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Lightened
connecting rod and piston, prior to assembly. |
Lightening and
balancing the engine’s rotating assembly components involves removing metal
in strategic locations using a variety of methods and special tools, and
therefore should only be attempted by a qualified technician. Removing too
much substrate in the wrong areas could weaken the components being
modified, resulting in engine failure.
For this article, we used our high performance Mercury 2.5-litre 260
horsepower engine. We had
Jay Smith Racing Engines modify our flywheel,
connecting rods, and wrist pins, while
Marles US1 Racing lightened and balanced
our Mercury high performance pistons. All components were factory stock
prior to modifications, and weights were measured before and after the
process.
Lightening Pistons and Top-Pinning
Traditional 2-stroke Mercury V6 pistons utilize a pressed steel pin in the
ring groove to prevent the piston rings from rotating. In high performance
applications, this has proven to be a less than ideal approach for securing
the piston ring, since these locating pins have a tendency to work
themselves loose during high RPM use. When that happens, the results are
usually catastrophic and very expensive to repair – damaged sleeves,
pistons, and heads. On the flip side, sometimes the factory locating pin
holes were drilled too deep, and the pins simply sink below the piston
rings, allowing the edges of the rings to enter the ports, resulting in
damage similar to that mentioned above.
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Locating
pin failure will result in very costly damage to
your engine. Note broken piston ring and piston scoring. |
John Marles of
US1 Racing has developed a unique process for installing locating pins
into the top of the piston, rather than the sides. The process starts with
removing the old locating pins and carefully inspecting the piston under a
microscope for any damage. A new locating pin hole is drilled into the
piston crown in a location that will allow the boost charge to cool the pin.
Remember that the pin is steel, and the piston is aluminum, so proper pin
placement is crucial for engine reliability. The new pin is pressed into the
piston using a six ton press, milled, and then countersunk into the piston
crown. Finally, the pin is welded into place. Marles uses a special
high-carbon steel locating pin that is more dense than the piston ring. This
will prevent the piston ring from wearing the locating pin down over time.
The actual welding process and machine are unique to US1 Racing, and are
critical components of the process. Marles’ custom welding process allows
the pin to be welded while not allowing the piston’s temperature to go above
120 degrees. A standard welding process would overheat and warp the piston,
rendering a close tolerance fit impossible.
Our test boat is equipped with Marles’ top pinned pistons, and with many
hours of hard testing under its belt, the pistons show no signs of impending
failure.
Marles US1 Racing and Jay Smith Racing also perform the delicate and precise
task of lightening, balancing, and angle cutting pistons. The benefits of
lightening pistons in any combustion engine have long been known, and this
modification becomes even more beneficial with today’s high-RPM V6 engines.
Less weight on your rotating assembly means less bearing loads, which
translates into faster acceleration and greater reliability. The key to
successfully lightening pistons is knowing where and how much metal to
remove.
Lightening and Balancing Connecting Rods and Wrist Pins
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Close-up detail of lightened and polished connecting
rod. |
Some may ask why factory stock engines – even high performance engines – are
not internally balanced from the factory. The answer is simple: balancing and
lightening engine components is very labor and time intensive. This extra
layer in the manufacturing process would add to the cost of the engines
considerably. The benefits of this process become worth more as an engine’s
potential to make power and develop more RPM is increased.
We had Jay Smith Racing Engines lighten and balance our Mercury V6
connecting rods and wrist pins. Balancing these components will not only
make life on your crankshaft and bearings a little easier, but it will add
to the running quality and acceleration potential of your engine. JSRE uses
a seven-step polishing process to lighten the connecting rods from bare
casting to a polished finish. During this process, a 120-grit flapper wheel
is used to produce a lateral grain on the sides of the connecting rod. This
metal ‘grain’ helps reduce the chances of failure by stress propagation to
vital areas.
Below are some typical weight measurements before and after lightening:
Lightened wrist pins start at 55 thousandths of an inch at the end of the
pin, and then taper to stock thickness toward the center. This is the same
technology used to lighten wrist pins in Pro Stock cars. JSRE recommends the
use of full-length wrist pins to avoid them pulling out. Additionally, new
custom wrist pins are now used that are made to a weight of 82 grams, and require no
cores.
Our connecting rods were all weighed on a calibrated scale - a crucial piece
of equipment for the success of this process. The lightest rod was then
taken first and lightened by removing material from the outside edges – but
the process is not as simple as it sounds. The rods must be lightened while
maintaining their strength. Substrate is removed in a lateral direction,
creating a ‘grain’ in the metal that will reduce longitudinal stress
transitions. Wrist pins are progressively honed to reduce
weight in specific areas, and then balanced as a set.
What are the
overall benefits of this precise machine work to your engine? First
and foremost, engine reliability - especially during constant high-RPM use.
We also observed slightly improved idling quality, and since unbalanced
and rotational weight has been greatly reduced, the engine has more
potential to accelerate more quickly. If you're serious about your
high performance outboard, and achieving greater performance and reliability
is important to you, then the above described modifications make sense.
After all, who wouldn't want more performance and reliability?
It's a win-win situation for any high performance boater.
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Contact Information |
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Jay Smith Racing Engines |
Marles US1 Racing |
12807 Erin Lane
Dayton, TX 77535 |
31700 Tick Canyon Road
Agua Dulce, CA 91390 |
(281) 576-5088
Fax: (281) 576-5886 |
(661) 250-7157 |
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www.jaysmithracing.com |
www.us1.cc |
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