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Old 09-08-2015, 11:09   #1
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Alignment of propeller shaft to engine

I was wondering about techniques to align shaft to motor. On motors used in industrial locations we use laser or dial indicator methods to adjust motor mounts. To ensure alignment is within a specific tolerance, what methods can be used while vessel is floating? I'm more interested in situations on sailing catamarans.
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Old 09-08-2015, 20:31   #2
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Re: Alignment of propeller shaft to engine

You loosen the coupler behind the transmission until you can insert a feeler gauge between the 2 coupler pieces. You measure all the way around and if you want a proper job, shoot for no more than 0.002" difference. More than that will cause premature bearing wear in the rear transmission bearing and the shaft bearing. It also will cause noise that can impact fishing. If you take the time to get a .002" difference, you'll be better than most of the boatyards I've seen. Many yards just get it close and put in a "flexable" spacer and call it good. A couple years later you have repairs they won't accept blame for causing.
To achieve alignment, the engine front moves in the direction of the largest reading. Some engines have adjustable mounts, but in most cases, you add or take out shims under the mounts. Sometimes shims are needed between the engine and the mounts. While making adjustments, slack the holding bolts to all the mounts. After tightening the mounts, recheck measurements. If you set on land you have to recheck in the water.
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Old 10-08-2015, 07:03   #3
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Re: Alignment of propeller shaft to engine

Thanks for telling me a procedure to align shaft. With industrial electric motors the motors have a keyed shaft projecting from motor housing around six inches, the connection to the equipment shaft is by a coupling. Have you ever seen any marine engine motors like this or are all equipped with a hole to insert propeller shaft into? Are there any videos showing alignment procedures that you know of?
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Old 10-08-2015, 07:36   #4
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Re: Alignment of propeller shaft to engine

Google "propellor shaft alignment". Look at videos and you'll be overwhelmed.


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Old 10-08-2015, 08:52   #5
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Re: Alignment of propeller shaft to engine

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Originally Posted by EllisElectric View Post
I was wondering about techniques to align shaft to motor. On motors used in industrial locations we use laser or dial indicator methods to adjust motor mounts. To ensure alignment is within a specific tolerance, what methods can be used while vessel is floating? I'm more interested in situations on sailing catamarans.
Take Lepke's advice and be prepared for a few gray hairs. It's not easy but as he said worth the close tolerance in the end.
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Old 10-08-2015, 08:58   #6
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Re: Alignment of propeller shaft to engine

The proper way to align a shaft is not a feeler gauge. Mount a dial indicator to one shaft and set the clock on the other, with no bolts. Rotate one shaft 360. Then put the bolts in and rotate 360 again. Need less than a thou both times. Thats the way I learned in the US Navy...years and years ago.
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Old 10-08-2015, 09:25   #7
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Re: Alignment of propeller shaft to engine

I agree that the more precise the fit between the two coupling halves the better, however, I have also seen where regardless of how much time is spent trying to get the fit perfect, there maybe installations where it's just not possible.

When we installed the new engine on my boat 6 years ago, I worked very closely with an accomplished mechanic to get as good a fit as we could but in the end we had to accept it being out by .040", a far cry from .002". I have since put over 2,500 hours on the engine, traveling over 40,000 miles (far too many of them under power) and the cutlass bearing remains tight, the dripless packing not leaking a drop.

I am not recommending people tolerate an out-of-round installation but merely offer this as an anecdote of my personal experience.

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Old 10-08-2015, 09:33   #8
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Re: Alignment of propeller shaft to engine

This is correct for a fixed propshaft. But nowadays wet prop shafts have a flexibele gland sealing.

Therefore it is also important to have the shaft more or less in the center of the propellor tube.

But that is rather difficult because you can not adjust the shaft without removing the seal.

