Stern Drive Conversion
I have inherited a 25' MirroCruiser with a 305 and a pre-Alpha Stern Drive
(the one with loop on the top bearing cover).
I have never had this in the water yet.
I have never owned a boat before but I am pretty tech savy.
I needed to repair a few things including:
- the motor (new pistons and valves and I converted it to an electric fuel
pump).
- rewired the charging and added an additional battery with optional solar
charging.
so I took it out and while doing that was surprised to see "REDONE" stamped
on the side of the STERN DRIVE. There was an "O" ring when I took the drive
off the transom gimbal but I see no rubber hose connecting through to the
closed cooling system - It appears to blanked off at the transom end.
There is a pipe in through the hull with a valve and that connects via a hose
to a seawater pump fitted to the engine..
My assumption is that the pre-Alpha drive has been converted somehow.....!!!!! |
Bennie
Feb 15
|
| Hey!! That's my line!! :>) |
Short
Feb 16
|
| That's a good fix and it will probably last you for a while. I used JB weld to form a mount for a down draft carb on my International
Super MTA and after ten years, it's still working. :>) |
Short
Feb 16
|
| You should look at the float bowl vent tube on the old carb. Often on boats
they are shaped like an upsidedown J rather than a straight tube. This
causes the fuel to go down the throat of the carb if the float gets stuck.
Instead of spilling around the intake. If you can swap the vent tube that
would be good. Occasionally marine carbs have o-rings on the throttle shaft
as well to further limit fuel leaking but that is not so common. My holley
is a marine carb but the only difference is the J tubes, it does not have
o-rings on the shafts. Also any rubber fuel lines you use should be from
your local boat store. All rubber fuel lines for boats are double walled.
The thing with gas and boats is that if it leaks anywhere the gas vapors
will collect in the bottom of the hull. Then a spark and kaboom. I'm not
surpirsed about your alternator, I can not see anything about mine that
makes it marine and I know for a fact it is the original merc alternatior. You'll probably want to get another shifter plate. That whole shift
mechanism is a real rube goildburg on mercs. It uses the tension on the
cable housing to activate the stall switches. This momentarily stalls the
ignition so it will come out of gear. Yiou can tell when it's not working
right as the boat will be almost impossible to get out of gear. Usually you
pull so hard that when it finally comes out it goes into the opposite gear.
You have to be in the water to check as on land it will shift fine without
the interupt working. The gears are designed so that the pressure against
the prop causes them to want to stay engaged. Also important that the shift
cable housing be free to move, not wiretied or otherwise fastened at the
engine end except where it is mounted to that plate. It can be real finicky
to get working and having the plate broken will just make it harder. You
could fabricate one if you're really into that sort of thing. If you search
online you will find that there are a number of boat salvage places that
sell used parts. |
James
Feb 16
|
| Converted to what? Alpha's still have a built in raw water pump. Both alphas and pre-alphas
can be used with out the built in raw water pump if a suitable pump is
driven by the engine that uses a thru-hull pickup. What you have is not
unheard of. |
James
Feb 15
|
| How did you power the electric fuel pump? In the event that you didn't ....
consider providing it's power in a manner that the power is removed if the
engine is not running, even though the ignition may be "on". Often, this is
accomplished by powering it through an oil pressure switch. Eisboch |
Eisboch
Feb 15
|
| I don't know......It is stamped redone on the outside of the stern drive. Is
it OK just to run the Sterndrive without pipes hooked up since the water
route through the Transom goes to a blank off plate? I was worried about
the stern-drive it's self needing cooled.... The boat definitely has a
through hull raw water pickup that flows through the heat exchanger and out
via the exhaust.
Remember I am OK with anything mechanical (engines, gearboxes etc) but I am
unfamiliar with the needs of sterndrives.... James wrote: |
Bennie
Feb 15
|
| It is on the same circuit as the coil...When ign switch is off - no fuel.... Eisboch wrote: |
Bennie
Feb 15
|
| Sorry for being a bit slow but I thought there was a potential problem if the
RAW water pump on the Stern Drive was just ignored....
Hopefully I can learn this stuff quickly. Bennie wrote: |
Bennie
Feb 15
|
| I suspected that might have been the case when you mentioned that you were
new to boats.
