Big End Blues
By Lohring Miller
NAMBA Safety Chairman
As the power and rpm of gas engines
increases, they have begun to experience
various mechanical problems. When you
consider that our engines started as 23
cc, 2 hp weedeater engines over 15 years
ago, it isn’t surprising that some
unchanged components are showing
signs of overloading. This is especially
true in 30 cc, 18,000 rpm engines that
develop well over six hp. The toughest
problem is the connecting rod big end
bearing. This problem is aggravated by
the short connecting rod. Typical racing
two stroke rods are twice the stroke
length. The Zenoah 50 mm length rod
hasn’t changed even with increased
stroke.
A custom engine builder who used
standard Zenoah crankshaft assemblies
started to see connecting rod overheating
eight years ago. His solution was a
slotted rod, more bearing clearance, and
more oil. That was only a stop gap.
Since then, even more rods came back
with a nice blue color. Others failed
explosively. See the following pictures
below.
Continued on page 12
PROPWASH
April 2012
11
Gas Scale Hydro History
By Marty Shallenberger
NAMBA Scale Chairman
It all started when Roger Newton went to a District Three race where they were
running Classic Thunderboat's. Roger came back from that race and we spoke about
what he saw. We both agreed Gas power was a direction we wanted to go with Scale
Hydroplane racing in the Northwest, as we saw that 1/8 Scale Nitro turnout was
dwindling and we wanted a way to keep Scale Racing alive. Roger built the first Gas
Scale Hydro and made the hull fit the Classic Thunderboat rules and detailed it like a
true Scale Hydroplane. This was about the time that Roger passed away, and a group
of us decided to continue with the class. As we continued to talk, we decided that we
also needed modern hulls to get people to accept the class, so we created a Gas Scale
Master Hull Roster that is 20 percent larger than eighth scale (this is where the 1.667
scale number came from). This scale was chosen to roughly mirror the Classic
Thunderboat class; any larger and a lot of the hulls would not be able to fit under the
NAMBA sixty inch maximum length limit; any smaller and we would have a hard
time fitting the engines in the modern hulls. For a proof of concept we built the 76
Olympia pickle fork and four other modern winged hulls and ran them with the
Classic Thunderboat's. At first we used G class engines but quickly found that the
boats needed more power, so we started running GX class engines and found the boats
were reaching 1/8 scale nitro speeds.
So where are we now? We have 20 plus hulls registered in the PNWTA club that
are in different stages of completion. We have hulls and cowlings being built and sold
by established manufactures. We have builders following our lead in other NAMBA
districts. We have a twelve race series scheduled for the class in District Eight that
will collimate at the NW Scale Championship race in October.
To summarize, this class is much like the Classic Thunderboat class in size but it is
a true Scale Class that includes modern hulls. We understand that this class is not for
everyone but for those that enjoy building and racing scale boats, this NAMBA
class proposal gives everyone standards to work from. This same type of early
standards is what allowed 1/8 scale to become such a great class as builders in all the
different boating organizations had the same hull rules to follow so they knew that a
boat built in one organization would be legal in the other organizations so we believe
that early adoption is key for the class so everyone is building to the same hull
specifications.
Gas Scale Class Rules, Photos and the Gas Scale Master Hull Roster can be found
at www.pnwta.org
Marty Shallenberger with his Gas Scale Hydro Miss Budweiser
Big end blue on the crank