by Had Robinson
Threadlock is a special type of glue that helps keep threaded parts from loosening. Small 2 cycle aircraft engines experience tremendous vibration because they are made as light as possible. The vibration will loosen fittings after just a few hours of running time. Vibration will also cause various sheet metal parts to flex and eventually break from fatigue and pilots should always be on the lookout for cracks in aluminum parts of their paramotors, including in the frame.
Here is a photo of what can happen when bolts get loose and hit the propeller.
There are three common types of threadlock.
- RED The type is the strongest threadlock. Threaded parts that are assembled with RED can only be disassembled by using heat from a torch in order to dissolve the bond. It should be used on threaded studs that are inserted into an engine case or cylinder. This includes the studs that hold the redrive on and the exhaust port studs that screw into the cylinder.
- BLUE The most common threadlock. Parts that are assembled with BLUE can be disassembled with ordinary tools.
- GREEN This type is known as "wicking grade" because it can be applied AFTER the threaded parts are assembled. It has the strength of BLUE.
How to apply
Threadlock should be applied to absolutely clean threads. Clean ALL parts prior to assembly with ordinary spray-type brake cleaner that is available from any auto parts store. Use compressed air to remove every trace of the brake cleaner before the threadlock is applied to the fastener. Tighten all fittings to the recommended torque value.
Where to apply – and where not to
MOST THREADED FASTENERS Miniplane and other manufacturers recommend that ALL nuts and bolts be assembled using medium strength (BLUE) threadlock. Failure to use thread lock will invariably result in things falling apart at the most inconvenient time.
Note: Important parts of paramotors may not be assembled with threadlock at the factory. Pilots should be certain that the redrive and exhaust port studs have been assembled with RED threadlock. Test these fasteners to see if they cannot be unscrewed with reasonable force. If you can remove the studs with ordinary tools, they were not assembled with RED threadlock.
DO NOT USE THREADLOCK ON SCREWS GOING INTO THREADED INSERTS, SPARK PLUGS, SHAFT NUTS, HEAD NUTS, SMALL CARB PARTS, DRAIN/FILL PLUGS!
Do not use threadlock on threaded inserts. They are commonly used in the frame where they hold the back plate and in plastic moldings. They will loosen/fall out if threadlock is used on the screws inserted into them. The threaded insert in this Polini frame that holds on the back plate is useless because it just turns so the buttonhead screw cannot be inserted OR removed. Use a lock-washer with inserts, if needed.
Do not use threadlock on fasteners in threaded holes that enter cavities or spaces that must be sealed e.g. the crankcase. Threadlock will not adequately seal the threaded hole. Instead use BLUE or GRAY RTV sealant. Though not as good as threadlock, the RTV will do double duty in sealing the enclosed space as well as holding the fastener. Such fasteners should use a lockwasher and be torqued properly to ensure that they do not loosen.