M25 XP ENGINE NOISE

[Tim Weber]

I have an M25XP with about 1600 hours on it. In checking over the engine this past Spring, I noticed a "tapping" or "ticking" sound from the front of the engine. It is very similar (both frequency and pitch) to the sound you would expect to hear if the valve clearances needed to be adjusted.

The problem is, the sound seems to be coming from the front of the engine, roughly  inside the triangular area formed by the alternator belt (between the three pulleys). It's possible it could be the alternator or the valves, but I don't think so. I may try to use a piece of tubing as a makeshift "stethoscope" to see if I can pinpoint it, but need to be careful.

I have not noticed any problem in engine performance or cooling. I have been Zen-like in my practice of lubrication changes ever since I've owned the boat (1991). I'm not overly concerned at this point, just curious if I have a big problem in my future. Any ideas would be appreciated.

[Ray & Sandy Erps]

Sounds like you have the skills to narrow it down.  I guess one thing you could do to rule out the alternator and fresh water pump is to remove the fan belt and run the motor a bit to see if the sound goes away or not.  I can't think of anything that would be tapping in the location you described though.  Tapping comes from up top in the valve train.  Knocking comes from down below in the crankshaft and whirring comes from up front with all the stuff that spins.  

Your tube for a stethoscope works.  I've also used a long handled screw driver quite a bit to locate funny noises.  Put the blade against the suspected source and the handle against your ear.

[Ron Hill]

Tim : Apparently this "ticking" has nothing to do whether the Xmission is in gear or not.  
If you further want to narrow down the source, remove the drive belt.  You can idle the engine (if it's cold) for about 3-5 minutes.  That might be just enough time to find it and eliminate the alternator, internal water pump or the lower drive bearing.  A thought.