Balancing Drums

[Buckshot]

Has anyone tried to balance their drum rotors?

How about the crank shafts?

I have been talking with some engine builders (race car engines) and have found that there is a percentage formula that can be used to figure how much weight to hang off the crank pin for balancing.

-Buck-

 

[warlokboats]

buck

if i remember correctly it is 1/3 of the weight of piston/rod assy. mounted on the crank pin. as for the drum i have not been there yet. hope this helps and somebody else can say this is right or not.

jon

 

[Jim Allen]

Has anyone tried to balance their drum rotors?
How about the crank shafts?

I have been talking with some engine builders (race car engines) and have found that there is a percentage formula that can be used to figure how much weight to hang off the crank pin for balancing.

-Buck-

Hi Mr. Buck,

I use 1/3 the total weight of the piston, pin & rod as posted. I add two, .375 dia, carbide pins to bring the counterbalance up to 1/3. This is necessary because I have a full disk crank. I have balanced inverted drum rotors in a magnetic balancer. The 1/3 amount works well in the 20,000 to 30,000 rpm range.

Jim

 

[Buckshot]

Has anyone tried to balance their drum rotors?
How about the crank shafts?

I have been talking with some engine builders (race car engines) and have found that there is a percentage formula that can be used to figure how much weight to hang off the crank pin for balancing.

-Buck-

Hi Mr. Buck,

I use 1/3 the total weight of the piston, pin & rod as posted. I add two, .375 dia, carbide pins to bring the counterbalance up to 1/3. This is necessary because I have a full disk crank. I have balanced inverted drum rotors in a magnetic balancer. The 1/3 amount works well in the 20,000 to 30,000 rpm range.

Jim

Thanks Mr. Allen and Jon,

That is in line with what I've been told be the engine guys I have spoke with which is around +/-30% of the rod, wrist pin, keepers and piston but none could reassure me that it would be correct for the high rpm range.

I checked two drum valves one from a MAC .45 and one from a CMB .45 hr and was very surprised at my findings.

Thank You!

-Buck-

 

[Jim Allen]

Has anyone tried to balance their drum rotors?
How about the crank shafts?

I have been talking with some engine builders (race car engines) and have found that there is a percentage formula that can be used to figure how much weight to hang off the crank pin for balancing.

-Buck-

Hi Mr. Buck,

I use 1/3 the total weight of the piston, pin & rod as posted. I add two, .375 dia, carbide pins to bring the counterbalance up to 1/3. This is necessary because I have a full disk crank. I have balanced inverted drum rotors in a magnetic balancer. The 1/3 amount works well in the 20,000 to 30,000 rpm range.

Jim

Thanks Mr. Allen and Jon,

That is in line with what I've been told be the engine guys I have spoke with which is around +/-30% of the rod, wrist pin, keepers and piston but none could reassure me that it would be correct for the high rpm range.

I checked two drum valves one from a MAC .45 and one from a CMB .45 hr and was very surprised at my findings.

Thank You!

-Buck-

Are you going to keep that information a secret? Check a Rossi inverted drum & get another surprise.

 

[Buckshot]

Are you going to keep that information a secret? Check a Rossi inverted drum & get another surprise.

No, sorry. I didn't think anyone would care.

The MAC drum is out of a VERY strong running motor and the CMB drum is out of a box stock new motor. The MAC drum has the ramp in it and the CMB dose not as it has the stationary slug. The MAC drum was WAY out of balance and the CMB was pretty close to being balanced. I guess this shouldn't be too surprising as the MAC drum has the heavy ramp cast in the drum.

-Buck-

 

[Don Ferrette]

Are you going to keep that information a secret? Check a Rossi inverted drum & get another surprise.

No, sorry. I didn't think anyone would care.

The MAC drum is out of a VERY strong running motor and the CMB drum is out of a box stock new motor. The MAC drum has the ramp in it and the CMB dose not as it has the stationary slug. The MAC drum was WAY out of balance and the CMB was pretty close to being balanced. I guess this shouldn't be too surprising as the MAC drum has the heavy ramp cast in the drum.

-Buck-

Hmmm, here's a twist on that.....

Can the out of balance drum do anything to offset the out of balance state of the crank based on the points of imbalance of both pieces? Just thinking out loud here....... :blink:

 

[Topfuel666]

Are you going to keep that information a secret? Check a Rossi inverted drum & get another surprise.

No, sorry. I didn't think anyone would care.

