Engine Balancing

[Jim Allen]

Very interesting. Since you & I are the only people in the world able to make this thing, I would like to ask you some other questions? Feel free not to answer at any time. You know my timing is 34/63 with a symetrical case window of 82 deg & a total bell window opening of 127 deg, which means the window is wide open for 45 deg. I would like to know what your case window timing is & your bell window timing is? Feel free not to answer here. What did you see with the later opening & later closing, since our total timings are 209 deg compared to 208 deg? Are you still dynamically balancing the bell valve?

Jim

Jim i arrived at the timming # with the zimmerman disc. As it is way to much work making new bell drum's. The later open cleaned up the bottom end of the power band,as it is hard to over come the g-force on the fuel system. I did not change the opening in the case window's,just made a new bell drum with different timming # and reset the balance. Jack

Thank you for that information. At some point I'll have to make a valve that opens at 24 deg ABDC for the boat engine. Thanks again Jack.

Jim

 

[Jim Allen]

Rod,

One other thing I just noticed. At one time I did use Dave's formula. The connecting rod was aluminum. The total weight of the piston, pin & rod was 28.8 gms. I never ran one of those aluminum rods above 24,000. When I changed to steel rods, the total weight of the steel roller rod assembly was 35.5 gms. Maybe this is why I went to a lower number on the crank counter balance, because now I was running the engine beyond 30,000.

Jim Allen

 

[dwilfong]

Dave states he uses the small end weight for his calculations.

So let me talk this out.

using the small end weight and adding the piston ,pin and clip weight. make a bob weight 55% of the total?

Take the total weight of the rod add the piston,pin and clip them make a bob weight 33% of the total?

I am thinking the small end weight is the critical weight as this is true reciprocating weight?

The big end weight is considered rotating weight?

Just thinking out loud here.

 

[Jim Allen]

Dave states he uses the small end weight for his calculations.

So let me talk this out.

using the small end weight and adding the piston ,pin and clip weight. make a bob weight 55% of the total?

Take the total weight of the rod add the piston,pin and clip them make a bob weight 33% of the total?

I am thinking the small end weight is the critical weight as this is true reciprocating weight?

The big end weight is considered rotating weight?

Just thinking out loud here.

The rotating weight is the bottom half of the rod. If it has a roller assembly, the roller assembly would also be included as part of the rotating weight & the crankpin length inside the rod.

The reciprocating weight is the upper half of the rod, the piston, wrist pin, circle clips, any roller assembly parts, thrust washers, piston ring & wrist pin plugs.

 

[Marty Davis]

Can someone post a link to Dave Marles balance discussion?

 

[Greg Settle]

Firstly, any material that you can remove to reduce the reciprocating mass (piston/wristpin/ring/top half of rod) will make an improvement in engine performance, maybe not noticeable at lower rpm's but certainly at high rpm's plus it reduces stress on the engine parts. This will affect the balance of the engine but not greatly. However, it is a fact is that it is IMPOSSIBLE to balance a single-cylinder engine. The best that can be done is a compromise. The crankshaft counterweights will partly balance the reciprocating mass (piston/ring/wristpin/top half of rod). but this will introduce an out of balance at 90 degrees to the line of the cylinder but we have to put up with that.

Use a good quality scales, digital if possible. Take apart the crank assembly, weigh the bottom half of the rod and then the top half of the rod. Then weigh the piston/ring/clips/wristpin as one assembly. Add the weight of the top half of the rod to the weight of piston/ring/clips/wristpin. Now you need to take a percentage of this weight of between 50 to 60%. Lets say we use 55%.

Add this 55% to the weight of the bottom of the rod and machine a piece of brass or steel of this weight to fit over the crankpin. Reassemble the crank with this weight in place and balance the crank on the ballrace surfaces on 2 knife edges. If the crank rotates because its heavier one side than the other( which it will do) you must grind metal off the heavy part of the crank-webs around the crankpin area or wherever until it does balance. At this point you will have balanced the engine to a balance factor of 55%. This balance factor will vary from engine to engine and is rpm dependent to a certain extent but at 15,000 rpm a factor of 55% is not too far off.

N.B. Bear in mind that it is not possible to balance a model engine with a single sided crank to anywhere near the optimum balance factor. All that can be done to improve the situation is to remove as much material as possible from around the crankpin area of the rod and if possible add weight to the counterbalance by installing tungsten or copper inserts such as used sometimes by CMB and Novarossi.

 

[Marty Davis]

Marty; Dave Marles has a good balancing article in his technical data. J.O'Donnell

Jack:

Do you use his formula information for your balancing? With your 60 engines for teather cars, they MUST run very smoothly at the high RPM that they are turning?

Marty; The one i use is similer to Dave Marles data. And yes it does make a big difference

Jack:

I guess that I need to ask the question better....

Are you willing to share the formula that you use to balance your engines? If so......please do.

