Engine knocking

[Doug Miller]

I had some work done on my Yanmar diesel in my Hunter 34 about a year ago (water damage to the engine from a full Racor caused by water in the diesel tank). The engine works now but feels like it is only firing on two of the three cylinders. It does not idle well but seems to be ok on higher RPM. Not sure if there is anything I can do about this. The more troubling problem is the engine mounts were replaced and the engine goes out of alignment occasionally. A loud knocking is noticeable at certain RPMs. I have successfully adjusted the mounting bolts and fixed the problem but it will occasionally go out of adjustment again. Thoughts on whether this is a serious problem that others have or is this symptomatic of a bigger problem. Thanks.

 

[Pete]

two out of three

check your injectors you could have damaged one with water in the fuel and causing a miss or have a fuel pump problem Just a thought on the engine mounts try some loctite on the threads to see if this help them from backing off and getting loose. The vibration from a poor running engine could also be a problem hope this helps!

 

[Gordon Torresen]

Engine knock? Injection and alignment.

The metering of fuel to the injectors is much more critical at low speeds. Considering the amount of fuel for each squirt is almost immeasurable, plus or minus 10% would be less so. The work done after water gets to the injector pump, and possibly the injectors, should be done by a shop that specializes in that type of work. The proper calibration of your pump requires special test equipment and expertise. Loose motor mounts should not be happening. Correcting loose mounts requires aligning the shaft to the boat and then aligning the engine to the shaft. When all is properly in line, the top nuts on the mount should be torqued tightly enough so that they, in combination with the proper lock washer, will not loosen. The same holds true for the bolts that hold the mounts to the engine beds. The knock you describe, that goes away when you tighten the mounts, is sure to be the shaft hitting the inside of the shaft tube.