allowing enough of the prop shaft threads to engage securely into
the engine. We replaced the stock prop/spinner with three Du-Bro
#8 Flat Washers. This allows the spinner to fit perfectly.
❑
4) Before mounting the propeller to the engine, take the time
to make sure it is balanced. NEVER use an unbalanced propeller
on this or any model. Also, NEVER use a propeller that has been
previously damaged in any way.
The Spinner Assembly bag includes an aluminum adaptor ring,
specifically made for the Norvel
™
.074 engine. This adaptor ring
fits into the molded recess in the back face of the spinner base.
Insert the propeller shaft bolt - with the three washers in place -
through the propeller and the spinner back plate. Tighten the prop
bolt firmly to the engine, aligning the propeller with the upright
orientation spikes.
Press the spinner cone in place to the backplate, aligning it into
the recesses in the backplate. Secure the spinner in place firmly
using the two provided screws.
FINAL ENGINE SET-UP:
❑
1) The Norvel
™
.074 R/C engine has an offset head idle stop
bolt installed into the left side of the carburetor body, just behind
the needle valve. This bolt is in place to limit the travel of the
throttle arm at low throttle.
We have found that if this bolt is completely removed, the throttle
lever is free to move further forward in low throttle movement with
the throttle servo. This means that an even lower idle speed can
be obtained. However, you must experiment a little to obtain the
lowest possible reliable idle speed, without killing the engine. Our
experience with this simple modification has given us very reliable
low speed idle characteristics and - after adjusting the trims on our
transmitter - even the ability to use the "Throttle Cut" feature,
available with some transmitters.
❑
2) Now is the time to give some thought to the propeller that
you will use on your engine. We have used a variety of propellers
on our own Little Extra ARF models and have learned that
different brands all seem to have different prop shaft hole
diameters. For reference, the Norvel
™
.074 engine has a prop
shaft diameter of .157". Typical prop sizes for the Norvel
™
.074 are
6 x 4, 7 x 3, and 7 x 4. APC produces great props in these sizes
but they are produced with large diameter shaft holes.
For
example, the APC 7 x 3 prop has a shaft hole measuring .185" in
diameter. Therefore, in order to use an APC 7 x 3 prop on our .074
engine, we used a 5/16" length of K&S 3/16" o.d. aluminum tubing
to "sleeve" the prop shaft hole down to the diameter that fits onto
the engine's prop shaft bolt.
Finally, some propeller brands come with shaft holes that are
smaller than the prop bolt. This requires that they be drilled out to
fit. For accuracy, always use a drill press.
❑
3) With the Norvel
™
.074 engine, we found that in order to
mount both the propeller and the provided spinner onto the
engine, the aluminum prop/spinner that comes with these
engines, must be replaced. This is because it is too deep, not
13
Idle Limiting Bolt
