Do you have access to SB production data? I would love to know what year my mower was made. (2887).
Hello Voytek S Alas, no records survive from the later SB period.
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Heavy Flywheel = Light Clutch and Light Flywheel = Heavy Clutch
Hi Max, the thing is that the light-flywheel Kirby powered both the 33 and 45. The same power unit was coupled to both clutch designs.
I can only make this point: - The 45 was the first SB scalable reel design - meaning that it could be made in 14, 17, and 20" variants - all with the padded alloy cone clutch. The 33 was a one-size design.
For me, the padded clutch, using die castings, simply saved SB money - at a time when reel mowers were being challenged by the rotary revolution.
As we know mower engines need a certain amount of rotatable mass to stop the motor kicking back on start up and low rpm .
The alloy cone clutch with the light alloy flywheel doesn't seem like it would be enough to overcome the kick back problem.to me unless the alloy cone clutch is a lot heavier than it looks ( eg has a metal weight cast inside it)
I've never owned or worked on a Scott Bonnar reel mower so I can only comment on what I see from the images but I don't think the alloy cone clutch has a heavy weight cast inside.
Mower manufacturers don't always use a cast iron flywheel to increase the rotatable mass when using a light rotatable mass on the pto side of the crank (eg alloy cone clutch / alloy pulley ,light bar blade with light boss)
I quickly had a look at 3 Flywheels 2 Wipac and 1 Phelon ,I have limited knowledge on Scott Bonnar reel mowers but have seen a few removed Kirby motors ,I saw Scott Bonnar motors using Phelon Flywheels but have no idea what type of cone clutch was originally attached to these motors .
Looking at the 3 flywheels I have ,the light Phelon flywheel weighs 620 grams ,the light Wipac is 650 grams and the heavy Wipac is 1,360 grams ,so I would think the light alloy cone clutch would use a heavier Wipac or heavier Phelon flywheel compared to the Kirby motor with the heavy cast iron cone clutch.
The heavier alloy flywheel weighs more than 1 litre of water and a little more than double the weight of the light alloy flywheel.
That's what I was thinking looking at the parts but can't confirm without more info or having the two different Scott Bonnar cone clutch mowers in front of me.
Max, The mass of the things attached to the shaft is only a part of the equation - the distribution (or otherwise diameter) of it/them is another important part. It is called "moment". Light weight but large diameter disk will produce larger moment of inertia then heavier but smaller diameter one. I am sure you agree with me. Cheers Voytek
Yes well done Voytek the Scott Bonnar 33 looks a very successful restoration , you'd be happy the 33 turned out this well.
I know if two cylinders have the same mass but different diameters, the one with a bigger diameter will have a bigger moment of inertia, because its mass is more spread out. Similarly, if two cylinders have the same mass and diameter, but one is hollow (so all its mass is concentrated around the outer edge), the hollow one will have a bigger moment of inertia.
A rotating object also has kinetic energy ,It follows that the rotational kinetic energy given to the flywheel is equal to the work done by the torque.
The more mass an object has, the more kinetic energy it has.
If I have an empty drink can and compare it too a heavier smaller solid off cut of metal rod the off cut will have more kinetic energy than the empty drink can.
I know what you were referring to Voytek with the " Light weight but large diameter disk " but I just thought I would explain how the mass of an object can still be a critical factor.
My SB33 is back in one piece after the rebuild, the cone clutch without any friction material works well - I just needed to adjust the "adjuster" lock bolt to stop the clutch disengaging and away we go.
