Recently my engine has developed a knock. It's not very loud but you can hear it. It is noticeable at idle and low rpms and is hard to hear at high rpms but is there. I have done a lot of reading on this site and others to try and diag this myself. So far I have done the following:
1. Compression test 102,98,90,102,100,98.
2. Verified spark
3. Used a mechanics stethascope to isolate the sound to #4 cylinder (top right when looking at the motor from outside the back of the boat). The knock can be heard while listening at the cylinder head and also lower towards the crank. Can also hear a little knock in #5 cylinder but weaker. Not sure if it is bleeding over from #4. No knocking can be heard on any other cylinders. No knocking coming from flywheel or lower unit.
4. Plugs looked pretty good except for #4 which had some fouling but not much.
5. Tried pushing on the piston with a screwdriver and got no movement that I could tell.
Some background: On my last trip out my engine started to run rough as I was idling down a canal on my way out. Pulled over to a dock to check my plug wires. Shut off the motor and pulled off the cowl. plug wires are new and they were all good but noticed that cylinders 4,5 and 6 were wet. Water all over that side of the engine. Started engine and discovered the thermostat housing cover {plastic} had blown apart and water was running down across the wires and plugs. At this point I was only a couple of hundred yards from the ramp so I just idled back and pulled the boat. Ordered a new thermostat cover and cleaned and regapped all plugs. Let everything dry out for a couple of days. blew out plug wires with compressed air to be sure they were dry. Motor runs fine. Dont think this has anything to do with the knocking but thought I should mention it just in case.
So my question is What is my next step? Should I pull the head on that side? Is there anything else I can do before I get that involved. I am pretty handy and am not afraid of tackling motor issues but have never pulled a head or dealt with piston issues before. So far on this motor I have:
1. Replaced the water pump and thermostats
2. Replaced the plug wires and plugs
3. Rebuilt the starter
So help me out guys. What's next?
1. Compression test 102,98,90,102,100,98.
2. Verified spark
3. Used a mechanics stethascope to isolate the sound to #4 cylinder (top right when looking at the motor from outside the back of the boat). The knock can be heard while listening at the cylinder head and also lower towards the crank. Can also hear a little knock in #5 cylinder but weaker. Not sure if it is bleeding over from #4. No knocking can be heard on any other cylinders. No knocking coming from flywheel or lower unit.
4. Plugs looked pretty good except for #4 which had some fouling but not much.
5. Tried pushing on the piston with a screwdriver and got no movement that I could tell.
Some background: On my last trip out my engine started to run rough as I was idling down a canal on my way out. Pulled over to a dock to check my plug wires. Shut off the motor and pulled off the cowl. plug wires are new and they were all good but noticed that cylinders 4,5 and 6 were wet. Water all over that side of the engine. Started engine and discovered the thermostat housing cover {plastic} had blown apart and water was running down across the wires and plugs. At this point I was only a couple of hundred yards from the ramp so I just idled back and pulled the boat. Ordered a new thermostat cover and cleaned and regapped all plugs. Let everything dry out for a couple of days. blew out plug wires with compressed air to be sure they were dry. Motor runs fine. Dont think this has anything to do with the knocking but thought I should mention it just in case.
So my question is What is my next step? Should I pull the head on that side? Is there anything else I can do before I get that involved. I am pretty handy and am not afraid of tackling motor issues but have never pulled a head or dealt with piston issues before. So far on this motor I have:
1. Replaced the water pump and thermostats
2. Replaced the plug wires and plugs
3. Rebuilt the starter
So help me out guys. What's next?
