Engine alignment needed

[yelkenli]

When replacing my stuffing box, I find that the shaft coupling is higher than the transmission output bracket. I believe the shaft is where it wants to be (is straight and aligned by the cutlass bearing and stuffing box which is on a super rigid thick hose). So I am planning to raise up the engine. I am guessing about 1/8 inch or so.

I read some forum threads talking about adding wood, etc. I don't think I want to go there. Maybe on my next haul out, I might replace the mounts or some other more drastic upgrade.

My main question is adjustment consists of loosening the top nut, and turning the bottom nut to raise or lower. Correct?

 

[Rich Stidger]

Actually you need to raise all 4 of the mounts, and raise the front a bit more than the rear in order to keep the engine aligned but higher.

 

[NYSail]

You may need to shim the mounts as you don’t want the engine to be at the top of the mount bolt…… lower the better. And how do you know if your shaft is aligned perfectly through the strut? Are you on the hard and can see it? Remember when on the hard the hull shape changes.

 

[Jim Legere]

You may need to shim the mounts as you don’t want the engine to be at the top of the mount bolt…… lower the better. And how do you know if your shaft is aligned perfectly through the strut? Are you on the hard and can see it? Remember when on the hard the hull shape changes.

Engine mounts are designed/engineered to use the whole length of the stud for adjustment. If the OP can't get enough adjustment using the full range of the stud, it's likely that the engine mounts have sagged or failed; shimming old mounts is not recommended. Good point about aligning engine with the shaft when the boat is in the water - you can get close on the hard but final checks should be made afloat.

 

[Captain Larry-DH]

My main question is adjustment consists of loosening the top nut, and turning the bottom nut to raise or lower. Correct?

Correct. You might need to adjust front and rear engine mounts. Use a feeler gauge all around the circumference of the interface between the coupling and the transmission output plate. You are looking for no more than .002“ difference between positions at 180-degrees from each other all-around. As noted in other posts, final alignment must be done in the water.
ps - do not align it while sitting on the engine (yes I did once). LOL

 

[yelkenli]

Thanks all for the advice.

The boat is on the hard. I really do not want to, nor have time to change the mounts in any way. I understand the desire to keep the engine low on the mounts, but agree with @Jim Legere. Otherwise, why put that length.

The shaft looks like it is directly through the log. The log hose is thick and rigid and perfectly aligned with the log IMO. That puts the shaft directly in the middle at that end.

I replaced the cutlass bearing. So I assume the shaft is correct at that location.

When I put it in the water, if the cutlass bearing, log, and engine can move relative to each other, then I will do the alignment when in the water. Makes no difference, and people at the club are asking if they should assign me the work space permanently.

Regarding @Captain Larry-DH comment, this transmission output has four arms for the bolts. I do not recall yet if there is a gap at each that can be measured, but I will look for that for adjustment.

 

[Captain Larry-DH]

That puts the shaft directly in the middle at that end.

It’s not a question of whether it’s in the middle. It’s critical to get the alignment true between the 4 arms in your case, and the shaft coupling. You start by sliding/fitting them loosely together, then use the feeler gauge between the interface at opposing sides. Any slight difference will cause shaft whip, which gets worse at higher RPMs and causes vibration. In extreme cases (it doesn‘t take much) the shaft whip can cause permanent shaft bending.

 

[dmax]

Courtesy of Ralph Johnstone, follow these instructions, a bit of work but worth it and you'll know that all of the components are aligned correctly:

 

[jssailem]

There are no assumptions in this process. The statements by the sailors above are great guidance. @Ralph Johnstone's write-up is worth every minute you take to understand the details. Thanks, dMax, for sharing it.

Though you may not be able to see it, there is plenty of space for the shaft to "sag" from the cutlass bearing to the transmission. You will see it when trying to get the spacing between the transmission and shaft couplers correct.

http://www.dieselmotors.info/boat/boat-diesel-alignment-of-the-propeller-shaft.html

 

[Ralph Johnstone]

As outlined in the instructions on alignment (post #8), the alignment you are looking for (and most difficult to achieve) is the angular alignment :

​

This is assuming both flanges are true to their their respective shafts. The instruction manual will take you through proving if the flanges are true.

