MR43T - the mercruiser 120 and the best plug for it

[fizzle]

howdy,
i believe that the valve cover for my mercruiser 120 says to use the mr43t spark plug.
and thats what is fine with me - but i just got hassled into buying autolite 26 spark plugs for the boat.
they are a little bit longer - and the term is that they've got more electrode in "the wind" was why i should get them.
they guy that sold me on them - reportedly was a marine mechanic and worked on thousands of these 120's and says that the heat range on these autolite 26's are better.
but my fear is that the plug - because its a quarter inch longer - will arch on the pistons and slowly burn a hole through it.
is that a reasonable concern?
and does anyone else use the autolite 26 in there mercruiser 120?
thanks for your time

 

[Silly Seville]

Re: MR43T - the mercruiser 120 and the best plug for it

Hi Fizzle...Welcome to iboats! I have the same motor in my bowrider and did the very same thing you are suggesting. Big mistake! I tried the Autolites, Bosch and Champions just trying to experiment with different electrode designs, heat ranges and gap settings to "improve" performance. Ha! What a joke. The Mercruiser recommended MR43T marine plugs worked the best for me, and they are still less expensive than the other so called high performance plugs! If you want to play with your ignition system...dump the points, condenser and the old coil for a Pertronix set up. I love mine!

 

[Don S]

Re: MR43T - the mercruiser 120 and the best plug for it

and does anyone else use the autolite 26 in there mercruiser 120?

Probably not many use a Ford spark plug in a GM engine. IF you don't want to use the AC plug, use the NGK BR6FS plug.

Does your 120 have a year or serial number?

 

[fizzle]

Re: MR43T - the mercruiser 120 and the best plug for it

i'm sure my engine has a serial number but i don't know it - its in a 1976 galaxy so i'm sure its the same vintage. I've got the petronix system and also love it - as i use it in my dual point distributor in my tr 3. and its never let me down.
but my big fear is arching on the pistons - if thats impossible - then i really don't care what spark plug i've got - though i generally only have faith in NGK - but thats due to years of dirtbikes and suzuki outboards.
so should i chuck the autolite 26's and just pick up a set of mr43t's?
thank you for your help

 

[Silly Seville]

Re: MR43T - the mercruiser 120 and the best plug for it

Probably not many use a Ford spark plug in a GM engine

Don is a GURU...I am just a novice. Mercury Marine wants you to use a GM plug for a reason. I see no value in messing with what has worked successfully for over 30 years!

 

[fizzle]

Re: MR43T - the mercruiser 120 and the best plug for it

turns out that mercury marine wants you to use the autolite 26 in the 2.5.
its on one of the TSB's from the late 70's - i guess they were trying to reduce the smog with a smaller plug that was tucked way into the head (the mr43t) - but it caused way to many problems in the marine engines because it would foul so easily.
the TSB says to use Autolite 26.
so i gues there is quite a bit of use for a ford spark plug in a GM engine.
did ford own mercury back then?
they own Jaguar and Land Rover now - so i'd never buy one of those either.
but autolite 26.
check the old TSB's
thanks for your help
stay safe

 

[Don S]

Re: MR43T - the mercruiser 120 and the best plug for it

turns out that mercury marine wants you to use the autolite 26 in the 2.5.
its on one of the TSB's from the late 70's -

What's the service bulletin number? I have all of the bulletins from 1973 to 2007 and I sure can't find anything from 73 through 80 on that spark plug change.

 

[daydreamer1252]

Re: MR43T - the mercruiser 120 and the best plug for it

fizzle.....have you read the TSB yourself or only had it reported to you by someone else?? Don is pretty well up on TSBs....I wonder if there may have been confusion....or if you had read it yourself....30 years is a LONG time to remember such a small piece of info....Oh and Mercury (automobiles) have always been a Ford product....

 

[fizzle]

Re: MR43T - the mercruiser 120 and the best plug for it

yeah i read it - thats where i got the smog crap from.
you better get to checking through those TSB's - to confirm this.
i had already hassled this old guy about it twice.
i'm not going back to waste a couple more hours chatting about the 2.5liter.
but i don't know the number of the TSB - i should have realized that this would get petty - but i didn't write anything down - i just wanted to make sure that i did break anything.
so yeah.
when you find that TSB - post it.
then there won't be any more questions about stupid spark plugs.
and people sticking to crazy theories about nothing.
good luck
and of course thank you for your time and efforts in helping me resolve my issues.
stay safe

 

[Don S]

Re: MR43T - the mercruiser 120 and the best plug for it

Like I said, I did look at them, twice, and their isn't one. All I need is the number of that Mercruiser service bulletin, and I will post it.

turns out that mercury marine wants you to use the autolite 26 in the 2.5.
its on one of the TSB's from the late 70's - i guess they were trying to reduce the smog with a smaller plug that was tucked way into the head (the mr43t) - but it caused way to many problems in the marine engines because it would foul so easily.
the TSB says to use Autolite 26.

Smog was not an issue Mercruiser was dealing with in the late 70's.

I really don't care if you want to use Autolite plugs in your engine, but if you are going to start quoting service bulletins, you need to be able to back up what you say.