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Surface Gap vs Electrode spark Plugs

L

leachy

Regular Contributor
Hi There,

Is there an advantage of one over the other. My motor had surface gap plugs but the Merc deal gave me the conventional electrode type as a replacement. I didnt realize until I got home. Apparently they are equally compatible but mercury fitted the surface gap.
 
1986 model, 4 cylinder 75hp.
1000013987.jpg
 
My repair manual for 3 and 4 cylinder 2 strokers which includes 60 Jet through 125 HP engines lists the OEM surface gap and the alternative conventional plug. I find that the substitutes do a better job in my engines. Reasons are posted via news media outlets as to the reason for the SG. Apparently I don't boat the way data led to the OEM plug being SG.

Nice clean rig. Looking at your wake its moving right along.
 
As long as they are creating a good strong spark (and not fouled or worn out), the plugs have very little to do with how well the engine runs. This is true for any engine.
 
I believe your engine came with L78-V surface gap plugs in 1986. Conventional gap plugs were offered as a better alternative for an engine that trolled or idled alot to reduce misfire or fouling.
 
Texasmark said:
My repair manual for 3 and 4 cylinder 2 strokers which includes 60 Jet through 125 HP engines lists the OEM surface gap and the alternative conventional plug. I find that the substitutes do a better job in my engines. Reasons are posted via news media outlets as to the reason for the SG. Apparently I don't boat the way data led to the OEM plug being SG.

Nice clean rig. Looking at your wake its moving right along.
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It gets along ok, top speed is about 35 knots. I was taking for a test run after lifting the engine 2". I was probably doing around 24knots in that pic, my usual 4200-4500 rpm cruising speed.
 
leachy said:
It gets along ok, top speed is about 35 knots. I was taking for a test run after lifting the engine 2". I was probably doing around 24knots in that pic, my usual 4200-4500 rpm cruising speed.
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Its obvious to me that your boat has a lifting type hull, like low dead rise at the stern and maybe reverse chines. That flat wake at 24 knots didn't come from a deep V. I assumed that you were up around 35-40 MPH. I have a reverse chine in my Crestliner and it does get the hull out of the water and makes for a fast, smooth, dry ride.
 
Texasmark said:
Its obvious to me that your boat has a lifting type hull, like low dead rise at the stern and maybe reverse chines. That flat wake at 24 knots didn't come from a deep V. I assumed that you were up around 35-40 MPH. I have a reverse chine in my Crestliner and it does get the hull out of the water and makes for a fast, smooth, dry ride.
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Its a Glastron Trihull V156
 
leachy said:
Its a Glastron Trihull V156
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Well that explains the flat wake. The side sponsons deflect the water back down giving the boat lift from the energy contained in the deflection action. When I was in Austin I was aware that Glastron was built there and they were in lots of places. They made some beautiful boats and in their catalogs, lots of pictures were taken at up scale homes along the shores of Lake Austin. I never heard anybody gripe about one.

The sponsons on a tri-hull were good and bad. On a light boat they beat you to death as they did on my 1971 Chrysler 16' Sport Fury. I sold it the following year and bought a Caravelle 18' deep V tri-hull and the increased V and additional weight made for a much smoother ride.....at a fuel/power requirement cost.....but the family had a much better time.
 
fitz73222 said:
Boy do I have a clean 1978 90hp six with power trim that would get that V156 back into the low 50's where it belongs!
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Those engines are so rare here in Australia, most of them were used in salt water so they are all corroded and just dont exist anymore.
 
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