When replacing my stuffing box, I find that the shaft coupling is higher than the transmission output bracket.

Taking a wild guess here, I'm going to guess the drop in your engine height is due to the rubber in your mounts losing some of their elasticity due to age. Unfortunately, we all know what that means and it ain't pretty.

It's a slow slog if you find the engine alignment is way off but it's winter everywhere in the northern hemi, so what else have you got to do ?

 

[mermike]

Aren't you supposed to do the final alignment in the water?

 

[jssailem]

Yes

 

[Ralph Johnstone]

Aren't you supposed to do the final alignment in the water?

If you have open water nearby.

I'm pretty sure mine wasn't as it was 0.010" out on the axial after it had been aligned in the Hunter shop and then trucked from Florida to Vancouver B.C. I did the first alignment a couple of years after I got the boat.

 

[mermike]

Motor mount replacement is in my near future. I'm gathering as much info as I can.

 

[yelkenli]

After this marking is done, a reference
thickness feeler gauge blade is clamped
firmly between the faces of the coupling at
the bottommost measurement position. I use
a small pair of vise-grip pliers for this, and
an .015” feeler gauge

I might guess that you put .015 between the flanges at the bottom, and clamp the flanges together. Is this correct?

 

[Hayden Watson]

You cannot measure a 0.002" gap which is what you want to align to because the feeler gage is too floppy to insert into the gap. When I do my alignments, I use a 0.020 gage and a 0.022 gage as "go" / "no-go" gages. I tighten down all four flange bolts until the "go" gage will just slide out and then try it in the gaps at each of the four bolts. I keep adjusting until all four gaps are between the go and no-go. I rotate the shaft 1/4 turn and check again to make sure it is still good.

 

[dLj]

You cannot measure a 0.002" gap which is what you want to align to because the feeler gage is too floppy to insert into the gap. When I do my alignments, I use a 0.020 gage and a 0.022 gage as "go" / "no-go" gages. I tighten down all four flange bolts until the "go" gage will just slide out and then try it in the gaps at each of the four bolts. I keep adjusting until all four gaps are between the go and no-go. I rotate the shaft 1/4 turn and check again to make sure it is still good.

That's a good way to do it if you don't have a taper gauge. I use a Starrett No. 270. Much easier to use that the two feeler gauges. It begins at 0.010" going to 0.150" on one side, 0.3 mm to 4.0 mm on the other side. This allows you to start measuring anywhere along that scale so getting the flange to a specific gap is less critical. Plus you can continue to watch alignment as you approach the lower limit.

dj

 

[NYSail]

Ok so this is a topic and a task I haven’t done personally. Last boat after I changed mounts had a mechanic do it. New boat appears fine with no abnormal wear on the cutlass or vibrations and mounts are still good. So my question…… I know it is best to do the alignment when boat is in the water and hull shape is settled, however, how do you know when the shaft is perfectly inside the cutlass when you can’t see it? Is it a zen feel of the shaft you get from experience?

 

[Rich Stidger]

Ok so this is a topic and a task I haven’t done personally. Last boat after I changed mounts had a mechanic do it. New boat appears fine with no abnormal wear on the cutlass or vibrations and mounts are still good. So my question…… I know it is best to do the alignment when boat is in the water and hull shape is settled, however, how do you know when the shaft is perfectly inside the cutlass when you can’t see it? Is it a zen feel of the shaft you get from experience?

.....AND, additionally, how can you tell when the shaft is straight in the stuffing box if it sags under its own weight?

 

[Captain Larry-DH]

.....AND, additionally, how can you tell when the shaft is straight in the stuffing box if it sags under its own weight?

It matters not whether the stuffing box or the cutless are straight. They have some degree if slop built in (if properly sized) and will wear into alignment if slightly off. When aligning the engine to the shaft (the focus of the thread) You need to be concerned with only 3 elements:
1) shaft is straight within acceptable runout limits (.005”)
2) coupling is properly faced (.002”)
3) transmission plate alignment to coupling face is within .002”.
# 1 and #2 are measured off the boat at a machine shop. Any prop and shaft service facility does this every day, and your local boatyards know where to send it. #3 is the subject of this thread. If any one of these things is out of true it will result in excessive vibration.