frank2644
Member
After a 20 minute trip, with the engine running great, and then slow trolling around my destination for a couple of minutes my engine suddenly died. Upon restart it made a horrible fast clanking/banging noise and I shut it down immediately. Got towed back to home slip.
Upon inspection, # 5 spark plug gap was bent closed and i/2 of the ceramic insulator is missing, like something hit it. #5 cylinder also has zero compression. #3 has about 90 lbs, while other cylinders 115-138 lbs. Inspection camera shows one of the #5 valves sitting maybe 1/8" deeper into the head than any other valve, making me think the valve seat is missing. No apparent damage to piston or cylinder walls and no metal pieces in view. The piston seems to go up and down normally. Pulled both valve covers and everything looks clean and seems to be operating normally while cranking.
Wild guess: somehow the valve seat broke free and hit the spark plug, then the pieces were blown out through the exhaust. I put a new plug in and started the engine, the horrible clanking/banging noise caused an immediate impulse to shut it down and I did. The new plug doesn’t show any damage. Adjusted the clearance on the recessed valve...no difference in sound.
I have been around engines and heard rod knocks, lifter noises, etc. Usually those noises are not terribly loud and sometimes related to engine RPM and not terribly concerning. However, the noise from my engine, leaves little doubt that something bad is happening and causes an immediate knee-jerk reaction to shut the engine down. The noise is pretty fast, giving the impression that it’s not related to happenings in any one cylinder or valve. And the sound is not very dull or deep sounding and has a clanky aspect. It’s hard to describe. Although, my impression of the sound may be distorted given that the hard starting requires pretty high throttle opening and high rpms upon startup.
I have to believe that noise is related to the spark plug damage but I can’t figure out what it is. Any suggestions as to what could be causing that noise?
Thanks,
Frank
Upon inspection, # 5 spark plug gap was bent closed and i/2 of the ceramic insulator is missing, like something hit it. #5 cylinder also has zero compression. #3 has about 90 lbs, while other cylinders 115-138 lbs. Inspection camera shows one of the #5 valves sitting maybe 1/8" deeper into the head than any other valve, making me think the valve seat is missing. No apparent damage to piston or cylinder walls and no metal pieces in view. The piston seems to go up and down normally. Pulled both valve covers and everything looks clean and seems to be operating normally while cranking.
Wild guess: somehow the valve seat broke free and hit the spark plug, then the pieces were blown out through the exhaust. I put a new plug in and started the engine, the horrible clanking/banging noise caused an immediate impulse to shut it down and I did. The new plug doesn’t show any damage. Adjusted the clearance on the recessed valve...no difference in sound.
I have been around engines and heard rod knocks, lifter noises, etc. Usually those noises are not terribly loud and sometimes related to engine RPM and not terribly concerning. However, the noise from my engine, leaves little doubt that something bad is happening and causes an immediate knee-jerk reaction to shut the engine down. The noise is pretty fast, giving the impression that it’s not related to happenings in any one cylinder or valve. And the sound is not very dull or deep sounding and has a clanky aspect. It’s hard to describe. Although, my impression of the sound may be distorted given that the hard starting requires pretty high throttle opening and high rpms upon startup.
I have to believe that noise is related to the spark plug damage but I can’t figure out what it is. Any suggestions as to what could be causing that noise?
Thanks,
Frank