U joints?
When you installed the transom assembly, did you follow the tightening sequence and number of passes until the 25 foot pounds was achieved ?

Do you have matching flywheel cover and inner transom plate ? Some rear mounts used the fiberous washer and spring, the newer ones i don't think use them. An old rear flywheel cover won't align with a newer inner transom assembly and vice-versa and with wrong/incorrect stack between the rear mounts.

There are pictures and mercury service bulletins connection with the rear mounts on here and all over the internet.

Thanks, I've read that a soft transom might cause this type of behavior, but I I'd like to rule exactly every other thing out before having to face that fact.

Yeah I'm hoping it'll be an outdrive issue. Yes, I've done everything by the merc instruction with torque-procedures, paying extra attention to the old vs new washer-situation so those are correct. I'm pretty meticulous 🙂.
That would only affect the height, not the lateral adjustment though.

in my opinion, this is the alignment tool you need, (in conjuction with the shaft), It fits into the transom assembly and on the alignment shaft tool. It wont sit flush unless the engine crankshaft, drive coupler, gimbal bearing and outdrive bellhousing are all in alignment.



Here is the part number



It diagnoses ; improper gimbal ring height. improper/ sunken rear engine mounts. Mis-aligned gimbal bearing, bad engine coupler via spinning 12-3-6 & 9 and other engine alignment issues, etc.

And, IF, you have the bearing hangar from a alpha/bravo driveline it can also show an out of square/flush/parallel inner transom plate to transom assembly.



It is also absolutely neccessary if you ever decide to install an engine other than the way mother mercury would have you do it all the while using some but not all aftermarket parts in such a way as to pull engine install and alignment directly out of your ass and have it work

I have offshore mounts for engine (front) and trans (rear) tubular hoop style.

Coupled to ASD6s.
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​With zero alignment adjustment, what is the best process to ensure parallel alignment?