posted 05-30-2005 10:47 PM ET (US)            

The narrower the gap, the faster the plug wear.

Nice square corners on the electrodes helps make a reliable
spark. Gross over simplification, and not technically
correct, but you can think of the sharp corner as
concentrating the electrons. And it's the sharp corners that
wear first.

All you need is a enough spark to start the fuel burning,
every single power stroke. Once the fuel starts, nothing
electical is going to have any influence on it.

posted 05-31-2005 07:43 AM ET (US)            

The spark kernel may perhaps transverse the gap quicker if it is smaller, but that is not timing.

posted 05-31-2005 08:16 PM ET (US)            

I would have to assume that if there were some special advantage in terms of improved performance to be obtained with gapless plugs, that internal combustion engines of all kinds would use them. Instead, they seem to only be found in certain two-stroke outboard motors.

OMC recommends gapless plugs for sustained high-speed operation. There is no reason given, but I would assume that perhaps their use would avoid problems with the plug gap eroding away which might occur in engines that were run perpetually at very high speeds.

posted 06-02-2005 08:51 PM ET (US)            

At first, my question was what happens when plugs begin to wear and .030 begins to change. New plugs start out at .030, but wear, and do I need to regap them? If so how often?

Now, after reading this, I am wondering what the effect of uneven wear is. I would suspect under normal conditions that all four plugs should wear equally, and uneven wear may be signs of problems. However, what if one plug is gapped slightly different, not noticeably, or one cylinder behaves differently - how will performance be effected?

Must I continually inspect the plugs to achieve optimum performance?

Great topic.

posted 06-02-2005 09:52 PM ET (US)            

The difficulty of removing, checking, and installing spark plugs varies with different engine brands and models. Outboard motors seem to need much more frequent attention to the spark plugs than modern automobile engines. For example, my 1995 car is running on the original spark plugs, but, before you think I have neglected it, there are only 56,000-miles on the car. With an outboard motor, I think 100 hours is a reasonable interval to check the plugs.

If your engine uses surface gap plugs, which are common in many Mercury engines and some Yamaha models, you do not have a gap to erode. You can still check the plug for wear or fouling.

posted 06-03-2005 07:23 AM ET (US)            

Because most CDI system's voltage output varies with the speed of the flywheel, as plug gap increases the motor may be harder to start. With more wear on the plugs, the starter would have to crank the motor over faster to generate enough voltage to "light the fire". A worn starter or marginal battery along with corroded terminals could keep the motor from firing up with worn plugs, yet be OK with brand new ones gapped correctly.

posted 06-03-2005 08:00 PM ET (US)            

The man who sold me the plugs crossed out the ".040" on my note paper and wrote in .030. He told me that he always gaps everything to .030 and that I should, too. Unless the old plugs are truly, horrendously corroded, they were set to .040.

posted 06-03-2005 08:50 PM ET (US)            

Jimh, thanks again. My plugs are easily reached and the plugs are cheap. I noticed they come factory gapped at .030, but I put a gap measurer on my keyring and check them often. For me, if the plugs foul, starts become harder and it wears my batter y and starter. So, I keep a fresh set and change them at the first sign of a problem, or clean them if that's all they need.

posted 06-03-2005 09:29 PM ET (US)            

Having a clean set of plugs in the tool box as CFCAJUN suggests is a good move.

posted 06-03-2005 10:59 PM ET (US)            

"Surface gap plugs," said Dave, "are only advantageous if the engine is going to consistently run above 4,000 RPM on a long term basis. They are the absolute coldest [temperature range] plugs you can put in an engine."

I bought six new QL77JC4 plugs from Dave. After I run the Fuel System Cleaner additive through the engine with this tank of gas, I'll be installing the new plugs. Gap set at 0.030, per the specifications.

I am with Chuck on this. The engine manufacturer probably tested plenty of plugs before picking one.

