Morris Minor Owners Club

Hi

Yesterday when I turned the engine, I heard a hissing sound. Turned out that one spark plug must have been cross threaded. The plug is therefore not sealing.

Is there ny easy way to repair thie thread in the head without removing the head?

Thank you

i would see how far the damage has gone.
If you can still screw the spark plug in the correct thread then lucky escape I think.
If not, it will have to be a head off job I think, as when you come to retap it or whatever, then you cannot risk bits of metal falling into the cylinders - no matter how small!

It's pretty much impossible to 'cross thread' a spark plug.... How did this happen? When was the engine last run - was anyone messing about with the plugs? As above - take it out - throw it away - and try fitting a new plug in the hole. Spark plugs are only ever 'nipped up' - best to use a speed brace - nothing more.

Its not uncommon for spark plugs to strip threads in alloy heads (which of course isn't whats fitted to a minor).

You get helicoil kits to replace stripped threads

Hi Best to use your fingers to replace the plug,to feel if there is any undue resistance ,if non then screw as much as you can with finger pressure the tighten 1/4 to 3/8ths of a turn .DO NOT over tighten ,no need to .Fingers crossed

If the thread is stripped then its head off and as suggested earlier a Helicoil kit.
You effectively tap out to a predetermined larger size and insert a coil that has an inside dia the same as the od of the plug.
Armstrong used to make them.
It may just be the metal seal under the plug though.

Can you tell from the old plug if it has stripped the thread in the block?

A very flattened appearance I'd say.
To cross thread a spark plug would take a lot of force to get the plug in and should be ringing alarm bells very early on.
How about a picture?

Yep a pic would be good, we need to determine the condition of the thread in the head.