Re: Cross threaded Spark plug threads
 

Michael Pardee wrote:
> "jim beam" <nospam@example.net> wrote in message
> news:l_WdnSuLKOokTB3Z4p2dnA@speakeasy.net...
>
>>Michael Pardee wrote:
>>
>>>A thread chaser is not likely to be useful on the aluminum head; the
>>>remaining metal won't support the spark plug well enough. Got the tee
>>>shirt on that, just with worn threads!
>>
>>you got unlucky. if done right, the chaser works perfectly - it depends
>>on whether it was started where the original threads started or whether it
>>cuts a whole new thread - /then/ you don't have much supporting metal and
>>the helicoil is essential. if the head's already off, you can chase from
>>the piston side as the crossing hardly ever gets all the way to the bottom
>>of the hole. use a plug from the piston side first too to force as much
>>of the old thread back into shape as well.
>>
>
> Not so much unlucky as I made a poor choice - it was in a Lotus with a
> Renault engine,

those are quite a good little engine!

> and the threads were not even crossthreaded, just worn out.
> I wasn't even accelerating hard when I heard a POP and a sound like a
> lawnmower... the plug had probably been in for months at that point.
>
> Maybe a Honda head is more robust and not as sloppy.
>
> Mike
>
>
i've seen this on a honda head - plug had apparently been loose forever.
eventually the plug just pulled/wore out the last few threads, and
then, as you say, loud chugging noises. as long as there's enough
thread to hold the plug, it should be ok. the seal comes from the
gasket/washer on the plug and bolts only need 3 threads to hold under
most circumstances.