Yanmar 4BY2-150 knocking/rattling

[Salty7]

I have a Yanmar 4BY2-150 in my 2012 25SC. I have noticed some rattling/knocking as I decelerate; the noise occurs between 1,950 rpm and 1,650 rpm. It sounds like loose lifters but that cannot be as it has overhead cams. The injectors and valves are completely silent below 1,500 rpm and the engine sounds completely normal above 1,950 rpm. The engine only has 200 hours on it and there is no problem with its performance or any other indication of a problem. Has anyone else experienced this? It is not a loose beauty cover which has been the source of noise for some folks.

 

[BB marine]

Tony, I have not experienced that with the 4BY2 but I have experienced a rattling and vibration on any engine that I have owned or worked on in a specific RPM range. In general any rotating equipment will have what is called a critical speed. Most of the time the marine engine manufacture will design the engine to have the critical speed adjusted to an rpm that is normally not used. An area that the boats performance is not good. This Rpm range is usually 50 to 100 rpm somewhere in the mid range of the engines operating rpm.. This is normally done by balancing, Flywheel or Harmonic balancer. There are other factors that can increase the vibrations or harmonics, loose motor mounts unbalanced prop shaft or prop. 4 cylinder engines are naturally a higher vibrating engine so when running through the critical speed the noise and rattling can be more pronounced. If your engine never did this before at this speed or was not as noticeable. Something changed. The first place I would look is the prop. It will take a small amount of change in a prop especially one that is operating in a tunnel to cause amplified vibration. The area that you are experiencing the knocking/Rattling is in the midrange and based on your description it happens as the engine is passing through a small window RPM range. It comes on and then goes away. Take the boat out and try to find the exact rpm where the Knocking/ Rattling is. See if you can duplicate it a few times and record the rpm and range. Example: 1750 to 1800, or 1850 to 1900 Find out where it starts and where it goes away. Call Mack Boring and talk to a service representative there and ask where the designed critical speed of the engine is for the 4BY2. If it turns out that it is in that range but should be not as noticeable as what you are experiencing then look further at mounts, alignment, shaft and prop. Those are variables that can change. Also check the engine for loose fasteners, make sure the engine protective cowling is tight. Open the hatch up when operating at the point that you hear the noise and try to locate the noise maker.

A second component that can cause noise during deceleration is the Turbo. That is a long shot but sometimes long shots are culprits.

My guess is critical speed + a few loose nuts and bolts!

 

[GaylesFaerie]

Also check the engine for loose fasteners, make sure the engine protective cowling is tight.

I had a nasty rattle at certain RPMs on my 4BY2-180 (also 2012 vintage) and it was the engine cover. There are two and on mine it was the larger one with the Yanmar name in yellow on it. With the engine running I placed my hand on the cover and the rattle stopped. There are 4 fasteners if I remember correctly. One at the back, one on top, and two on the front of the engine where the cover curls over about an inch. I also think the two at the front have integrated rubber grommets that may split over time allowing the rattle and need to be replaced. I may be mistaken on that but check. Finally, I completely eliminated the rattle by placing some black neoprene rubber under a section of the cover that seemed to be the noisiest offender. HTH, Gary

 

[Salty7]

Thanks Gary and Brian, all good thoughts and helpful. I am starting to work through figuring this out. One thing that is new is a hired a "professional" to do some routine service on the engine, change the fuel filters and replace the water pump impeller, usually I do it all myself. So today, while checking the covers, I found all the fasteners tight but, looking at the engine from the front, I discovered the starboard cover to be right on top of the rectangular pipe beneath it, I think that is the charged air pipe. I suspect the noise is wastegate chatter, as I am taking the load off the turbo the wastegate chatter is now transmitting through to the cover which is grounded to the motor instead of riding on the rubber isolator. I remember finding this guy standing on the beauty covers. I'll let you know what happens after I get the covers fully isolated from the motor again. I guess I am back to doing my own maintenance.

 

[Salty7]

I am declaring this fixed! I discovered that the "professional mechanic" who worked on my boat stood on the engine covers and bent the starboard cover. The result was the front edge of the cover was riding on the air pipe beneath it. I do think the noise is created by the turbo as the engine slows down. The engineers who designed this engine went to great lengths to tune that noise out by designing a cleverly isolated set of covers. If you own one of these engines don't stand on the covers or let "professionals" stand on them either!

 

[BB marine]

A second component that can cause noise during deceleration is the Turbo. That is a long shot but sometimes long shots are culprits.

My guess is critical speed + a few loose nuts and bolts!

I guess long shots sometime come into play!!!

 

[CaspersCruiser]

I discovered that the "professional mechanic" who worked on my boat stood on the engine covers and bent the starboard cover.

One of my biggest peeves— paying someone to screw up my stuff. I do well enough all by myself!