Best Spark plugs for 1992 mercruiser 350 Mag?

[tmh]

OK, based on some feedback in another thread I plan to at least change out my spark plugs because I really don't know how old they are. (even though the engine is running OK, so i'll keep the old as spares maybe). What do folks recommend and where to get them (local or web)?

I did search this and found Bond-o's recommendation for someone else wit a 350 (I think) of

Ayuh,....

The Best plugs for it are AC Delco, MR43T......

But I want to make sure this applies to my engine also, as I'm not exactly sure of the differences. Also, is there a specific socket I need to change these (a rookie mechanic) AND do they come properly gapped or do i need to do this and if so what gap?

Thanks.

 

[John_S]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

Bondo is right with the plugs, as long as someone didn't add vortec heads to your engine. NGK is good equivelent: BR6FS. If you read up on projected tips, and want to try them: NGK BPR6FS. I ran them for a year before switching to vortec heads. They seemed to fowl/miss less on long no wake zones.

Buy a spark plug specific T type wrench that has a tappered socket. Less than $10 at auto discounters and will get by the tight exhaust manifold.

Always check and gap if neccessary.

 

[tmh]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

Bondo is right with the plugs, as long as someone didn't add vortec heads to your engine. NGK is good equivelent: BR6FS. If you read up on projected tips, and want to try them: NGK BPR6FS. I ran them for a year before switching to vortec heads. They seemed to fowl/miss less on long no wake zones.

Buy a spark plug specific T type wrench that has a tappered socket. Less than $10 at auto discounters and will get by the tight exhaust manifold.

Always check and gap if neccessary.

OK, the Vortec heads thing is a good point. I still am not sure if they were added or not (totally forgot to check the heads id # as was recommended previously). The engine DOES have the 8-bolt manifold pattern I've seen discussed here as a vortec type but I am not sure the heads were replaced 9my engine vintige is pre-vortec from what I'm told). IF it's vortec heads, then different plugs?

 

[John_S]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

"IF it's vortec heads, then different plugs?"

Yes, NGK BPR6EFS or AC equivelent.

 

[Bondo]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

The engine DOES have the 8-bolt manifold pattern I've seen discussed here as a vortec type but I am not sure the heads were replaced 9my engine vintige is pre-vortec from what I'm told).

Ayuh,...

If it's in fact the 8 bolt intake manifold,... They Have to be Vortec Heads....
That's the only way that configuration can be done.....
And,...
The AC Delco # is MR43TS....

 

[tmh]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

OK, thanks for the info Bondo. I had a long discussion on this in my thread when I repowered the boat but I totally forgot to look closely to make sure. I do remember the 8-bolt intake manifold though, 99% for sure, I just seemed to recall someone telling me to check the ID # on the heads to make sure they are Vortec,

Based on how much power and speed I gained over my 305 2bbl (200 hp) I would think they do have more power than the 260 hp cover says so Vortec makes sense.

If I get the plugs recommended for Vortec and somehow I screwed up and it's not, is that a big issue or just not optimum? Also, do they come with the proper gap or do I have to do something other than screw out the old and in the new? I will get the specific tool from Harbour Freight or whereever.

 

[Bondo]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

Also, do they come with the proper gap or do I have to do something other than screw out the old and in the new?

Ayuh,....

It takes a 5/8" plug socket.....
And,...
While they are usually kinda Close on the Gap,...
With shaking,+ whatnot during shipping,... They should Always be checked,+ set to gap....

I also dab the threads with Anti-sieze when installing they to about 35ft.lbs.(Calibrated Elbow style)...

When you pull the plug Wires off the plugs,....
Twist'em before you Pull,... They tend to Stick,+ sometimes the wire can be pulled Apart,...
Because of this,... I usually dab the wire sockets with a silicone based electrical Grease....

Good Luck,... I know Wrenches are Foreign to you.....

I will get the specific tool from Harbour Freight or whereever.

Btw,.....
Sears, Craftsman's are a Good Quality Tool, at a Fair Price......
My toolboxes have Way More Craftsman tools in them than Snap-On's.....

 

[tmh]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

Thanks for the details, Bondo. You are correct that wrenches and me haven't been lifle long friends! However, I have a hard time paying the marina mechanic to do the fairly simple things i ought to be able to do, so i try. Changing the plugs as PM isn't too bad when it's DIY, at the Marina they'd charge $45+ (1/2 hr) to do it and mark up each plug from what I can get them for. so I'm out $90 or so. I don't begrudge them doing this, btw, it's a fair business and one pays for the service. I'd just rather learn how to do some things as i go.

LAST question on this......what IS the proper gap for these AC Delco # MR43TS plugs in my engine?

Thanks again for all the help.

 

[Bondo]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

LAST question on this......what IS the proper gap for these AC Delco # MR43TS plugs in my engine?

Ayuh,.... No it Ain't..........

Ok,... What is the Igntion System on your replacement motor,..??
The Same 1 as from the Original motor,..??
For that matter,...
Are the Dressings on this motor, All from the Old motor,..??
If so,...
This manual will pretty much directly apply to your motor,....

 

[Mkos1980]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

Those are not the correct plug. You want the MR43LTS. They dont make a MR43TS. Just MR43LTS and the Pre Vortec MR43T

 

[Bondo]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

Oops,... you're Right,... I forgot the "L"....

 

[tmh]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

Hey guys, anyone know a web site where I can cross-reference Champion plugs? I tried to check the plugs on the boat today (had my kids look as no way i can see small writing on a hidden plug!) and i currently have Champion plugs - couldn't get the specific code off them but I will next week when i take them out. I'd like to know what i have and compare it to the AC Delco #'s.

Thanks.

 

[John_S]

Re: Best Spark plugs for 1992 mercruiser 350 Mag?

I am sure a google search will find some cross-ref charts.

Merc indicates cross to Champion is RV15YC4 in non-vortecs, and RS12YC in vortecs.