# Shaft Alignment Calculation?

Discussion in 'Diesel Engines' started by internetturk, Jan 10, 2007.

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### internetturkJunior Member

Hi everbody, anybody know how to calculate Shaft Alignment Calculation?
thanks

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### JangoSenior Enthusiast

I assume you're talking about alignment of propeller shaft to gearbox/engine?

If you have a typical flanged coupler, 4" or 5" in Dia, mate the shaft flange to the trans flange and adjust Engine up or down until you have .003 in. or less clearance between the flanges on the opposite sides touching.

If you have larger flanged couplers you can increase the clearance proportionately.

Jango

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### StianMSenior Member

Calculations.

You nead to know the diameter off the shaft and the stiffnes, diastance betwen bearings and so on.

Why do you nead to do that annyway?

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### internetturkJunior Member

i have a diameter and stiffnes but how can i determine bearing offset values?

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### MMNet SEAJunior Member

Hi Jango,

I am busy changing engines and gear boxes . the new engine is smaller than the last and its gearbox flange will be brought up to flange on the prop shaft.
Here is the question:- the propshaft is running through its cutlass bearing then through its stuffing box , it has 2/3 inches fore & aft movement available. Does the clearance factor come into this equation ??

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### JangoSenior Enthusiast

If I understand your question correctly, fore and aft shaft movement has nothing to do with Alignment.

I define "Aligning the propeller shaft" as attempting to put the propeller shaft on "exactly" the same axis as the gear box output. It has been found that a misalignment of NO more than .003 in 4.00 or abt. 0 deg. 3 min. of angular misalignment is acceptable.

Hope this is clear

Jango

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### MMNet SEAJunior Member

Thanks , "Angular" gives further clarity in the depths of the engine room.

(are you where Napoleon spent some time ?)

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### TerryKingOn The Water SOON

The interesting challenge is figuring out how much to move/shim each motor mount to correct for a specific shaft MIS-alignment.

I've only done this with "estimate-and-try and do that again" until it's close enough.

There are three variables: the shaft to shaft misalignment angle, the misalignment axis angle, and the offset of the two shafts.

I THINK I once heard about a spreadsheet that could take those three variables, along with the dimensions of the motor mounts relative to the flange mating surface, and give the plus and minus vertical and horizontal distances to move for the front and rear motor mounts. Anyone seen such a thing??

Since this has so many degrees of freedom (like raising the front motor mount causes a shaft-to-shaft offset that has to be compensated at the rear motor mount) it's hard to get right!

Heck, it's Just a little Trigonometry !

9. ### FrostyPrevious Member

As if that wasnt difficult enough. It is also necessary on some mounts such as Barry mounts for instance to also get even weight distribution.

These particular mounts are very good at noise and vibration damping however setting them up is tricky.

A gap is purposely left under the rubber to check the load of the mount.

Although Barry mounts have left ways of doing this I think it is important to try to do the same with other mounts.

Feeling the tension of the load nut would give some indication of its load.

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### ZackmanJunior Member

Just curious, has anyone ever tried to use reverse dial method, like you would on pump to motor alignment? If you can get two dial indicators to swing the circumference of the "coupling", the rest such as calculating misalignment and the shimming required would be a simple.

11. ### FrostyPrevious Member

The thing is the shaft is not rigid, it is movable and should be.

I like to lubricate the cutlass bearing with washing up liquid then whilst inside drop the shaft out and lift half the play and offer the shaft to the drive flange

I would then expect the shaft to sit nicley and cleanly into the flange resess. Then measure round with a feeler guage.

It should be noted at this point that any flexible drive coupling has to be removed and you mate the shaft with drive flange ONLY.

Heres another point cleanliness of the 2 mating surfaces is very important.

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### TerryKingOn The Water SOON

Dial Indicators

Can you please explain how this works? What information do you get "out" of this approach? It seems to me that you also need information about the geometry of the engine/transmission and motor mounts to know how much to move/shim each mounting point to get alignment in one 'pass'..

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### ZackmanJunior Member

Terry, it's fairly involved to discuss but is very easy to do. Here is a link to a site which gives a step by step procedure. http://www.alinemfg.com/procedure.htm And yes you would need to know the distance to the moveable feet. The more accurate the measurements for distance the closer you will be to true alignment after the first pass.

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### RMSOSFJunior Member

Most engine rooms would not have the room for that tool setup. On larger craft, I simply set up the side to side alignment first, then I use 4 portable Enerpac jacks and 4 dial indicators. I loosen the mounts, set the dial indicators on each mount then start jacking or lowering until I have perfect alignment. Take the readings from the dial indicators and there I have the shim sizes I need.

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