Vibration in engine drive

[Delawaredave]

Newbie. 82 Hunter, Yanmar 8hp diesel. Seems like excessive vibration when running.

Reason for this post: looking for advice on how to isolate the source of the vibration and fix.

The cutlass bearing has some slight play when grabbing the shaft. Now that boat is out of water, I want to check this play against other boats.

Besides the cutlass bearing, what else could be causing the vibration ?

Do props every need re-balancing ?

I assume engine mount alignment is a possibility ? I've not measured runout, but the coupling beween the driveshaft and transmission seems true.

The stuffing box does provide any support, right ? It is a just a flexible seal joint, and does not provide shaft support or alignment ?

Thanks for any input !

 

[Captn TJ]

Newbie. 82 Hunter, Yanmar 8hp diesel. Seems like excessive vibration when running. Reason for this post: looking for advice on how to isolate the source of the vibration and fix. The cutlass bearing has some slight play when grabbing the shaft. Now that boat is out of water, I want to check this play against other boats. Besides the cutlass bearing, what else could be causing the vibration ? Do props every need re-balancing ? I assume engine mount alignment is a possibility ? I've not measured runout, but the coupling beween the driveshaft and transmission seems true. The stuffing box does provide any support, right ? It is a just a flexible seal joint, and does not provide shaft support or alignment ? Thanks for any input !

Lots of questions to answer. And more to ask.

First is the vibration new to the boat and/or does it happen at a consistent rpm. On a previous boat I had a slight vibration at only a certain rpm - changed out the prop and it went away

All of the above questions you asked all could add to vibration. Easy check: look for nicks on the prop if none - assume this is a fixed blade then you should be ok. If feathering or folding look for looseness in the blades

If I had any play in the cutlass I would change it out. This is a reasonably easy, inexpensive project and since the boat is on the hard I would do it just to eliminate it as a potential problem.

The other two issues that could add are either the coupler or the mounts. Both require the boat to be in the water. I would not trust my eyes for proper alignment and would recommend always using a feeler gauge. It would take just the slightest variance to cause a problem. I have always checked when the boat goes in the water since the hull has more support in the water then on the hard and especially if I adjust the rigging. If all three are good or resolved and you still have vibration then check the motor mounts. You may be able to check visually for deterioration and of course it would be self evident with the engine running.

FYI The stuffing box does not provide support.

 

[Captn TJ]

One additional point - check the bolts/nuts on the motor mount to make sure they're not loose.

 

[Delawaredave]

Thanks ! The vibration is constant - not at certain RPM. Seems to be proportional to RPM.

First boat for us - we purchased in March 2013 - vibration has been with us the whole time.

Thanks again.

 

[Chief RA]

Delawaredave: Common since would lead me to check the prop right away as the likelihood that it struck something is high. Hope for this also as its an easy, cheap fix to get the prop balanced. Chief

 

[David in Sandusky]

Cutlass play <1/16th

Up to 1/16th of play on your cutlass bearing is OK according to Neil Calder, and my modest experience.

I'd check for a bent shaft - that was the problem on our boat.

Check shaft alignment at the coupling after the boat has relaxed in the water.

 

[Benny17441]

A main reason is cracked or soft motor mounts. Good motor mounts absorb most of the engine vibrations. If your boat has the originals they are more than 30 years old and probably need replacement. Do not go by what the rubber looks like as they may look good to the eye but they can be shot. Some vibration is inherent to the single cylinder Yanmar engine but is not severe. Adjust the valves, replace the filters, check the engine alignment and most of all the motor mounts.

 

[hewebb]

I replaced my motor mounts during an engine change and realigned the coupling with the boat on the trailer. This was my first try at getting the alignment correct-not sure I got it right. I ran the engine for 6 hours and the vibration increased when in gear. With the boat in the water, for three days, I attempted to realign the coupling. In doing so I found that the ears on the transmission were not true. The fore/aft alignment was thirty thousands off to each other. (Used a dial indicator) I machined spacers to take up the difference in spacing. They were numbered to match the numbers I placed on the transmission ears. The prop shaft and coupling run out was within one thousandth of an inch. I took great pains to insure everything was aligned correctly. That eliminated 90 % of the vibration. Not sure when or how the ears on the transmission got out of alignment. The boat always had a lot of vibration since I owned it and I was not smart enough to realize there may be a problem. Just thought it was normal for the little diesel. I also replaced the cutlass bearing during the engine change.