Vibration from Universal 5424

[MarkSF]

I get a vibration when in forward gear, that's noticable between 1300 rpm and 2000. So I end up cruising at either 1300 or 2000rpm. It results in cupboard doors etc. vibrating throughout the boat.

The history is that a local boatyard installed a new Hurth transmission, had the prop balanced, and a new propshaft was installed, all just before I bought the boat 2 years ago. It's had the vibration since I bought it.

This is a Universal 5424 with 2:1 Hurth transmission and 3 bladed prop.

I'm assuming the two most likely causes are the prop, and a misaligned driveshaft? How can the driveshaft alignment be improved and can this be done in the slip?

I'm also wondering if the problem could be worn out engine mounts. They are 28 years old now.

One problem is I don't really know what to expect. Anyone else with a 3 cylinder?

[holmek]

A collapsed engine mount would result in the engine vibration being directly transmitted the hull. A worn cutlass bearing will shudder like crazy. Misaligned gearbox/propshaft coupling will do the same. elliminate step by step. Vibration with engine running but not in gear? Y/N. Vibration only when in gear? Y/N. Vibration only in forward but not in rev. Y/N. etc.

[Sailmonkey]

We've got a three cylinder Kubota engine also. Vibrations that bad are almost always caused ny alignment (except when they're caused by a bad injector).

Alignment is easy to check and must be done in the water. To check it, unbolt the shaft coupling from the transmission, then without pulling the shaft aft, turn the shaft and see if there are any gaps between the two coupling faces.

If the mounts are worn out or even broken the vibrations can be pretty bad too. Grab the top of the engine and violently push/pull/shake it and see if there is extra movement in any of the four corners

[MarkSF]

Thanks for the info. Yes the vibration is only when in forward gear. Reverse is much better.

One thing is I can't actually see any rubber in the engine mounts. I've heard they were solid epoxy? Sounds strange to me. Or is there no rubber because it's long since evaporated...

[Sailmonkey]

Post a pic of the mounts. If someone mounted a 3cyl directly to the hull without rubber mounts you'll feel every single vibration good and bad.

[MarkSF]

Will do, but can't until the weekend. There's definitely an engine mounting between the engine and stringer, but I can't see any rubber core inside it.

To be honest the vibration I can live with, it's the noise that it creates I can't stand. Worst is a sort of thud at prop rpm.

[Pato]

Was the alinement ever checked after initial install if not its the most likely cause of your problems. I would check each mount make sure all adjusting nuts are tight aswell as the bolts holding it in place. Check for any cracks around mount locations. Note when you check your alinement make sure the coupler is clean scotch bright pads should be ok to clean up coupler. It does not take much to create a big vibration when thing a spinning that quickly

[MarkSF]

Well you know how it goes, they were supposed to check the alignment at install but I suspect they didn't do so when it was back in the water.

[Pato]

We won't hook up couplings until the boat is in the water and mounts have settled then we can do final alinement And generally we check it a week later after some hours have been put on

[MarkSF]

OK that's actually quite encouraging, after 2 years maybe it's high time the alignment was re-checked especially as it was probably never done in the water.

I'm thinking of soundproofing the engine compartment but it sounds like I should get the alignment checked first.

[Pato]

Yea it really does not take much to change by a couple thou and create a vibration. The acceptable tolerance is 1 thou per inch of flange. I would imagen you have a 3 inch coupler so 3 thou is the max you can be out without a problem

[Pato]

If access is good and coupler and bolts are clean it shouldn't take long to check If it need to be adjusted it can pita depending on access to all four mounts. Sometimes having 2 people will make it easier and faster