1/10,000 of an inch

Once the engine was positioned roughly where it needed to be and I had determined how much of the original rails needed to be cut out, I moved the engine and went at it with the saw.

I ended up with what seemed like an alarming pile of scrap aluminum.

Next step was to build new engine bed rails out of 3/4" x 4" aluminum flat bar about 5" lower than the originals. We were careful to replace any structural integrity lost in the cut out with additional reinforcements, and then some.

Once these main structural components were in place, the engine was moved back and measured for the actual pads that the mounting bushings would attach to.

These pads were then fabricated using TIG welding process for increased strength, dry fitted to make sure they were right and welded in place.

At this point, the rubber bushing mounts could be fitted to the engine and the assembly loosely positioned.

Final alignment could now proceed.

How does one determine this? Most of you aren't asking, and eyes are surely glazing over, but I'm going to answer anyway. The end of the transmission and the prop shaft have matching couplings that have finely machined surfaces. The two plates are about 6" in diameter and are ultimately bolted together to form a solid bond between the engine, prop shaft and ultimately propeller. In order to determine alignment, the engine is eased toward the prop shaft until the two surfaces are almost but not quite touching. Now the gap is measured on all four axises. Using built in adjustments on the four engine bushings, the engine is then moved up, down, or sideways until one has an even measurement on entire circumference of coupling surfaces.

Just how anal one wants to get at this point, determines how long a process this will be.

Took me all afternoon, resulting in an alignment that is within 1/10,000 of an inch.

How thick is that? About the thickness of a human hair. How important is it? Very.

Misalignment translates into vibration which not only creates noise that is transmitted throughout the entire vessel, but results in accelerated wear and premature failure in drive line components. John Deere designs it's engines with an internal counterbalance to keep vibration to a minimum, this feature combined with the care taken in the installation translates into a quieter running power plant which in turn will be appreciated every time we start the engine.