Engine alignment

[hallp]

Hi all,
I have a 1979 blue seas trawler.
My starboard engine had vibration around 1200rpm.
I have hauled the boat and removed the prop shaft. I placed a piano wire between to aft side of the A bracket and the engine coupling.
It seems the engine is around 9mm low based on the position of the wire where it passes through the stern tube.
Can I adjust engine height by adjusting the center nuts on the mount, or do I need to shim under the mount.
Below is a picture of my rear engine mount.
If I need to lift the engine what is the best method, can I jack against the hull if I block it out to spread the load.
Thanks
Phil

 

[OldDan1943]

Best guess, yes.
Maybe it is time to change motor mounts?

 

[av8r]

Yes you can use the engine mount nuts to adjust the alignment. The usual method is to unbolt the shaft flange from the transmission output flange and use feeler gages to adjust the 2 flanges to parallel. Several threads here on the process or google prop shaft alignment.
The black motor mount looks like it is a replacement. Recommended interval for shaft alignment is yearly.

 

[av8r]

I just re-read the original post, alignment should be be done in the water since blocks or slings can flex the hull differently than floating.

 

[Fish53]

Pretty hard to align an engine to the shaft coupling without a shaft coupling? I agree it's only possible to do rough alignment out of the water and if you're doing it anyway you should replace your flexible mounts first.

 

[Pete Meisinger]

Why did you remove the shaft, and therefore, why did you pull the boat?

The alignment should be done in water with the shaft backed off the transmission a fraction of an inch.

Put it back together, put it back in the water and start the normal alignment process. You may find you have other problems causing the vibration.

pete

 

[Keysdisease]

It may be the angle of the photo, but is the engine bracket parallel to the mount? The bracket to mount angles should be parallel and shimming is the recommended way to correct

 

[DDW]

That would be a pretty floppy boat to get 9 mm of misalignment when blocked. And if you only have a P bracket and no second bearing, just disconnecting the coupling and letting the shaft hang will not give you an accurate picture. On a 30+ year old boat, starting by replacing the mounts might be the right direction.

 

[rgano]

Do not make any adjustments now on a hunch that you need to address the 9 mil difference you see. Getting the shaft straightened and the prop checked will ensure that once you are in the water and get a good alignment you will have a smooth ride. If you still have that 9 mil difference between the transmission and shaft flanges (connecting bolts removed) once you are back in the water, simply cranking up or down on the aft motor mounts will likely not resolve the issue. You could well end up having to work with the forward mounts too. There is a very specific method to do this alignment involving drawing the two flanges together checking alignment top and bottom and side to side with feeler gauges, making adjustments to the mounts and then repeating the process of measurements. At some pint you rotate the shaft 90 degrees to check for a bent shaft. Lots of patience is required.

 

[Lou_tribal]

I am so glad to have a universal join!

L

 

[hallp]

So my next move is to replace the engine mounts.
By having two plugs with a 1.5mm hole turned up the same diameter as the shaft I placed one plug in the shaft coupling at the motor and one at the p bracket and ran a wire between them.
The 9mm offset from the centre of the stern tube is real.
I am now assuming the engine mounts have collapsed or I have some major flex in the hull.
Prior to hauling the boat which was coming out for winter anyway, I had a dial indicator on the shaft and turned it by hand, this showed some distortion.
I have had the shaft checked for straightness and the propeller checked.
I will pull an engine mount and inspect today.
Cheers
Hallp

 

[rgano]

I thought there looked to be a little distortion of the stringer under that one mount you showed us, but I could be mistaken. You seem to be aimed in the right direction. Hopefully, after launch all will align well and smoothness will ensue!

 

[OldDan1943]

I am a chicken and realize, somethings are best left to the professionals. Changing motor mount would be one of those things, in my mind.

 

[rgano]

I am a chicken and realize, somethings are best left to the professionals. Changing motor mount would be one of those things, in my mind.

