Spark plug gap

[alk]

Still trying to get my 1999 7.4 mpi running right, not there yet. I figured I would change the plugs, even though mine look ok, they are six or seven years old, maybe more. Specs call for ngk brp6efs, gapped to .045 as per seloc manual. I don’t have a real merc manual unfortunately.

Problem is that the plugs come out of the box at .032, and ngk tells me that the most you should increase or decrease the gap is .008, or you’ll die a painful death. Well, not exactly, but they say the plug will be bent or twisted too much to be reliable. So trying to decide if I should stretch them to only .040, and ignore the seloc specs. Or go all the way to .045, and ignore ngk’s warning.

 

[Bill D.]

Do cross referenced other brands, champion, etc, have the same gap restriction?

 

[alk]

not sure how champion feels about opening their plugs up that wide. I am not sure if they even spec what size they come out of the box, or if it’s random.

.045 does seem like a large gap,

 

[getakey]

I'd find different plugs. Expanding the gap that much seems like a lot. That said, I have not gapped plugs in a long time

 

[Bill D.]

045 does seem like a large gap,

Yep, does sound wide. What were your current plugs gap when you pulled them?

 

[alk]

My current ones were .032 - looks like whoever put them in ( l don’t think it was me, I bought this motor used back in 2016) took them right out of the box and installed them. But just went out and looked on the sticker on top of the motor, to confirm the gap. and while they specify an ac delco plug, it is indeed .045. I might go with champion, or delco, even though i just spent thirty bucks on the Ngk.

 

[Bill D.]

. I might go with champion, or delco, even though i just spent thirty bucks on the Ngk.

FWIW— I have a number of full sets of new plugs hiding in junk drawers becuausI bought them and then thought better and went back to what was original and familiar.

 

[alk]

I called NGK support this morning - they told me that I should have opened them to .041, or at most .044 - and ran them. But since I already gapped them to .045 i would be best to just leave them be, and run as they are.

I’ll probably go seek out some ac delco’s. They were the OE plugs on this motor.

 

[Bruce Herrington]

I always chose the narrow gap because as they burn, the gap can widen. Did I say that right?

 

[alk]

Found some ac delcos today. they come out of the box at .042. I think I’ll just install them. When did spark plugs get so complicated; or did ngk just scare me off with some warning they put out to avoid warranty claims?

 

[Bill D.]

. I think I’ll just install them.

Good plan! Now that I tink about it everytime I have been concerned about my initial plug choice ngk was involved. My old FICHT 225 had major carbon build up issue’s and everybody was playing with plug choices and installations. I think I bought every brand of snake oil made including those with the “forked” tongue. Pretty sure ngk’s were in it when it blew up. Of course non of it was plug related, just plain bad design.