Stripped Spark Plug Threads

[stereomike]

I had an older boat I just bought with a 150HP BlackMax Merc (I think 1979?) into the shop, mechanic did a compression test and says all cylinders are fine, everything running good.

The next day I had it in the water and it sounded like a backfire, then later when I was idling there was a small explosion / flame came out from under the cowling.

I took the cowling off to see one of the spark plugs hanging loose. The spark plug threads appear fine, but the threads in the cylinder have been worn down, they almost feel smooth.

Could the mechanic have done anything to cause this to happen? Or was it just bad luck / timing?

 

[Chris1956]

Re: Stripped Spark Plug Threads

The mechanic could have done it, or it could have been done over the years. Pull the head and put in a helicoil or solid insert. It is not a big job on a 2 cycle motor.

 

[JB]

Re: Stripped Spark Plug Threads

Helicoils are the most popular fix for stripped threads. They work but they are steel and change the heat flow from the plug to the alloy head.

Though I know of no failures due to this I still recommend the TimeSert, which is a threaded alloy sleeve. It will have nearly the same heat transfer characteristics as the head.

 

[stereomike]

Re: Stripped Spark Plug Threads

Thanks for the replies... Does the TimeSert take longer to do than the Helicoil? I will be having a shop fix it.

 

[gss036]

Re: Stripped Spark Plug Threads

It might be a small amount more on the time end, but the results will be worth it in the long run. Maybe go back to the mechanic and talk with him/them and just maybe they might share the blame and cut the cost a little bit.