Great Planes Sportster Bipe 40 Kit - GPMA0510 - Manual (Page 27)

2. PREPARE THE FIREWALL
Minus
Mark the top of the firewall. Mark the centerline of the engine on the firewall and center the mount in
position. The thrust line of the engine should be in the same position as shown on your plan. Drill holes and install
blind nuts. Temporarily install mount and trim the mount bolts that extend into the tank compartment. Drill hole for
throttle pushrod to carburetor, making sure the throttle pushrod does not interfere with tank.
Distance A
(length of
2
cycle
engine/mount and
spinner back plate)
Next bolt the engine to its mount. If you use a Hayes mount, position the engine as far back as possible
leaving sufficient room for engine and/or carburetor clearance. Make sure you don’t put in any right or left thrust.
SPORTSTER BIPE
B
3-3/4”
(CB Spinner)
Then measure the distance from the back of the firewall to the thrust washer. To do this, place the engine
and mount on a flat surface and put a straight edge across the thrust washer. Measure back from this straight
edge to the back of the mount. This is distance
“B”. Refer to the drawings and the chart shown here. We are
measuring this distance so we can determine how far back to move the firewall so the engine will fit into the nose
of the model.
B
B
Figure 1
3- 29/32“
(Dubro Spinner)
3-7/8” (Goldberg Spinner)
2- CYCLE ENGINE
GREAT PLmES MOUNT
.
I
AND
I
4-CYCLE ENGINE I
& D
HAYES MOUNT
Now let’s figure out how far back to move the firewall from the normal 2-cycle position. We have already
figured out for you the “A” distance of the Sportster Bipe which is 3-3/4”. The chart below also takes the spinner
used into account. If you use a different spinner then mentioned, just measure your backplate depth and add that
distance to the above measurement.
Distance B
(length of
your
4
cycle
engine and
mount
Equals
?
(Distance to
move firewall
back)
?
?
?
Basically all we’ve done here is to measure how long your new mount and engine is, allow for some
spinner backplate space, and subtract the distance shown on the plan (A) from the distance you measured (B).
The result gives you the distance you have to move the firewall back. See Figures 3 and 4 also.
27