Flywheel Balance Weights

[Brian Coombs]

I have designed a new small diameter steel flywheel for my new engine, which is based on a 28oz balance 302, the question is if I reduce the diameter of the flywheel, do I need to increase the balance weight? if so how do I calculate the new weight?

BC

 

[Jac Mac]

I have designed a new small diameter steel flywheel for my new engine, which is based on a 28oz balance 302, the question is if I reduce the diameter of the flywheel, do I need to increase the balance weight? if so how do I calculate the new weight?

BC

When you say you have designed a 'new' flywheel do you mean you have machined an existing 28 oz flywheel down to a smaller diameter, if so and you have not touched the counterweight area cast/machined into the flywheel the answer is NO-BUT you should have the 'new' flywheel balanced with the complete crank assy- the reason being that there may have been areas of higher/lower density in the area machined away which will now have caused an imbalance condition from the original factory work.

Now if you have made a new flywheel from scratch and need to attach/machine the counterweight at a smaller distance from the crank centerline then you have to re calculate that weight to suit.
The " 28 oz " is actually 28 oz at a distance of 1" from the crank centerline, so the further out you go the less actual weight you have to attach or remove if you decide to drill holes etc or a combo of both if reqd. From memory I think it goes like this
( DO NOT Quote me, I am not perfect on some of this stuff )............. 28oz @ 1" radius,... 14oz @ 2" radius,... 7oz @ 4" radius,... 3.5oz @ 8" radius. Remember the weight is attached/placed at a specific point in relation to the Flywheel/Crankshaft Flange bolt pattern.

You could also consider going with neutral balance where mallory metal is added to the crank counterweights so that your flywheel and damper can be neutral/non weighted.

Jac Mac

 

[Brian Coombs]

Thanks,

That all makes sence now,

Thanks again,

BC

 

[Dave Bilyk]

Jac Mac,
thanks for clearing that up for me too. I now understand that it is actually a 28 oz.in balance moment being incorrectly quoted as 28 oz weight. In which case, the actual weight x radius needs to be chosen to = 28 oz.in

Sometimes torque is incorrectly quoted in the same way, lb instead of lb.ft, or N instead of N.m

regards

Dave

 

[Ross Nicol]

Yep when I went to refit my original motor I couldn't find the counter weight for the flywheel which balanced it to 50oz.Had to remove the crank to balance the assembly all over again.My new motor has an internally balanced crank so the flywheel can be neutral as Jac Mac says.Not to mention that I can refit the same balancer it had before.A much better situation for me as I can change flywheels if needed.
Ross