What killed this plug?

[gobucs1]

1981 Johnson 25 HP motor, running at WOT for approx 1 to 1.5 miles at 16-17 mph then motor sputters then dies approx 15 seconds later.

Got to restart barely and back to port to find plug in lower cylinder. I have never had a problem before with plugs on this motor.

Any ideas? Looks like possibly metal/steel?

This is the plug that I replaced it with then ran at WOT in neutral in a bucket for 2 minutes at home and this is how it looked.

Motor also still has 125 compression on both cylinders after finding this plug. This the same it had the last time I tested it.

If pics are not clear enough I can try to get better ones.

Thanks!

 

[bktheking]

Re: What killed this plug?

Knock that "goodness" out of the plug and try a magnet on it. Find out if it is indeed metal.

 

[gobucs1]

Re: What killed this plug?

Knock that "goodness" out of the plug and try a magnet on it. Find out if it is indeed metal.

Yes it is magnetic....thats always good.

(Nice Merc in your avatar)

 

[bktheking]

Re: What killed this plug?

Aluminum wouldn't stick, steel does, rings aren't aluminum :OHOH:

Thanks, I'm waiting to run it on my 14, I'm getting a restore mark 20 as well, love those old mercs.

I wouldn't run your motor until you find out what did it, that's like pissing blood, your shouldn't have steel stuck in your plug. To start, pull off the head and inspect, possibly the side covers as well so you can get a closer look without tearing it down. Are your lower unit screens in tact where the water pickup is?

 

[gobucs1]

Re: What killed this plug?

Possibly preignition eating the cylinder? But what caused this all of a sudden and how do I fix this?

Does this mean the motor is junk now?

(I am trying to rebuild a mer super 10 but not getting that far as I bought it in pieces, like boxes of pieces and its been a challenge)

 

[bktheking]

Re: What killed this plug?

Don't know until you dig into it, may not be a ring at all. Not necessarily junk but that much metal in any motor albeit it a car, outboard, lawnmower, doesn't look good.

You rebuilding a KG7? Same powerhead as my KH just doesn't have the shifting. You know about John's old merc site?

 

[gobucs1]

Re: What killed this plug?

Take the head gasket off and see the damage? The motor runs fine now with a different plug and still has compression?

No, I don't know what site you mean

 

[bktheking]

Re: What killed this plug?

Does the plug look normal after you removed the metal? Or was it the plug itself that broke down.

Totally up to you if you pull the head, I'm kindof paranoid about that stuff.

Johns merc site, good knowledge from Merc boys on the site, tonnes of parts and experts

http://www.pfs-ware.com/phpBB3/index.php

 

[gobucs1]

Re: What killed this plug?

I took the plug out saw what it was and just grapped a new one I had and installed it after blowing out the cylinder. I have not removed the metal yet but the plug looked good besides the debris on it.

I also am not a fan of removing the head gasket as that can cuase other problems and broken bolts there are not fun.

Thanks for the link!

 

[bktheking]

Re: What killed this plug?

Well that's up to you, roll the dice I guess.

 

[emdsapmgr]

Re: What killed this plug?

If you don't want to pull the head, shine a light inside the spark plug hole have a look. If the piston top looks shiny and pitted, the piston crown may disintegrating.

 

[bignefan]

Re: What killed this plug?

If its not metal thats is a bridge gap the causea are
1.Excessive carbon in cylinder
2.Uses of none recommened oils
3 immediate high speed operation after prolong trolling
4. improper fuel-oil ratio
Rite out of the book

 

[glassmaster68]

Re: What killed this plug?

kinda looks like it might be getting hot ,,like leaning out,if it is too lean,it will burn a hole in your piston or just start melting it,and the plug as well ,,was that a really old plug that had been in for a while?any thing like a screw go in the intake?if it was an old plug,maybe it has just been heated and cooled so much,it started breakin up,,,,, a pump up hose can have a leak and have trouble pulling fuel at wot,,that would prob lean it out also

 

[emdsapmgr]

Re: What killed this plug?

If the block has a water circulation problem internal to the powerhead, it could affect one cylinder more than the other. If it runs hot, you could wind up with this problem. I have seen mud, sand and weeds internally lodged in powerheads-in different spaces. Any of which could cause a water flow restriction and a lean firing condition on a cylinder eventually resulting in aluminum piston degradation.