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Chianti's Revenge

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So, I was always led to believe that on marine engines. You should always use NGK plugs as they are most suitable for the marine environment.
I pulled a plug this morning to take a look at it. It was an AC Delco plug. Also on the info tag on my engine. It displays the number for delco plugs.

I am curious to see what everyone else uses. and am wondering if, in an inboard using an automotive tune up vs marine would make a difference..
This is my first stern drive.
 
Your engine is a SBC.
I would stick w/ the AC Delco plugs, they do have a marine version....I think it's MR43*****.
 
Personally, I prefer NGK. I put them in everything I own that burns gasoline. Outdoor power equipment, autos and trucks, boats. NEVER had a problem with NGK. BTW, they have a customer service department that can give you technical information on the parts they sell. Hope this helps.
 
There is an issue with some plugs swapping from one manufacturer to another.

Re: NGK Plugs instead of champion

The problem that NGK plugs often cause is that resistor suppressed plugs (those with a 'R' in the number) are often listed, supplied and used as equivalents of the Champion 'Q' series plugs, which are inductively suppressed

Resistor plugs are not suitable for the OMC CDI ignition system.

There are now inductively suppressed NGK plugs equivalent to some of the Champion Q series. These have a 'Z' in the number.

For example NGK BZ7HS-10 is equivalent to the commonly used QL77JC4 but the often listed BR7HS-10 is not .

( the -10 in the NGK number indicates that it is supplied ready gapped at 1.0mm so will need re-gapping to 0.7 - 0.8mm ( 0.030")for OMC engines)

When suppressed plugs are not necessary unsuppressed plugs ( no R or Z in the NGK number) can be used

For example when the unsuppressed L77JC4 is acceptable NGK B7HS ( or B7HS-10) can be used.

Note however that suppressed plugs ( Champion 'Q' or NGK 'Z' series must be used in engines with VRO or OMS)

The NGK plugs which would be suitable for a 1992 40 HP Johnson are BPZ8HS-10 ( re-gapped to 0.030")

B= 14mm thread size,

P = projected insulator

Z = inductive suppression

8 = heat range ( Note lower numbers are hotter in NGK plugs)

H = ½" thread reach

S = standard centre electrode

-10 = pre-gapped at 1.0mm

Dont ask why other makes can use NGK resistor plugs ... I dont know the answer!
 
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