Thanks for all the comments so far!
Right now I am guessing that it is a design flaw:
The engine stringers already have pieces cut out to
fit the engine. The boat had the current Yanmar from
day one, but I guess the engine space was designed
for the atomic 4, and poorly adapted to the Yanmar
by cutting out pieces. (The fuel filter had also been
touching the steps, which was corrected by a previous
owner by moving the steps a bit.)
The pump issue is a problem, because the constant banging
on the stringer slowly tilts the pump towards the engine,
releasing tension of the belt: => No cooling water.
I don't think that the engine has been used a lot, so
this problem could have been there unnoticed all the time.
(Two almost new impellers I found support this theory:
No cooling Water => change impeller.
This reestablishes belt tension,
=> problem solved until next time, and
an almost new impeller to keep on the boat.) (*)
What should I look for to determine if something is
wrong other than the engine mounting tolerances?
Here is some more information:
- The gap between the water pump and the engine stringer
is between 1/2" and 1", which seemed too little to me,
hence the idea of cutting off more fiberglass.
What do you say: How much clearance should there be?
- Vibration doesn't seem excessive for a 2 cylinder diesel,
although I am not an expert at judging this.
I saw 4 cylinder car engines shake almost that much,
a five cylinder Mercedes (car) diesel about the same.
- Alignment is not part of the problem, the banging happens
in neutral as well.
Vibration stays the same (or even goes down a bit, I think)
with the propeller engaged. I haven't looked under full load,
just at a bit above idling in the slip.
- The rubber engine mounts seem ok, no visible breakage,
Thanks again for all input,
(*) This brings me to another question:
Where do I get cheaper Yanmar parts?
I paid $36 for the impeller, that seems
an awful lot of money for a tiny piece
It has 'Johnson' imprinted on it. Are
outboard parts cheaper?
> Any of the tools mentioned will work, but I'd try to find out what
> caused the problem--unless you're sure this is a design flaw. you may
> weaken the engine stringers, or if you may have bad engine mounts as
> mentioned above, which may also be affecting your alignment. At any
> rate, the one thing I wanted to add is, if you are using a power tool,
> esp. if you are grinding, wear a tyvec-type overalls. You may sweat a
> bit, but it sure beats the glass-itch. If you get glass itch,
> alternate very hot and very cold water in the shower. It won't get rid
> of it, but the scalding sensation will make you forget about it for a
> good luck.
> mickey >> Stay informed about: Cutting Fiberglas: How?