Engine Fan Hub Tip
Raptor 50 V2
Building Tips
2006 Jan 27
There have been numerous reports of the fan hub coming loose. This can be attributed to an improperly torqued prop nut or cranking over the engine when flooding occurs, hydro lock.
Do not use a piston locking tool when installing the cooling fan hub.
This tool is screwed on to the engine's cylinder head where the glow plug is installed. The design of the tool stops the piston from extending through its full range.
The concentration of the applied pressure between the piston and piston locking tool during the fan assembly or removal will severely damage the upper surface of the piston. This stressed area cannot be seen with the naked eye and will fail during engine operation.
(1) This end for 90 size engines
(2) This end for 30/50 size engines. Flat side up towards piston.
1) Insert flat side of crankshaft locking tool towards lower piston sleeve.
I strongly advice on purchasing a crank shaft locking tool.
Remove the four screws securing the engine back plate.
Note the back plate orientation and take care not to damage the paper gasket.
With the piston in the full down stroke position, install the crank shaft locking tool with the flat part of the tool resting on the lower piston sleeve.
1) Modified open wrench for removing tail rotor bearings.
2) TSK Fan Hub Wrench modified as a fan hub puller.
3) Home fabrication fan hub wrench using 1/16" aluminum sheet metal. Courtesy of John Curtis.
1) Lower piston sleeve.
2) Piston shown at full down stroke.
Hand tighten the cooling fan using slight to moderate pressure. Avoid using excessive force as this will damage the internal components of the engine.
The key element in ensuring that the fan hub will stay secured will be done with a fan hub wrench.
You can make a simple fan hub wrench using a sheet of aluminum cut out as shown in this photo.
Do not use the 3mm hex screws that will be use to fasten the clutch when using a fan hub wrench.
There is a potential that the 3mm hex bolts can be weaken when used in conjunction with the fan hub wrench.
1) Do Not use the 3mm hex bolts that will be used to mount the clutch assy.
2) Apply LocTite Adhesive.
1) 3mm Hex Bolts used STRICTLY for installing the fan hub assembly.
Apply loctite adhesive to the propeller nut and tighten using a fan hub wrench and cross wrench / ratchet.
Orientate the wrenches so that you can grasp the fan hub wrench and cross wrench between the palm of your hand and fingers.
Squeeze both wrenches towards each other (see photo).
1) Grasping both wrenches between the palm and fingers and squeeze will yield a better feel of the amount of torque applied.
This grasping method technique will give you a feel of the amount of force (torque) you are applying.
Visually inspect and ensure that there are no foreign objects inside the engine.
Re-install the paper gasket and engine cover plate. The flat side of the cover plate should be installed so that it faces towards the cylinder head.
Secure the four bolts. Loctite is not necessary but retighten the four bolts when the engine is hot.
References
In automotive terminology, a hydrolock is the immobilization of an engine's pistons by a liquid (usually water, hence the prefix "hydro-"). Hydrolocking occurs when liquid fills a cylinder on the intake stroke and, due to the incompressibility of a liquid, makes the compression stroke impossible. This, in turn, prevents the entire engine from turning, and can cause significant engine damage if one attempts to forcibly turn over or start the engine. http://en.wikipedia.org/wiki/Hydraulic_lock
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