I Can't Screw a Spark Plug Into My Mower

Damaged Plug

• The easiest potential problem to fix is a damaged plug. Check your user manual to find out the proper size plug for your mower, or read the model number off of the side of the old plug. Lawn mower spark plugs can be purchased at most any lawn or home improvement store. If the new plug does not screw in properly, the problem is with the engine cylinder or threads.

Improperly Sized Plug

• Double check to make sure that you have a plug in the right size. Check the model number of your lawn mower with the user manual, as it is possible you have the incorrect user manual and have consequently purchased the incorrect spark plug size. These kinds of mistakes happen, and eliminating them first is a good way to avoid causing more damage to your mower, trying to screw in the wrong plug.

Dirty Cylinder

• The cylinder threads in the lawn mower's engine can become fouled with oil residue and carbon. Clogged threads will prevent a spark plug from screwing in to the cylinder, and may cause damage if you attempt to force the plug in. Clean the threads using carburetor cleaner or brake cleaner, available from any automotive supply store.

Stripped Threads

• Over tightening or cross-threading a spark plug in to its cylinder can lead to stripped threads. Once threads a stripped, no amount of tinkering will make your spark plug fit in to the port properly. You will need to purchase a spark plug thread repair kit, and re-thread the port before a new spark plug will fit properly.