Force 150 spark plug question

[HotTommy]

I am fixing a 1993 Force 150 outboard that was disassembled when I bought it. The old spark plugs were missing. One parts source listed two different plugs for my particular engine. One was Champion L-76V and the other was QL-76V. How can I determine the correct plugs for my engine?

 

[Frank Acampora]

Re: Force 150 spark plug question

L 76 V is the Mercury surface gap electrode plug. I don't remember but I think the QL is a resistor plug. both have the same heat range so both should be correct. I would use the QL only if you have ignition interference with electronics on board.

 

[Jiggz]

Re: Force 150 spark plug question

In addition to Franks input, the NGK substitute for Champion's L76V is the BUHW. For some reasons others prefer the NGK's over Champions, me included.

 

[MikDee]

Re: Force 150 spark plug question

IMO, I don't like surface gap plugs. I like to run standard resistor plugs, especially in the Force engines. The resistor plugs seem to absorb any, & all, leaky spark energy directly to the firing tip, especially if you have metal spark core plug wires which can also cause radio interference, and arcing through the wire insulation, and grounded metal wherever it may happen to touch. That's why you would get a good jolt if you happen to touch the wire when the engine is running. Surface gap plugs put too much stress on the electrical system. From experience with my old 1989 Force 125hp motor, which was before surface gap plugs were made, I believe?

 

[Jiggz]

Re: Force 150 spark plug question

"Surface gap plugs put too much stress on the electrical system."

Besides your post is there any other reference for the above? Or is this more like a IMHO? If it is a IMHO, what physical evidence support such claim, i.e. on the electrical components. Does it really burnt out more plugs than usual? Burnt more CDM or coils than usual? Or maybe burnt more wiring than usual? Stator, Trigger or even magnets getting burnt than usual? Just curious on how you came out with such a claim.

 

[MikDee]

Re: Force 150 spark plug question

The gap on a surface drive plug is about .060", whereas the gap on standard plugs usually runs .030" - .045". More stress is put on the whole ignition system because of this, leaving a weaker spark in the combustion chamber at TDC. It just makes sense IMHO. This is what I found, from my "seat of the pant's" experience with these. I'm not an electrical engineer, take this as you want

 

[MickLovin]

Re: Force 150 spark plug question

I go with the plug type the manufacturer advises me to use, but in this case I am using the NGK surface not the champion. The surface plug is known for a better spark output as advised in my manual. In regards to the statement about the gap, isn't it also true to say that the area for the spark to jump to is much bigger than the prong on a non surface gap? If the electrical systems of the day couldn't handle these type they wouldn't have specified them.

 

[jerryjerry05]

Re: Force 150 spark plug question

The 93/150 came in 6 different models.
Any idea what your model# is?
The early ones came with UL-18V the later ones came with L-76V or QL-76-V
IMHO ??? The surface gap plugs have always been what I've needed.(am I smarter than the engineers)
Champion or NGK I have a hard time finding Champion or I'd buy them.
I've found NO difference in either.
The idea that the SGP are tougher on the system is BS.(IMHO)
IF??? it was harder on the system there'd be no SGP.

 

[Frank Acampora]

Re: Force 150 spark plug question

MikDee: You have been lucky. Bent electrode plugs are a hotter heat range than surface gap plugs. They have been known to melt holes in the piston crowns and really should not be used in Chrysler/Force engines. Surface gap plugs have been around since AT LEAST the 1960s and were used on the Chrysler Motorola electronic ignitions.

Getting back to heat range: Simplified Explanation---Because the porcelain insulator in a surface gap plug is completely enclosed by the steel shell, the cooling path from center electrode to head is much shorter than with bent electrode plugs. Additionally, so much less of the insulator is exposed to combustion heat that the insulator simply does not get as hot.

These ignition systems were designed to produce the sort of voltage necessary to fire a surface gap plug ( I believe around 60,000 volts) so there is no "added stress" to the ignition system. True though: The surface gap plugs DO tend to foul much easier. But, just because, for example, OMC uses a QL77 bent electrode plug, it does not mean that that is the correct plug for all outboards. Heat range of plugs takes MANY factors into account including combustion chamber design, gas flow through the cylinder, combustion temperatures, flame front travel velocity, and cylinder cooling. Then there is the simple trial and error method too. We use this because we don't have the tools and knowledge the engineers do and we waste a lot of engines.

