Engine Vibration.

[amgrant1979]

Hi Guys we have had an on going problem with a vibration on our Stbd engine.

Background
Several years ago we had the STBD shaft pulled to replace a cutlass bearing and then developed a vibration. I showed the mechanic who did the work and he blamed the engine mounts. funny how no vibration before the work and a week on the hard and a new cutlass and it has a vibration hmmmmm.

When the boat got pulled next I got a call from the yard telling me i should get the mechanic back as the STBD propeller wasn’t installed correctly. I did this and the mechanic reinstalled the prop with no charge. However we now still had a vibration.

Since then I have had the Props pulled and re-pitched to develop the RPM as per Tonys guidance and by Tony’s prop guy in Oxnard. I have replaced all mounts with the recommended Barry Mounts and Had the engines professionally aligned (by a different Mechanic). We have all new cutlass bearings on both shafts in the P bracket and in the hull (2 per shaft). We also had the STBD shaft spun up to check that it true and balanced on the bench. and the alignment re-checked after all of this. Also had all the stuffing box packing redone during this time.

Yet we still have a vibration on the STBD Engine. the engine runs smooth out of gear but as soon as you but it in gear there is a vibration.

I’m at a bit of a loss to where to go from here but I’m wondering because we ran it with the vibration for a couple of seasons that maybe we have damages the rear bearing on our twindisc Gearbox? The shaft is hard mounted to the gearbox output on our boat.

Anybody got a suggestion of where to go from here? I will endeavour to get some photos and a video up when i get a chance bit overwhelmed with work and life at the moment.

Thanks in Advance

ANDREW

yet w

Topic

[Rob Schepis]

By eye, no gauge? We’re talking thousandths of an inch.. Has someone put a feeler gauge to the couplers? How about those pics Phil requested?

[amgrant1979]

It got pulled to renew the bottom paint, once it was lifted we could see the cutlass where the shaft goes through the hull had become loose and backed out of its holder.

I have also undone the coupler and Rea attached it moving one hole at a time. Whilst I didn’t have a gauge on it to my untrained eye in made no difference to the vibration.

Cheers

Andrew

[Tony Athens]

I have a question:

Background
Several years ago we had the STBD shaft pulled to replace a cutlass bearing and then developed a vibration. I showed the mechanic who did the work and he blamed the engine mounts. funny how no vibration before the work and a week on the hard and a new cutlass and it has a vibration hmmmmm.

Exactly why did you pull the vessel to make this repair?

Tony

[Rob Schepis]

Did you have the machine shop fit & face a new coupler to the shaft. When you’re doing your alignment checks at the coupler are you recording the readings and then rotating the shaft/coupler to a different orientation on the gear flange and taking new readings to verify the faces are both true?

[Philip]

Sounds like it’s either the torsional coupling or the transmission. Good news is the torsional coupling can be inspected when the transmission comes out and if it’s bad you can skip tearing into the transmission. I suspect the engine is smooth when the prop shaft is disconnected as it needs a little load to chatter away. This points to the torsional coupling. What year and how many hours on the engines?

Hopefully others will chime in and either confirm or call me out…..

Either way, how about some good quality pictures of the engines and transmissions and a few of the “dust”around the engine/transmission joint?

[amgrant1979]

I know its the STBD Engine because Ive been in the engine room and see that engine shaking and the port Is rock solid could set my coffee on the port.

The Stbd Engine in gear at idle has noticeable movement (fwd gear only) . the vibration is noticeable during power up/down around 1100-1400 rpm . outside that range there is no noticeable vibration unless you go look at the engine and there is some movement but it is very rapid at operating RPM, 2600 typically for us. There is no noticeable wear between the engine and the gearbox.

I have not inspected the Torsional coupling (had to google it to know what it was). There is some dust on both gearboxes which I assumed was clutch dust? looks like very fine rust powder but easily wipes off the gear box housing. This is present on both gearboxes in the same quantity.

I have also run the boat in gear with the shaft coupling disconnected and there is no noticeable vibration unless the shaft and prop are connected and spinning.

Cheers

Andrew

[Philip]

Tell us more about the vibration. How do you know it’s the Stbd side and not the port? What rpms? Same at all rpms? Is it at idle speed and less noticible as rpm increases? Or does it get worse as rpm increases?

Have you inspected the torsional coupling? Any signs of wear at the transmission to engine joint? Any dust etc?

Phil

[Author]

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