Shaft/Engine Re-Alignment

[pwrobert]

25 Years ago I had SS strust made by my prop shop and they have done well. When the 6BTA’s were installed they were remove and reset as part of the engine install.  That was back in early 2019.  All has been well. However, I took my extended family out to see the 4th of July fireworks back last summer (’22).  I anchored up with dozens of other boats just out of the intracostal and watch the show.   However, when heading back to the channel (  about 175 yards)  I struck hard a submerged object.  So hard it lifted the boat enough to knock down any that were standing.  Did not take on water but had the boat hauled the next AM.  Turns out the objust was what was left of a broken off information marker – likely concrete and steel. Keel, transducer,prop, shaft and strut damage.  Took most of one blade off the port four blade Nibral and bent two other blades.  But the main thing was the strut was bent to Port about 12-15 degrees.  All at 675 RPM.   All of these parts were removed and sent to the prop shop and all straightened.  I did the transducer and hull work while the others stuff was done by prop shop and yard crew. After the running gear was re-installed I asked about how did it go re-bedding the strut.  They said it didn’t need it.  Just new bolts and 5200.  “Everything lined up great”. I haven’t used the boat much in the months since and started my check list and running things a little to make sure no issues ahead for a June trip to the Abacos.  But.. There is a significant vibration starting at 1600 and increasing up through 2200 RPM which was as far as I wanted to push things. I just had the boat out to do the bottom paint last week and was not aware of things until my return trip home (12 miles).  Can the alignment be checked in the water at my home dock sufficiently?   Is it “Kosher” to  support the shaft “drop” from the Dripless shaft seal by only cracking a gap between the flanges of the coupler and letting the male/female rings of the coupler provide the support.  Will the Gaps really be free enough to show where things stand and just do the feeler gauge testing? Or is this another haul-out and starft over? Thanks

Topic

[lpmcc]

Yes I have, and yes, I followed your directions.  I only really have one spot on the shaft to measure with a dial gauge and that is 4″ behind the coupler (v-drive boat).  My question is where the high & low spots are, and by how much, give you any guidance as to what adjustments in the motor mounts need to be made?

[Clark Leighs]

Have you used a dial indicator?    NOt trying  to be a snark  but unless you have some idea how to use one properly then describing what is req’d over the net is going to a long winded affair.

I can think of several ways but you will need a magnetic stand to hold the dial indicator,   some sturdy C clamps, a piece of steel that can be clamped to the , hopefully nearby , engine mount so the indicator stand has a solid mounting.  Flat plate or a good size piece of steel angle.  Or use a flat plate and a heavy angle clamped to the stringer

I have also used a HEAVY piece of steel , approx 1″ thick and 12″ square or thereabouts that is heavy enough to not be bumped and moved easily or all will be lost and the whole shebang will have to be reset..

Set up the indicator so  it can be used on the shaft and/or the shaft side coupling. and carefully rotate the shaft.  Set the indicator plunger so it is already compressed  0.30 or so and then rotate the legend disc to 0 zero it so you can see if the shaft wobbles  + or – and how much keeping notes.  Also use a marker pen to note the high and low points and what the measures are..

Then rotate the shaft and keep the notes and marks.

 

You may have to do this several times over the length of the shaft.    THere may be minimal runout at the coupling increasing as you get to the stuffing box end.

I am not though an expert at this but have checked my coupling , both sides on occasion this way.

[lpmcc]

Dial Guage?

Tony/Rob, can you comment if using a dial gauge to measure shaft runout could be helpful in setting/adjusting the alignment?  If, so how to use?

 

Thanks

[pwrobert]

What I Found today

Ok today I have the boat at my home dock and decided to take things apart and see how far off the coupler was.

Right off the bat it wasn’t as far off as I expected (10 thousands) but I did need to move the engine on it’s Seaboard engine mounts a little.  Moved the front of the engine to starboard and the rear tiny amount to port.  Dropped the starboard front mount 2 hex flats up. Most of the out of true was more Open on the 3:00 position and a little at the 12:00. 

The engine mounts were examined after the accident and the coupler was checked and “faced a little”.  The props on the boat now are not the pair that includes the damaged/repaired one.  My other recently dynamically balanced pair are installed.  Just for grins I sent back the repaired one and it’s mate and asked that they be “matched” and balanced.  Reports came back that a little tweaking was done to my now spare set and they should be a pretty true match if ever needed.

I cant sea trial until next week and the proof will be in the pudding.  Fingers crossed that there is not some other issue.  Countdown to my Abaco trip in 6 weeks puts things on edge.

[Rob Schepis]

Were the isolators inspected carefully after the impact?

Have you put an eye on the shafts as you increase rpm’s for a visible?

Yes, in the water with the bolts loosened and just enough space between the flanges for the feeler gauges.  Start with that.  If that checks out within spec you may need to haul.

Don’t rule out a prop blade being out.  I’ve seen props come back from shops that were not true and have seen props get a blade twisted because of the method of reinstall (chocking out on the blade when tightening)

One thou per inch of coupler dia is the max but half of that is a good target.

[lpmcc]

To add to his questions, can you align an engine/shaft using a dial gauge on the shaft vs feeler gauge at coupler?  Spin the shaft, note any runout, and will that tell you what to adjust (up/down, sideways, etc.)?  And what is max allowable shaft runout?  If I remember correctly, it is half a thou per inch of coupler.  i.e. for a 6″ coupler it would be 3 thou?

[Author]

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