This debate of bent electrode versus surface gap comes up every couple of months in some form or another and just like a-holes, oil types, and ethanol gasoline, everyone has an opinion. Suffice to say that the design engineers have a reason for specifying a particular (in this case) Spark plug.

 

[HotTommy]

Re: Force 150 spark plug question

Thanks to all. As I don't expect a RFI problem, I'll go with the L-76V or its NGK equivalent.

 

[MikDee]

Re: Force 150 spark plug question

I go with the plug type the manufacturer advises me to use, but in this case I am using the NGK surface not the champion. The surface plug is known for a better spark output as advised in my manual. In regards to the statement about the gap, isn't it also true to say that the area for the spark to jump to is much bigger than the prong on a non surface gap? If the electrical systems of the day couldn't handle these type they wouldn't have specified them.

Because a surface gap plug has a ring for the spark to jump to, it doesn't mean it has a fire-ring that it will jump to. Chances are that it will only fire in one spot of that ring (the point of least resistance). That's like the same principle of a multi-tip spark plug, it will only jump to the one with least resistance at that time. Your service manual is not the bible, and sometimes does not pertain to real world operating conditions. I see no advantage of the SGP firing from the edge of the center electrode to the edge of the ring, over a single electrode plug having less area to get fouled, that would tend to stay cleaner, longer from combustion. IMO, a single concentrated spark point, is better then a variable one randomly somewhere on a ring?

Besides my old 89' Force 125hp, I had an old 69' Evinrude 115hp the specified either std. plugs, or SGP, and I found both ran better on std. plugs!

 

[Jiggz]

Re: Force 150 spark plug question

The gap on a surface drive plug is about .060", whereas the gap on standard plugs usually runs .030" - .045". More stress is put on the whole ignition system because of this, leaving a weaker spark in the combustion chamber at TDC. It just makes sense IMHO. This is what I found, from my "seat of the pant's" experience with these. I'm not an electrical engineer, take this as you want

Just so we are referring to facts rather than conjectures, the gap for the BUHW if 0.051" while the L76V is 0.050". And since the above was your IMHO, no further discussion required but do thank you for sharing your personal opinion.

 

[MickLovin]

Re: Force 150 spark plug question

Well sorry to say MikDee, I am not a marine engineer and I can only go by what they have specified, so unless you are a marine engineer ( I am an electrician though and understand electrical principles), I will be staying with the surface plug. In regards to the service manual not being the bible, I don't think the engineers designed motors to not run in the "real world" also "IMHO" is just that your opinion. The only stress on the electrical system would be on the coil delivering the HV to the spark plug, the coil is only a transformer converting 12v into 500v+ and actually at that voltage little current is used, for the difference in resistance of the spark plugs we are talking about at that high voltage, wouldn't create much difference in current drawn from the coil. The voltages will remain the same only the current drawn from the coil will vary, and it wouldn't vary much. A better spark results in more fuel burnt and cleaner running, the surface plug had a better spark as you noted with more stress on the electrical and as stated in my 3 different manuals. If you believe yours a fowling more, maybe it is your compression, not the plug itself. May I ask have you had an electrical failure from these plugs?

 

[Frank Acampora]

Re: Force 150 spark plug question

OK Guys---Let's not get pissy!

I told you that like a-holes everybody has an opinion on this subject. Do we want to start another ethanol-oil brand-lower unit lube- argument?

If MikDee wants to use bent electrode plugs in his engine and it makes him feel better, LET HIM! It is his engine, he can do as he wishes, and you are never going to change his mind.

Quotes: "Don't confuse me with the facts." "God grant me to power to change things I can, accept things I can't change, and the wisdom to know the difference."

 

[MikDee]

Re: Force 150 spark plug question

the gap for the BUHW if 0.051" while the L76V is 0.050"

Thanks for that, it's all ancient history since I've dealt with these plugs. Don't you think it takes more power for the spark to jump a .051" gap, then a std. plug's .035" gap? Any excess power could be used to better burn the combustible mixture. The only advantage I noticed with SGP's was a better idle, or at trolling speeds,,, maybe because they run cooler at that setting?

To MickLovin, I never said a SGP had a better spark then a conventional plug. I never had a fouling issue with either plugs, just that I felt the SGP's didn't provide the maximum engine power.

 

[MikDee]

Re: Force 150 spark plug question

It's all Cool Frank,,, I know you're the Force Guru! Rightfully So!
We'll all use what we're comfortable with. I'm flexible, I'd probably try the SGP's again, to compare if the need arises.

