#3 Spark Plug, MR-1

[arew~SX230]

So I changed my spark plugs today, this is the start of my third season with the boat, a 2007 that had less than 30 hours on it when I bought it, and probably has slightly less than 130 now. All of the plugs came out easy enough, and looked great from an insulator and contact/gap point of view. However the number 3 plug on both engines had rust on the non threaded bit at the cylinder end.
Has anyone definitively figured out what causes this to occur?

Thanks,
Andy

 

[Murf'n'surf]

That's a common issue of those engines. Many of these sparks have been snapped off so be happy yours came out.

The issue is that there is an exhaust port that is open near the #3 cylinder and allows moisture to rise into the cylinder.

 

[arew~SX230]

Is it just a proximity thing, or is it the propensity off the MR-1s to come to rest with the #3 exhaust valve open?

Am I over thinking it, and should just change the plugs every year and consider myself lucky they all came out intact after potentially being in there for 10 years

 

[Stuntmanmike]

I would definatly change them every year, and put Anti-sieze on the threads. It gives you the ability to see what the burning condition is in each cylinder.

 

[itsdgm]

Is it just a proximity thing, or is it the propensity off the MR-1s to come to rest with the #3 exhaust valve open?

Am I over thinking it, and should just change the plugs every year and consider myself lucky they all came out intact after potentially being in there for 10 years

Yeah, you're very lucky if you had them in for 10 years. I agree with @Stuntmanmike, change them every season and use anti seize.

 

[Murf'n'surf]

Is it just a proximity thing, or is it the propensity off the MR-1s to come to rest with the #3 exhaust valve open?

Am I over thinking it, and should just change the plugs every year and consider myself lucky they all came out intact after potentially being in there for 10 years

I remember that @Cobra Jet Steering LLC had a good explaination ...How 'bout it Jeff...got yer ears on?