I'd like to hear about experiences regarding detonation and pre-ignition in Mercruiser 2000 5.7L 350 250hp engine with about 86 hours on the engine. Ever hear of the center electrode of spark plug that came out of the ceramic insulator and caused a cylinder to detonate? Or, is the missing spark plug electrode the result of some other cause? Any ideas and thoughts will be helpful.
abrazen1-I had a similar thing happen where the ceramic around the electrode came apart in the cylinder. I started looking around trying to figure out why and found that two of the spark plug wires were reversed, therefore, the plug was firing at the wrong point of the stroke. If you have had any work done lately you might check it out. If it is pre-detonation, be very careful...it will tear up a motor very quickly. Been there done that.Good luck.
Let me expand on my initial post. While on the river we slowed down to cross over a passing boats wake, then when we tried to accelerate we had limited power and the engine sounded strange. Immediatly after coming to a stop/idle the boat stalled. As the boat was started again and the hatch was being opened, you could hear a knocking from the engine. Immediatly nursed to ramp and pulled the boat. That day we had filled up the boat w/87octane fuel, been using the boat for about 5 hours prior to this occuring.
After taking the boat to the shop, they had torn down to find the problem: cyl 4 and 6 zero compression, tuliped intake valve, burn/charred pistons (4,6) and piston head 6 had small 3/8 piece missing from the crown. In addition cyl 6 spark plug center electrode was gone, but the insulator was intact (it appears). The inital cause diagnosed by this repair shop said, "the damage was caused by detonation, and the detonation was caused by the center electrode falling into the cylinder, heating up and causing the dentonation." I'm not buying it ... electrode don't just "fall", there has to be another root cause for the problem, so I'm using this board to get some ideas.
The boat has 82 hours and has been kept in tip top shape and according to manufacteres specs, we're outside Merc's warranty, and given the initial diagnosis, Ext. Warr does not cover spark plugs ... so we're looking at a new or rebuild to get moving again.
abrazen1 -
Sorry to hear the bad news about your engine. I have the exact same engine except it's a 1997 and I am also going through some problems though not exactly like yours. I have a few opinions - Maybe the spark plugs that were being used were not gapped correctly or were not the correct spark plug for this marine engine. Maybe your engine is not tuned properly or out of timing causing the engine to run excesively hot. I cannot imagine what else could destroy a plug except for detonation & heat. Third - were there any other symptoms , noises , etc before all this happened. Fourth - have you had a tune-up or any work done recently on the boat.
Good luck
Thanks I appreciate it ... As far as the spark plugs ... we had our 50 hr boat service completed and nothing was identified at that time. If we were having a problem related to that I'm sure they would have noticed some symptom on the spark plugs. Especially since we were experiencing some dieseling. But we did not have any warning from strange engine noises, or performace issues except for when it happend. We were going to be taking it in this month for a service - and, well I guess we are - just not the service we would have liked. Thanks for the ideas; good luck on your problem.
I just remembered one last thing I should have posted earlier. A friend of mine had a problem some time back where he took the boat to get a tune-up. After this he took the boat out on the lake. Everything was great at first untill he noticed a considerable loss of power in the engine followed by some serious noises. He got towed back to the launch ramp and his vacation was over immediately. Took the boat to a local shop in Havasu (not the one that had tuned up the boat) as it turned out the shop advised him that the plugs on the engine were not the right ones. It appears as if the shop that tuned his engine had mistakingly used a different spark plug. They think that the plugs caused the problem because they were just getting way too hot. The spark plugs that should have actually been used were a lot shorter than the plugs found inside the engine. After taking it back to the shop that had caused the problem they helped him out with the labor to fix the engine but he forked out money for parts. In the end the motor got fixed but now he always double checks everything before hittin the water, and especially after getting any maintenance done anywhere.
Good luck
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