OMC V4 CD iginition spark plugs

[wiscoboater]

I received the service manual today for my 74 starflight 115. The manual calls for surface gap type plugs to be used. This motor when I got it, and every other V4 engine I have had was using standard electrode type plugs. Was there an issue with the surface gaps that most do not use them? Or should I follow the manual. Fouling problems maybe?

[chinewalker]

In my experience, the surface gaps don’t idle as well. I prefer the L77JC4 plugs. If electrical interference is an issue, you can use the QL77JC4.

[lotec]

For what it’s worth, in the past 35 years I’ve owned a number of the OMC cross-flow V-4s: ’78 85hp, ’84 140hp and currently a 1990 115hp. (probably over 3,000 hours of sea-time running them!) The ’78 and ’84 both called for the surface-gap plugs and ran terribly with them, the plugs would foul and had a very short life-span. I believe the manual called for them specifically to help prevent fouling and having hot-spots on the pistons.

The NGK gapped equivalent has been my plug of choice, I can’t ever remember having a failure or fouled plug since switching to them. (Nor have I melted a piston.) Oddly, I believe the 1990 V-4 manual does specify a gapped plug – so maybe OMC learned something after 21 years of making that motor!

I’m sure Don, Dan or Pappy can give you the complete answer here.

[frankr]

For what it’s worth, the 1970-71 three cylinder loopers about drove me crazy, trying to make them run right. They were supposed to run surface gaps, so they should run with surface gaps, right? Well life got much better when I gave up and started installing l77JC4 plugs. The darn motors would actually run!! Interestingly enough, their predecessors, the 55hp loopers ran fine on surface gaps.

Heh, heh, I even tried a set of surface gaps in my truck. Barely made it out of the driveway.

[beerman57]

Sounds like both should be tried. My friend with an 80’s to early 90’s OMC V4 swears by NGK surface gap. Years ago, like 20, OMC V6 if I remember right, took out the NGK’s and put in Champion QL or L77JC4’s, whichever it called for, and the ignition problem went right away.

[billw]

When I was doing a lot of that work, we always chose L77JC4s, with very good results.

Long live American manufacturing!

[wiscoboater]

Thank you all for the insight. I thought it was strange I had never seen anyone running those surface gap plugs. Glad I asked before I bought a set.

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