surface gap spark plugs vs. standard tip spark plugs

[Cedar Ridge Greg]

I have 1977 Chrysler 55 Maga power 2, 2 stroke outboard motor on a 14 Ft glastron tri hull. The service manual recommends autolite 2892 or equivalent. This is a surface gap plug that has no bendable tang to adjust the gap. I bought the boat with autolite 4092 plugs installed have been running with these plugs. The motor is hard to start after long periods of trolling. What are the pros and cons of using the surface gap type of plugs?

 

[Daviet]

Re: surface gap spark plugs vs. standard tip spark plugs

I am not sure about Chrysler, but on OMC products, I find the center electrode type plugs give a better idle and low speed operation.

 

[Silvertip]

Re: surface gap spark plugs vs. standard tip spark plugs

If the ignition system was designed around surface gap plugs, that's what you use. There are some situations (although few) where very unique operating conditions benefit from a change in plug type. When that change is made it must be made very cautiously. Attention to heat range and frequent reading of plugs is necessary until you are convinced the correct plug is being used for those conditions.

 

[JimS123]

Re: surface gap spark plugs vs. standard tip spark plugs

I had a 1970's vintage Rude that came with surface gap. Always had issues with fouling. One year I had it tuned by the dealer and he put in std gapped plugs. He said there was a factory service bulletin that recommended the change. It ran a lot better after that.

 

[Frank Acampora]

Re: surface gap spark plugs vs. standard tip spark plugs

Surface gap plugs are a much colder heat range than bent electrode plugs. In a Chrysler or Force engine with electronic ignition, bent electrode plugs are too hot and may cause piston damage. I have seen Chrysler engines with nice 1/4 inch circular holes melted in the tops of the pistons.

While the surface gap plugs WILL give you fouling problems, especially under prolonged slow speed operation, it is much more preferable to remove and clean plugs than to replace pistons. Understand that there are some people that take exception to this line of thought and will say that bent electrode plugs will not cause problems and will solve fouling issues. I, on the other hand, have seen the damage and tend to be more conservative. It is your engine and your money, you make the choice. I only use surface gap plugs in my engines and carry a spare clean set with me in case I need to change them on the water.

In addition to the autolite plugs, you can use Champion L20V, UL18V, and L76V (Mercury plug). NGK BUHW is good too.

 

[Texasmark]

Re: surface gap spark plugs vs. standard tip spark plugs

I experimented with the optional plugs mentioned in my service manual which were the normal type plugs. Over time I played with it and one day did a spark experiment. I found that the SG plugs had a lot stronger spark than the regular plugs. I didn't say heat rating, I said stronger spark. I have them back in and have been running them ever since.

Mark

 

[Silvertip]

Re: surface gap spark plugs vs. standard tip spark plugs

Spark appears stronger on surface gap plugs because the gap is wider and therefore requires a stronger spark to jump the gap. That principle by the way, works on flooded engines. Hold a plug wire slightly off the plug and the second gap allows the stronger spark to fire the plug. I had to use that technique on a golf cart last week.

 

[Texasmark]

Re: surface gap spark plugs vs. standard tip spark plugs

Spark appears stronger on surface gap plugs because the gap is wider and therefore requires a stronger spark to jump the gap. That principle by the way, works on flooded engines. Hold a plug wire slightly off the plug and the second gap allows the stronger spark to fire the plug. I had to use that technique on a golf cart last week.

Getting technical, energy follows the square of the voltage or current depending on whether you are talking about a capacitor or inductor so it stands to reason that with a larger gap you will need more voltage to jump it hence it will be hotter.

Mark

 

[Cedar Ridge Greg]

Re: surface gap spark plugs vs. standard tip spark plugs

I would like to thank everyone who responded to my thread. I am new to 2 strokes and me and several of my friends were unaware of surface gap plugs. It has been learning experience for all of us. I will put the manufactures recommended surface gap plugs in see how it runs. Thanks Greg