I've been advised by someone far more knowledgeable than I that it should
only be powered
if the engine is running .... via oil switch or other sensor ... and not
powered from the
ignition switch only. Unlike a car or truck, on a boat you don't want the
potential of the fuel
pump pouring fuel on a fire. If carbureted, you also want the bowl overflow to be plumbed back to the
fuel supply line before the pump and not simply dumped into the bilge like
an automotive carb would do. Just stuff to think about. Eisboch |
Eisboch
Feb 15
|
| You'd better get that fixed pretty quick. It wouldn't pass a CG
inspection as it is. Your insurance won't pay for the ensuing fire
damage either(I've denied claims for fires from faulty owner repairs or
mods - many boat policies specifically exclude coverage). Rob |
trainfan1
Feb 15
|
| No good! There should only be fuel when the engine is cranking (to start),
or there is oil pressure (engine running). The latter could save your engine
as well. If the oil pressure drops for any reason, the fuel pump will cut
out, and the engine will stop before you melt the block. If the ign switch
is simply on, and the engine isn't running, the fuel pump should NOT be
moving fuel. --Mike |
Mike
Feb 15
|
| I suspect you will find it does not have a raw water pump in the outdrive.
The raw water pump is just to supply cooling water to the engine. I gather
you have not taken the outdrive apart. No real reason to if it does not
supply cooling water. You should change it's fluid and check the old fluid
for signs of water. You need to wire your electric fuel pump to the cranking terminal of the
starter and to an oil pressure switch. Best of luck with your new boat :-) |
James
Feb 16
|
| Thanks for all that info - for the time being while I get this running while
OUT the water I can leave it alone but I will definitely work out away to
either relay it via the oil pressure switch or something similar so it only
feeds fuel if the crank is rotating. Again brilliant advice from you all.
Thanks. Anyone have more thoughts about the raw water pump and the possible need to
cool the stern leg?
I don' know if I need that...... I am a going mechanical and electronics guy -
planes .....yes. Boats....not yet!! I did see that that alternator was not a Marine version but I have worked out
a way to "seal" it so no sparks get out. The starter looks like a marine
version though.
Thanks again on the pump issue - almost certainley save me a bit of grief! |
Bennie
Feb 16
|
| Hi James,
I have drained the old oil and refilled it - from the bottom up I understood
was the way to do it, Didn't see any emulsified oil or traces of water. The
skeg is a bit damaged - do you know where you can buy these things that fit
over the damage - without welding?
Thanks... |
Bennie
Feb 16
|
| over the damage - without welding?<< Google is your friend. Search on 'skeg guard' --Mike |
Mike
Feb 15
|
| I should have explained this thing is a long term project. It was all siezed
up due to the engine not being covered. The guy who tried to fix it was a
mechanical moron with even less electronics/electrical experience. The
wiring loom engine and to the panel was totally fried and I have had to
rewire 80% of this thing. It it not wrotten anywhere and the interior was
all in good shape so that is why I have been spending time on it. The motor
now runs like a sewing machine with good compression. What I did have to do
was swop the carb with a van carb since it was corroded completely. My
intention was to make a good one out the the original body and the levers etc
from the van carb - but it seems to and run well with the van carb....
I have had to rebuild the remote motor control - it was siezed up too. The
plate on the back that covers the gearing in the control and holds the two
cables was broken. I am looking for a new one - any ideas? As a temporary
measure I have plastered the back with JB weld and aluminium mesh and the put
an extra mount for the cable extension onto the support panel.
Am I making stupid assumptions?
Additionally, I have made an engine alignment to so the crank/adaptor/stern
shaft are all aligned well - within about 2mm in straight line and in height -
am I correct with that?
Thanks to you all for your "expert" advice. |
Bennie
Feb 16
|
| feeds fuel if the crank is rotating.<< Ok, I want to make sure you really understand this... it's important. The
fuel pump should only be working when the engine is cranking to *start*, OR
there is oil pressure. When you're cranking the engine to start it, there is
no oil pressure, but you need fuel. Once it's started, AND you have oil
pressure, the fuel pump works as well. The scenario you want to avoid is a
running engine, being fed fuel, with NO oil pressure. James' advice is dead on. The pump needs to be wired to the cranking
terminal of the
starter *AND* (not OR) to an oil pressure switch. --Mike |
Mike
Feb 15
|
| better yet, On a Delco starter, That is, if it's a GM motor, the Delco
starter should have two small terminals on the solenoid switch. one
for "start" (S) and the other is "relay" (R) .
Instead of wiring the fuel pump to the (S) terminal as perscribed,
wire it to the (R) terminal which is an inner switch, that when the
starter is cranking it will provide a full 12v shot to your fuel
pump. If you wire the pump to the (S) terminal, the voltage pull from the
pump itself, can rob you of power to the pull-in coil[s] in the
solenoid, giving weak solenoid performance, causing the starter not to
work properly. |
Tim
Feb 15
|
| The bowl overflow should be handled by the vent tubes. They are J tubes and
dump the extra fuel into the carb throat. If a ford, the engine will still
use all the fuel and keep running as Fords love gas. |
CalifBill
Feb 16
|
