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Seized spark plug


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Had engine in for winterizing decided to have plugs changed motor ran great all year,merc 135 optimax

mechanic said 1 plug was seized and didn't want to cause any damage so left it in.pesonally I don't think he wanted to spend time

was very busy.What if any problems can I expect in Spring.

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I’ve stripped plugs in my outboards before. Pretty sure the repair was called heliarching? Sure I spelled that wrong but my guy was able to fix it both times pretty easily and inexpensively.


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He was probably afraid of breaking the plug off and that would be a real pain. The plugs are  each about $25-30 too. What about spraying some WD40 on it let it sit for overnight and then see if it loosens up? There is a special extraction tool that can be used if it breaks off....not sure how expensive.

Edited by Sk8man
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If motor is accessible during storage, I‘d wrap a rag around the plug and soak it in penetrating oil.  Leave it sit and give a another shot of oil occasionally.  After it has sat, try to loosen.  If it doesn’t come then more oil.  I have had pretty good luck with this method when you have time to let things soak.  Might want to consider a dab of never seize on the plugs as well.

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Ive had one seize and crack, blew out while the boat was running, I called my dad, the dude drove 6 hours while I was in the military to help. He made a few small cuts with a small metal blade from the hole in the broken plug outward towards the threads being careful to stop before cutting into the threads. This relieved some of the pressure holding the piece into the head. He then heated the broken piece with a torch and used an easy out to remove it. Pressure was the key here, not applying too much pressure. 

 

This info will help if you try to remove it and it breaks. It appears the soaking method is the best bet here. But if it breaks when you try to remove it... here is step 2.

 

Good Luck!!

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Good Question !

#1 Why was the spark plug " seized " in the first place ? Over tightened in the first place ! There is a torque specification for plugs or just get the feel of it ! Another reason for DIY ! Always put anti-seize cpd. on the plugs when changing them !

#2 As posted use penetrating fluid on the plug ; use a high quality product ! WD 40 is not a high quality product but like bad breath better than nothing LOL !

#3 At this stage you my need heat [ dissimilar metals expand at different rates ] which may loosen the plug or allow the penetrating fluid the work better ! The best way would be to bring the engine to operating temperature , if not use a propane torch !

Again let us know how you made out !

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with the oil soaking the plug put a steel punch on the top of the plug of it a tap it with hammer LIGHTLY every so often it helps to get the oil through the threads

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  • 2 weeks later...
Just a follow-up was successful removing plug.Soaked several times with penetrating oil,tapped plug carefully with small punch,and finally plug loosened and backed out threads look ok.Thanks for all the helpful info.

Get some anti seize on those threads. That will help future removal no doubt. This site is awesome isn’t it.


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  • 2 weeks later...

NGK does NOT recommend anti seize. Plugs, as long as they are not the black steel type, are plated to prevent seizing. Spend your money on a torque wrench to prevent overtightening. It will save stripped out threads and seizing from its number one cause, overtightening.

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Still not sure about the anti  " Permatex Anti-Seize Lubricant " [ sorry for the pun but I get that way after not been able to go fishing !] argument ! Do as you wish I will continue to use it unless I get a good reason not to ! How about putting 30W oil on the plug , which I have done ! 

Again that spark plug was probably overtightened but how would you ever know ?

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Didn't think this would take off like this, but it got me off to do some research and I found some pretty interesting, at least to this old shop teacher, stuff pertaining to threads, bolts and TORQUE.

(I just wrote a long, long explanation of what's going on when you tighten a bolt and decided to delete it because who really cares except race car drivers and astronauts)

I always try to follow manufacurer's recommendations. Somebody a lot smarter than me writes them, and for good reason. That's why the NO ADDITIONAL LUBE position. I say additional because the plating is there to provide a controlled amount of slippage so torque readings are consistent.

Yesterday I changed my plugs and had just looked this up. Factory plugs in a 2017 Merc 90 Fourstroke. 556 hours. Thats a lot of heat/cool cycles.

No evidence of lube on the old plugs, and they all came out just fine. New ones went in dry, torqued. Will let you know at 1000.

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I agree with Frogger and Prof T.........and am compelled to offer how much simpler the mask issue is. I grew up knowing that someone who thought and knew more than I did was, for the moment, the Expert. Sort of a KISS  thing, I guess.

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