Balancing Drums

[Buckshot]

You got it wrong.I am using 65 % of the weight of the reciprocating mass ( not rotating mass ) to balance the crank alone.

Drum or disc should be balanced neutral and alone.

On K&B 3,5 OB some even made a larger hole on one side of the flyweel to balance the whole assembly.

Also remember the difference about static and dynamic balance.

Is this important ? I dont know. On a CMB 45 RS and new Hydro version the balance of the crank are way different, yet the reciprocating mass ( piston, wrist pin, clips and conrod ) are the same.

Blueprinting an engine is a complete different story.

Kim

I agree Kim about the reciprocating mass and leaving the drum out of the picture.

I just think that balancing to 65% of that mass is high. I'm thinking +/- 30% is closer due to such high rpm's in this application.

-Buck-

 

[Tom David]

You got it wrong.I am using 65 % of the weight of the reciprocating mass ( not rotating mass ) to balance the crank alone.

Drum or disc should be balanced neutral and alone.

On K&B 3,5 OB some even made a larger hole on one side of the flyweel to balance the whole assembly.

Also remember the difference about static and dynamic balance.

Is this important ? I dont know. On a CMB 45 RS and new Hydro version the balance of the crank are way different, yet the reciprocating mass ( piston, wrist pin, clips and conrod ) are the same.

Blueprinting an engine is a complete different story.

Kim

Kim, I made a mistake, I meant to say reciprocating mass.

My point that I wanted to make is that you can not take the drum or

disc out of the picture when we are talking about rotating mass.

They are spinning in the same axes at 1:1 and they are mounted in

the same crankcase. If you balance the drum or disc neutral you can

exclude them and work with the counter balance on the crank as you

have described. Problem is, try and balance a disc neutral!

I include the drum or disc as part of the rotating mass in counter balance

Of the reciprocating mass.

 

[Tom David]

You are right on with that thought Don.Number one: Crank and drum (or disc) are spinning in the same axes.

Number two: Both crank and drum (or disc) are spinning 1: 1 ratio.

If you want to balance your crank at 60 or 70% of rotating mass, you must

Include drum or disc. Or balance the drum or disc neutral ! That is hard to do.

Hello Tom.

The drum is supported by the drum housing and just being driven by the crank. If the drum out of balance it is creating vibration and harmonics that is robbing power and in these small applications every little bit counts. It is not directly related to balancing the gyratory mass.

Just some more thoughts.

-Buck-

Hello Buck, It is important to remember that both drum and crank

are spinning in the same axes in the same crankcase. The dynamic

forces of drum (while spinning) will effect the dynamic forces of the crank.

 

[Dr Hydro]

I just think that balancing to 65% of that mass is high. I'm thinking +/- 30% is closer due to such high rpm's in this application.

-Buck-

A while back I read somewhere that some engine builder(rc) balanced to 40% of the mass. Just my 2 cents. Jim

 

[Tom David]

I am sorry guys, but I am having a hard time walking away without making

one more point.

Earlier, Kim made a good point how someone used the flywheel

On a K&B 3.5 outboard (to work in conjunction with the crank)

as part of the rotating mass and counter the reciprocating mass.

The flywheel is CONNECTED to the flywheel in the same axes

spinning 1:1.

 

[Buckshot]

You are right on with that thought Don.Number one: Crank and drum (or disc) are spinning in the same axes.

Number two: Both crank and drum (or disc) are spinning 1: 1 ratio.

If you want to balance your crank at 60 or 70% of rotating mass, you must

Include drum or disc. Or balance the drum or disc neutral ! That is hard to do.

Hello Tom.

The drum is supported by the drum housing and just being driven by the crank. If the drum out of balance it is creating vibration and harmonics that is robbing power and in these small applications every little bit counts. It is not directly related to balancing the gyratory mass.

Just some more thoughts.

-Buck-

Hello Buck, It is important to remember that both drum and crank

are spinning in the same axes in the same crankcase. The dynamic

forces of drum (while spinning) will effect the dynamic forces of the crank.

I'll agree they are spinning in the same axis and the same crankcase, but don't see how it will effect the reciprocating mass as it is supported in a drum house by itself. If it is out of balance it is not trying to pull the crank pin off the crank rather it is creating a vibration imbalance/harmonic.

-Buck-

One note is that this is dependent that the crank pin and its drive slot in the drum are in harmony.

 

[Buckshot]

I am sorry guys, but I am having a hard time walking away without makingone more point.

Earlier, Kim made a good point how someone used the flywheel

On a K&B 3.5 outboard (to work in conjunction with the crank)

as part of the rotating mass and counter the reciprocating mass.

The flywheel is CONNECTED to the flywheel in the same axes

spinning 1:1.

