Motor alignment advice

[sesmith]

Last summer, we had a new shaft, coupling (split coupling), and cutless bearing installed on our Seaward 25 (yanmar 1gm10 motor). It was a vacation saving repair. I ran for the parts, who were made up for me at a marine machine shop, and had a local marine mechanic do the work. When he did the motor alignment, he told me he was able to get the top and bottom of the coupling within tolerance, but was only able to get it side to side within .023". He told me there was no adjustment slots on the mounts, and suggested I remove them and slot the mounting holes and readjust when I got the chance.

After we returned from our trip, I took another look at the mounts and noticed one hole on each mount was slotted, allowing you to twist the motor some for adjustment. I was able to get the motor adjusted to within .004" top and bottom, side to side. The motor has never been so smooth since the work, and I didn't really notice much difference (if any) since I readjusted things. I also moved the the shaft anode closer to the strut as I noticed he had it quite far away. This actually helped smooth it out even more.

When I pulled the boat this fall, I noticed the shaft was not centered in the stern tube, and was very close to the port side of the stern tube (see 1st pic. below).

I replaced the PSS seal (something we didn't get a chance to do this summer), and realigned things on the trailer. With the shaft centered in the in the stern tube, I was again fine top to bottom, but had about a .023" gap on the starboard side of the coupling. So I decided to try for a compromise...a mostly centered shaft and close as I could get with the feeler gauges. Due to clearance issues, I can't get the front of the motor any more over to the starboard side, and moving the rear of the motor to port pushes the shaft further out of being centered in the stern tube. About the best I could get the gap down to was .014" on the starboard side of the coupling. See 2nd pic below to see the view of the back of the stern tube.

There is no indication of any problems with the strut. Eyeballing it with a square shows no signs of it being bent (or loose). I'm assuming, the boat was probably this way when it was manufactured?? The last 2 pics. are looking aft at the cutless bearing. The prop shaft seems to be pretty well centered there. If anything, centering the shaft in the stern tube would even make the fit better at the cutless bearing. Of course, this is opposite to what would improve the fit at the coupling with the feeler gauges.

So...I'm tempted to just call it close enough, but is there anything else I should try?

 

[RoyS]

Too bad that you cannot get at all of the mounting bolts. As long as your shaft has some visible clearance at the stern tube that should area should be ok. The misalignment at the coupler may be an issue. Put the transmission in neutral and see if the shaft rotates by hand without binding. You could try a flexible coupling which are readily available. I would revisit the front mounting bolts. Sometimes the enclosures that prevent access are not impossible to remove. Good luck.

 

[sesmith]

Thanks for the reply, Roy. Access is not a problem. Nothing is binding up, and even with the horizontal misalignment at it's worst (ie .023" gap at coupling), there was not really any noticeable vibration. There is no noticeable motor movement with rotation either. The attached pic. shows the interference problem that prevents much more front adjustment to starboard. Since I took that pic, I slotted the front most mount bolt holes a little to get as much adjustment as I could. I also ground the top corner of the fiberglass mounting pan (for lack of better words) for a little more clearance in the area where the bolt head might hit it (seen near the oil filter).

Also, this article made me wonder if I was needlessly worrying about getting things perfect.

http://www.yachtsurvey.com/Alignment2.htm

 

[RoyS]

Good article you found there. If you find that you are able to achieve the parameters stated in that article I think you will be OK. The clearance at the oil filter is unfortunate but if it is not striking the stringer when the engine is running you can probably ignore it. If that is a Yanmar engine Mack Boring sells adaptors for remote mounting oil filters for some of those engines. See their online catalog.

 

[sesmith]

Thanks. The oil filter clearance is fine. There is a bolt head that can be seen near the oil pressure switch, that is the only issue. I think that picture was taken with the motor centered. It was closer to contacting the stringer after I moved the front of the motor. You can see where I took a file to the corner of the stringer previously. I filed a little more out there when I had the front mounts off. No clearance issue at present, but just no more room to do much more with the front of the motor. I watched this before, when the boat was in the water with it in forward and reverse, to see if the motor rocked enough for it to be a problem. It didn't, so presently, I'm ok clearance wise.

My thought is that the real issue is the location of the cutless bearing strut (probably from the factory), but trying to adjust / shim that into alignment might be just opening a can of worms that I don't need to (and probably shouldn't) open. Sometimes I'm just better leaving things alone...and / or I'm missing some obvious solution, which is the reason for the original post.

 

[Maine Sail]

Fine tuning side to side is always the most difficult. It is also not uncommon for struts and stringers and engine mounting to not line up from the factory. Do the best you can to get it smooth. With Yanmar's, after a side to side adjustment, I grab the engine and manually wiggle it pretty hard. The mounts can have some memory and a hard wiggle will relax them, especially when it is cold..