Many years ago I had a 62' Impala 4spd 327/300hp, and put Champion (non resistor) J8's in it, and copper based Packard 440 wires, because that's what I heard the local track guys were using,,, Well, radio reception was "Static Only",,,lol, and on a damp night under the hood it was a veritable light show of arcing everywhere! I didn't know what was wrong???
How much current do you think was getting to the plugs at that time?

Quite awhile later, on a whim, I decided to try "resistor plugs" RJ8 Champions, OMG, that fixed everything!

 

[Frank Acampora]

Re: Force 150 spark plug question

MickDee: You are laboring under a misconception about what a spark plug spark does. It does nothing more than ignite the fuel/air mixture. It doesn't matter whether the spark is 1000 degrees or 10,000 degrees, red, yellow, or blue-white. As long as it is hot enough to do the initial ignition, it is good enough. Once the mixture has been ignited it burns away from the initial ignition point so there is no further use for the spark-- it is in an already burned mixture and useless. That is why--except in racing applications- a multiple spark discharge is just a waste of money.

Excess power needed to jump a smaller gap will not burn the mix better. It is like you trying to jump a small puddle. If you apply just enough force to clear the puddle, your legs have done the job. If you jump harder and clear the puddle by five feet, your legs will have also done the job but there will be no real advantage--your object was not to get wet. Excess power will however insure a solid spark under compression pressure so there is an advantage to having something more than the bare minimum needed for ignition.

And of course, it takes a higher voltage to jump a larger gap. (That is why high tension wires are spaced far apart and the insulators are ribbed. Air is an excellent insulator) Electronic ignitions designed for surface gap plugs deliver this higher voltage. Specifically to Force engines with Prestolite: The ignition is very much like a magneto. At low flywheel speeds voltage is marginal for ignition. That is why with Prestolite ignition, fouled plugs may or will give hard starting and stalling at idle but will run fine at high speed. Thus for any Force engine exhibiting hard starting or stalling problems, the first step is to change the plugs.

 

[Jiggz]

Re: Force 150 spark plug question

"Don't you think it takes more power for the spark to jump a .051" gap, then a std. plug's .035" gap? "

With all due respect, I will have to disagree with the above. There is a reason why there are wider gapped plugs and why some have narrower gaps. This is all part of the ignition system design. A wider gapped plug provides a larger arc or spark but also requires a higher working coil voltage to produce such spark or arc. On the otherhand, a narrower gapped plug provides a smaller arc while at the same time requires a lower working coil voltage. Usually pull start engines are designed with lower working coil voltage due to the fact it can easily be generated by the built in generator (alternator) without much effort, hence uses narrow gapped plugs. The opposite is true for larger engines.

Your claim that narrow gap plugs requires less power or wider gapped plug requires more power is immaterial because it is all part of the engine's ignition system design. Otherwise, there is no logical reason to manufacture wider gapped plugs and all plugs should be designed narrow gapped just like the BP7HS which only has 0.7mm or 0.028" gap. Remember it is all about efficient combustion which can either be achieved with a smaller arc (spark) or a larger arc (spark) that the ignition system design will be based on to support.

Have you tried adjusting your plug gaps to really small gap like maybe 0.0001" and see if that makes your ignition system more effective?

 

[MickLovin]

Re: Force 150 spark plug question

All coils are set to have certain output (H.V) their primary will be of cause 12 volt in auto and marine unless it is a 24 volt system, it will depend on the secondary coil to what voltage output it is. The voltage output will never change in a coil unless it is faulty or unless you input a different voltage on the primary.
So in theory if you do put std plugs in place of a surface gap plug, you would make the coils working current lower, not it's voltage. If the coil is designed to work with SGP you could possibly reduce the amount the coil is working (Power = Current * Voltage)with pronged plugs.
Also it was I who said the SGP had a better spark as noted in my manual. But also I understand everyone's personal preference in how they run their motors and I am not suggesting your wrong by running the std plug. Just disagree on your theory of the SGP, nothing wrong with a good debate anyway

 

[oldboat1]

Re: Force 150 spark plug question

interesting, even for mere mortals. I've used a surface gap spark tester for years, with the idea that if the ignition system (magnetos in all of my old '50s stuff) will fire the surface plug in the tester, I'll have good spark for the standard bent electrode plugs used in the motors.