Unless the flywheel is indexed to the crank and on the crank during the balancing process it will be void in the picture. If the flywheel is balanced as well as the drum than the work will be in the crank counter weights in relation to the rod, pin, clips, and piston.

-Buck-

 

[Tom David]

You are right on with that thought Don.Number one: Crank and drum (or disc) are spinning in the same axes.

Number two: Both crank and drum (or disc) are spinning 1: 1 ratio.

If you want to balance your crank at 60 or 70% of rotating mass, you must

Include drum or disc. Or balance the drum or disc neutral ! That is hard to do.

Hello Tom.

The drum is supported by the drum housing and just being driven by the crank. If the drum out of balance it is creating vibration and harmonics that is robbing power and in these small applications every little bit counts. It is not directly related to balancing the gyratory mass.

Just some more thoughts.

-Buck-

Hello Buck, It is important to remember that both drum and crank

are spinning in the same axes in the same crankcase. The dynamic

forces of drum (while spinning) will effect the dynamic forces of the crank.

I'll agree they are spinning in the same axis and the same crankcase, but don't see how it will effect the reciprocating mass as it is supported in a drum house by itself. If it is out of balance it is not trying to pull the crank pin off the crank rather it is creating a vibration imbalance/harmonic.

-Buck-

One note is that this is dependent that the crank pin and its drive slot in the drum are in harmony.

 

[Tom David]

I am sorry guys, but I am having a hard time walking away without makingone more point.

Earlier, Kim made a good point how someone used the flywheel

On a K&B 3.5 outboard (to work in conjunction with the crank)

as part of the rotating mass and counter the reciprocating mass.

The flywheel is CONNECTED to the flywheel in the same axes

spinning 1:1.

Unless the flywheel is indexed to the crank and on the crank during the balancing process it will be void in the picture. If the flywheel is balanced as well as the drum than the work will be in the crank counter weights in relation to the rod, pin, clips, and piston.

-Buck-

Sorry hit wrong button on last post.

Buck, would you agree that the drum or disc is considered a

rotating mass?

 

[Buckshot]

I am sorry guys, but I am having a hard time walking away without makingone more point.

Earlier, Kim made a good point how someone used the flywheel

On a K&B 3.5 outboard (to work in conjunction with the crank)

as part of the rotating mass and counter the reciprocating mass.

The flywheel is CONNECTED to the flywheel in the same axes

spinning 1:1.

Unless the flywheel is indexed to the crank and on the crank during the balancing process it will be void in the picture. If the flywheel is balanced as well as the drum than the work will be in the crank counter weights in relation to the rod, pin, clips, and piston.

-Buck-

Sorry hit wrong button on last post.

Buck, would you agree that the drum or disc is considered a

rotating mass?

Rotating mass..Yes

Regards

-Buck-

 

[Tom David]

I am sorry guys, but I am having a hard time walking away without makingone more point.

Earlier, Kim made a good point how someone used the flywheel

On a K&B 3.5 outboard (to work in conjunction with the crank)

as part of the rotating mass and counter the reciprocating mass.

The flywheel is CONNECTED to the flywheel in the same axes

spinning 1:1.

Unless the flywheel is indexed to the crank and on the crank during the balancing process it will be void in the picture. If the flywheel is balanced as well as the drum than the work will be in the crank counter weights in relation to the rod, pin, clips, and piston.

-Buck-

Sorry hit wrong button on last post.

Buck, would you agree that the drum or disc is considered a

rotating mass?

Rotating mass..Yes

Regards

-Buck-

Would you agree that (if assembled correctly) the drum or disc

Is TIMED with the crank and is spinning in same axes 1:1?

 

[Tom David]

It is almost impossible to balance a ramped drum neutral on

today’s high performance engines.

That is why manufacturers use the drum WITH the crank to counter

Balance the reciprocating mass!

 

[Buckshot]

I am sorry guys, but I am having a hard time walking away without makingone more point.

Earlier, Kim made a good point how someone used the flywheel

On a K&B 3.5 outboard (to work in conjunction with the crank)

as part of the rotating mass and counter the reciprocating mass.

The flywheel is CONNECTED to the flywheel in the same axes

spinning 1:1.

Unless the flywheel is indexed to the crank and on the crank during the balancing process it will be void in the picture. If the flywheel is balanced as well as the drum than the work will be in the crank counter weights in relation to the rod, pin, clips, and piston.

-Buck-

Sorry hit wrong button on last post.

Buck, would you agree that the drum or disc is considered a

rotating mass?

Rotating mass..Yes

Regards

-Buck-

Would you agree that (if assembled correctly) the drum or disc

Is TIMED with the crank and is spinning in same axes 1:1?

Spinning in the same axis at 1:1 yes.

I don't understand your term TIMED as the drum will only work correctly one-way.

Think this...

