Eng/Shaft Alignment Procedure

[Traveler 45C]

I’m getting ready to replace an eng mount that has sagged (871/M20’s). I know one of you guys have been down this road. I could use some advice.

Surprisingly, the shafts, cutlass bearings and struts all looked great. I was amazed to find the shafts centered in the bearings in spite of the sagging mount. The picture shows the shaft log of the effected side.

First question (for now): What is the proper procedure for aligning the eng to the shaft?

 

[yachtsmanbill]

First of all, you need to upgrade all 4 of those mounts. My 12s use a rigid rear mount that supports the rear on the bell housing and the gear. Pretty conventional. You'll need a 1-1/8 slugging wrench as the coupling bolts are extremely tight, and impossible to break with anything less than that unless you can get at them with a 3/4 drive impact wrench. IMHO that is...
There are 2 things to consider on the algnment itself; AXIAL and RADIAL
(or angular) mis-alignment. Draw two circles superimposed on one another on paper; thats' the AXIAL. Then picture a side view (or top view) where the faces ARE NOT parallel and thats the ANGULAR.
For best results, the alignment should be done in the water as the hull will settle into its' running shape. The parallel can be checked with feeler gauges and the radial should be done with a dial indicator. If you are good with this stuff, you can clean and verify the two coupling diameters and measure with a depth micrometer and compare the differences. In some cases you need to measure "shaft sag" once the units are split, but with 2-3 bearing supports and a stout shaft dia. this is pretty negligible. As with any precision measurements, cleanliness is a must. That includes the mount faces ( and shims if used ) because once separated, dirt and rust will play HAVOC with consistent numbers, and you will only want to move a 5000# power unit once if you can !!
When you make adjustments, re-tighten everything and re-measure your couplings to verify that mount squeeze has put everything where you want it. Feel free to email me if you need elaboration on this.
The pics show the rear and front motor mounts and the coupling on the 12-71Ns w/ MH20 gears. Notice shim packs under the mounts! ws