14.5 HP Briggs and Stratton Engine Spark plug won't thread in

[sstar 1]

Hi I was replacing my Toro 1438HXL Wheel horse spark plug and I took the old spark plug out and let the engine sitting in the garage for 3 days before I find time to do the replacement, Finally when I had time last night and try with the new one its not threading in. Also the old one doesn't thread in. So I thought that cold (49 degrees here in No. VA) had made the aluminum head shrunk and waited give it a try on morning, and still its not thread in this morning. Is this a common problem, should I heat the engine head with a propane torch or so to get it to above 60 degrees?  I am sure the thread has not stripped off while removing the plug, I can see clearly no any visible mar or stripping. Advise please.

 

 

[Sarge 3,464]

Hold the two plugs together , threads against one another to compare thread pitch . It should be a common 14x1.25mm thread size , they can be a pain to get threaded back in - it has to be perfectly straight .

Sarge

[Achto 28,802]

Weather temp should have little to no effect on changing the spark plug. I have changed plugs on engines with aluminum heads in temps well below 0 degrees fahrenheit.

Edited December 29, 2016 by achto

[sstar 1]

probably I had damaged the thread when I measure the dead center while adjusting the head valve gap.

2 hours ago, Sarge said:

Hold the two plugs together , threads against one another to compare thread pitch . It should be a common 14x1.25mm thread size , they can be a pain to get threaded back in - it has to be perfectly straight .

Sarge

They do match, and I did had this new plug installed for some time before I took it off to adjust the head valve gap and probably while doing that I might have damaged the thread. 

[953 nut 57,998]

          Perhaps you can find a friendly local mechanic that would loan you a spark plug tap so you can chase the threads.

[lynnmor 7,577]

You will need to re-tap the threads.  It is a delicate operation and the threads can be ruined if the tap is not started on lead.  Taps for the purpose are available at auto parts stores.

 

There is no need to poke around to find top center for adjusting valves.  Simply turn the engine till the valve is fully open, then give it one full turn.  Works for any four stroke engine, but of course some will insist that I am wrong.