Engine/shaft alignment
- Thread starter Manny
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How good should a shaft alignment be?
I measured mine this weekend after thinking about this and got the following:
Top .674
Port .72
Stbd .77
Bottom .674
From this I read that the aft part of my engine is twisted a little toward the port. Is it far enough out that I need to adjust? I should also note that I have an R&D Flexible shaft (attached picture) coupling on the shaft and used the alignment marks on it to measure with the feeler gauge (other attached picture).
I measured mine this weekend after thinking about this and got the following:
Top .674
Port .72
Stbd .77
Bottom .674
From this I read that the aft part of my engine is twisted a little toward the port. Is it far enough out that I need to adjust? I should also note that I have an R&D Flexible shaft (attached picture) coupling on the shaft and used the alignment marks on it to measure with the feeler gauge (other attached picture).
Attachments
Flexible couplers only take care of 'transient' misalignment due to varying torque output of the engine/prop ... they shouldnt ever be considered a 'substitute' for static alignment perfection as they are not 'constant acceleration/rotation devices' - they 'wobble' when the alignment is 'off'. Only if you have a super expensive 'constant velocity joint' can you run a misalinged engine without adverse effects. You can adversely wear out transmission, etc. bearings etc. with a flex coupler just as fast as without one.
You really can't do a proper shaft alignment with a flexible coupler. The flexible coupler needs to be removed and if the existing coupler and the transmission do not mate up for adjustment, a machined spacer needs to be made to replace the flex coupler until the alignment is achieved and then the flex coupler can be reinstalled. Any machine shop familiar with this process can make one for you at a very inexpensive price. Chuck
Actually, it works quite well as long as there is a flexible stuffing box and only one bearing at the strut or aft end of the shaft log as the case in most sailboats. Here is a 1400 horsepower boat running with solid steel couplings between engine and shaft and very flexible mounts. One of her sisterships has been running with this arrangement for nearly two decades.
Not quite!!!! the gap is measured when you slightly 'slide back' the coupler thats mated to the propshaft (towards the aft of the boat) ... away from the trans., etc. Then put a feeler gage between the open space between the coupler faces and 'slide back' (forwards) the mating face of the coupler that attached to the propshaft. Then you rotate the feeler gauge around the outer margins (circumference of the coupler faces) and note how much 'difference' there is between the two faces ... usually 0.001" is near perfect.
Your sketch only measures the bolt lengths of the coupler bolts .... subject to many 'many tolerance issues in the bolt manufacture and the amount of torque that you put on each bolt.
What you want to do is get the FACES of the couplers to be perfectly parallel and 'in-line' / centered with one another .... so that when you put the coupler back together ------ the springy/elastic shaft has NO bend in it. Yes, a few pounds force from the side will bend the shaft ... although the bend may/will be 'microscopic' is still a bend and that will impart 'side forces' to the rest of the 'machinery' as the shaft rotates.
Yup, rpwillia,
Rich is right.. The measurements that are listed are bogus for alignment because if the top and bottom are the same, misalignment can then only be left/right .. so one would be larger than the top/bottom measurement and one smaller.. Again, as has been noted, the flex should be removed and the (allegedly) parallel faces of the solid coupling halves measured. Good luck with the measurement!
Rich is right.. The measurements that are listed are bogus for alignment because if the top and bottom are the same, misalignment can then only be left/right .. so one would be larger than the top/bottom measurement and one smaller.. Again, as has been noted, the flex should be removed and the (allegedly) parallel faces of the solid coupling halves measured. Good luck with the measurement!
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Here is how I got the measurements
The R&D Coupling documentation states that the coupling can be used for doing shaft alignment. The red bolt shown in the picture is the one you use to get your measurements as it faces a corresponding bolt on the other surface. The documentation had me make the measurements by rotating the shaft around to each of the point and then measuring between the red bolt and it's corresponding face. In that way you are using the same exact point on the coupling every time and eliminate any flex or irregularities in the flex coupling (i.e. measure at top with red bolt, rotate to port and measure at red bolt, rotate to bottom and measure at red bolt and rotate to starboard and measure at red bolt - then repeat).
The R&D Coupling documentation states that the coupling can be used for doing shaft alignment. The red bolt shown in the picture is the one you use to get your measurements as it faces a corresponding bolt on the other surface. The documentation had me make the measurements by rotating the shaft around to each of the point and then measuring between the red bolt and it's corresponding face. In that way you are using the same exact point on the coupling every time and eliminate any flex or irregularities in the flex coupling (i.e. measure at top with red bolt, rotate to port and measure at red bolt, rotate to bottom and measure at red bolt and rotate to starboard and measure at red bolt - then repeat).
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[/FONT]PYI said:
PYI said:
PYI said:
With regard to #1: I would try your best to get that to .003" or better.
With regard to #4: The max differential they want to see when moving the coupling 360 degrees and measured at points in-between is .01".
Personally I think those installation instructions are very, very weak. Who in the world has a 1/2" thick feeler gauge set???? As rpwilla indicated he has a measurement of .6" or well over 1/2" between the bolt head and flange..? You can not make fine alignment adjustments out of .6" and .7" gaps..
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