Make movement to the flexibel end and try to find the center of the tube. Then try to fix the shaft in that position and then do the alignment.
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Old 10-08-2015, 10:09   #9
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Re: Alignment of propeller shaft to engine

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The proper way to align a shaft is not a feeler gauge. Mount a dial indicator to one shaft and set the clock on the other, with no bolts. Rotate one shaft 360. Then put the bolts in and rotate 360 again. Need less than a thou both times. Thats the way I learned in the US Navy...years and years ago.
I'm sure you a right but couldn't follow your brief explanation. You and Lepke may be talking about two different aspects of the same beast. I think, you where speaking of flange concentricity. and he was speaking parallel of the flanges. Both good points since alignment is a three axis affair. So one isn't worth a damn without the other. Good luck to anyone doing it in a confined engine compartment.
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Old 10-08-2015, 10:15   #10
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Re: Alignment of propeller shaft to engine

Vererkbr has it right. center the prop shaft in shaft tunnel first...then align engine afterwards. serious damage possible if spinning shaft contacts tunnel sides. I fashion a jig out of plywood to hold the prop shaft while aligning engine.
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Old 10-08-2015, 10:54   #11
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Re: Alignment of propeller shaft to engine

I'm 67. My way is very old school. My pop was a chief engineer and that's how they did it before dial indicators were common items in tool boxes. I watched him do a triple expansion Liberty ship engine. The engine was apart except for the beds and crank, but it still was a bear to move. However, old school has worked well for me on older setups. The noise aspect I discovered when commercial fishing. I often set engines for others and some boats that didn't "fish" suddenly started catching fish. Most had their engines aligned recently by some boatyard.
My shafts are so closely aligned I have to leave my mains in gear when anchored or docked in a current. Otherwise the props continuously spin. I leave my packing loose since I have a wood boat, a little extra water in the bilge isn't an issue and 70 year old shafts are hard to come by.
Also, older couplings have a ridge and matching trough in the coupling faces that help keep the couplings in line. They were probably made where the ship/boat was built. Whenever I've need couplings, I have them made.
I've never run into the flexible gland, but .040 should have destroyed the transmission (in my experience).
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Old 10-08-2015, 11:04   #12
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Re: Alignment of propeller shaft to engine

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Originally Posted by Lepke View Post
I'm 67. My way is very old school. My pop was a chief engineer and that's how they did it before dial indicators were common items in tool boxes. I watched him do a triple expansion Liberty ship engine. The engine was apart except for the beds and crank, but it still was a bear to move. However, old school has worked well for me on older setups. The noise aspect I discovered when commercial fishing. I often set engines for others and some boats that didn't "fish" suddenly started catching fish. Most had their engines aligned recently by some boatyard.
My shafts are so closely aligned I have to leave my mains in gear when anchored or docked in a current. Otherwise the props continuously spin. I leave my packing loose since I have a wood boat, a little extra water in the bilge isn't an issue and 70 year old shafts are hard to come by.
Also, older couplings have a ridge and matching trough in the coupling faces that help keep the couplings in line. They were probably made where the ship/boat was built. Whenever I've need couplings, I have them made.
I've never run into the flexible gland, but .040 should have destroyed the transmission (in my experience).
I PMed you. Do you have crash boxes?
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Old 10-08-2015, 13:36   #13
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Re: Alignment of propeller shaft to engine

Are engines bolted down firmly at the motor mounts or is it bolted to flexible motor mounts?
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Old 10-08-2015, 14:09   #14
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Re: Alignment of propeller shaft to engine

I replaced the whole works this spring on my Ericson 34'; From flange to cutless. I used the method Lepke suggested. I got the stuffing box assembly from Algonquin; apparently one of the best sources. What I got from them was top quality for only about $100. After placing the rubber house portion over the shaft tube, and aligning the engine as per Lepke's procedure, I could not get a .015" feeler gauge between the transmission and shaft flange portion!!
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Old 10-08-2015, 14:11   #15
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Re: Alignment of propeller shaft to engine

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Are engines bolted down firmly at the motor mounts or is it bolted to flexible motor mounts?
The little boats we're working with on this forum all have (rare exceptions) flexible mounts. These things are not like the main propulsion engine on a ship that is aligned and set in chockfast hard to the beds.
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