Jet drive noise issue

[werdna87]

Hello everyone ! I have recently acquired a Halmatic Pacific 24 Jet drive rib.

It has a 1994 Yanmar Diesel 6LYA-STP which was fully rebuilt in 2012 and has single figure running hours. It is coupled directly to a Castoldi 06 Jet drive. There is no gearbox between the engine and jet just a direct flexible coupling.

On the first outing after a 500 mile tow from Wales to Scotland, on increasing RPM from 3000 to 3500 there is a loud noise coming from the stern of the engine / front of the jet. There are no major vibrations however the noise becomes alarming and unbearable, It is definitely an abnormal noise.

The rib was tested prior to the journey and performed impeccably at high speed.

After a short time perhaps 5 minutes the noise dissipated and normal crusing could be resumed , however after increasing RPM above 3500 the noise returned.

I have attached a short clip of the issue , i would be most greatfull if anyone has any suggestions.

So far the following has been investigated:

- Alternator belt tension - checked and replaced with a new OEM part.
- Choked pump jet - Boat currently out of water , entire volute inspected and found to be clear.
- jet drive gearbox - oil level was slightly low and there are some signs of emulsified oil OUTSIDE of the gearbox however internal oil was relatively clean, oil was topped up and that is when the noise cleared for a while. Could be coincidense , but hydraulics ( steering and flow deflector control ) have been suggested as possible issues.
- Engine has been run to max RPM (5000) with jet clutch disengaged with no issue what so ever , noise is only evident when engine is under load.

[beamishken]

The rpm could be your problem 6ly is only supposed to rev to 3300rpm with rated continuous running rpm of 3100rpm
High idle is 3650 without load

[breezeblock]

sounds like a bolloxed bearing any lift on the shafts

[werdna87]

Originally Posted by beamishken

The rpm could be your problem 6ly is only supposed to rev to 3300rpm with rated continuous running rpm of 3100rpm
High idle is 3650 without load

Just to confirm i made a mistake on the engine model , Its the 6LY2A-STP model. Not sure if that makes a difference? I am doing the rev numbers from memory as it was a few weeks ago that i had the run , but i was sure the the noise was occurring around the 3000-3500 RPM mark , and i was sure it makes out at 4000RPM at full throttle. Perhaps there is an issue with the tachometer. That aside she won't make the plane under those rpm , will sit at around 10-15 Kts.

[werdna87]

Originally Posted by breezeblock

sounds like a bolloxed bearing any lift on the shafts

That a good idea , i was thinking something similar but with the coupling. It would be an easy check, if a hard repair !

[werdna87]

Sorry you are correct , all my reported RPM's are 1000RPM higher than they were . My mistake !

[breezeblock]

can the rotor spin on the shaft possibly worn spline sheared key

[werdna87]

Originally Posted by breezeblock

can the rotor spin on the shaft possibly worn spline sheared key

In short i have not checked , but thats easily done. There were no major performance issues or vibrations to suggest that the impeller was spinning on the shaft.

[matt h]

Blade creep on the impeller or drive impeller bearing??

[werdna87]

Originally Posted by matt h

Blade creep on the impeller or drive impeller bearing??

As there was no adverse vibration on or transmitted from the stern I am inclined to think that there is no issue with this impeller it's self whether that be creep / cavitation / blockage . It won't hurt to pull the impeller and inspect as it's fairly straight foreward while the boat is on land.

I am starting to think bearings may be a good shout though , whether the engine or the jet .