We have had at least one .46 in a .40 case up here in NEPRO that came directly from Great Planes
Here is an excerpt from the August NMPRA newsletter.......Hobbico should know about this by now:
Another topic we discussed also
has to do with 424 class engines. It
appears that there have been a few
Thunder Tiger .40 engines bought
for use in 424 class and Club 40
class racing that have been found
to actually be .46 displacement
engines. Apparently, the engine
case has “40” under the exhaust,
and the box said that the engines
were .40’s, but they apparently
had cranks, cylinders, pistons and
heads from .46 Thunder Tiger
engines installed. It is not known
how many engines have been found
in this configuration, but it we have
heard about a “few” so far.
I have been in touch with some
contacts I have at Hobbico, the
current importer of Thunder
Tiger engines and other products.
Several engines from their
inventory of Thunder Tiger 0.40’s
were inspected and found to be
the correct .40 cu.in. displacement.
The difference between a Thunder
Tiger .40 and .46 is approximately
1mm of stroke and approximately
0.9mm of bore, both larger in the
.46. The stroke of the .40 is 19mm
and the stroke of the .46 is 20mm.
It is not known at this point how
the apparent mix-up happened
or how many engines may have
been shipped in the incorrect
configuration. If racers believe
they have or are unsure if they
have received a Thunder Tiger
PRO .40 that actually has .46
internal parts, please contact
HOBBICO TECHNICAL SUPPORT
at:
[email protected]
or phone 217-398-8970.
It is fairly easy to measure the
engines with a depth micrometer
and/or a dial caliper. If you do not
feel that you have the capability or
equipment to inspect your engine,
contact the racers in your area
to obtain some help measuring
the bore and stroke of your
engine. If you don’t have access
to anyone who can help you with
the inspection, contact HOBBICO
TECHNICAL SUPPORT at the email or phone number above for
assistance.
Now, with this knowledge, it is the
responsibility of all racers to ensure
that the engine(s) they have is
(are) the correct displacement.
Just because it appears that
a few engines may have been
shipped from the factory in this
configuration, it does NOT mean
it is legal to compete in AMA 424
racing with an engine that displaces
.46 cu.in. If you are caught with
one of these engines during an
inspection at a contest, you will be
disqualified, whether you knew it
was a .46 or not. It is the pilot’s
responsibility to get the engines
inspected BEFORE the start of
competition.
We also need all Contest Directors
where Thunder Tiger .40 engines
are being used to plan to do
inspections at their contests for
the foreseeable future. Please
be prepared to inspect at least
the engines from the planes of
the trophy positions and fast time
and also be prepared to inspect
engines for racers who cannot
measure their engine themselves.
This action should also be planned
by the Club 40 folks at their races
as well.
It is regretful that we appear to
have this complication for the 424
and Club 40 racers, but it does
not appear to be widespread like
a full shipment of engines from
the manufacturer, based on the
quantity we are aware of and the
fact that the engines inspected
from Hobbico’s inventory were
found to be correct. We just have
to deal with it going forward.
AMA class 424 racing (and other
classes as well) have benefited
from the high quality, consistency,
and relatively low price of the
Thunder Tiger .40 engines for
many years, back to at least the
mid-1990’s. We do need to thank
them for continuing to make a good
product that we can utilize in 424
level racing