The MAC drum is out of a VERY strong running motor and the CMB drum is out of a box stock new motor. The MAC drum has the ramp in it and the CMB dose not as it has the stationary slug. The MAC drum was WAY out of balance and the CMB was pretty close to being balanced. I guess this shouldn't be too surprising as the MAC drum has the heavy ramp cast in the drum.

-Buck-

Hmmm, here's a twist on that.....

Can the out of balance drum do anything to offset the out of balance state of the crank based on the points of imbalance of both pieces? Just thinking out loud here....... :blink:

Meaning, balance the rotating assembly as opposed to the individual pieces after they are balanced? The assembly should in theory then float in the bearings..........wonder how tough that would be to accomplish?

 

[Buckshot]

Hmmm, here's a twist on that.....Can the out of balance drum do anything to offset the out of balance state of the crank based on the points of imbalance of both pieces? Just thinking out loud here....... :blink:

Yes it could be.

-Buck-

 

[Don Ferrette]

Are you going to keep that information a secret? Check a Rossi inverted drum & get another surprise.

No, sorry. I didn't think anyone would care.

The MAC drum is out of a VERY strong running motor and the CMB drum is out of a box stock new motor. The MAC drum has the ramp in it and the CMB dose not as it has the stationary slug. The MAC drum was WAY out of balance and the CMB was pretty close to being balanced. I guess this shouldn't be too surprising as the MAC drum has the heavy ramp cast in the drum.

-Buck-

Hmmm, here's a twist on that.....

Can the out of balance drum do anything to offset the out of balance state of the crank based on the points of imbalance of both pieces? Just thinking out loud here....... :blink:

Meaning, balance the rotating assembly as opposed to the individual pieces after they are balanced? The assembly should in theory then float in the bearings..........wonder how tough that would be to accomplish?

Exactly. What made me think of this was back in the days of when I built my big block muscle car engines. Crank, rods, pistons all went together to get balanced as a rotating assembly, not as individual parts. I may be comparing apples to oranges but there has to be some similarities in theory.... :blink:

 

[ids987]

Are you going to keep that information a secret? Check a Rossi inverted drum & get another surprise.

No, sorry. I didn't think anyone would care.

The MAC drum is out of a VERY strong running motor and the CMB drum is out of a box stock new motor. The MAC drum has the ramp in it and the CMB dose not as it has the stationary slug. The MAC drum was WAY out of balance and the CMB was pretty close to being balanced. I guess this shouldn't be too surprising as the MAC drum has the heavy ramp cast in the drum.

-Buck-

Hmmm, here's a twist on that.....

Can the out of balance drum do anything to offset the out of balance state of the crank based on the points of imbalance of both pieces? Just thinking out loud here....... :blink:

Meaning, balance the rotating assembly as opposed to the individual pieces after they are balanced? The assembly should in theory then float in the bearings..........wonder how tough that would be to accomplish?

Exactly. What made me think of this was back in the days of when I built my big block muscle car engines. Crank, rods, pistons all went together to get balanced as a rotating assembly, not as individual parts. I may be comparing apples to oranges but there has to be some similarities in theory.... :blink:

I wondered about this myself before, but came to the conclusion that, as the drum (or disk) valve is not tightly coupled to the crankshaft, it is really a separate rotating assembly (and should ideally be balanced in its own right). Not saying I'm right - just my thoughts.

Ian

 

[Buckshot]

Exactly. What made me think of this was back in the days of when I built my big block muscle car engines. Crank, rods, pistons all went together to get balanced as a rotating assembly, not as individual parts. I may be comparing apples to oranges but there has to be some similarities in theory.... :blink:

That is exactly why I'm balancing the crank using the 1/3 or 30% method of the total weight of the rod, wrist pin, pin clips, and piston which is the rotating mass and balancing the drum because it is driven by this rotating mass. If the drum is out of balance in this situation than it is a rotating parasite.?? I think.? In my feeble mind the drum is not part of the rotating mass.

More thoughts?

-Buck-

 

[Jim Allen]

Are you going to keep that information a secret? Check a Rossi inverted drum & get another surprise.

No, sorry. I didn't think anyone would care.

The MAC drum is out of a VERY strong running motor and the CMB drum is out of a box stock new motor. The MAC drum has the ramp in it and the CMB dose not as it has the stationary slug. The MAC drum was WAY out of balance and the CMB was pretty close to being balanced. I guess this shouldn't be too surprising as the MAC drum has the heavy ramp cast in the drum.

-Buck-

Hmmm, here's a twist on that.....

