Engine alignment needed

[Captain Larry-DH]

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.

To add to my prior post - the best way ti go about this is to take your prop, shaft and coupling out of the boat and send them to a prop shop so they can be measured and trued up. Do this before installing and aligning to the engine transmission, and if you do your part correctly you won’t have to diagnose excessive vibration.

 

[Hayden Watson]

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?

Depending on how stiff the shaft log (rubber hose between stern tube and packing gland) or bellows to dripless you can have almost no sag or maybe a little sag. On my boat, when I had a traditional packing and used a proper Buck Algonquin 6-ply log there was negligible sag because that hose was very stiff. I now have a Lasdrop dripless packing which uses a silicone log that is noticeably softer. I can get the shaft to move up and down or back and forth about 1/4". I adjust my motor mounts so that the axial alignment is in the center of that range and then do the angular alignment from that point.

 

[yelkenli]

On my boat, when I had a traditional packing and used a proper Buck Algonquin 6-ply log there was negligible sag because that hose was very stiff.

This is the case for my boat. I cannot see how that 4.5 inch long hose could sag, so the stuffing box that holds the shaft is dead center of the log. Being 3 feet or so from the cutlass bearing, the shaft location is set. This ignores any run-out of the shaft or damage to the cutlass bearing strut. I cannot see this shaft sagging either (comment above). So next step for me is getting the transmission flange to meet the shaft coupling, and then working through the alignment procedure.

 

[Captain Larry-DH]

So next step for me is getting the transmission flange to meet the shaft coupling, and then working through the alignment procedure.

I recommend bringing the shaft and coupling to a prop shop and have them “face“ (true up) the coupling before putting them back in the boat. It’s inexpensive and easy now when the boat is out of the water; if you launch the boat and experience vibration - that ounce of prevention now will keep you from chasing gremlins and having to haul out mid-season to do it later. Bring the prop too. If they find anything else they can fix it.

 

[Ralph Johnstone]

So next step for me is getting the transmission flange to meet the shaft coupling, and then working through the alignment procedure.

You're right, so far. Follow the manual which I (and a few others) attached, and it tells you :

- how to tell if the shaft is straight :

- and how to tell if the coupling flange is true :

No sense in your spending many hours hauling the shaft out of the boat, dragging it to a machine shop, and then having someone else tell you what condition it's in for a lot of your hard earned money. Yes, if either of these two items do prove to be out of true, then it's off to the machine shop and leave your wallet behind on your way out. But if both items prove to be true, a waste of time and money.

I was lucky when I received my 1999 Hunter 310 trucked up from Florida, in that the prop shaft and its shaft flange were in perfect shape. Angular alignment was a whole 'nother story however. I've never hit anything with the prop or brutalized the shaft in any way so I'm assuming these two items still remain perfect. I do check my angular alignment occasionally but I'm just too lazy to bother checking the prop shaft and flange for trueness again.

Your shaft and flange may very well prove to be perfectly true unless they've been abused.

 

[Hayden Watson]

You're right, so far. Follow the manual which I (and a few others) attached, and it tells you :

- how to tell if the shaft is straight :

View attachment 228902​

- and how to tell if the coupling flange is true :

View attachment 228903​

...

Your shaft and flange may very well prove to be perfectly true unless they've been abused.

This was why I said to check the flange gap, then rotate the shaft 90º, check again, ... after you have checked it through a full rotation, changes in the gap at each flange will tell you if you are bent or out of true.

 

[Ralph Johnstone]

if you are bent or out of true.

I've been told I'm both after a few drinks .

I prefer to use a dial indicator like this :

​

........ rigidly mounted and held against the side of the shaft to check for any shaft bend.

Measuring only the flange face deviation gives one a measurement with both the flange being out of true and shaft being bent combined together depending on the condition of each component.

 

[dLj]

I've been told I'm both after a few drinks .

I prefer to use a dial indicator like this :

View attachment 228925
​

........ rigidly mounted and held against the side of the shaft to check for any shaft bend.

Measuring only the flange face deviation gives one a measurement with both the flange being out of true and shaft being bent combined together depending on the condition of each component.

Hard to get precise measurements without the shaft in a lathe with a precise support while turning the shaft.

dj

 

[Ralph Johnstone]

Hard to get precise measurements without the shaft in a lathe with a precise support while turning the shaft.

That was Rube Goldberg's machine shop in its finest hour when I measured that :

​

No digital cameras back then so no picture proof.

This is a bad dream of what it looked like back then. A piece of 3/4" plywood was held to the hull floor with double sided tape, fore and aft. One or more wooden wedges were gently tapped into place to ensure there was no sideways movement of the board. The few grams force exerted by the dial indicator mounted on the plywood did not even threaten to move the board or indicator. With the shaft flanges unbolted and the packing gland backed right off, there was little resistance to turning the shaft.

It was close enough for what I wanted, I was satisfied none of the measurement devices were flapping in the breeze, the shaft appeared straight, and it's obvious why I never bothered doing that again. It was fun at the time but ........ meh, never again. I've never hit anything with the prop, never abused the shaft, so it's probably still as good as the one day I checked it.