And, at what RPM are you balancing to?

 

[Jack ODonnell]

Marty; Dave Marles has a good balancing article in his technical data. J.O'Donnell

Jack:

Do you use his formula information for your balancing? With your 60 engines for teather cars, they MUST run very smoothly at the high RPM that they are turning?

Marty; The one i use is similer to Dave Marles data. And yes it does make a big difference

Jack:

I guess that I need to ask the question better....

Are you willing to share the formula that you use to balance your engines? If so......please do.

And, at what RPM are you balancing to?

Marty; I will try to explain what i do. This came from a 2 cycle motor cycle racing article,i believe it was from England about 20 years ago. I take the rod with piston,pin,clip's as a unit. I place the big end of the rod on a flat surface that is even with the top of a gram scale.Now with the big end of the rod on the flat surface, place the piston,,pin and the top end of the rod on the gram scale. This is what they call G-weight (transiatoric masses). I record that weight in grams. Take the rod off of the piston and weigh the rod by it self. Record that weight. Now take 83% of the first weight (the G-weight) and add that to the total weight of the rod. Now these two weight's together will be the bob weight that you will attach to the crank pin. The crank with the bob weight should set natural any way you set the crank.( just like ballancing a prop) Most of the time you will need add to weight to the counteweight of the crank. J.O'Donnell

 

[Geraghty]

Rod,

One other thing I just noticed. At one time I did use Dave's formula. The connecting rod was aluminum. The total weight of the piston, pin & rod was 28.8 gms. I never ran one of those aluminum rods above 24,000. When I changed to steel rods, the total weight of the steel roller rod assembly was 35.5 gms. Maybe this is why I went to a lower number on the crank counter balance, because now I was running the engine beyond 30,000.

Jim Allen

Jim,

That makes perfect sense to me......About 25 years ago I was "kind of forced" into the balancing game.....

I had a Picco .90 Marine that would put my hands to sleep carrying it to the water.....The motor vibrated so bad that I couldn't even keep fasteners tight with Loctite.

I tried the 60% thing and shazaam......the feeling in my hands came back and fasteners stayed tight and in place so I really stopped looking any further......

As I recall I tried the 55 & 65% thing but honestly never could see a performance difference .......but then again,I was probably just too stupid to recognize the improvement.......

Rod

 

[Marty Davis]

Marty; Dave Marles has a good balancing article in his technical data. J.O'Donnell

Jack:

Do you use his formula information for your balancing? With your 60 engines for teather cars, they MUST run very smoothly at the high RPM that they are turning?

Marty; The one i use is similer to Dave Marles data. And yes it does make a big difference

Jack:

I guess that I need to ask the question better....

Are you willing to share the formula that you use to balance your engines? If so......please do.

And, at what RPM are you balancing to?

Marty; I will try to explain what i do. This came from a 2 cycle motor cycle racing article,i believe it was from England about 20 years ago. I take the rod with piston,pin,clip's as a unit. I place the big end of the rod on a flat surface that is even with the top of a gram scale.Now with the big end of the rod on the flat surface, place the piston,,pin and the top end of the rod on the gram scale. This is what they call G-weight (transiatoric masses). I record that weight in grams. Take the rod off of the piston and weigh the rod by it self. Record that weight. Now take 83% of the first weight (the G-weight) and add that to the total weight of the rod. Now these two weight's together will be the bob weight that you will attach to the crank pin. The crank with the bob weight should set natural any way you set the crank.( just like ballancing a prop) Most of the time you will need add to weight to the counteweight of the crank. J.O'Donnell

Jack:

I appreciate your sharing this. With your 60 engines in the Teather Cars, the engine MUST be well balanced to turn the amount of RPM's that they must turn. By the way, how many RPM's do you turn?

Thanks again.... I will try this out.

 

[Jack ODonnell]

Marty; Dave Marles has a good balancing article in his technical data. J.O'Donnell

Jack:

Do you use his formula information for your balancing? With your 60 engines for teather cars, they MUST run very smoothly at the high RPM that they are turning?

Marty; The one i use is similer to Dave Marles data. And yes it does make a big difference

Jack:

I guess that I need to ask the question better....

Are you willing to share the formula that you use to balance your engines? If so......please do.

And, at what RPM are you balancing to?

Marty; I will try to explain what i do. This came from a 2 cycle motor cycle racing article,i believe it was from England about 20 years ago. I take the rod with piston,pin,clip's as a unit. I place the big end of the rod on a flat surface that is even with the top of a gram scale.Now with the big end of the rod on the flat surface, place the piston,,pin and the top end of the rod on the gram scale. This is what they call G-weight (transiatoric masses). I record that weight in grams. Take the rod off of the piston and weigh the rod by it self. Record that weight. Now take 83% of the first weight (the G-weight) and add that to the total weight of the rod. Now these two weight's together will be the bob weight that you will attach to the crank pin. The crank with the bob weight should set natural any way you set the crank.( just like ballancing a prop) Most of the time you will need add to weight to the counteweight of the crank. J.O'Donnell

Jack:

I appreciate your sharing this. With your 60 engines in the Teather Cars, the engine MUST be well balanced to turn the amount of RPM's that they must turn. By the way, how many RPM's do you turn?

