I took the long road
to the conversion as it was decided that the motors
solid motor mounts, so a complete teardown of the engine assembly
was needed. Thanks to Dick Davis for
fabricating these beautiful mounts, it’s to
bad they are hidden.
Million thanks goes
out to Dick Davis and William Petrino
<>for all of
their help in making this project such a success!
A little background history on Merc Speedmasters
by Sam Cullis
>When the first Merc 6 cylinder motor was introduced in 1956,
chief engineer promised that there
would eventually be 2 special high
speed lower units for them. The stock lower units were very good up
into the low 50 mph range.
One of the special lower units would be for
boats that could run in the 50 to 80 mph range and the second special
would be for boats that could run more than 80 mph. Merc was
already making racing lower units for their
very popular (and now
famous) 2 and 4 cylinder racing motors that were running up to about 75
mph on small racing boats,
but these were not really big enough for the
6 cylinder motors.
Two years went by and Kiekhaefer turned away from producing the special
lower units for the 6's for sale to racers.
Instead a side project came
up that called for a special lower unit under a special short mid
section for a world speed record attempt.
A lot of testing at Lake X
lead to the Merc Mark 75H which raised the speed record to 107 mph in
1958, a full 7% increase over
the previous record held by a one off
special outboard motor based on a car motor. A very limited number of
Mark 75H motors
with 1:1 gear ratio units were sold, probably 50, in
addition to the 50 or so prototype pieces made before actual production.
Three more years went by and Kiekhaefer got wind of Scott McCulloch
prepairing to introduce a racing lower unit for their
3 cylinder 60 hp
motor. At about the same time Scott got their racing stuff to market in
1961, Mercury released the
2 special racing lower units they had
promised 5 years earlier in 1956.
Right off the bat in 1961 Merc released 2 versions of the 1.5:1
Sportmaster and 4 versions of the 1:1 gear ratio Speedmaster.
Sportmaster came in right and left hand rotation with a 2 piece drive
shaft to accomdate the 2 different crankshaft
spline sizes in the 70
and 80 hp motors. Speedmasters came with full length driveshafts for
either the 70 hp crank
spline or 80 hp crank spline, both types in
right hand and left hand rotation. In general the internal works and
the first version Speedmaster was directly derived
from the bottom end of the Mark 75 H lower unit, but altered to fit
directly on the bottom of the Merc 700 & 800 midsection. Water
inlet is at the bottom front of the nose. Before the end of 1961
heavy duty version of the 80 hp type came out with stronger bearings in
the upper driveshaft bearing position.
With the introduction of the 100
hp six in 1962 an improved version of the Speedmaster was released with
different housing and different water inlet position.
The Sportmaster was not a commercial success, because in 1961 there
were very few boats that ran between 50 and 80 mph.
You either had a
pleasure boat that went something under 50 mph or a raceboat that went
well over 75 mph;
only a very few boat racers used them with success.
Cosmetically a 1961 Sportmaster looks very much like a
Merc 450 or 500
fishing lower unit. Almost all of them were set aside and lost or
mistakenly trashed as unused 50 hp units.
Water inlet is the same place
as fishing Mercs and many other brands of the 1960 era, from prop spray
an inlet on the bottom of the cav plate.
By 1964 racers were really punishing the Speedmasters in marathon
racing under the 100hp stock motors
and 110-115+ hp modified motors.
Some races were won by fast pit changes of worn out Speedmasters
on the course before the other guy changed out his busted
lower unit and got out. Merc's answer to this was the
Speedmaster" introduced in 1965. Again the gear ratio was 1:1 and
forward only ... no neutral or reverse.
The Super version also came in
right and left hand rotations. The Super Speedmaster was stronger than
Speedmaster because it had 2 driveshafts one behind the
other turning opposite directions driving 2 gears on the prop shaft.
Equal loading (more or less) of the gear pairs was acheived by making
the lower driveshaft sections very thin.
So thin that they flexed. The
Super Speedmaster prop shaft was also supported by more bearings as
were the dual driveshafts.
Super Speedmasters (SSM's) were sufficient until hp approached 150. At
150 hp right hand SSM's were still up to par,
but left hand SSM's could
not take the load. Merc's solution for boats running 2 motors wanting
one RH rotation prop
and one LH rotation prop was to run one motor
backwards and make a few minor changes to a RH SSM to allow it to
with CCW input and output. A second tier solution was to use the first
MerCruiser sterndrive Super Speedmaster
which had turned out to be a
little weak for sterndrive use. This SSM was called a MC-1 SSM for
"MerCruiser type 1 Super Speedmaster"
The first V-6 racers used the same SSM's as the inline 6's. The only
significant change was the introduction of 14:15
gear ratio instead of
14:14. As power dramatically increased with the V-6's 2 larger heavier
SSM's were introduced:
the VI and the IV (6 and 4). The 6 is larger
than an inline SSM, but slim and trim compared to a big fat type 4.
VI and IV only bolt up to the special racing mid section, no longer an
accessory fit to the std mid.
As far as putting one on your 150 the ideal one to find and use is a RH
SSM or MC-1 SSM.
A few words of caution:
start in gear forward only
is a big fat pain in the butt
props for all Speedmasters
start at 15 inches of pitch and go up
into the 20's.
These are the equivalent of 30 to 42+ inches of pitch at
the 150's std 2:1 gear ratio. If your boat isn't already running 80 or
plan on spending $600 or more for a custom made prop to use a SSM
at lower speeds
SSM gears and bearings are
tiny, wear is instant and continual.
Change your gear lube EVERY time you
use the SSM
exercise caution buying a
used SSM. You are probably buying a used up piece that needs $1000
worth of rebuild
don't expect much if any
speed increase on a rig over 550 pounds with driver. SSM's were just
not made for this use<>