Preparing to ReRig a 26' American Offshore , # 5 w/Trans plug in , with No Stand Off box . Boat originally had 3 point mounts, offshore front , bellhousing plate , and rubber mounts on trans to inner transom plate . The mounts are all swiss cheese and I would like to make new ones . I like to do things right the first time and make it look nice.
1. Cant find what Alignment tool is used to check , engine- trans - drive alignment . I have a factory manual , and the part number it gives is for a alpha/ bravo shaft that we all have. 91-57797A-3
2. Is the Bellhousing plate mount necessary with the transmission mounts on the inner transom plate? I would think it would be only for a standoff box with a drive line ?
I could really clean up the bilge and make some room if I could eliminate the rear bellhousing plate.

Can you post some pics of the mounts, and how it is mounted ?
Was under the impression that all #3-4-5 speedmasters required the rear plate mount (as pictured), and did not / could not use the inner transom plate as the rear engine mount like alpha bravo and trs.

If your rear mount is the mercury part number (like pictured) and is not molested, or rusted real bad and you are making custom mounts i would buy it.

From my research .... it appears to be a Mixture of parts from an 800-900SC , 500 Bulldog and various other components.
It has the Port Trans mount bracket 47340A1 , Starboard bracket 47334A2 .
Engine mounts similar to Front 849143T and Rear 844346T.
From the Parts Diagrams on BAM , it appears to have used all 3 Mounting Points .




Sooo.... Next question is , Does anyone have the Rigging Guide for the #5 ? Ive looked all over Ebay and cant find anything.
I'm just worried about Alignment now , but since it doesnt have a Gimbal bearing , I would think that their isnt any issue as far as that goes?
I am going to make all new engine mounts for the stringers.
Does anyone have any nicer made motor plates available ! The Merc ones look like they have been cut with a dull fire axe!
Wow I finally figured out how to post Pics!

1st and second pic is a 496 front offshore mount. It clears the 9 quart pan on the 496.
Not sure if it would clear the big pan on your engine, it also has good room on both sides of the engine for mounting and plumbing in the accy's.

Last pic is a special tool mercury makes that slides onto the alignment tool and into the gimbal housing.
You put the alingment tool into the transmission or coupler and then slide on the plate, any gaps between the plate and gimbal housing means the engine is not aligned

The special tool pictured is for a bravo drive and the shaft was made by a friend of mine.
Mercury makes the plate for bravo and trs.

Unknown if the plate exists for the #3-4-5, and i have never installed or aligned a speedmaster, but
alignment is important, trs doesnt have a gimbal bearing either and the plate is needed for correct alignment.
the shaft and plate you could make or have made assuming you can or have connections since you said your making new engine mounts.

Last 2 pics are mine and couldnt have installed the engine the way i did with out the plate.

I have the Alignment Shaft , and can make the Plate on my Lathe . I was hoping somebody , that had done this on there boat.
Would jump on here and have a part number of the Merc tools and procedures to do this .
I have the Merc Service Manual but it only gives the line up shaft part number .
The previous mounts arent the nicest , and I want to straighten them up , by refabbing the Stringer Mounts with 5/16 plate and
Sandwich mounting them through the Stringers .
I may have to wait till Wed and call BAM and ask Mark if he knows .

Call Albert or Randy at Cobra . they sold me a new Merc set for $350 shipped. He has quite a few upstairs.

You can use one or the other but not both.
I would run the rear mount plate and not use the mounts on the transmission.
I don't remember Merc having an alignment tool for those drives. I did have one that I made but I don't remember seeing it recently. The last time I used it was probably close to 30 years ago.

Thanks Marc , I looked up the parts manual on your site for the 700-900sc and it shows All 3 Mounts being utilized?
BUP found me the part number for the Alignment shaft and Ive ordered it . Do you think I should just Eliminate the trans mounts ?
Thank you for replying Marc.