First, thanks for your advice Rodbolt and others.
Here's an update on my "knocking" problems on my 2001 250 Yamaha. 200 hours and looks like I burned a piston / cylinder. I made some posts here while trying to figure out why the motor was "ticking". (and it wasn't the O2 sensor draw tube) Here's an update and a word to the wise on the importance of good fuel flow on these motors.
Mechanic pulled the heads and noticed moderate scoring on the exhause side of #5 cylinder wall. By the way compression was great on all cylinders.
It's been running great so I've been racking my brain trying to figure out what happened. Then, I remember running it lean about 25 hours ago. After a mile run from the ramp it stalled. Realizing I had a fuel issue I found it would run if I pumped the priming bulb. I got back to the ramp by pumping the bulb to force fuel into the motor. The motor would run a bit and then stall after running out of gas. I would quickly pump the bulb again and it would pick back up and run for a minute. Once back at the ramp I noticed a major leak from the VST tank o-ring AND realized I accidentally left the engine mounted water/fuel separator loose after cleaning it that morning. The motor kept running out of fuel since it was sucking air in those places. I now reason that this cycling was likely running the #5 cylinder in a lean state. Scored the #5 at the exhaust port. Then after about 15 hours it developed a ticking noise likely due to the melted ring catching on the exhaust port.
NOW FOR THE REBUILD
For you guys who rebuild motors can I get an opinion? The motor is otherwise in GREAT shape and I really didn't think I needed a new or rebuilt block. Plus I am saving about $2,000. My mechanic sent the block for machining. Bored the #5 .040 over. Honed the others. We are replacing the #5 piston (obviously) and wrist pin. Replacing the rod bolts, main bearings, and rod bearings even though they all looked great. Had the injectors tested and cleaned. New O2 sensor. Cleaned the VST filter. He will test the fuel pressure and TPS after assembly.
Anything I may be missing? Since I am "in" the motor might as well make it new again.
Keep your fuel system in shape!
Here's an update on my "knocking" problems on my 2001 250 Yamaha. 200 hours and looks like I burned a piston / cylinder. I made some posts here while trying to figure out why the motor was "ticking". (and it wasn't the O2 sensor draw tube) Here's an update and a word to the wise on the importance of good fuel flow on these motors.
Mechanic pulled the heads and noticed moderate scoring on the exhause side of #5 cylinder wall. By the way compression was great on all cylinders.
It's been running great so I've been racking my brain trying to figure out what happened. Then, I remember running it lean about 25 hours ago. After a mile run from the ramp it stalled. Realizing I had a fuel issue I found it would run if I pumped the priming bulb. I got back to the ramp by pumping the bulb to force fuel into the motor. The motor would run a bit and then stall after running out of gas. I would quickly pump the bulb again and it would pick back up and run for a minute. Once back at the ramp I noticed a major leak from the VST tank o-ring AND realized I accidentally left the engine mounted water/fuel separator loose after cleaning it that morning. The motor kept running out of fuel since it was sucking air in those places. I now reason that this cycling was likely running the #5 cylinder in a lean state. Scored the #5 at the exhaust port. Then after about 15 hours it developed a ticking noise likely due to the melted ring catching on the exhaust port.
NOW FOR THE REBUILD
For you guys who rebuild motors can I get an opinion? The motor is otherwise in GREAT shape and I really didn't think I needed a new or rebuilt block. Plus I am saving about $2,000. My mechanic sent the block for machining. Bored the #5 .040 over. Honed the others. We are replacing the #5 piston (obviously) and wrist pin. Replacing the rod bolts, main bearings, and rod bearings even though they all looked great. Had the injectors tested and cleaned. New O2 sensor. Cleaned the VST filter. He will test the fuel pressure and TPS after assembly.
Anything I may be missing? Since I am "in" the motor might as well make it new again.
Keep your fuel system in shape!