boat spark plug

[salmonee]

Do boats use a larger size spark plugs than cars?

I recalled testing a boat last summer w/ a 60 yamaha motor. My car plug socket didn't fit over the motor plug? Anyone know what size socket as I want to pick one up.

 

[The_Kid]

Re: boat spark plug

two sizes. 5/8 and 13/16

 

[Utahboatnut]

Re: boat spark plug

I think the two sizes are 5/8"(small plug) and 13/16" which is the standard size or at least what I call a standard size. If you do buy one get an actual spark plug socket for your ratchet. They have the rubber insert in them which holds the plug better makes it alot easier if your plugs arent dropping into the bilge. I like to use a 3/8" drive setup 1/2" is too much for plugs in my opinion, they don't need to be in that tight. Also a swivel or U-joint and a few different length extensions are always helpful especially for those rear plugs. Always start and thread in by hand so you KNOW you aren't cross threading. Have fun if you are doing plugs on a V-8 I/O

 

[salmonee]

Re: boat spark plug

Thanks for the info.

 

[Chris1956]

Re: boat spark plug

Actually, a lot of Chevys use 12MM spark plugs, and a lot of Fords use 18MM plugs. Most of the larger outboards, I have seen use 14MM plugs.

There is therefore no coorelation.

 

[reelfishin]

Re: boat spark plug

18mm plugs in Fords are rare these days, they dropped that size when the dropped the 300 I6 in the F150 back in 1996. There may be a few medium duty engines that used that size for a bit longer.

I think however he's talking about wrench size, not thread size.
About 80% of all boat motors will use a 13/16" plug socket, as was very common on most cars for a long time. Some boats, mainly I/O powered boats, use the smaller 5/8" wrench size. Both however usually are 14mm thread size.

There are a few odd outboards out there which use smaller plugs, I've seen a few 18mm, and a few 19mm/3/4" wrench sized plugs on outboards and I believe one with an even smaller wrench size but it was one of those tiny Asian built single cylinder air cooled outboards.

In general, though most outboards call for a far different plug application wise than most cars.