Merc 888 spark plug question

M

matt 57

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I'm being confused looking for correct spark plugs for my motor.
It's Merc 888 302 block ser # 4654593.
According to service manual (p.8A-6) I should use AC-R42T for my serial number. However, they are not listed in cross reference on p.8A-13, 14.
PO used AC-MR43-T. I'd appreciate if anybody might be able to clarify this. :confused:
Thank you.
 
ErieRon

ErieRon

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Re: Merc 888 spark plug question

Mine calls for the same plug. As far as I know, that plug is now an RV12YC in a champion, and a AR6FS in NGK (if 18mm Thd.), and BR6FS In NGK (in 14mm Thd.).

I switched to NGK years ago and have had great service out of them.
 
M

matt 57

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Re: Merc 888 spark plug question

Thanks ErieRon. It's 5/8 hex 14 mm.
I just wonder why R42T are not listed in cross reference in the original service manual so I can't cross ref it to Merc part mumber.
 
ErieRon

ErieRon

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Re: Merc 888 spark plug question

I just think the alternative plug, and/or the Info. wasn't available at the time of printing. If I recall, I used the R42T for years after 1984.

Make sense?:rolleyes:
 
M

matt 57

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Re: Merc 888 spark plug question

What would make a perfect sense to me is to have OEM part number and then look for an alternative if I want to. At the time of printing they listed R42T but didn't cross ref it to OEM part number. I'll take your advise about NGK and make some more research on the net later.
Thanks again.
 
Bondo

Bondo

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Re: Merc 888 spark plug question

Thanks ErieRon. It's 5/8 hex 14 mm.
I just wonder why R42T are not listed in cross reference in the original service manual so I can't cross ref it to Merc part mumber.
Click to expand...

Ayuh,... The R42T is a Steel bodied automotive plug,+ the MR42T is the Marine rated plug with an Alloy body....
The "M"s are more rust resistent...
 
M

matt 57

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Re: Merc 888 spark plug question

Thanks Bond-o.
I read a few old posts and did some internet search so I've learned some.
So much more to learn about engine marine applications.
 
zbnutcase

zbnutcase

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Re: Merc 888 spark plug question

Change 'em on schedule and rust isn't an issue. 'nutcase
 
M

matt 57

Seaman Apprentice
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Messages
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Re: Merc 888 spark plug question

Rust might be a minor issue because of salt water environment.
But my main concern is heat range of plugs.
The engine is old, '77 with unknown history.
 
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