The drive shaft coupling on the back of the engine and the center of the gimbal bearing must be precisely alinged or you will ruin the coupling. Replacing the coupling requires removing the engine from the boat.
The manual calls for using a special Mercruiser alignment tool that inserts through the gimbal bearing inner race and into the coupling to check alignment. Adjustments are made to the front engine mounts as required to achieve perfect alignment.
Once the alignment is close enough to get the Mercruiser alignment tool in place it is the right tool and the ONLY tool for finishing the job properly.
Also the gimbal bearing is free to be adjusted for angle within its carrier to a small amount. (This is so that it can accommodate differing transom angles. It is not for the above center line alignment.)
HOWEVER IF.......
A) either the gimbal bearing is not tilted correctly in its holder (?correct? varies by boat),
B) if the engine is out of alignment more than just a small amount,
you can't get the alignment tool to slip into place. So you are stuck with a trial and error approach until you get it close enough for that to happen.
SOLUTION......
I found a tool that helps you make a rough pre-alignment. After a rough pre-alignment you should be able to use the Mercruiser tool to complete the job properly.
THE TOOL:
The tool I found that works well is a rod which makes a close, but not terribly tight fit into the splined shaft hole in the coupler; it has a cylindrical fitting on it a little smaller than the inner bore of the gimbal bearing; and it has a long enough handle to stick out the back of the bell housing.
It is also cheap and readily available:
It is a Lido ?Extend and Lock Multi-Use Rod.?
The 30 to 48 inch version.
U.S. I.P.C. (product bar code) 028705003218
http://www.storagesuppliesplus.com/unit/8332662/
This is one of those extendable shower curtain rods. It has a smaller diameter tube that is just the right fit for the splined-shaft hole on the coupler. Not too tight, not too loose.
It also has a collar on it where the small diameter extender tube goes into the larger diameter tube. This collar has a generous chamfer on it and an O.D just slightly less than that of the ID of the gimbal bearing.
The larger diameter tube makes a handle that sticks out the back of the bell housing.
USE:
After you get your new shower curtain rod get it ready for use. Toss the mounting hardware and fittings. Remove and toss the plastic insert from the end of the small tube.
If you extend the small tube around 12 inches you can then, from behind the bell housing, feel around to gently slip it into the coupling. The angle of the tube sticking through the transom shield will now show you which way you need to adjust the engine front mounts. Rough align the engine as needed so that the rod comes out through the middle of the gimbal bearing..
Next set the extender tube to the right length so that the collar where the two tubes join slips into the gimbal bearing with its back face about flush with the back of the gimbal bearing. That's about 9 1/8 inches from the end of the small tube to the front of the collar on my 3.0L but yours may be different. With the small tube once again inserted into the coupling the back edge of the collar on the tool will now help you to visualize which way to tilt the gimbal bearing. This tool is not strong enough to use to tilt the bearing. You must do that by some other means.
If the tilt was way off, you may have to repeat the first step.
Once these two rough-alignment procedures are accomplished switch over to use the proper Merc alignment tool to get precise final alignment.
USING JUST THIS TOOL WILL NOT GIVE YOU A PRECISE ENOUGH ALINGMENT!
Do not get cheap and try to use it instead of the proper alignment tool. You will damage your coupling and have to pull your engine to replace it.
The manual calls for using a special Mercruiser alignment tool that inserts through the gimbal bearing inner race and into the coupling to check alignment. Adjustments are made to the front engine mounts as required to achieve perfect alignment.
Once the alignment is close enough to get the Mercruiser alignment tool in place it is the right tool and the ONLY tool for finishing the job properly.
Also the gimbal bearing is free to be adjusted for angle within its carrier to a small amount. (This is so that it can accommodate differing transom angles. It is not for the above center line alignment.)
HOWEVER IF.......
A) either the gimbal bearing is not tilted correctly in its holder (?correct? varies by boat),
B) if the engine is out of alignment more than just a small amount,
you can't get the alignment tool to slip into place. So you are stuck with a trial and error approach until you get it close enough for that to happen.
SOLUTION......
I found a tool that helps you make a rough pre-alignment. After a rough pre-alignment you should be able to use the Mercruiser tool to complete the job properly.
THE TOOL:
The tool I found that works well is a rod which makes a close, but not terribly tight fit into the splined shaft hole in the coupler; it has a cylindrical fitting on it a little smaller than the inner bore of the gimbal bearing; and it has a long enough handle to stick out the back of the bell housing.
It is also cheap and readily available:
It is a Lido ?Extend and Lock Multi-Use Rod.?
The 30 to 48 inch version.
U.S. I.P.C. (product bar code) 028705003218
http://www.storagesuppliesplus.com/unit/8332662/
This is one of those extendable shower curtain rods. It has a smaller diameter tube that is just the right fit for the splined-shaft hole on the coupler. Not too tight, not too loose.
It also has a collar on it where the small diameter extender tube goes into the larger diameter tube. This collar has a generous chamfer on it and an O.D just slightly less than that of the ID of the gimbal bearing.
The larger diameter tube makes a handle that sticks out the back of the bell housing.
USE:
After you get your new shower curtain rod get it ready for use. Toss the mounting hardware and fittings. Remove and toss the plastic insert from the end of the small tube.
If you extend the small tube around 12 inches you can then, from behind the bell housing, feel around to gently slip it into the coupling. The angle of the tube sticking through the transom shield will now show you which way you need to adjust the engine front mounts. Rough align the engine as needed so that the rod comes out through the middle of the gimbal bearing..
Next set the extender tube to the right length so that the collar where the two tubes join slips into the gimbal bearing with its back face about flush with the back of the gimbal bearing. That's about 9 1/8 inches from the end of the small tube to the front of the collar on my 3.0L but yours may be different. With the small tube once again inserted into the coupling the back edge of the collar on the tool will now help you to visualize which way to tilt the gimbal bearing. This tool is not strong enough to use to tilt the bearing. You must do that by some other means.
If the tilt was way off, you may have to repeat the first step.
Once these two rough-alignment procedures are accomplished switch over to use the proper Merc alignment tool to get precise final alignment.
USING JUST THIS TOOL WILL NOT GIVE YOU A PRECISE ENOUGH ALINGMENT!
Do not get cheap and try to use it instead of the proper alignment tool. You will damage your coupling and have to pull your engine to replace it.
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