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post #7 of Old 01-20-2009
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Exclamation Paying attention to shaft alignment and driveline care

Originally Posted by Pub911 View Post
Not sure I follow, sorry for being thick-headed. How am I going to get to those tolerances by looking up the shaft log, it's 3ft long and has a cutless bearing in one end, and the other end is another 3 ft from the tranny.

While we're at it, do I need a 'pilot shaft' or similar tool to aling the clutch-plate, like you do when you put a clutch in a car?

I don't think you are thick-headed at all. I think you are asking some great questions and I would suggest you get Nigel Calder's book Boatowners Mechanical & Electrical Guide 3RD Edition, if you don't already have it. It is considered by many, both professional and recreational boaters alike, myself included, to be the book!. You will be able to read up on the systems and understand better what you are taking on.

Drive system alignment is covered quite well in Calder's book. Here is another link on the subject. Marine Engines : Drive System Alignment by David Pascoe, Marine Surveyor

You do not need a pilot shaft as the clutch like plate you see in the your diagram is the damper plate which is bolted directly to the fly wheel and therefore is already aligned with the input end of the reverse gear. It's job is to absorb the impact of going in and out of gear, just like the clutch plate does on a manual transmission on a car, but there the similarity ends as the damper plate is never disengaged from the flywheel.

Maine Sails' wonderful pictures and description of alignment measurements/procedure have to do with "moving" the engine to get the two coupling faces as close to parallel to each other as possible, which is usually .004 inches. This is done by measuring how far out of parallel the faces are by using feeler gauges in the gap between the coupling halves on the outer edge of the flange at 12, 3, 6 and 9 oclock which will indicate how straight your drive system is from the front of the engine crankshaft to the end of your prop shaft.

The alignment procedure is critical and key to proper drive line operation, and component longevity (meaning: motor mounts, cutless bearing, stuffing box, transmission output shaft seals and bearings!) It does not matter if the vessel is a large commercial boat or a small cruising auxiliary such as we are talking about here, it must be done and the same rules apply except for the costs when the system fails.

The v-drive Maine Sails has can be a lot of "fun" to work with. because of the way his drive line is folded back over itself. His system also absorbs propeller thrust differently than a straight inline system like yours does and in some ways is more sensitive to damage from misalignment! You can see he takes pride in and great care of his vesel and her systems! I will try to post some photographs of the same drive that was not so well looked after in another boat, but that is another story. Another thing of note about his v-drive is the output shaft is hollow and the prop shaft actually passes through the output shaft on it's way out to the stern tube. This design is kind of cool in that it keeps the coupling out where it is easy to get at. Many other V-drives have output the shaft and coupling down under the drive where it is hard to access for work.

Learning how to align the drive system is an exercise in time and patience depending on your mechanical skill level. If you have not done it before or are not sure about the procedure. It may well be worth having a professional check and do any final adjustments before and after the vessel is in the water to make sure you are spot on or it may cost you big time in the long run (think of the parts list above in the preceding paragraph $$$). Not to mention having a drive line casualty while on a long summer cruise away from your home port because of drive line issues that should have been addressed by a proper installation and alignment in the first place. The delay and change in plans can also have an effect on crew attitudes as well

Nothing like opening the engine compartment at the end of a long day of sailing and seeing transmission fluid all over the pan under the reverse gear! Along with the coupling set screws worked loose and the coupling wobbling on the shaft. I can tell you from personal experience this is where Maine Sails V-drive is an advantage and comes into it's own in terms of access, removal and repair.

Another side effect of misalignment and a strong motivator for proper care of your drive system is if you have a dripless stuffing box will be possible large amounts of water appearing in your bilges at times. I also suggest installing a high water alarm. Your vessel won't sink (at least while you are on board!) but having water in the bilges when you expect them to be dry can be disconcerting!

Your alignment can be gotten pretty much done on the hard but then should be checked again after the vessel is launched and the mast stepped and tuned to working tension and she has had a few days to sit in the water and get her "in water" shape back. A boat will sometimes change shape enough to throw shaft alignment out enough to cause problems. The least of which can be vibration or later premature wear and failure of critical parts.

Pub, all in all this will be a great learning experience for you in the ongoing effective management, operation and maintenance of your vessel and I encourage you in your endeavors.

I also took a look at your posts and see that your vessel is "mature" in terms of her age. Since you are going to be taking things apart. I see you have already done a great deal of work on your vessel. Do you know how old your motor mounts are? Now may be a good time to replace them as well depending how old they are. That way when you put her all back together you will have a clean slate in terms of your drive line.In other words if it was my boat or clients I would want to be starting on a level playing field which means checking all of the parts of the drive line. Cutless bearing, shaft ( is it straight not pitted?) Is the shaft half of the coupling square to the shaft? Is your shaft the proper lenght(not more than shaft diameter between the last bearing (cutless) and the forward end of the propeller. You have to look at your drive line in terms of all of its parts and if you start next season knowing what the status is of all the components you will be able to isolate and mitigate any small problems before they become big ones.

Good Luck!

ABYC Certified Master Technician

"It's not just about the vessel... more importantly it is about the people, their safety and their vessels in that order. "(PFJ 1952-1986)

Last edited by JHJensen; 01-20-2009 at 09:40 AM.
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