Hamilton HJ274 rumble at high speed

[buchandiver]

My HJ274 recently started giving loud rumbling noise at high revs - shaft & bearings seem OK but will check when stripped down. Just took it out of water today and noticed that the steering lipseal is dislodged - could this be cause of rumble if the nozzle starts to vibrate?

 

[baeckmo]

What power, rpm and boat speed?

 

[buchandiver]

370hp diesel, rumble starts at around 2600rpm up to engine max at 2800rpm - speed dependant on load (or weed on hull) - say around 16 knots upward. Haven't run at high speed since apart from a few test runs before I craned boat out today.

 

[baeckmo]

That would be the most critical speed range in terms of cavitation. If it has been operating without rumbling at this speed before, you should look for any disturbance or blockage in the inlet. The Hamilton manuals are often very good when it comes to operating data. Normally you find a thrust/speed diagram with power as a parameter; check that your boat is within acceptable range.

Check inlet grating, there must be no marine growth, no fingers bent or displaced, no nylon rope twisted around shaft, no plastic bags, no nylon stockings wrapped around vane leading edges........

Check impeller inlet, vane leading edges, check radial gap between vane tip and housing.

Check that you have the correct jet nozzle for the engine/boat wheight, and that it is not damaged.

And, of course, make shure the hull is not full of barnacles, or overloaded. How often do you check which stuff on board is really necessary?

 

[buchandiver]

Boat does 28 knots lightly loaded with clean hull. Jet/engine was spec'd by Hamilton for boat when it was built 8 years ago & it's been fine ever since. Grating is fine & clear with no debris (we're divers so clean/inspect it regularly whilst in water), shaft clear. The noise doesn't seem like cavitation - plenty of thrust, just rumble/rattling noise from jet, thrust bearing not hot.

 

[baeckmo]

Aha, that's another story then. What kind of transmission shaft do you use? Any kind of cardan links or elastic couplings? Not unusual to find a worn and noisy cardan bearing in a layshaft; the rumbling is carried to the hull through the jet housing.

Can you feel any radial play when gripping the shaft through the cleaning lid?

How about the steering nozzle and its bearings or the reverse deflector, bearings and linkage? Is the outlet stator firmly bolted to the housing?

 

[buchandiver]

Cardan shaft - universal joints each end.

No radial play in shaft. Steering nozzle etc all good, just in process of strip-down to change the anodes & check/replace cutlass bearing.

 

[baeckmo]

Mmmhm..... How about engine mounts? Anything on the engine that will touch a fixed object on hull when the engine is "leaning over" due to shaft torque increasing?

Exhaust muffler moving, vibrating, swinging?

 

[buchandiver]

Engine is good & solid, no muffler - exhaust via flexible hose - pretty sure it's either the jet or driveshaft. Will drop out the driveshaft & check bearings.

 

[buchandiver]

Cutlass bearing was fine, removed impeller -perfect, wear ring perfect. Removed main bearing housing (some water ran out) & seals - the split pin holding aft waterseal cap & spring was broken, looked like spring had backed-off allowing the seal to pass water. Aft oilseal just a black mess & emulsified grease at aft end of bearing - however the bearing 'seems' fine. Still to clean parts & inspect fully.

Suppose question is with bearig good, but waterseal & aft oilseal shot, would this have caused the noise?

 

[speedboats]

Carbon seal and spring would've been bouncing around on the mainshaft in front of the impeller. This could have created a 'rumbling' sound as the impeller tries to cavitate.

It is likely that the bearing is knackered, the emulsified oil and water isn't the greatest at lubricating. I'd bet a dime to a dollar it was the bearing, it wouldn't have got hot because it was water cooled! It is a QJ308 (309? can't remember which) split inner and brass cage. A similar bearing is available with a plastic cage (nylon, PE?), but it isn't up to the task so don't consider it as a 'cheaper' option (It'll be an expensive lesson). If it has been run in water it will have a significantly shorter life now, they are not overly expensive so I'd consider replacement anyway.