Diameter of Bolts
mm / inches
Nm / inlb
|M6 / 1/4"|| 9 - 10 / 75|
| M8 / 5/16"|| 15 - 17 / 140|
| M10 / 3/8"|| 23 - 25 / 300|
NB: the bolts MUST be DRY (no oil)
The above table can be used, but the best way of tightening a wooden propeller is to use your common sense (observation and a bit of care using the Allen key or spanner). The tightening torque required varies according to various factors such as the number of bolts, their size and thread, the total surface of the plates (propeller plate and rear plate), hardness of the wood, etc... "Torque" spanners have a very long handle and you will hardly note any effort in reaching the final tightening; just use their scale as a guide.
The bolts MUST be DRY (no oil).
Assemble the parts and hand tighten the bolts. Then use your spanner to give each bolt two or three turns at a time moving from bolt to bolt in a star pattern (going from one bolt to the one diagonally opposite, and then the next diagonally opposed pair); you will note that the consistency (the force needed to tighten) increases with each step and you MUST stop when this consistency suddenly gets solid, and always before chaffing the wood. The metal parts should mark the varnish, but not sink in.
If the bolts have not been touched for a long time, they should be checked with the flat spanner or Allen key to ensure that they are still at the final consistency explained above. This should be done especially at the beginning of the dry season (end of spring) and then once again once summer has set in.
When a new propeller has been installed for the first time, the tightening must be checked after the first 6 to 10 hours of use.
When the propeller spins, the tips should pass through the same point with a maximum deviation of 3 mm. To make an adjustment of 1 to 2 mm you can intentionally reduce the tightening of the bolts beside one of the blades, and then excessively tighten the opposite bolts. You must then tighten the first bolts (which will have loosened slightly) back to the "normal" tightening position.
Installation of a double propeller:
In the following picture you can see the correct way to mount the two 2-blades which make up a double or 4-blade propeller. You must match the two letters which indicate the correct position, the 2-blade engraved with letter "A" which goes next to the engine, and that marked "B" on the outside.
You must also fit a washer between each bolt head and the mounting plate.Obviously, in addition to a correct mounting (tracking & tightening), the propeller needs proper maintenance
. Just the remains of dead insects on the propeller surface cause the engine's maximum RPM to increase by about 50 revolutions, and performance to drop slightly.