There does seem to be a certain panache associated with NGK plugs. I passed on a ten-pack new NGK inductor suppresor plugs when I sold my old boat. After we get the rest of the set-up dialed in on the new boat, we may experiment with a different plug. For now, the OEM recommended will be fine.

posted 06-04-2005 01:02 AM ET (US)            

Is your suggestion, Jim, that .030 would be more appropriate? This motor is the only one of the three that we currently run for which I have not yet obtained the OEM shop manual.

posted 06-04-2005 01:23 AM ET (US)            

See this prior post..

http://continuouswave.com/ubb/Forum3/HTML/008607.html

posted 06-04-2005 09:24 PM ET (US)            

ngk.com
championsparkplugs.com

posted 06-05-2005 09:42 AM ET (US)            

It is also much more common now than in the 1980's for a boat powered by an outboard motor to have a radio, and reducing RFI is very important for improving radio reception. I have noticed that my Evinrude outboard (with the plugs gapped at 0.030-inches) is remarkably quiet in terms of RFI. I can copy very weak signals on my VHF Marine Band radio without interference from the ignition sparking. On many other outboard-powered boats I have noticed much higher levels of spark plug generated RFI. Perhaps this is due to the much wider gap on the surface gap spark plugs they use. These seem particularly bad for RFI.

In the Champion nomenclature, the Q in the part number denotes an inductive radio frequency suppressor which has been designed to work specifically with marine capacitor discharge ignition systems. This combination seems to work very well for me.

In summary:

Surface Gap Plugs:

--coldest temperature range to suppress pre-ignition, so less heat to clear fouling deposits;
--less erosion of plug electrode at sustained high-speed operation;
--more electrode area, so less prone to fouling;
--higher cost (almost double);
--higher RFI potential.

Here is what Champion says about the surface gap spark plug:

"Champion surface gap V plugs have a .050-inch annular configuration with no ground electrode. Engineered for extremely cold application, the firing tip is nearly impervious to pre-ignition, however, fouling deposits can be problematic. These plugs have extremely limited use in racing and require a special high energy ignition system and a very rapid rise time(CD). Constructed with a nickel shell for faster heat dissipation and copper core or double copper (when noted) for further heat removal, all racing plugs are non resistor (unless specially noted)."

posted 07-27-2005 09:06 AM ET (US)            

Gap TOO WIDE: affects high speed performance.

posted 11-18-2005 12:40 PM ET (US)            

1) mechanic says NGKs that I use in Yamaha 40 come pre-gapped and went on to say that new plugs that have the cardboard cylinder around electrode are all pre-gapped.

2) I have gapped a lot of plugs but what is best gap tool? Wire, the disc thing, feeler gauge? I'll pay for the best.

posted 11-18-2005 12:40 PM ET (US)            

1) mechanic says NGKs that I use in Yamaha 40 come pre-gapped and went on to say that new plugs that have the cardboard cylinder around electrode are all pre-gapped.

2) I have gapped a lot of plugs but what is best gap tool? Wire, the disc thing, feeler gauge? I'll pay for the best.

posted 11-21-2005 12:25 PM ET (US)            

The gap is right.

The piece that comes from the side is parallel to the surface
of the tip. If it isn't, it will erode quickly where they
are the closest together, and then you will have a wide gap.

Best is to buy plugs that are pregapped correctly. This will
often be a -xx number on the end where xx is the gap (maybe
in metric).

If you actually have to regap them, there's a tool that works
like a pair of pliers. Turn a dial to position the right
feeler guage, put the plug on the gauge, squeeze gently,
done, and the side wire WILL be parallel to the tip.

posted 06-23-2007 10:36 PM ET (US)            

I'd run the part number AND BRAND the motor maker recommends.
That's what they had in the engine on the dyno. "Equivalents"
are only close.

posted 06-27-2007 07:48 PM ET (US)            

TommyBoy: what plugs were in there? How many hours on them?