Yanmar 2GM20F:  Templating and Foundation Modifications
This page was last updated on 2 August 2001.

TUESDAY 7/31/01 

Bright and early the day after hauling and removing the old engine, I was back on the job.  The first thing to do was to rig up a string through the center of the stern tube--the string represents the center of the propeller shaft, which is the most critical measurement when installing an engine.  I passed a string through the tube from inside, and tied it to a pencil, which I then taped across the exterior of the opening--attempting to get it dead center, but I'll come back to it later to be sure.  Moving back inside, I drew the string up tight, and secured it to a board that spanned across the front of the engine box.  I moved the string and board around until I could visually see that the string was passing through the center of the stern tube.  I went back outside and checked the pencil, and made some small adjustments now that the string was under tension from the inside.  Then, I checked it again from the inside.  Perfect.

Next, I placed the engine template on the beds, passing the string through the holes in the template projections.  Just before doing this, I adjusted the flexible mounts so that they were approximately in the middle of their range, which would allow me the freedom to make adjustments in any direction.  Immediately, it was obvious that my calculations were right--I'd have to raise the engine beds somewhat.  That's easy--I'm just glad I didn't have to cut them down, or change them altogether.  Raising the template a little by hand, I estimated that 3/4" would be a bout perfect.  I left the boatyard to go home and search my scrap pile for some suitable oak to do the job.  I found just enough, and milled two pieces to 3" x 23" to fit the existing beds.

My plan was to epoxy the boards in place,  and to hold them temporarily with screws to allow me to continue working while the epoxy set up.  Plus, the lags that secure the engine mounts will pass through the oak, further securing it. The oak strips are really just shims--the structure of the foundation is already in place.  Transferring my marks that I made after removing the old engine to the sides of the foundation, I sanded the paint off the tops to give the epoxy a good surface to bond to.  Then, I cleaned both surfaces with Acetone, mixed up a thick epoxy mixture, applied it to the bottoms of the boards, and screwed the oak pieces into place.  I cleaned up the goop that squeezed out, and I was ready to continue.

Setting the alignment template back on top of the new oak shims and lining it up with my marks, I could see that now I just had to make some minor adjustments to the nuts on the flexible engine mounts.  The forward end was sitting a little too low, and the aft end a touch too high.  I made the appropriate adjustments, and the string came nicely into place through the center of each hole in the template extensions.  If anything, I left the adjustment a little high, since the manual states that the engine should compress the mounts by about 3.5mm when it is installed.

With my final adjustments made, I ensured that the template was properly lined up with the fore and aft marks I made earlier (to ensure that the existing shaft would properly mate with the new transmission coupling) and then marked the boltholes that would secure the mounts to the foundation.  Then I removed the template and drilled pilot holes for the lags screws that will hold the mounts in place when I install the engine.  I labeled each mount for its location as well, since the adjustments on each are slightly different--they need to go in the proper places on the engine in order to keep my pre-alignment perfect.

Before proceeding, I reinstalled the stuffing box and slid the shaft in from the inside--remember, the coupling is still installed.  I pushed the shaft as far aft as possible to keep it out of the way.  With that done, it was time to hoist the new engine into the boat.  

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Glissando, Pearson  Triton #381

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