Here's a tip:

When out of the water lube the cutlass bearing with glycerin. Now when checking the alignment for the engine tighten the coupling bolts and spin the shaft by hand in neutral. It should spin easily. If it feels uneven or seems "tighter" to rotate at certain points it is still too far out of alignment. Try to get it to within .004" on land and the final adjustment can be made in the water.

 

[sesmith]

Thanks. I'll give that a shot when I attack it again in the spring. I needed to walk away from that part of the project for a little while BTW, how close is too close to the side of the stern tube. I know I can probably get the coupling clearance close to .004", but I was pretty close to the stern tube, at that point. I'm sure it will be some sort of a compromise, but wonder how close is too close, as I don't want it rattling against the stern tube.

 

[Charles Erwin]

023" is too far out and no amount of magic (shaft saver, hope, nor ignoring the situation) is going to fix this. The strut or the forward motor mount position needs to move such that the shaft centers in the tube. Perhaps a bit of both.

If this was my project I would start by centering the shaft first. Start by grinding off the outboard edge of the front mount - where the mount joins stringer and interferes with the vertical structure. Elongate the mount holes in both front mounts (two each) such that there is enough room to permit left/right movement of the motor.

Then work on shaft alighnment

Charles

 

[GonzoF1]

Maine Sail,

I am curious about your opinion on Pascoe's article Mr. Smith posted above. I have JUST come out of the yard where I spend thousands having the drive system aligned. Props balanced (PropScan to Class 1), shafts straightened, and engines aligned to within .003 at the coupling (in-water after resting for a few days). And while the boat feels MUCH better and smoother now, Pascoe's article made me feel that we didn't do enough. As-in, I did ask the yard about aligning the cutlass, but was assured that isn't normally a problem. now I wonder if I will waste money by having to go back and check the cutlass next year in the yard.

Thanks!

 

[Maine Sail]

Thanks. I'll give that a shot when I attack it again in the spring. I needed to walk away from that part of the project for a little while BTW, how close is too close to the side of the stern tube. I know I can probably get the coupling clearance close to .004", but I was pretty close to the stern tube, at that point. I'm sure it will be some sort of a compromise, but wonder how close is too close, as I don't want it rattling against the stern tube.

The problem with being off-center going through the stern tube is the packing gland can "pre-load" the shaft and add to vibration issues. You can also develop shaft-bump where the shaft actually rubs or bumps the inside of the shaft log. With a PSS being perfectly centered is slightly less of an issue than with a very stiff rubber hose packing gland or solidly mounted bronze gland but still you want it to be centered as much as you can when motoring level or otherwise if motor sailing you may be creating even more problems..

 

[sesmith]

Thanks much for the help.

 

[sesmith]

Thanks again for the help, everyone. I attacked it again today and was able to get the shaft centered in the stern tube first, and then was able to get the motor lined up to within .004"-.005" side to side (and dead nuts top to bottom). I had to lengthen the slots I cut in the front mounts some more, and grind out a little more of the stringer in the area where the bolt head of the motor mount bracket was kind of close. The key was Maine Sail's suggestions of lots of wiggling, and glycerin lube of the cutless bearing to get a good feel of things. I'll check it again when it's back in the water, but now back to my other projects.

 

[AnsleyS]

Sesmith,

Make sure that you let the boat sit in the water for 24 hours or more before you check the alignment. It is hard to believe that fiberglass boats distort when out of the water but they do and it takes a while for these tensions to release. It is an education to loosen the shaft before the launch and check it a day later when you know that you had it aligned on the hard.

 

[Richard Bryer]

I found that the shaft log on mine had enough inside dia that I was able to take a piece of 1" inside dia ( the dia of the shaft) pipe, cut it lengthwise and insert the two pieces snugly inside the shaft log and around the shaft. I did this with the coupling disconnected from the transmission so that I could then move the engine into alignment with the centred shaft.

 

[sesmith]

I found that the shaft log on mine had enough inside dia that I was able to take a piece of 1" inside dia ( the dia of the shaft) pipe, cut it lengthwise and insert the two pieces snugly inside the shaft log and around the shaft. I did this with the coupling disconnected from the transmission so that I could then move the engine into alignment with the centred shaft.

That would definitely make the alignment process easier. I've also read of using wood wedges to accomplish the same thing. In my case, the PSS seal made it impossible to do this from the inside of the boat. I replaced an older unvented version with the newer vented version, which is a little longer. Definitely no room to work with the PSS seal in it's uncompressed state. From the outside, I just couldn't find anything around to wedge it in place.

So just a lot of trips in and out of the boat to check progress. It seems like it's such a simple thing to do, but it can get confusing. To keep it simple in my simple mind, I just looked at it as a 2 step process...get the shaft centered, then adjust the motor gap at the coupling to fit the shaft, and do whatever I had to do to accomplish that (thanks for the nudge, Charles Erwin).