With the age of the Sundowner Tug fleet and so many owner changes of boats as well as engine/transmission upgrades, I thought it essential to cover a topic not yet discussed in the Forum. Upon commissioning a new inboard engine boat, the boat should rest in the water a few days BEFORE alignment of the engine/transmission to its driveshaft at the flanges. Presumably, alignment was done at the original builder site; but transport from Taiwan to America and subsequent haulage/s may affect this critical interface. Any engine/transmission replacement or serious prop strike encounter also requires new, precise shaft check/alignment per the above in-water rest period.
Think of the engine/transmission shaft flange as usually a four bolt arrangement on the flange with the alignment to the following drive shaft flange needing to have equal, but very slight flange spacing measured in thousands of an inch with calibrated feeler gauges.
Your engine/transmission combination should have (usually) four engine-mount alignment bolts with split-lock washers on the engine beds for our size/weight engine/transmission combinations. That is where your alignment adjustments will take place.
Measure with feeler gauges at the four cardinal points of the shaft flanges their clearance. It should be as equal as possible at the cardinal points (N,E,S,W) at just a few thousands of an inch. If unequal large clearances are measured at these points, the engine/transmission mounts must be adjusted to bring the flanges alignments into as close as possible equal, but slight spacings.
How much clearance is too much? If any of the cardinal measurement clearances around the flanges' circle is six thousands of an inch or greater, you need to decrease the clearance as measured at those points as equal as possible. You will know if your shaft flanges are not properly aligned (out by six-thousands or more at any cardinal point) by the intense howl noise of the misalignment with engine in gear, shaft turning, heard from in/or out the engine room.
If you do not feel up to this task yourself, which takes some time and effort, a good marine mechanic would be familiar with the required job. It is a back and forth process between motor mount slight adjustments to measurements at the shaft flange clearances with some logical thought involved to achieve the required shaft alignment.
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