I finally got a mechanic down to the boat last week. I’ve been meaning to do this since before I
bought the boat, but never got around to it.
I knew the news would be bad. Do
they ever give good news?
The port engine is very hard to start. It has to be cranked for 60-120 seconds (not
continuously) before it will fire. When
it does, it only runs on one cylinder and understandably very rough. After it has warmed up for a few minutes, the
other cylinders will start to fire, after which it is fine and will run all
day.
A diesel engine is pretty simple. It doesn’t have spark plugs, but instead
relies on the air in the cylinder being heated by compression and a fine spray
of fuel being injected into the cylinder at the right time to cause combustion. Simple, but precise. The piston has to fit perfectly in the
cylinder to create the compression, and the fuel has to be sprayed at the
perfect time, in the perfect pattern, and under very high pressure.
I have managed to put together a few pieces of the boat’s
story. The engines were commissioned in
November 2000 by a mechanic in Sarasota.
This was interesting because I didn’t know the boat had ever been in
this area. I have a logbook that starts a
year later in November 2001, in Fort Lauderdale, when the engines have 145
hours on them. The logbook contains
several entries that indicate that the port engine had problems even then. It mentions some “blow by” and that the
engine was accidentally run with the raw water intake closed, causing it to
overheat.
The overheating back then could very likely be root cause of
my problems today. When metal gets hot
it gets soft and expands. Getting soft
can lead to deformation, and expansion within the small tolerances of a
cylinder can lead to increased friction and wear (which leads to more heat and
more friction until your engine seizes).
Overheating is not conducive for maintaining compression inside the
engine.
The “blow by” he notes is a compression problem, but is
related to the rings at the top of the cylinder not fitting correctly and
allowing gas to escape. It is usually a
relatively easy fix and not a long-term problem.
Generally, the first thing a mechanic wants to know when he
encounters a diesel that won’t fire is if there is compression. This can be done by removing the glow plugs (little
electrodes that pre-heat the air in the cylinder for easier starting), fitting
a pressure gauge, and cranking it. It is
hard to say what pressure is good and what is bad, but the cylinders should all
be about the same. It is definitely bad when
you have one cylinder that is 50% higher than the others, and that cylinder
works when the others don’t. Alas, this
is the case.
It is a pretty safe bet that what is going on inside the
engine is that the engine has to be turned over (either by the starter, or by the
“good” cylinder) until the pistons heat up from enough friction to expand and the
pressure rises enough to allow combustion.
While the engine is turning over, the injectors are dumping fuel into
the cylinders, which washes away the lubricating oil. This increases the friction and helps the
cylinders to heat up and thus fire earlier, but it also causes wear and the
starting problem will get worse and worse until someday the engine just won’t
start.
What is the solution?
Well, the piston has to be made to fit perfectly in the cylinder. The cylinder therefore has to be bored larger
(probably half a millimeter) and fitted with larger pistons, or the cylinder
has to be sleeved and re-bored to the original spec and the pistons replaced. Of course this can’t be done in the boat so the
engine has be removed and re-installed, adding about two days of labor. Ballpark estimate: $4,000.
Now, this isn’t all that terrible in boat-money terms. Where it gets complicated is when you
consider that after spending the four grand, I’ll still have a pair of tired
old 30 horsepower engines that really probably should have been 40s or 50s to
begin with. The real question here is do
I want to take this boat long-distance with these engines? Ballpark estimate for two new 40HP engines and
matched propellers: $40,000.
The mechanic that did this compression test for me was the
same guy who commissioned the engines in 2000.
I did that on purpose. He helped
me collect some of the pieces of the history puzzle. Also, he wrote in his 2000 report that the
boat motored at 9 knots. Now, I’ve spent
some time on this boat and the only time I’ve seen 9 knots is with a nice
breeze and a big sail. The best I’ve
seen under power is about 5.5. I wanted
to meet the man who said this boat went 9 knots on these engines. He verified that it did indeed happen and
noted that the engines did not achieve anywhere near their rated RPMs.
As I’ve alluded to before, there are many factors to
consider when trying to maximize boat speed and minimize fuel consumption. The boat’s shape and weight are
constants. The engine manufacturer
considers the RPM a constant. The gear
ratio is a constant. There are
environmental considerations such as temperature, wind, and sea state, but the
main variable is the propeller. What
diameter, how many blades, what blade pitch?
Apparently, it is possible to pitch the propellers such that the boat
can go 9 knots, but the engines can’t turn them at the speed the manufacturer
says is ideal. How bad this is, I don’t
know. I also note that however the props
were pitched then, and however they are now, the engines do run faster, but
still don’t get what the manufacturer considers “cruising speed”.
The boat has fancy feathering propellers that orient
themselves to the water when sailing to reduce drag. They have adjustable pitch, but unfortunately
the boat has to be pulled out to make the adjustment. Pulling this boat out is not something you do
casually. I know that the propellers
were removed and sent off to be serviced by the manufacturer sometime after the
commissioning. Whether the pitch was the
same when the propellers were returned I don’t know, but this seems the most
likely point at which the pitch would have been changed, perhaps inadvertently.
All stuff to consider.
In the meantime we plan to run the port engine as-is. We found that all the glow plugs were dead
(probably from a tricky control panel switch that keeps them on unnecessarily)
so those are being replaced. They really
aren’t necessary in this climate, but anything that can raise the temperature
in the cylinders is a good thing. Since
we already had the injectors out, we figured it wouldn’t hurt either to have
them cleaned on the chance that a bad spray pattern was inhibiting combustion. When that is all done and the engine is back
together I’ll have to find another mechanic to come take it all apart again and
give me a second opinion before I consider going any further.
Update 11/03/08
After reassembling the engine with the new glow plugs and the rebuilt injectors it starts amazingly well. Like immediately. It still runs unevenly when it is cold, and it seems to not warm up as quickly, probably due to the water getting colder, but at least I don't have to crank it nearly as much. The mechanic's bill was $1,500 and while I'm not pleased with some of his billing practices, I think it was money well spent. The starboard engine has now begun starting sluggishly and probably needs the same treatment. I'll be doing that one myself.
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