I am having a weird noise coming from below deck behind my engine from about 2100-2400rpm. It’s a deep, loud grumbling that’s coming from behind the engine (yanmar 3YM20). The noise is rpm dependent, and it happens in forward, reverse, and neutral. 3000 rpm cruise, I don’t hear it at all. Noise can be heard from 1900-2600, but from 2100-2400 it’s REALLY loud. 90 hours on the engine. Maybe 15 of those hours put on this season. Does anyone have any insight to what this noise might be? I took a video from the front of the engine, which sounds more or less normal. The second video shows the noise coming from the rear. Sounds like it might. E coming from below deck. Thanks!
Strange grumbling noise behind engine
- Thread starter BERK30
- Start date
It sounds a bit like something I had a few years ago, and it turned out to be a cutlass bearing. We limped home for about an hour and maybe I could’ve gone a bit longer, but I got her attended to right away. I meant to add that I dove under the boat and gave the prop shaft a good lateral wiggle. That produced a similar noise, and there was play that should not have been.
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I agree with you both. It does sound like it could possibly be bearing related, but it’s likely not the cutlass bearing because the symptoms remain in neutral. The noise coming from the rear is certainly not normal. It has never made this noise before. It’s a bit hard to catch on video, but it’s a low pitch, deep rumble. Somewhat similar to a bad wheel bearing on a car.
Do you have good raw water flow out the exhaust? You might check the condition of your water pump impeller.
An impeller with missing vanes can make a hollow booming sound as more vanes break off.
An impeller with missing vanes can make a hollow booming sound as more vanes break off.
If I heard a grumbling behind the engine, my first reaction would be to immediately locate the admiral.
Water flow out of the exhaust is good. I swapped it out with a new oem one anyways because the old one had unknown years on it. Kept the old one as an emergency spare. Unfortunately, still having the noise and vibration. Thanks for the suggestion
Not sure what you mean by your question. I checked the engine mounts and they visually look ok. Harmonic vibration is a possibility. There is a good amount of vibration associated with the noise. Any advice where to start checking? Visually, the harmonic balancer does not appear to be excessively vibrating. Not sure how to test that
Hard to tell from a visual inspection if the motor mounts are OK. The rubber hardens over time and can transmit more vibration.
Check the engine alignment in the shaft log.The engine can be perfectly aligned to the shaft, but the shaft is in the wrong place, i.e., rubbing against the shaft log. Weak motor mounts can cause the engine to sag with the shaft then touching the shaft log.
Yanmar engines by design are noisy. When designing a combustion chamber for a diesel it can be designed to be quite or to start without a glow plug. Yanmar opted for the no-glow plug route.
Does it make the noise in neutral at the dock ? (Shaft won't spin from water passing it at the dock and you can safely diagnose it there)
Can you safely access the engine, drive, and shaft safely while it's running ?
If so, and it was me, I would use a mechanics stethoscope and try locate the source. Ymmv
Can you safely access the engine, drive, and shaft safely while it's running ?
If so, and it was me, I would use a mechanics stethoscope and try locate the source. Ymmv
A long screwdriver works as well
Stick the end of the screwdriver against an area the noise may be coming from and stick your ear close to the handle. Can be a very good way to isolate where a noise is emanating from.
True.
When you are testing a running engine, that is risky though. Depending on what area you are checking. A stethoscope is very cheap and with the long probe you can access most anywhere, including belt driven components.