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Yanmar 2GM20F:
Engine Template
This page was last updated on 26
July 2001.
NOTE: On this page,
you've actually gone back in time a bit. I built this engine template
prior to hauling the boat and removing the old engine, since this was
preparatory work I could do before committing to the project. But for the
sake of chronological continuity, it makes more sense for this page to be at
this order in the sequence of work involved in replacing the engine.
Once again, I found myself building an engine alignment
template. Who knew that I'd be doing this again so soon? It was only
a little over a year ago that I built my first template
for the Yanmar SB12 engine that I initially installed in the boat.
The first step, which I took care of before even ordering the
new engine, was to find out how much, if any, I would have to modify my engine
foundation. I was a little worried that it would be necessary to cut the
foundation down. However, when I started comparing dimensions, I figured
out that, if anything, I might only have to raise the beds a little less
than a half inch. Raising is easy, since I only have to add an oak shim or
something. Obviously, the shaft and the shaft angle are constant, no
matter what engine there is, so the only real changes have to do with the height
of the coupling relative to the engine beds. This is good news.
Once the new engine arrived, I was ready to get to work.
I built the template before the boat was even hauled, as it was an easy thing to
get out of the way, and the template will be one of the first things I need once
the old engine is removed.
Please click
here to view a dimensional drawing of the Yanmar 2GM20F. It gives all
the important dimensions necessary to construct a template like mine.
Using the supplied dimensional drawing, I constructed a simple
plywood platform, carefully laid out to represent the basic dimensions of the
engine. The most critical part of building the template is to exactly
locate a surface to represent the transmission coupling, and to properly and
accurately locate the four engine mounting holes, which was easy enough using
the drawings.
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When
I made the first template, I found it easier to make the plywood rectangle a
little shorter than the ultimate dimensions of the engine, and then add extensions
to the ends as necessary to represent the exact locations of the critical
components, such as the transmission coupling flange. For the new engine,
the forward end of the template is less important, since I already know the
engine will fit nicely in my engine bay. The aft end,
however--representing the coupling--remains critical. To locate the
coupling, I randomly decided that my extension would be exactly 2" beyond
the end of the plywood rectangle. Therefore, since the measurements used
to locate the four engine mount centers are referenced to the coupling flange, I
measured forward and located each mount center--remembering to account for the
2" overhang at the rear. Then, I added my extension to the aft end of
the template (shown to the right). To account for the vertical piece of
plywood at the aft end, which projects down and represents the actual face of
the transmission coupling, I subtracted the thickness of the plywood from the
2" overhang measurement. These pieces are simply screwed together and
onto the plywood template.
The
vertical piece at the end is designed to exactly represent the transmission
coupling, and the offset from the engine mounting flanges (which are represented
by the bottom of the plywood template). This is 2.95" as indicated in
the drawing, so I carefully located and marked the center and drilled a
1/4" hole (to allow a centering string to pass through later). I
sawed a slot into the hole to allow the string to slip in. With the
measurements made and the hole drilled, I carefully installed these pieces so
that the center of the hole was exactly 2.95" below the bottom of the
plywood template. To make this easier, I drew several reference marks on
the piece before installing it. I added an identical piece to the front
edge of the template. When the template is installed on the boat later,
the centering string, which will run though the stern tube into the boat, will
run right through these holes, and I will be able to adjust the engine beds or
adjustable mounts as necessary. With these pieces installed, I mounted the
template on the four rubber engine mounts--there are two different densities of
rubber, so the ones marked "75" go at the aft and, and the ones marked
"100" go at the forward end, according to the manual.
Next:
installing the centering line in the boat (after removing the old engine) and
modifying the engine beds if necessary to allow for perfect engine placement and
alignment.