exploding spark plugs!??

[skierrrr]

Hello,<br />I have a 1970 sea ray 18ft. tri-hull with a mercruiser 120. After a significant loss of power I found that a sparkplug had blown apart and ruined the valves in one fo the cylinders.Bad plug? Bad luck? Well it was time for a valve job anyway. Along with the valve job, I had the carb rebuilt,full tune including wires. On the break in voyage the engine had a similar loss of power and I experienced the same sinking feeling in my gut. Upon exam. I discovered not one exploded/dismantled plug, but two! What is going on? I can only guess that somehow the ignition is delivering too much current or voltage. Could someone please offer a fix? By the way, the plugs are the correct size. <br /><br />Thanks

 

[trog100]

Re: exploding spark plugs!??

i cant imagine the ignition delivering enough voltage or current to cause that.. are we talking about the center electrode plus insulator coming off and ending up in the cylinder or the porelain outside end breaking off..???<br /><br />trog100

 

[Don S]

Re: exploding spark plugs!??

Bet it was a Champion spark plug.

 

[skierrrr]

Re: exploding spark plugs!??

trog 100-<br />Yes it was the center electrode as well as the insulator. I was thinking about changing the complete ignition to an electronic ignition including new coil and all associated components.<br />Thanks for your reply

 

[trog100]

Re: exploding spark plugs!??

don might have point..he he.. i was kinda exepecting him to say something like he has.. he he...<br /><br />if so.. your best bet is to try another more "respected" make of plug possibly in a cooler heat range.. ie.. one that runs cooler..<br /><br />if not go for a cooler running plug anyway.. <br /><br />learn how to read your surviving plugs.. he he.. it is possible that u have weak mixture thats causing this and it needs sorting before it does other damage..<br /><br />and electrodes coming off shouldnt wreck your valves.. the bits should just blow out the exhaust.. make sure the whole thing isnt running too lean and too hot.. and quickly..<br /><br />trog100

 

[Don S]

Re: exploding spark plugs!??

So, what kind of plug was it? If it's Champion, they just do that sometimes, and nothing has to be wrong with the engine to cause it. You may be just working out of a bad batch of their plugs if you're getting them from the same supplier. Like trog mentioned, the electrode should not cause any major valve problems. That small piece usually just goes out the exhaust.<br />Running to lean could cause the problem to be worse. You could get a high voltage probe and check the voltage, but that shouldn't be causing the plugs to explode.

 

[Buttanic]

Re: exploding spark plugs!??

1 Type of plug nose too long for that engine and connecting rod stretch at higher RPM causing plug tip to contact piston. 2 Timing too far advanced causing detonation. 3 Plug heat range too hot again causing detonaton. Used many a Champion and never had one just come apart even in some of my racing engines. The crossover charts from one plug manufacture is a guide and if you change brands (AC to Champion)the heat range of the replacement may not be right especially on a marine engine operating under heavey load.

 

[rabidfish]

Re: exploding spark plugs!??

I'm with Buttanic on this one...<br /><br />What Champion plug was in it? What was the timing?<br />Is the timing advancing as specified? how about the fuel... when did you buy it, is it still good?<br /><br />Got alot of questions to answer here to determine the real cause.

 

[DHPMARINE]

Re: exploding spark plugs!??

Next exploded sparkplug I see will be my first one.Do you have any pics ?<br /><br />DHP likes Champions wants info

 

[trog100]

Re: exploding spark plugs!??

checking to see if the outer electrode is still where it should be (the one u bent).. would tell if the pistons are hitting..<br /><br />tell u one thing.. there is a lot of confusion about which plugs go in these engines.. long or short reach.. <br /><br />trog100

 

[Don S]

Re: exploding spark plugs!??

No confusion about the plug length, the 120's NEVER took long reach plugs, only the newer 3.0L engines. Besides that he said he had the correct plugs in there.<br />Rod Stretch....I doubt that's going to be a concern. The piston would hit the head first.

 

[Laddies]

Re: exploding spark plugs!??

Last summer I know of two engines screwed up by Champion Spark Plugs and the last I knew Champion was ignoring the problem, (both engines had warrenty send in to Champion, a rather lengthy process and have been ignored) I have sold Champion plugs for over 40 years and have sworn by them, I hate Japenize products but am considering going to NGK plugs next summer--Bob

 

[skierrrr]

Re: exploding spark plugs!??

All,<br /><br />Thank you so much for taking time to respond and help with my problem. I'll have the head removed later today and will asess for piston damage caused by plugs being too long (if that's the cause). I'm a novice mechanic but have a friend who is a master Mercedes mechanic. I've printed your suggestions for him to read and will post further info if you are interested. Thanks to all of you. I am always amazed at how small our world has been made web forums.

 

[rabidfish]

Re: exploding spark plugs!??

My own personal thoughts here: Keep the car guy away from the boat.<br /><br />The best mechanics of any kind are great mechanics because they know their limitations...

 

[trog100]

Re: exploding spark plugs!??

pulling the head isnt a bad idea.. let us know the answer when u find out what was causing the problem..<br /><br />trog100

 

[Don S]

Re: exploding spark plugs!??

I would like to know the outcome also...... Would still like to know what kind of plug you had.

 

[flashback]

Re: exploding spark plugs!??

Check for inversion... water in a cylinder will destroy a plug, among other things.....

 

[skierrrr]

Re: exploding spark plugs!??

I just examined the head with the dreaded "car guy". He pointed out a few things.<br />-slight evidence of rust in the #3 intake portion of the manifold. Possibly a crack inside the manifold. <br />-the boss that holds the throttle linkage to the manifold may have a vacuum leak<br />-the #3 exhust valve was melted<br />-I recently had the carb rebuilt(maybe the mixture was too lean)<br />All or part of the above could cause "hot ignition" which woul cause the plugs to melt (not explode)or so I'm told....so I'm going to have the head rebuilt again, have the intake manifold magnafluxed and have the carb shop re-check their work. What do you think?

 

[Don S]

Re: exploding spark plugs!??

slight evidence of rust in the #3 intake portion of the manifold.

This could be from a riser gasket starting to leak, a riser leaking, manifold leaking or leaking exhaust valves causing exhaust (and water) to be sucked back into the combustion chamber on the intake stroke.<br /><br />

-the boss that holds the throttle linkage to the manifold may have a vacuum leak<br />

Would be a VERY SMALL vacuum leak, and wouldn't cause the exploding plug problem, or even an overly lean problem.<br />Adjusting the mixture screw/s on the carb after it's installed is not something your carb shop can do. that can only be done with the engine running, after the ignition system is in proper time and dwell. The float level could be low, which could cause a lean mixture at higher rpms.<br />Was your mechanic able to check the advance mechanism in the distributor. A non working advance would sure cause a detonation problem.

 

[skierrrr]

Re: exploding spark plugs!??

Don<br />you raise some good points, I'll relay them to Randy(my mechanic)