engine/shaft coupler alignment? - SailNet Community

   Search Sailnet:

 forums  store  

Quick Menu
Boat Reviews  
Search SailNet 
Boat Search (new)

Shop the
SailNet Store
Anchor Locker
Boatbuilding & Repair
Hatches and Portlights
Interior And Galley
Marine Electronics
Other Items
Plumbing and Pumps
Sailing Hardware
Trailer & Watersports
Clearance Items

Advertise Here

Go Back   SailNet Community > On Board > Gear & Maintenance
 Not a Member? 
Old 04-20-2008
Junior Member
Join Date: Oct 2007
Posts: 9
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 0
richrand is on a distinguished road
engine/shaft coupler alignment?

I searched the forum and found a bunch of posts on this issue, but none that got to my question. So hear it is:

I just installed a new (used) inboard 1GM diesel engine replacing a BMW D7.

I've connected the shaft coupler to the transmission and there is an ever-so-slight wobble as I rotate the shaft by hand. I spent a few hours aligning the engine to the coupler and I just can't seem to eliminate it.

First, I read here that final adjustments should be made on the water with the rig at tension, not on the hard, so I know I'm not done.

Second, do I just need to keep trying to get it perfect, or is this little wobble acceptable? My instinct is "no", but I've never done this before. I keep thinking about how much the engine is going to bounce around when it's running.

Reply With Quote Quick reply to this message Share with Facebook
Old 04-21-2008
Valiente's Avatar
Senior Member
Join Date: Jun 2006
Location: Toronto
Posts: 5,491
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 10
Valiente has a spectacular aura about Valiente has a spectacular aura about
Is the wobble from the engine mounts, or from looseness in the shaft? Can the mounting nuts be raised or lowered to align the engine itself?

Is the keyway firmly on the shaft side of the coupler? Is there a "grub screw" from the collar of the coupler to the shaft? Is there room to put in a rubber-type "Drive Saver" that might compensate (and eliminate some vibration)?

Do you have a traditional stuffing box and is it slotted into a thrust bearing? Are various hoses and clamps loose?

Do you know if the shaft is in fact straight? Is there play in the cutlass bearing? They wear out and there's a special tool for sliding in replacements.

As you can see, there are a number of variables involved here, including the fairly unpleasant prospect of something loose in the transmission itself, but you didn't mention oil pouring out, so I'll assume that's OK.

Get a knowledgeable owner to have a look. It's unlikely this can be diagnosed over the Internet. All I can do is what I've done here: give you a list of the things I would check if I found shaft play.
Reply With Quote Quick reply to this message Share with Facebook
Old 04-21-2008
Maine Sail's Avatar
Senior Member
Join Date: Jan 2003
Location: Maine Coast
Posts: 5,652
Thanks: 15
Thanked 163 Times in 128 Posts
Rep Power: 16
Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice Maine Sail is just really nice
Even with


If your wobble is more than .003" it is not acceptable..

Even with a Drive Saver or R&D Flex Coupling the alignment needs to be 0.010 inch / 0.25 mm BEFORE you install a flexible coupling! This is NOT a lot of variance and it CAN NOT normally be seen with the naked eye.

Without a Drive Saver, alignment between the propeller shafts coupling and the transmission's coupling can contain a variance NO GREATER than .001in (.25 mm) per inch of the coupling diameter. For example, if your propeller shaft coupling is 3” (76mm) in diameter, the maximum error that can be allowed in the alignment is .003 in (.076mm).

You can NOT do a proper alignment without feeler gauges and you CAN NOT see a .003 variance with your eyes!!

Improper alignment can destroy your transmissions output shaft seal, prematurely wear the engine mounts, damage the cutlass bearing and wear the stuffing box and shaft sooner than necessary. Final alignment should ALWAYS be done after about three to four days in water with the rig properly tensioned...

-Maine Sail / CS-36T

To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

© Images In Posts Property of Compass Marine Inc.

Last edited by Maine Sail; 04-21-2008 at 11:15 AM.
Reply With Quote Quick reply to this message Share with Facebook
Old 05-21-2008
Senior Member
Join Date: Jan 2007
Posts: 387
Thanks: 0
Thanked 0 Times in 0 Posts
Rep Power: 9
Northeaster is on a distinguished road
A couple of questions.

Halekai - Are you saying to line it up with the hard coupler, to get it very close. Then unbolt, insert the drivesaver (or R & D) and then rebolt, and check clearance. I have read that one owner found it easy to see the misalignment, with the disk in place, as the rubber is squeezed more on one side, etc.

Before I can line up the engine, I have read that you should center the shaft in the stern- tube. As the stern tube is over a foot away from the strut ( cutlass bearing), there is a fairly wide range of movement possible. There is some wear in the stern tube on one side, as the engine was likely out of alignment at one time or another. I can place the shaft as close to center as possible, and then adjust the engine mounts to allow the trannie to bolt up cleanly. However, it looks to me like the shaft is not bound so tightly in the cutlass bearing, that it cannot be "happy" turning, even if it is not in the center of the tube.
Reply With Quote Quick reply to this message Share with Facebook

Quick Reply

By choosing to post the reply above you agree to the rules you agreed to when joining Sailnet.
Click Here to view those rules.

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may post attachments
You may edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Proper shaft alignment Joshua Dawn Gear & Maintenance 20 12-13-2009 05:17 PM
Prop shaft alignment Jotun Gear & Maintenance 9 02-23-2007 11:13 PM
Saildrive prop alignment ThunderFog Gear & Maintenance 8 12-01-2006 10:46 AM
prop shaft coupler thurston Gear & Maintenance 2 12-31-2001 07:00 AM
Mast butt-step alignment jregar Gear & Maintenance 1 07-31-2001 10:26 PM

All times are GMT -4. The time now is 07:04 PM.

Add to My Yahoo!         
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2015, vBulletin Solutions, Inc.
SEO by vBSEO 3.6.1
(c) Marine.com LLC 2000-2012

The SailNet.com store is owned and operated by a company independent of the SailNet.com forum. You are now leaving the SailNet forum. Click OK to continue or Cancel to return to the SailNet forum.