Drum spinning in it's housing by itself. If it is balanced things are good.

Now spin the flywheel by itself. If it is balanced things are good.

O.K. If the rod, pin, clips, and piston are balanced than things are great right? Well how do you balance the rod, pin, clips, and piston? Counter weight on the crankshaft that it is attached to.

Now this means that the drum and flywheel should be balanced independently in my view.

Please help me see your view.

Regards

-Buck-

 

[Buckshot]

It is almost impossible to balance a ramped drum neutral ontoday’s high performance engines.

That is why manufacturers use the drum WITH the crank to counter

Balance the reciprocating mass!

O.K. So let's take the ramp out of the picture and make it stationary.

-Buck-

 

[Tom David]

It is almost impossible to balance a ramped drum neutral ontoday’s high performance engines.

That is why manufacturers use the drum WITH the crank to counter

Balance the reciprocating mass!

O.K. So let's take the ramp out of the picture and make it stationary.

-Buck-

Are you asking about making the drum stationary?

How could the engine run?

 

[Nigtmare]

It is almost impossible to balance a ramped drum neutral ontoday’s high performance engines.

That is why manufacturers use the drum WITH the crank to counter

Balance the reciprocating mass!

O.K. So let's take the ramp out of the picture and make it stationary.

-Buck-

Are you asking about making the drum stationary?

How could the engine run?

The new CMB has a stationary ramp...the 45 and 21 Hydro engines that i know!! The ramp is screwed to the housing and the drum spines around the ramp on the in side and around the housing bushings on the out side.

Nick

 

[Tom David]

It is almost impossible to balance a ramped drum neutral ontoday’s high performance engines.

That is why manufacturers use the drum WITH the crank to counter

Balance the reciprocating mass!

O.K. So let's take the ramp out of the picture and make it stationary.

-Buck-

Are you asking about making the drum stationary?

How could the engine run?

The new CMB has a stationary ramp...the 45 and 21 Hydro engines that i know!! The ramp is screwed to the housing and the drum spines around the ramp on the in side and around the housing bushings on the out side.

Nick

Good point!

But the drum is still not balanced neutral, and CMB is still counter

balancing the reciprocating mass with the drum and crankshaft combined.

 

[Jim Allen]

I am sorry guys, but I am having a hard time walking away without makingone more point.

Earlier, Kim made a good point how someone used the flywheel

On a K&B 3.5 outboard (to work in conjunction with the crank)

as part of the rotating mass and counter the reciprocating mass.

The flywheel is CONNECTED to the flywheel in the same axes

spinning 1:1.

Unless the flywheel is indexed to the crank and on the crank during the balancing process it will be void in the picture. If the flywheel is balanced as well as the drum than the work will be in the crank counter weights in relation to the rod, pin, clips, and piston.

-Buck-

Sorry hit wrong button on last post.

Buck, would you agree that the drum or disc is considered a

rotating mass?

Rotating mass..Yes

Regards

-Buck-

Would you agree that (if assembled correctly) the drum or disc

Is TIMED with the crank and is spinning in same axes 1:1?

Spinning in the same axis at 1:1 yes.

I don't understand your term TIMED as the drum will only work correctly one-way.

Think this...

Drum spinning in it's housing by itself. If it is balanced things are good.

Now spin the flywheel by itself. If it is balanced things are good.

O.K. If the rod, pin, clips, and piston are balanced than things are great right? Well how do you balance the rod, pin, clips, and piston? Counter weight on the crankshaft that it is attached to.

Now this means that the drum and flywheel should be balanced independently in my view.

Please help me see your view.

Regards

-Buck-

Buck,

It is impossible to completly balance a single cylinder engine's reciprocating mass with the crankshaft's rotating mass. What is achieved with the crankshaft's counter weight is a partial balance of the reciporcating forces only. The only single cylinder engine that can be balanced according to Ricardo's formula, which is; the total reciprocating weight (piston, pin & the upper half of the connecting rod) plus 1/2 the total rotating weight (bottom half of the connecting rod), is an engine with a hanger piston & that piston must have large windows. Attemps at balancing the reciprocating masses by adding weight to balanced rotating masses will not help because these independent rotating parts will now be out of balance.

Jim

 

[Green Meany]

I wouldnt worry about the drum because it is supported by the bush that it runs in so the inbalance is negledgalbe , it only would be a problem if the bush was badly worn... besides it is not subject to the same potentially off balance forces of the crank piston and rod

 

[Tom David]

I wouldnt worry about the drum because it is supported by the bush that it runs in so the inbalance is negledgalbe , it only would be a problem if the bush was badly worn... besides it is not subject to the same potentially off balance forces of the crank piston and rod

OK, so if my crankshaft is running in a bushing is its imbalance

NEGIEDGALBE?