fluted tap. I usually clean out all the holes before reassembly.

[Rich]

Not really, they will press all the crud into the threads and into the end of blind holes. Use a nice blunt plug (3rd cut) tap with a bit of grease in the flutes. The idea is to clean the crud (usually threadloc and sealant) out and not ran it to the end of the hole as that will cause the screw to bottom and you will then wonder why it has stripped so easily!