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SpcAlan1 02-28-2011 09:57 AM

Weird 'severe' vibration
 
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?

mitchb50 02-28-2011 10:10 AM

My guess is there was something wrapped around the prop that fell off after the first time you put it in gear

Mitch

RichH 02-28-2011 10:20 AM

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.

sailingdog 02-28-2011 10:35 AM

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.

LakeSuperiorGeezer 02-28-2011 10:53 AM

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.

travlineasy 02-28-2011 11:48 AM

Could be time to have the prop tuned and balanced. It only takes a tiny nick in a blade or the slightest bend to cause severe vibration.

Good Luck,

Gary :cool:

Faster 02-28-2011 12:07 PM

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.

SpcAlan1 02-28-2011 01:09 PM

I have not inspected the prop.
But I swear, when I loosened the 'gland' up - severe vibrations
I tighted up the 'gland' - smooth running.

that is my hypotenuse - only one way to prove/dis-prove it.

LakeSuperiorGeezer 02-28-2011 03:52 PM

Tightened Gland or Not
 
Quote:

Originally Posted by SpcAlan1 (Post 703276)
I have not inspected the prop.
But I swear, when I loosened the 'gland' up - severe vibrations
I tighted up the 'gland' - smooth running.

that is my hypotenuse - only one way to prove/dis-prove it.

Nothing to do with imbalance, bent or folding propeller since those would be vibrating whether the gland was tightened or not

SpcAlan1 02-28-2011 03:53 PM

I hope I was adjusting the 'gland' - I should have taken a photo.


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