Prop Shaft Alignment

[jpian0923]

I have a mis-aligned prop shaft and need help correcting it. I can see some scoring on the shaft at the stuffing nut. I can also see that when at low rpm, in gear, that the prop is clearly not spinning straight. I think the engine is too low for the shaft. I have read in a thread that the tail wags the dog and I kinda get it but my question is, How much much authority does the tail have over the dog? Should I un-couple and then raise the engine to meet the shaft coupling where it sits naturally?...or, is it ok to bring the shaft coupling down to meet the drive coupling?
Thanks much

[ArtJ]

usually the engine is shimmed until the two halves of the split coupling
measure equally all the way around as measured with a feeler gauge.

[hanleyclifford]

First disconnect the coupling and manually hand the shaft around in a broad circle. This will tell you several things. The cutless bearing has likely sustained some wear but may be OK once the alignment is corrected. Roughly in the middle of the wide circle that you are able to turn the coupling is where you want to support it temporarily with pieces of wood. I like to use cedar shingles but most anything will do. The "tail" has now taken it's (as nearly as possible) ideal position. Now the "dog" can be horsed into position using whatever means your engine mounts permit. The factory standard is .003" deviation from true. You will know the engine is in the "sweet" spot when you cannot get the .003" feeler gauge in between the coupling pieces.

[jpian0923]

Perfect word picture.Thanks.

[sastanley]

Jim,

You probably read that "tail wagging the dog" stuff in my thread from last year where Hanley or Neil told me the same thing. It seems very tedious, but once you get it close, it is simple adjustments with a 1" (25mm worked OK for me too) wrench on the motor mounts. Hanley also reminded me that it works a lot better if you use the AFT motor mounts for large scale adjustments, and then use the FORWARD mounts for the fine tuning when you get it close..at that point the aft mounts become the pivot point and it is easier to dial it in to that 0.003" spec by adjusting the front mounts.

I would put the fwd mounts in the middle, then adjust the aft ones to line up the coupler so it mates evenly with the shaft in that 'central' location in the shaft tube..at that point, the shaft half should slide right into the engine half easily and cleanly. Then you can get out the gauge and start your fine tune adjustments. I also had to move my mounts slightly from side to side since I had uneven gaps on the sides of the coupler. A pipe and a sledge hammer eventually moved them the tiny amount I needed.

[tenders]

Also, answer the question: why did the engine get misaligned? If it was due to the rubber (or wood) components of the mounts disintegrating you should most certainly replace (or repair) them before you spend time realigning.

[lat 64]

Just a story

I once worked on a shaft problem on a commercial fishing boat. The vibration was sometimes there, sometimes not. Someone figured out that the warm sun was warping the hull and putting the shaft out. They turned the boat around and the shaft alignment changed. I think is was a pretty crappy boat. No names here.
r.

[jpian0923]

I did notice some compression on the ply wood ( I think) that the engine mounts sit on. Have not made a real good inspection yet but wanted to head to the boat armed and ready! Thanks guys.

[sastanley]

Jim, there are a couple of penetrating epoxy products that will get into the wood and make it sound again...it won't displace (replace?) any moisture though...You'd have to get it dry first, then it will fill the voids & reinforce the rotten parts. Smith's CPES is my favorite..I used it to add some life to my bulkheads to hold off changing them for a couple more years.

[ndutton]

The tail wags the dog

The alignment to start with is between the cutlass bearing and the inboard end of the shaft log. Doesn't matter if the cutlass is in a remote strut or in a shaft log assembly in the boat's deadwood. With a good bearing, the shaft must be centrally aligned in the shaft log, even space all around. This can only be seen with the stuffing box removed. Once the shaft position is correct (the tail) you can then align the engine to match (the dog).

Ask Shawn what happens when a shaft isn't centered in the log (sorry buddy, but nobody has a more illustrative shaft alignment story than you).

[jpian0923]

Shawn, we're waiting! I want pics.

I did a closer inspection. The wood the engine is mounted on (not plywood but a strong laminated wood product. My mistake) is not in bad shape. It's wet and oily but still serviceable. The big issue was that One of the rear mounts was gone... Nowhere to be found. The other rear was so loose I could turn it by hand. Temporarily I moved a front mount to the empty rear so I could attempt to adjust the alignment. I used some thick washers to shim the engine. I did what Hanley suggested, somewhat, but sort of kept my eye on the stuffing box itself. At the point where the shaft seemed center in the stuffing box is where I felt the "tail" was in a good position. I'm sure it's not perfect but for now it might be better aligned than it was. By Hand cranking I think I see an improvement. Not able to fully test yet but will after I replace the hot section, manifold, carb and alternator...and start it up!

Some of you guys might remember I had the key in the drive side shaft coulping sheer off because the nut had backed it's way almost off, back some months ago, and had trouble getting the washer to seat properly. I'm happy to report that the nut had backed it's way out only about a groove on the shaft. My solution tonight was to remove the nut and washer and key and cut the key down by 1/8" and was able to get the washer to seat properly. I'm an idiot for not thinking of that months ago.

Every suggestion was helpfully. I appreciate it much. I've only had this boat (my first) and engine since May 10th, 2010 and I think I've almost had problems with every system (and repaired it) with the help of this forum. Yuz guyz are great!

[sastanley]

Well Jim, it all starts & ends in this thread - http://www.moyermarine.com/forums/showthread.php?t=4044

The real fun starts about post #123

But here is a little teaser for you...

[jpian0923]

Wow! Oh yeah, I remember that.

[edwardc]

How is it that that didn't sink the boat?

[sastanley]

ed, that pic was taken when the boat was safely on the hard again...I had removed the clamps and slid the stuffing box hose forward to expose the culprit. That is the hole that was worn from the shaft in between the hose clamps, so the hose & clamps were the only thing keeping the boat afloat. Additionally, I had chipped away all of the marine tex which was really what probably kept the boat from sinking.