Hello All!
I am a lawn mower newbie. I have MTD Yardmachine riding mower that I have been trying to change the spark plug on. I checked the manual to see what type of plug I needed. Bought the plug but couldn't get the plug to thread. Bought two new other plugs different manufacturers--they wouldn't thread either. Any help appreciated.

Thank-you

Are you scewing the plug in clockwise or counterclockwise? If counter to the way a clock's hands turn, that's the wrong way. Screw it in clockwise. I can't imagine why it's not screwing in ? Be careful you are not stripping the threads on the engine. That leads to a more serious problem. If you have trouble, have a neighbor or someone else try it.

It sounds like you have stripped the threads on the engine. The only other explanition is that you have the wrong plug. Examine the engine to make sure it is the factory engine. If the engine was replace then it could require a different plug than what the manual calls for. Please rate this answer

It does take a little practice and know how to install a spark plug especially if it is recessed in a somewhat hard to reach spot. They have to be "square" with the threaded hole or the threads won't engage properly. If the old plug came out fairly easily and you haven't used a wrench to force the new plug in at an improper angle you probably haven't damaged anything.

Cross threading a plug or any bolt means engaged the threads in a slightly off and improper angle and if you really tighten the part with a large wrench, forcing the part to turn you can damage the threads. Nearly all bolts tighten by turning them clockwise. Some applications where rotational direction might loosen a right hand thread, then left hand threads that tighten counterclockwise are used. An oddidity is that back in the 60's Chrysler used left hand threaded wheel studs on the drivers side of the car for some reason.