G'day Norm,

I thought we talked about this on a lot of occasions , that was why I made the PT video to show you don't need a lot of weight
on a PT to stop it kicking back under normal circumstances.

As we know



Flywheel Mass and Engine Dynamics:
The flywheel on an engine serves several important purposes: it helps smooth out the delivery of power from the engine, maintains momentum during the power stroke, and provides mass to aid in starting. The larger the flywheel mass, the more inertia it has, and the smoother the operation of the engine can be.

Direct Crankshaft Connection:
In a mower where the blade plate is directly attached to the crankshaft, the flywheel mass is effectively utilized throughout the starting process. The engine and blades are directly linked, meaning that when the engine gains momentum and starts firing, this momentum directly translates into rotational speed for the blades. The inertia of both the engine and the blade plate works together, making starting smoother and minimizing potential kickback.

V-Belt Drive System:
In a V-belt drive system, the engine's rotation is transmitted through the belt to the blade plate. This means that the mass of the blade plate does not contribute effectively to the flywheel effect because the load (the blade plate) is not rigidly connected to the engine.
When starting, the engine is attempting to overcome the resistance of the blade plate, but the V-belt tends to absorb some of the energy required to start the blades turning. As a result, the effective flywheel mass is reduced because some of the energy that would be contributing to inertia (as seen in a direct connection) is dissipated through the belt system.

Added Flexibility and Loss:
The flexibility of the belt system means that not all the rotational force generated by the engine is transmitted immediately to the blade plate. Slippage or tension variations in the belt can further reduce the effective mass that contributes to inertia during startup.
Additionally, if the blade plate has a significant mass itself, it requires more energy to start moving. The V-belt drive can cause a lag or delay in how effectively this mass contributes to the overall inertia during startup.

A V-belt drive system separates the engine's power delivery from the blade plate, which diminishes the effective flywheel mass during starting. The inertia and benefits of flywheel mass aren’t fully realized because the engine's energy isn’t transferred directly to the blades, leading to a potential for increased kickback and reduced starting efficiency compared to a direct crankshaft attachment.

I suggested adding mass to the crank on the PT crank with a v belt drive to overcome the kick back problem but that's not
the only way to overcome the kickback problem.I've suggested other ways before but because you had the weight working
you weren't interested in trying something else ,which is fair enough.



Retard Ignition Timing:
Retarding the ignition timing can help reduce the likelihood of kickback. If the ignition fires later in the compression stroke, it allows the piston to move down before the combustion pressure can push it back up, minimizing the abrupt force on the starter mechanism. However, this may also affect engine performance, so finding the optimal timing is essential.

Adjust Decompression Mechanism:
Decompression Timing: Modifying the decompressor to activate later can be effective. A decompressor helps relieve cylinder pressure during starting, making it easier to turn the engine over. If you delay its activation until the engine is at a point where it has started turning over, the compressive force can be reduced, effectively lowering the likelihood of kickback.
Automatic vs. Manual Decompressor: Consider utilizing an automatic decompression system that engages during starting but only releases after startup. This allows maximum assistance during start without affecting operation once the engine starts running.

Starter Engagement Mechanism:
A more sophisticated starter engagement mechanism can help manage the initial load on the starter. A system that smoothly ramps up the tension in the belt or utilizes a soft start can reduce the kickback effect.

Using an Anti-Kickback Starter:
There are starters designed specifically to minimize kickback. These starters can incorporate features like a ratcheting mechanism that allows the starter to disconnect under certain load conditions, preventing the rotational forces from being transmitted back to the starter cord.

Improved Belt Design and Tensioning:
Review the design of the V-belt drive. Using a belt with different material properties or improving tension management can help ensure a tighter grip and reduce slippage. Proper belt tension can minimize energy losses and allow for better power transfer, also aiding in smoother starts.

Flywheel Design:
If you cannot add weight, consider designing a flywheel with a different configuration. A flywheel with more mass towards the edge (increased rotational inertia) can store more energy and provide smoother power transmission, to help eliminate kickback.


Cheers
Max.