Noisy Diesel

[agaliha]

The 3 cylinder Yanmar diesel in my boat has almost 500 hours on it. It runs great, but is making more noise that it did when it was new...more "knocking." Is this to be expected or what causes could be suspected?
Thanks!
Agaliha

 

[Warren Milberg]

Two suggestions....

(1) most diesel fuel sold these days is ULSD (15 ppm sulphur). It used to be 5,000 ppm. Most of this fuel (at least in my sailing area) is also rated at 40 cetane. My Yanmar requires at least a cetane rating of 45. As a result, I add a little Pri-D and cetane booster to my fuel. So, you may want to check the cetane rating requirements for your particular engine and make sure that is what you are putting in the tank.

(2) it may also be that your engine is up for a valve adjustment. Incorrect valve clearance could be the cause of knocking, too. You can check this yourself with a feeler guage or have a mechanic check and/or adjust the valves for you. If you have never done this before, it may be worth it to hire a pro and watch him do it the first time.

 

[jviss]

Consult the service manual

Agree 100% with Warren. In addition, there may be a bunch of things to do at 500, perhaps even re-torquing the head, which will also require a valve clearance adjustment.

 

[Steve Dion]

Yes & yes...

I would have to agree that these items could be the problem. If you notice that the noise is more prevalent when the prop is spinning then you may need to have the cutlass bear checked.

 

[Nereussailor]

Noise

I have an older Yanmar in my Hunter 30.A couple of years ago, It was making noise but only when in gear. The motor ran great and didn't burn oil. It turns out that the noise was coming from the transmission. What had happened, was the motor mounts had worn out and created more movement of the prop shaft. It caused the alignment to be way off, which caused the rear seal of the transmission to wear out prematurely on a cruise out to Lake Michigan. I ended up replacing the Transmission, the packing gland, the stern tube, the motor mounts, and the cutlass bearing. A few thousand dollars later, everything works great. $400 for motor mounts would have saved lots of money if the PO would have done routine maintenance.

 

[agaliha]

This site is so good

Thanks for the advice and opinions. I'm going to schedule a visit from Doctor Diesel and watch him do his thing. Valve adjustment is the most likely, but if not he will find anything else.
Agaliha