12 Laws To Building The Perfect Clutch

The quest continues to build our helicopters as perfectly as we can. The last time we looked at "Building the Perfect Head." This time, we will show you the laws of building a perfect clutch and clutch assembly. Many times, we find our helicopters shaking and shivering before leaving the ground. Usually the first thing we look at is the head, making sure everything is balanced. Numerous parts on our helicopters, from the tip of the canopy to the end of the tail, can generate a vibration. A misaligned clutch can transfer its vibration throughout the heli and cause excessive wear on the clutch liner or bell.

1.There are many styles of clutch assemblies on the market. Identify what style of clutch you are using and what tools are required for each type. The most common type of fan and clutch are the thread-on style. This style allows for easy installation and does not require specialty tools. Collet-style fans require the use of a dial indicator, to ensure that the fan is spinning concentrically.



2.Start by removing the back plate of your nitro engine. This will give you access to the piston connecting rod. We use this rod to lock the engine's crankshaft so we can tighten the fan.


3. If using a collet style clutch assembly, install the first collet over the crankshaft and slide it all the way down until it bottoms out on the bearing. Some kits require using a washer that is included with the engine, before installing the collet. This will space the whole clutch unit correctly.


4. Install the fan onto the crankshaft. If using a screw-on type fan, apply a generous amount of thread locking compound to the crankshaft and carefully screw it in until it bottoms out on the bearing or washer. Use a crankshaft-locking tool and tighten the fan by using a rag over the fan. You can also use a fan hub wrench, which will tighten better than a rag and your hands. Using a collet-style assembly, slide the fan over the crankshaft until it sits on the collet.


5. Install the second collet, followed by a nut, if using that style. Give the fan a light tap on top of the hub to pre-set the fan. Tighten down the nut until you can feel the fan seat in the collet, but do not crank it down. The fan must be dial indicated as you tighten the fan. It is best to tighten down a little, dial indicate, then tighten down a little more, and repeat the process until the fan is tight. When using a threaded fan, install the nut and apply a small amount of thread lock on the nut and tighten down the fan.


6. Dial indicating the fan can be somewhat tricky the first time you install your clutch. Using a vise to hold the motor is one of the easiest methods to use to check the alignment of your clutch. Use a dial indicator with a magnetic base and mount it to the vise. Tighten down your engine using a rag around the motor mounts. Grip the mounts in the vise, but do not over tighten the vise or the crankcase may crack. Place the probe on top of the hub and zero out the indicator. Next, rotate your motor without a glow plug installed and find the high spot on the hub. Give the hub a tap on the high spot with the plastic end of a screwdriver. Repeat the dial indicating procedure as you tighten down the fan in small increments, until you have a perfectly level fan and hub.


7. After dial indicating the fan and hub, tighten down the nut and recheck the alignment. The clutch should not be more than .002 off.


8. Next, we move on to the clutch bell. The clutch bell uses a liner to grip the clutch when the shoes are accelerated and thrown outwards. This liner is easily installed using the Quick Tip tool in Issue 21. Test fit the clutch liner in the bell and trim off any excess liner. Apply a small amount of epoxy to the inside edge of the clutch bell, then place the liner inside. Use the clutch liner tool by compressing the PVC together and releasing after it has bottomed out inside the clutch bell. Let the epoxy dry.


9. This is a perfect time to lube the bearings in the clutch bell and the one-way bearing, if your clutch is equipped with one. Use high quality grease, like Tri-Flow, to lubricate the one-way bearing in the clutch and the ball bearings in the clutch bell.


10. After the clutch liner has dried, remove the tool and trial fit the clutch inside the clutch bell. You should be able to fit a piece of paper all the way around the clutch, in between the clutch and liner. If you cannot fit the clutch inside, then a little sanding is required. Sand the liner down evenly, using medium grit sandpaper, until the clutch will fit. Take your time here, because if you sand down the liner too much it will have to be replaced.


11. Next, install the clutch to the fan hub. Use thread-locking compound on the bolts and tighten them down slowly, alternating from bolt to bolt. This will ensure your clutch is aligned on the fan hub.


12. Test fit your engine and clutch assembly on the mechanics to make sure everything lines up. The clutch should set inside the clutch bell nicely without touching any of the sidewalls. You can check this by rotating the bell after the engine is installed. If you feel any restrictions then you must adjust the alignment. If everything lines up, install your engine and tighten down the screws.

Conclusion
Taking your time here will allow your machine to operate smoothly without any vibrations caused by the engine. Alignment is the key when using the collet-style or "colleted" clutch. Drag-free clutches will allow your heli to retain more energy in an autorotation. This will also improve the idling performance of your helicopter.