Hello all! I've been reading thru these forums for a while, and have enjoyed many great threads. Something has come up on one of my engines, and I thought maybe some folks on here could offer me some advice...<br /><br />I have a 2003 28' CC with twin 2003 Yamaha 250HP HPDI motors. All the updates have been performed by a trusted 5-start cert. Yam dealer in my area, and they have always treated me well on past and present rigs. My current motors have just about 600 hours on them, and have performed great. Before a recent fishing trip, I started both motors, and heard a sound that is similar to a hard valve tap on a 4-stroke motor. It was very brief, maybe three or four seconds before disappearing for the rest of the day. The motors ran great for the day, putting a couple of hours on them and running about fifty miles round trip. The next morning, to try and diagnose the sound, I started the engines individually. The starboard motor started perfectly and ran super smooth and quiet, as always. The port motor started fine, ran fine, but after about thirty seconds made this audible tapping sound for about four or five seconds before fading away and not returning. I fished a couple days later, with the same thing occuring in the morning and not returning the rest of the day over the course of a couple hours of operating time and 60 or 70 miles of water round trip. I called Yamaha and documented it with them, and they wanted a compression check taken. Sure! I had a dealer come down and do the comp test, and of course the motor didn't make the noise. It sounded fine. Compressions were all right in the money around 110 to 120 PSI on all cylinders. The tech recommended a set of plugs, so I put a new set of plugs in and voila! No more noise at cold start! This was after about eight cold starts in a row making this same sound. Nearing the end of my season, I had about eight more cold starts after the plug change and didn't have any more noises. The motors ran flawless. Heck, even when she was making the noise at startup she still ran flawless throughout the day. Then, the day I hauled the boat, I started the engines to move the boat from the slip to the travel lift, and low and behold she made the sound for about three seconds just after start-up, and then it faded out. <br /><br />Yamaha, my local dealer, and myself are baffled. Considering the engine doesn't have any operational problems. She's smooth, powerful, and doesn't miss a beat. I even went so far as to shut down the starboard engine and run it on the port motor alone...no hutter, sputter, or noise. She ran fine with plenty of power even by herself. My usual tech heard the sound and said it resembled a wrist pin, but if that were faulty it wouldn't come and go so erratically, and only be at cold start idle. In my experience, wrist pins, bearings, rods, any internal knock would get louder when the engine is put under load. He offered the explanation that because the engines have been trimmed all the way in 24-7 and not tilted up due to the cold, that possible oil was seeping past the rings and laying in the combustion chamber creating a hydra lock causing the wrist pin to hit the needle bearing just for an instant after cold start. He said it was far fetched, but real tough to diagnose. All have said there is no reason to tear into it, because you might not find anything! Heck, they have also surmised that it could be something small that's loose in there that's only rattling if the motor is running a certain way.<br /><br />Does anyone have any ideas???? A tech rep suggested that maybe an injector was leaking when she was sitting, considering it only makes the noise very briefly and only after sitting overnight and it only does it on the very first start of the day. Another possile cause offered by another was that the gears weren't coming completely into neutral and they were clattering a bit at cold. What makes it even more baffling is that it stopped for a bit after a plug change! <br /><br />Thanks in advance!
