SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

Weird 'severe' vibration

3K views 28 replies 15 participants last post by  SpcAlan1 
#1 ·
I just bought the 1979 Islander 30 with the Volvo 13hp.
the engine purrs in neutral and can rev it up with no vibration at all - smooth as my F-150, ha.

The previous owner recommended me to 'loosen' the 'knuckle' to allow water to drip. - Inboard engines and this technique is greek to me - I assume to 'cool' the shaft? I do not know. Any suggestions on readings?

Well I did this under his observation and it drips 1 drop about every 2-3 seconds. Now I have this HORRIBLE vibration when in gear - it rattles the whole boat when just above idle speed. Very severe vibrations.

I went back and tightened the 'knuckle' back up to 1 drop per 5-10 seconds ( which was a minute adjustment - I mean maybe .5 degree turn.

Now the engine purrs in gear and I can really get some speed.

So, was this the fix? Or have I lost my mind?
 
#3 ·
Vibration analysis is a very complex science; changing the mass, changing the geometry .... and changing the forces acting internal to the system will change the 'natural frequency of oscilation' of the vibrating components.

Simple speak: If by tightening up the stuffing box radically alters vibrational performance would seem to positively indicate that the system is 'out of balance' and the tightening is merely 'shifting' the vibrational characteristics to 'another frequency / amplitude'.
It would very strongly suggest that 1. the coupler and engine alignment are 'out of whack' 2. the propshaft is bent.

Rx-
1. Realign the engine to the coupler, aiming for 'perfect' alignment ... ie.: less than 0,001" of run out as measured between face to face on the mating surfaces of the flanges. Of course you will on an old boat probably will find broken or 'frozen' motor mounts.
2. With the stuffing box 'released' (or packing removed or loosened so that the packing is no longer in contact with the shafting) use a dial indicating micrometer positioned near midshaft of the propshaft, rotate the shaft and measure if the propshaft is 'true' (virtually no deflection of the dial indicator) as the propshaft is turned through 360 deg.), Or remove the propshaft, take to a machinist (with a large 'set-up' table --- a huge heavy steel table calibrated for its flat surfaces) to verify the 'straightness' of the shaft, etc. If this is a shaft that has been in the boat for years of service, its 'much better' to remove it, have it re-'trued' by a machinist ... and have the 'journal area' where the stuffing box packing and the cutless bearing 'dressed' to remove and developed surface roughness and pitting of the shafting.

For a DIY validation/correction --- do websearch or forum-search on the proper methods for engine re-alignment and stuffing box repackiing methods ... and realign and repack with the goal of 'perfect' alignment and uniform 'side loads' on the shafting from the packing, etc.
 
#27 ·
.. and realign and repack with the goal of 'perfect' alignment and uniform 'side loads' on the shafting from the packing, etc.
Rich that's an interesting point about the 'side loads' from the packing. I know that you also own a Tayana 37 and just the other day I repacked the stuffing box. The shaft on the boat is 1 1/4 inch dia and the stuffing box should take a 1/4 inch packing, but I'ld used 3/16 previously and continue to use the 3/16 since it's not possible to fit the 1/4 inch into the box. Over on the TOG site I asked what others were using with the 1 1/4 inch shaft and Harvey said he also used the 3/16 inch since the box was not perfectly concentric around the shaft which then begs the question of unequal side loading. Have you noticed that the shaft is non concentrice with the stuffing box?
 
#4 ·
Yes, the dripping water is to cool and lubricate the shaft where the packing gland is. Have you dove or had someone dive to inspect the prop, shaft and strut? If not, you should. Also, have you tried loosening the knuckle again? If not, you should.

If the prop shaft, prop and strut are clear and there is no growth on the prop blades, and you loosen the knuckle and the vibration returns, then I'd recommend following Rich_H's instructions.
 
#5 · (Edited)
Grab the propeller and rock it from side to side. This is a test to see if the cutlass bearing is worn out. There should be minimal play between the cutlass bearing and the propeller shaft. When the bearing begins to break up this will cause strong vibrations in the stern. BoatWorks by editors of Sail Magazine covers this. This book is a series of published articles. There is a 6 page chapter on replacing the cutlass bearing, the chapter after that is Stuffing Box Maintenance. It's not that hard to do for the DIY person with this book as the instructions are good identifying what is happening in each picture, but does take time.
 
#7 · (Edited)
Is it a folding prop? A non-geared folding prop will occasionally fail to flip both blades open, resulting in unbelievably violent 'vibration' as a horribly unbalanced (single blade, effectively) prop turns. Usually coming out of gear and re engaging fixes it. This is probably the only way a strong vibration like that could 'come and go'.

On one of our previous boats we got into the habit of a quick burst in reverse prior to engaging forward gear; that usually prevented this occurrence.

I doubt very much it had anything to do with your gland adjustment.
 
#18 ·
He means rotating the prop shaft by hand... you're looking for 'run out' or a wobble in the shaft as it turns. You can usually grip the coupling at the back of the gearbox and get enough leverage to turn the shaft.
 
#17 ·
I'll bet the cutlass bearing is shot, in addition to an alignment problem.
 
#21 ·
I'd still like to know whether or not it's a non-geared folding prop... It's the most likely cause of an alarming amount of vibration that is likely to 'come and go'.
 
#23 ·
Stuffing box

If it is not vibrating now you likely have nothing to worry about. Yes it should drip but not too much. Over tight is the worst case as will cause wear on shaft and rob power that is for driving the boat. Do a thorough inspection of complete driveline on next haulout. Somewhere Mainesail has good article on cutlass bearing. If there was a serious defect somewhere it would still be felt and probably heard as well.
 
#24 ·
Also, after I adjusted it again, the vibration came back, but I then put it in neutral, then in drive - went away.

I wonder if its a motor mount or something.

well it is dripping non-stop - not 'running' but a constant drip - fills up bilge.
probably too much than normal.
 
#25 ·
Tightening the packing gland can be dicey and may take practice. What you want is for it to drip when the shaft is turning, and stop when it is not. Depending on how worn the packing material is it may not be possible, (time to repack). I often have to check packing boxes after using boat to make sure they stopped dripping. (a small tighten after done using the boat, then loosen back the next time I take it out). If tightening gland stops vibration something is wrong. See above. It sounds like your using the packing box for a cutless bearing.
 
#28 ·
I'm also going suggest a possible problem with the motor mounts. It may be as Rich suggested that when you tighten the stuffing box you are just transfering the movement to the hull (i.e., the box is helping to keep the driveline from moving around). If it is a Yanmar, they view the motor mounts as a wear item and suggest replacement every 5-7 years, as I recall. I replaced all four mounts on our Yanmar 2GMF this weekend and realigned the engine and WHAT A DIFFERENCE! In the process of replacement, I found that not only not only had the 27 year old original mounts gone soft (the rubber that is), but the stud on one of them was broken. The broken stud was not noticible until I pulled the mount becuase it was held in place by the weight of the engine. I hadn't even noticed it when the engine was running and I was checking the old mounts. Anyhow, if you decide to go that route, I highly recommend getting original Yanmar mounts. There are a lot of aftermarket ones out there, but my research suggested that a lot of people have trouble with them. It is an expensive replacement, but in our case well worth it.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top