an Outboard Motor By FLC member Dick Newco
This is the
first in a series of restoration articles that Dick
Newcomb has agreed to prepare for Brightwork. -Ed.
Compression tester (left), and spark checker
acquired a classic outboard motor, or you are looking
for one to buy. What should you check to find out
if you can restore it for your boat or collection?
The first step
should be the overall condition. Are all the parts
there? If not, for example, buying shrouds, cowels
or trim parts for the motor may wind up costing more
than the motor, if you can find them. Look for broken
cavitation plates, cracks in the gear foot, swapped
pieces that don't match. These are sure signs of trouble.
It is best to pass on motors like that unless they
are very rare.
Let's say the
motor passes the 'looks' test, what next? Most people
will try to pull the starter rope to see if it turns
over. That's a good idea but not necessarily the sign
of a "frozen" powerhead. In my experience 90% plus
of these "set up" motors really weren't hopelessly
rusted tight, especially Evinrudes and Johnsons. The
ones I've worked on typically seize up in the gear
foot where the driveshaft goes through a bronze bushing
to the pinion gear. A tiny amount of rust on that
driveshaft is all it takes to lock up the motor and
make it seem frozen, as if the pistons were melted
to the cylinder walls. This is very easy to fix. Mercurys
have a complex shifting connection that often gets
out of sync, that, too, can make the motor seem frozen.
Once you get
your prize home, it all boils down to spark, compression
and gas. There are two essential tools I'd recommend
you invest in if you are going to do any messing around
with engines, be they outboards or inboards: a compression
tester, and a spark tester (see picture). My compression
tester came from Harbor Freight Tools and cost about
$15. My spark checker was ordered through Sienna Marine
and was $45, well worth it.
The MOST important
test is spark! If you don't have spark, no amount
of gas or great compression will matter; your motor
will not run, period. They will run on bad compression,
and fairly well on dirty carburetors.
To test spark,
remove the spark plugs -- all of them so you don't
have to fight the compression. Attach the plug wires
to your spark checker and find a good ground to clip
it to. Position it so you can easily see it as you
pull the rope or crank, if it is an electric start.
You should see a nice blue spark jumping between the
points on the spark checker. Let's say you are only
getting one to fire (out of two on a two cylinder
motor, for example). There are several possibilities,
but the most likely causes are fouled or dirty contact
points or a bad coil. In future articles I'll describe
how to check, clean and/or replace these.
If you've got
fire (spark), move on to compression.
Since you already
have the spark plugs out you can check compression
easily. Squirt a little WD40 or oil into each cylinder
first. This lubricates the walls and helps the rings
seal. Carefully screw your compression checker into
the spark plug hole until it is snug. You don't need
to tighten it too much, in fact, just snug it up.
Now, pull the starter rope three or four times or
crank the electric starter for about 3-4 seconds.
Read your gauge. Great compression on a typical outboard
is 125+ lbs.; good is 100+; trouble is lower than
90. New rings and possibly pistons are a pretty major
overhaul. Sometimes it's easier to get a good replacement
Last is gas.
You can get a fair idea of weather your motor will
run (if it has passed the spark test and the compression
is good) by spraying a small amount of starter fluid
into the carburetor Turn the throttle all the way
open before you spray and do not put the choke on.
Then pull the rope (or crank). It should fire for
a short time -- even a brief pop will tell you that
it should run.
I'll go into
cleaning and rebuilding carburetors in future issues.