Value of Engine Balancing

[Charles P]

Just pondering before I send the parts off. 
Does anyone have qualified opinions on the value of dynamic balancing the full bottom end (crank, flywheel, rods, pistons) vs just the crank & flywheel?
It strikes me that crank whip must impact the value of balancing but how much?
I'm assuming that pistons and rods are statically balanced. 

Thanks 

Charles

[Ruairidh Dunford]

Charles,

I dynamically balance all my cranks and flywheels together.

I try to get the rods and pistons as close to each other in weight as possible, using a digital scale.

This makes a tremendous difference in smooth running, highly recommended.

[Ian Williams]

I have run both fully balanced and unbalanced engines, I agree with Ruairidh it makes a marked difference and must reduce the stress on components particularly if you intend to rev the engine.

[Steve Jones]

Charles,

I dynamically balance all my cranks and flywheels together.

I try to get the rods and pistons as close to each other in weight as possible, using a digital scale.

This makes a tremendous difference in smooth running, highly recommended.

+1

Steve

[Alan]

I wouldn't build an engine without dynamically balancing the crank and flywheel assembly together as a unit. Static balancing is not good enough. The rods and pistons I just make sure are matched for weight.

[AllAlloyCup]

Would it be worth adding the Cluch cover( on an early coil engine) as well?
It’s a chunky item.

Also is it worth taking half an inch off the rim of the flywheel first?

BillG

[Hugh Barnes]

Sorry - added my two penne'th on the other thread before I saw this...

[Ruairidh Dunford]

Would it be worth adding the Cluch cover( on an early coil engine) as well?

You might also think about the possibility of adding some clutch components into the mix as well....

Bill and Hugh,

In the case of a an Austin Seven, for the balance to be effective, you must build up the entire flywheel assembly, this includes the entire clutch. Do mark it carefully so it can be reassembled in exactly the same way as it was balanced.

The only exception to this is the clutch plate, this must be left out for balancing.

With regards to lightening the flywheel Bill - my own experience is that it makes very little difference on a standard engine. However, if you feel you would like to do it you might like to consider machining it off as was done on the Brooklands (and possibly some Cup) engines, a lovely curve - so I understand.

[Hugh Barnes]

That is exactly how I did the Riley engine... Even to the obsessive point of marking each bolt head and threaded hole so the original blts went back in the same place when I finally assembled the clutch....

As an aside, the Riley flywheel and clutch weighed a ton, so I consulted various knowledgable people about lightening. The comments I got back were that a lightened flywheel in the Riley engine moved the harmonic frequency and the point of maximum effect would be moved right into the middle of the touring speed rpm. The only cranks I have heard of breaking in that engine were those that had been lightened.. Specific comments on the Riley engine and only added as an aside for interest..

[Ruairidh Dunford]

Even to the obsessive point of marking each bolt head and threaded hole so the original blts went back in the same place when I finally assembled the clutch....

That is the normal and correct procedure Hugh.