Did it as a complete novice. Lots of chain, shackles and several pole jacks going sloooowly and carefully....

 

[OldDan1943]

Did it as a complete novice. Lots of chain, shackles and several pole jacks going sloooowly and carefully....

And now I know who to call if I ever need to have my engine mounts changed.
LOL

 

[hallp]

Given the engine is around 500 kg and I am only lifting one end at a time I think if I spread the load with timbers I can jack of the hull. What do others think.

 

[rgano]

And now I know who to call if I ever need to have my engine mounts changed.
LOL

That was in 1987. You have NO idea how lazy the intervening years have made me! I am now quite happy to sit on the engine coaming and "consult."

 

[rgano]

Given the engine is around 500 kg and I am only lifting one end at a time I think if I spread the load with timbers I can jack of the hull. What do others think.

That's how I did it.

 

[DNT99611]

After changing the mounts start with the engine high. Much easier to do the alignment with gravity working for you. I have changed a number of mounts by jacking the motor off the hull.

 

[OldDan1943]

That was in 1987. You have NO idea how lazy the intervening years have made me! I am now quite happy to sit on the engine coaming and "consult."

I have learned to observe and ask just a few questions so as not to distract the tech. Costs more money if you distract them.

 

[kapnd]

If there’s room to jack up from underneath the motor, use sandbag or two to even out the load on the hull. Be respectful of the oil pan, it may be fragile!
If the motor has to come up a lot, do use spacers under the mounts.
Looks like a golden opportunity to attack the developing rust down there, before it gets out of hand.

 

[Tiffany]

The alignment should be done with the boat in the water, but only after it has 'rested' afloat for several days. It can not be done accurately on the hard or in a lift.

 

[ronobrien]

That would be a pretty floppy boat to get 9 mm of misalignment when blocked. And if you only have a P bracket and no second bearing, just disconnecting the coupling and letting the shaft hang will not give you an accurate picture. On a 30+ year old boat, starting by replacing the mounts might be the right direction.

It is suggested to suspend the coupling with a fish scale, tension the scale to the same weight as the coupling half. This will offset the "sag" from the weight of the coupling half. Then do your 2 axis parallel alignment.

 

[Comodave]

Try to put a block underneath the engine in addition to the jack. That way if it slips off the jack it won’t crash all the way down. And keep your fingers and toes out from beneath it…

 

[ProMaritime]

You also need to have the prop dressed and rebalanced. Normally you would remove it with the boat in the water. Unbalanced props are the first thing to test for before spending a lot of money. Put the boat back in the water for at least a week before messing with any other adjustments.

 

[Riff Raff]

Start in the water

As stated, start alignment in water. However since already on hard balance props. I my last boat had starboard engine prop you couldn’t turn on the hard, but just fine to manually turn while floating.

 

[PenBayCruiser]

I used a couple of 2x4s across my engine opening with 2 jack stands holding a rod. From the rod a small chain hoist is employed to lift that end of the engine. Works well and easily portable. Changing the 34 year old mounts in our boat did nothing for our vibration. I've been through alignment in the water, mounts, shaft straightness and harmonic damper. My next check, at haul out for the season, will be the torsional damper between the flywheel and transmission. Good luck!

 

[rgano]

I have learned to observe and ask just a few questions so as not to distract the tech. Costs more money if you distract them.

It can be so, but I like to think I have the balance right whereby I can actually be a little help in the step-and-fetch-it mode. I like the guy who I have now had aboard both the trawler and this boat, and we get along well. He is a near neighbor and charges me a bit less than the average charter sportfish boats he normally works on. Last time he was aboard we took a joy ride because he had time and was interested in comparing the ride to a twin boat which had a lot of vibration.

 

[OldDan1943]

Penbay, are we to assume you also had the prop turn and trued dynamically to a higher standard than the minimum?

 

[PenBayCruiser]

The vibration is noticeable in neutral. So, have not had the propeller looked at. Thought my set for lifting the engine might be useful. But, thanks!