Despite careful engine-to-shaft alignment, I have been unable to eliminate moderate vibration when motoring above about 2000 rpm in my 2005 h44. (In neutral there is no vibration.)The Maxprop appears to be in good shape and the shaft does not appear to be bent. The engine mounts are also fine. Friends' boats (not Hunters) have much less vibration under power. Have others been able to motor with little or no vibration?
Engine vibration when motoring in a Hunter 44
- Thread starter Larry Jackel
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Are you sure that what you are feeling is not prop wash on the rudder? I have the same configuration (44 DS/Maxprop) and do feel quite a bit of prop wash in the wheel in those speed ranges.
Some info I found on the web...
Vibration
There are enough thrills in boating without having the additional stress of a vibrating clunker below decks. Obviously some of the older style single cylinder engines can't avoid thumping and shaking around but there are one or two things you can do to reduce the effect.
In the 'olden days', one would bolt the engine directly to the engine bearers and direct couple the propshaft to the gearbox output flange. Hence every time the engine ran all the loud thumps and bangs would shake the boat and aggravate your best friends migraine , causing her / him never to go boating with you again. Before the odd one of you rush off to remove the flexible engine mounts from under the engine, remember that any vibration can cause the engine, and parts of the boat, to deteriorate at a speed that may out-distance your pocketbook.
If you don't have flexible engine mounts installed already they can be a little expensive to fit as the engine beds will need to be changed to suit, however, it is a very worthwhile modification. Never modify the engine mount feet, always modify the engine beds. Beware the installer who tells you otherwise.
To check if you really have a problem or it is in the imagination, 4/5ths fill a beer glass with water and hold it on the top of the rocker cover. If the water slops out, the vibration is excessive.
The common causes of vibration are listed below:
Vibration
There are enough thrills in boating without having the additional stress of a vibrating clunker below decks. Obviously some of the older style single cylinder engines can't avoid thumping and shaking around but there are one or two things you can do to reduce the effect.
In the 'olden days', one would bolt the engine directly to the engine bearers and direct couple the propshaft to the gearbox output flange. Hence every time the engine ran all the loud thumps and bangs would shake the boat and aggravate your best friends migraine , causing her / him never to go boating with you again. Before the odd one of you rush off to remove the flexible engine mounts from under the engine, remember that any vibration can cause the engine, and parts of the boat, to deteriorate at a speed that may out-distance your pocketbook.
If you don't have flexible engine mounts installed already they can be a little expensive to fit as the engine beds will need to be changed to suit, however, it is a very worthwhile modification. Never modify the engine mount feet, always modify the engine beds. Beware the installer who tells you otherwise.
To check if you really have a problem or it is in the imagination, 4/5ths fill a beer glass with water and hold it on the top of the rocker cover. If the water slops out, the vibration is excessive.
The common causes of vibration are listed below:
- The engine idle rpm needs setting correctly.
- Engine / propeller shaft misalignment.
- Faulty engine mount. The elastomer deteriorates due to spilled diesel, excessive weight and/or old age.
- Improperly secured engine mounts.
- Incorrectly selected engine mounts. The elastomer has a 'hardness factor' and stiffer mounts must be fitted to compensate for heavier weights, e.g., if a fridge compressor has been added. ( Use the genuine Yanmar mounts, they work well. )
- Mechanical trouble, e.g. an injector not set at the proper pressure, poor compression on one or more cylinders, valve clearances incorrect, incorrect fuel pump timing or a sliping gearbox/transmission clutch cone (slipping cone normally @ low rpm).
- Modified engine mount brackets. Don't change the engine, always change the engine beds!
- Propeller cavitation. The propeller is too small or the appendages in front of it are causing cavitation.
- Damaged propeller
- Damaged/bent propshaft
- Problem with shaft strut or p-bracket i.e.lose out of alignment with other stern gear
- Worn or damaged cutlass bearing
- Incorrectly sized propeller shaft tube. The old fixed type 'Admiralty' gland on the prop shaft tube meant the shaft to tube clearance could be about 1/16th inch and the two parts would never touch as the shaft was held in the central position by the gland. With the advent of the modern 'dripless' glands the shaft can move about with the flexibly mounted engine. This can occasionally cause the shaft to bounce on the tube, especially if heeled over while motor sailing. A larger diameter propeller shaft tube (about 2.5mm or 1/8th inch clearance) is one way of resolving this problem. Alternatively, install a thrust bearing or an 'Aquadrive' CV joint which will hold the shaft in the central position.
- Other things in the boat, like the pots and pans in the galley thrashing about.
- Engine imbalance from the manufacturer has happened twice that I know of and both of them were over 10 years old when they were complained about!
First step.
Wheel vibration is not quite the same as the engine vibration. Engine vibration you feel in the seat of your pants and should be minimal.
Notice here that after the head torque the problem went away or at least improved. Well after the head torque the valves were adjusted (or should have been). That is the easiest and cheapest thing to do. Incorrect valve adjustment will cause the valve timing to be off and from there it is down hill.
Wheel vibration is not quite the same as the engine vibration. Engine vibration you feel in the seat of your pants and should be minimal.
Motor mounts?
Cheap fix maybe. Tighten the bolts on motor mounts I had problem with vibes and just by tightening the bolts the vibes went away.
Cheap fix maybe. Tighten the bolts on motor mounts I had problem with vibes and just by tightening the bolts the vibes went away.
Larry: You mention that the shaft does not appear to be bent. Most likely, you will never be able to see a bend in the shaft unless it is extreme, and, it does not have to be extreme to cause vibration.
My personal evperience is that my shaft came from the factory bent in 2 places, and it took 2 seasons to come to that conclusion. The shaft shop showed me the location of the miniscule bends, but I could not see it with the naked eye.
After reinstalling, it was as if I had a new boat.
Good luck..... Jeff
My personal evperience is that my shaft came from the factory bent in 2 places, and it took 2 seasons to come to that conclusion. The shaft shop showed me the location of the miniscule bends, but I could not see it with the naked eye.
After reinstalling, it was as if I had a new boat.
Good luck..... Jeff
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