When going for SCAT crank should you lighten flywheel? If so, how much?

[Jim Brierley]

A heavy wheel helps on initial start of movement, after that it is mostly unnecessary. In the early years cars were still in the experimental stages, so small steps were taken. On a 1 cylinder engine, weight was needed to keep things turning, especially at slow speeds. A heavy wheel in our A's today may help on short hills, but on longer ones not so much as inertia of the wheel is static, but the speed of the car has changed, so it is a trade-off. A lighter wheel is better while accelerating and decelerating, so feels better from the drivers seat and once away from the stop sign, accelerates better. On such things as a hill climb, there is a big difference.

[updraught]

Slowing the engine with a 3.27 will store less energy so it will run out quicker on the hill. When you go to accelerate again the fly wheel will suck up a lot of energy again. That energy will be released in the future, but it may not be when you want it.

[M2M]

Originally Posted by updraught

Slowing the engine with a 3.27 will store less energy so it will run out quicker on the hill. When you go to accelerate again the fly wheel will suck up a lot of energy again. That energy will be released in the future, but it may not be when you want it.

Thanks. I guess I'll stick with a stock or a lightly lightened flywheel.

[M2M]

Originally Posted by wensum

These are made in New Zealand "These dampers are made by Murray Horn in Levin N.Z. His Company is Engine Restorations Ltd. His email is [email protected]
Murray says this is the best way to contact him.
The dampers are a straight fit to replace the standard Model A pulley. An added benefit is a shallow reverse scroll in the rope seal area to help contain oil."
The cost was around NZ$300 (much cheaper in US dollars.) The pulley probably requires the radiator to be removed and the front of the engine lifted above the front cross member. the pulley is a little deeper than the original pulley and comes very close to the front spring U bolts and so the fan belt needs to be fitted at the same time.

These harmonic balancer pulleys sound interesting, especially for a high hp road car or a race engine, but are they worth the cost for a tour 50hp engine?

[M2M]

Originally Posted by wensum

These are made in New Zealand "These dampers are made by Murray Horn in Levin N.Z. His Company is Engine Restorations Ltd. His email is [email protected]
Murray says this is the best way to contact him.
The dampers are a straight fit to replace the standard Model A pulley. An added benefit is a shallow reverse scroll in the rope seal area to help contain oil."
The cost was around NZ$300 (much cheaper in US dollars.) The pulley probably requires the radiator to be removed and the front of the engine lifted above the front cross member. the pulley is a little deeper than the original pulley and comes very close to the front spring U bolts and so the fan belt needs to be fitted at the same time.

Price including shipping is now 300 USD

[Terry Burtz, Calif]

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This reply is in regards to earlier comments regarding broken crankshafts, destroyed timing gears and other problems.

If a crankshaft is hung with a string and tapped with a hammer, it will ring like a bell at its' natural frequency.

When installed in a cylinder block, the crankshaft can ring at its' natural frequency at an RPM that is called "critical speed".

Every rotating shaft (including a crankshaft) has a "critical speed".

The critical speed occurs when the crankshaft rotates and has impulses (loads from power strokes [knock is very bad] or loads when the piston at TDC has to reverse direction) that coincide with the crankshafts' natural frequency.

Critical speed can be felt as severe vibration at certain speeds.

At critical speed, torsional deflections and stresses are at a maximum value and the cause of early fatigue failures.

There are several ways to mitigate the problem and they include a stiffer crankshaft, additional main bearings for better support, a crankshaft material that has more damping, or the addition of a harmonic damper at the front of the crankshaft.

Regarding the weight of a flywheel, weight is meaningless. What needs to be reduced is the polar moment of inertia.

Google is your friend. Research "critical speed of crankshaft", "natural frequency", "harmonic damper", and "polar moment of inertia".

[TDO]

what is the difference be twine the V8 clutch plate and the model a clutch plate

[wensum]

Originally Posted by M2M

These harmonic balancer pulleys sound interesting, especially for a high hp road car or a race engine, but are they worth the cost for a tour 50hp engine?

One member of the NZ Model A Club has fitted the pulley to his standard car and reports worthwhile improvements.

[Jack Shaft]

Flywheel mass improves driveability by storing kinetic energy,a heavier flywheel shifts smoother,for example.There is a point of diminishing returns both ways,light and heavy..Ford used a heavy flywheel to dampen torsional impulse in the stock crank.Harmonic balancers work great,both cam gear chatter and pulley fracture gone,with a smoother running engine.I added one to maximize the life of a stock crankshaft,should work good with the counterbalanced crankshaft as well