Torque specs for spark plugs on a 1998 Mercury 150XL 2 stroke

Luke415

Seaman Apprentice
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Apr 4, 2016
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42
Does anyone know the correct torque for spark plugs on this engine? I am assuming there is a specific torque...? I can't find it anywhere in the service manual.

Thanks
 

SkiDad

Lieutenant Commander
Joined
Jul 18, 2010
Messages
1,518
I always just tighten mine down finger tight and then a 1/4 turn with my wrench. I did my car recently and I did 15 foot pounds. If you want a little more on them do not go above 20 foot lbs.
 

Texasmark

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Dec 20, 2005
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14,544
Just remember you are screwing into cast aluminum. Don't over do it. When I was young and a naive youth, I ripped out a set of threads on a 10 HP Scott Attwater . Hasn't happened since and have had no problems. One of the considerations is whether you are installing a new plug or a used one that has had the gasket compressed. If new you have to keep the pressure on when you feel slight resistance (to compress the gasket) and be ready when the resistance takes a sharp rise....then is when I stop. Is it 20 ft-lbs? Don't know but been doing it for 50+ years and it works.
 

Luke415

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Apr 4, 2016
Messages
42
Just remember you are screwing into cast aluminum. Don't over do it. When I was young and a naive youth, I ripped out a set of threads on a 10 HP Scott Attwater . Hasn't happened since and have had no problems. One of the considerations is whether you are installing a new plug or a used one that has had the gasket compressed. If new you have to keep the pressure on when you feel slight resistance (to compress the gasket) and be ready when the resistance takes a sharp rise....then is when I stop. Is it 20 ft-lbs? Don't know but been doing it for 50+ years and it works.
Thanks everyone. Yeah I was scared because of the aluminum heads. Bought a Seloc brand manual which said it covers all 2 strokes from 90-00 but after finding which engines it ACTUALLY covers, mine is not included. Very misleading. Basically useless if you want a good service manual. And certainly no torque specs. I am not a mechanic by trade, but can figure stuff out fairly easily as long as it's not super complicated. On my vehicles, I've done pads/rotors, valve cover gaskets, valve adjustments, starter motor replacements, etc. Think I am going to download and print the manual off the web, the local Merc dealer said a manual specific to my engines (1998 150XL offshore 2 stroke, and 150CXL) would run me $100.
 

Texasmark

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Dec 20, 2005
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14,544
Thanks everyone. Yeah I was scared because of the aluminum heads. Bought a Seloc brand manual which said it covers all 2 strokes from 90-00 but after finding which engines it ACTUALLY covers, mine is not included. Very misleading. Basically useless if you want a good service manual. And certainly no torque specs. I am not a mechanic by trade, but can figure stuff out fairly easily as long as it's not super complicated. On my vehicles, I've done pads/rotors, valve cover gaskets, valve adjustments, starter motor replacements, etc. Think I am going to download and print the manual off the web, the local Merc dealer said a manual specific to my engines (1998 150XL offshore 2 stroke, and 150CXL) would run me $100.

Something I forgot to mention was the cleaning of the mating surfaces prior to applying the RTV. Sorta obvious but you never know. Back when I did some of this I stopped by an auto paint shop and got some zinc chromate primer. It is an acid etch used on airplane aluminum for one, and etches (control corrodes) the surface to prevent further environmentally generated corrosion. Not necessary but I just felt like doing it. Good luck.
 

Dukedog

Captain
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Oct 6, 2009
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3,235
Is it 20 ft-lbs? Don't know but been doing it for 50+ years and it works.

yeah, it is....

if ya gonna do your own stuff that 100 bucks will be tha best ya ever spent!.... i thought they was way over priced in '76 but found out "not so".....
 
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Luke415

Seaman Apprentice
Joined
Apr 4, 2016
Messages
42
yeah, it is....

if ya gonna do your own stuff that 100 bucks will be tha best ya ever spent!.... i thought they was way over priced in '76 but found out "not so".....
Yeah I think I'm going to buy it. I did find a manual online that seems to be the correct one:

http://boatinfo.no/lib/mercury/manuals/135-150-175-200.html#/528

Just not sure if this is specific to my serial #'s...

Good news is that both engines fired right up after not being ran for over 5 years. However, not much water is coming out of the 'tell tale' so now I'm going to change the impellers and thermostats...seems fairly basic.
 

Texasmark

Supreme Mariner
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Dec 20, 2005
Messages
14,544
Changing those is always the thing to do on a purchased used engine...then you know where you stand. On how much tell tale water, it depends on where it originates. Follow the hose. If it comes from the stat cover then the stat has to open before you get any and every time it closes, unless it has a bleed hole....for a dribble, you loose your water. If plumbed off the exhaust manifold plate, or directly off the engine block, then you should have a good stream proportional to engine rpm.
 
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