Gear noise Yanmar 4JH4AE/KM4A1

[Wilfred123]

Hi,

Was just wondering if anyone else has a Yanmar 4JH4AE with a KM4A1 gear and might be able to comment on the noise that my unit is making. I have taken a recording and uploaded to you tube, hope the link at the bottom works.

It ticks over at about 900rpm and there is no noise when in neutral but when I place in forward gear there is a really rattly noise coming from the gear box. It goes away when the revs are increased and seems to be better when I have been going along at say 1600 rpm and then bring it back down to idle speed.

I have checked the gear cable and this appears to be adjusted correctly but to make sure, I disconnected and operated the unit by hand and the noise was still there.

I thought changing the oil might help but again no difference (filled with SAE 30)

Is this a normal noise or should I get this looked at?

this noise is not present in reverse gear.

Forgot to add one further observation, when going into reverse gear there is a good positive klunk sound but when going into forward there is no positive noise, it just slides in with no klunk.

 

[earlybird]

Rather difficult to judge from a video, but that doesn't sound too clever IMO. Don't know the engine, but if it has a damper plate between the flywheel and the gearbox input shaft, I'd be concerned that has developed a fault. Too low a tickover speed can cause that type of rattle anyway, but 900 rpm is plenty on a 4 cyl. engine, and you say it's OK in astern, which seems a bit strange. A clunk on gear engagement suggests too high tickover if anything.
Can you use a screwdriver "stethescope" to maybe hear if the noise is coming from the flywheel area, or from the 'box itself.
I don't think it's a bearing, but you never know.
Someone with this engine might know better.

 

[pvb]

You posted the same question over 2 years ago, and presumably the boat's been used in the intervening period and the noise hasn't got worse. However, it certainly doesn't sound right and I'd be tempted to ask a Yanmar dealer for an opinion.

 

[Wilfred123]

You are right, I had forgotten that I had previously asked about this but drew a blank.
In the mean time, I did have an engineer have a look and had the damper plate replaced. But this made no real improvement.
I guess I will just have to have the unit removed and have a full inspection to find out what’s up.

 

[rotrax]

A Thames boater asked me to listen to his gearbox, which has exactly the same noise. He is embarrased coming into and out of Thames Locks with his gearbox rattling away.

Yanmar wanted to sell him a new box but when pressed would not guarantee the noise would go.

So, five years on, still rattling but working fine.

IMHO, if forward and astern engage and propel the vessel without slipage and its quiet at cruising speed, its likely to be ok.

If it aint broke, dont fix it!

 

[testmonkey]

just to rule out any other source for the rattling sound - any chance the source actually might be resonance from the propeller?

 

[rotrax]

Not IMHO-it appears to be the slower rotation of the engine causing the gear train to chatter. Pick up the RPM and it goes.

Our boat has a similarly derived Yanmar engine/transmission unit and makes the same noise with the engine cover up. With it down-the vessel has first rate soundproofing-its inaudible.