Can the out of balance drum do anything to offset the out of balance state of the crank based on the points of imbalance of both pieces? Just thinking out loud here....... :blink:

Meaning, balance the rotating assembly as opposed to the individual pieces after they are balanced? The assembly should in theory then float in the bearings..........wonder how tough that would be to accomplish?

Exactly. What made me think of this was back in the days of when I built my big block muscle car engines. Crank, rods, pistons all went together to get balanced as a rotating assembly, not as individual parts. I may be comparing apples to oranges but there has to be some similarities in theory.... :blink:

I wondered about this myself before, but came to the conclusion that, as the drum (or disk) valve is not tightly coupled to the crankshaft, it is really a separate rotating assembly (and should ideally be balanced in its own right). Not saying I'm right - just my thoughts.

Ian

I think you are correct Ian, when I consider failed attemps at balancing various types of rotors by adding weight in other places such as the crankshaft or flywheel.

Jim

 

[Kim J]

I dont agree about only using 1/3 of the weight of the reciprocating parts.

A Swedish model magazine ( Allt om Hobby ) in the early 80`s had an article about this.

John Oian ( boating section in Model Airplane News ) translated this article about two years later in the same magazine.

I have balanced several engines following this procedure with perfect results.

Kim

 

[Buckshot]

I dont agree about only using 1/3 of the weight of the reciprocating parts.A Swedish model magazine ( Allt om Hobby ) in the early 80`s had an article about this.

John Oian ( boating section in Model Airplane News ) translated this article about two years later in the same magazine.

I have balanced several engines following this procedure with perfect results.

Kim

Would you care to share this information with us?

-Buck-

 

[Kim J]

I dont have these articles anymore, but the method goes something like this:

- Measure the total weight of the piston, wrist pin, clips and conrod (+ needles if any ).

- Make a mandrel ( small engine aluminium, large brass ) to fit the crankpin with several washers / shims. The weight should be about 60 to 70 percent of the reciprocating mass. This figure depends about stroke and rpm. I used 65 % on my engines.

- Place everything on a balancer.

- The mandrel would now face downwards. On a front intake engine it will be slightly off.

- Remove washers / shims until the crank har rotated 90 degrees.

- The weight of the removed parts are what are needed to get the engine balanced.

- This weight should be placed opposite to the crankpin at the same radius.

- Now you have to calculate how much of tungsten carbide you need ( specific gravity between steel and tungsten ).

On a Rossi 91 I had to use three 6,4 mm ( 1/4 " ) pins.

Go carts with 100ccm engines got more traction in the corners when using the 60 % figure.

Also check :

www.prestwich.ndirect.co.uk/technical_balancing.htm

 

[Buckshot]

I dont have these articles anymore, but the method goes something like this:- Measure the total weight of the piston, wrist pin, clips and conrod (+ needles if any ).

- Make a mandrel ( small engine aluminium, large brass ) to fit the crankpin with several washers / shims. The weight should be about 60 to 70 percent of the reciprocating mass. This figure depends about stroke and rpm. I used 65 % on my engines.

- Place everything on a balancer.

- The mandrel would now face downwards. On a front intake engine it will be slightly off.

- Remove washers / shims until the crank har rotated 90 degrees.

- The weight of the removed parts are what are needed to get the engine balanced.

- This weight should be placed opposite to the crankpin at the same radius.

- Now you have to calculate how much of tungsten carbide you need ( specific gravity between steel and tungsten ).

On a Rossi 91 I had to use three 6,4 mm ( 1/4 " ) pins.

Go carts with 100ccm engines got more traction in the corners when using the 60 % figure.

Also check :

www.prestwich.ndirect.co.uk/technical_balancing.htm

Thanks Kim.

Those percentages are a lot higher than what I've heard so far.

Anyone else have some input?

-Buck-

 

[Tom David]

Are you going to keep that information a secret? Check a Rossi inverted drum & get another surprise.

No, sorry. I didn't think anyone would care.

The MAC drum is out of a VERY strong running motor and the CMB drum is out of a box stock new motor. The MAC drum has the ramp in it and the CMB dose not as it has the stationary slug. The MAC drum was WAY out of balance and the CMB was pretty close to being balanced. I guess this shouldn't be too surprising as the MAC drum has the heavy ramp cast in the drum.

-Buck-

Hmmm, here's a twist on that.....

Can the out of balance drum do anything to offset the out of balance state of the crank based on the points of imbalance of both pieces? Just thinking out loud here....... :blink:

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.

 

[Kim J]

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

 

[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-