Thanks again.... I will try this out.

Marty; With the gear ratio, tire size and the speed we are at. Just under 31000 rpm. I have used this formula in all my boat engines & Steve has used it in his r/c car engines. It does help.

 

[Marty Davis]

Marty; Dave Marles has a good balancing article in his technical data. J.O'Donnell

Jack:

Do you use his formula information for your balancing? With your 60 engines for teather cars, they MUST run very smoothly at the high RPM that they are turning?

Marty; The one i use is similer to Dave Marles data. And yes it does make a big difference

Jack:

I guess that I need to ask the question better....

Are you willing to share the formula that you use to balance your engines? If so......please do.

And, at what RPM are you balancing to?

Marty; I will try to explain what i do. This came from a 2 cycle motor cycle racing article,i believe it was from England about 20 years ago. I take the rod with piston,pin,clip's as a unit. I place the big end of the rod on a flat surface that is even with the top of a gram scale.Now with the big end of the rod on the flat surface, place the piston,,pin and the top end of the rod on the gram scale. This is what they call G-weight (transiatoric masses). I record that weight in grams. Take the rod off of the piston and weigh the rod by it self. Record that weight. Now take 83% of the first weight (the G-weight) and add that to the total weight of the rod. Now these two weight's together will be the bob weight that you will attach to the crank pin. The crank with the bob weight should set natural any way you set the crank.( just like ballancing a prop) Most of the time you will need add to weight to the counteweight of the crank. J.O'Donnell

Jack:

I appreciate your sharing this. With your 60 engines in the Teather Cars, the engine MUST be well balanced to turn the amount of RPM's that they must turn. By the way, how many RPM's do you turn?

Thanks again.... I will try this out.

Marty; With the gear ratio, tire size and the speed we are at. Just under 31000 rpm. I have used this formula in all my boat engines & Steve has used it in his r/c car engines. It does help.

Jack:

I remember watching your Teather Car run in Muncie Indiana and was TOTALLY amazed at the RPM's out of a 60 engine. It was one of the most impressive things I have seen.

Thanks a lot for sharing your knowlege with us. I will test this for my use and can't wait to see the results.

 

[Jim Allen]

Jack,

How does the bell valve stand up to the G forces the car produces?

Jim

 

[Jack ODonnell]

Jack,

How does the bell valve stand up to the G forces the car produces?

Jim

Jim; The first bell valve i made was alum. it did not work to well. After talking with you and following your drawing,i made the bell out of a-2 steel.So far it is bullet proof, but way to much work. Jack

 

[Jim Allen]

Jack,

How does the bell valve stand up to the G forces the car produces?

Jim

Jim; The first bell valve i made was alum. it did not work to well. After talking with you and following your drawing,i made the bell out of a-2 steel.So far it is bullet proof, but way to much work. Jack

I find it surprising that an art teacher named Paul Bugal invents the best induction system in the world, that can be used on a cantilevered crankshaft type engine. His engine also had an automatic fuel metering carburetor with one needle.

 

[hugh hargett]

Why Jim? I find what you guys do an art form. Its very beautiful to me to see all the different style motors and schools of knowledge!!!! Extremely informative. All you guys You,Marty,Jack, so and so on are really folks to look up too at least for me. The nostalgia and wealth of knowledge you guys bring to the sport is truly a "BEAUTIFUL THING". :wub:

 

[Jim Allen]

Why Jim? I find what you guys do an art form. Its very beautiful to me to see all the different style motors and schools of knowledge!!!! Extremely informative. All you guys You,Marty,Jack, so and so on are really folks to look up too at least for me. The nostalgia and wealth of knowledge you guys bring to the sport is truly a "BEAUTIFUL THING". :wub:

Especially when you consider the fact the bell valve thing was invented 50 years ago!

 

[Marty Davis]

Why Jim? I find what you guys do an art form. Its very beautiful to me to see all the different style motors and schools of knowledge!!!! Extremely informative. All you guys You,Marty,Jack, so and so on are really folks to look up too at least for me. The nostalgia and wealth of knowledge you guys bring to the sport is truly a "BEAUTIFUL THING". :wub:

Especially when you consider the fact the bell valve thing was invented 50 years ago!

Jim:

Where can we read more about his systems and him?

 

[Tom Foley]

Great reading , how do you attach a bob weight to the crank pin without interference ? Thanks !

 

[RodneyPierce]

Tom, its all done with the crank outside of the engine, bob weight hanging on the crank pin.