Engine Balancing

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Marty Davis

Well-Known Member
Joined
Sep 25, 2004
Messages
2,445
I have been working on a project to get a better balance on my engines and want to see what some of the experts are doing to get theirs smooth. I realize that it is nearly impossible to balance an 1 cylinder engine, but I know that we can get closer. I recently found that the Go Engine is not perfectly balanced. It was obvious on a friends boat with solid mounts. I personally didn't see any problem with my engine, but figured that I could improve my engine if it was not perfectly balanced.

Ackerman and I used the process of elimination back in the day with adding Tungsten Inserts (called Mallory) to transfer weight to the counter side of the crank. That worked well, but I am looking for a formula that I can apply across engines.

What is the formula that other are using to get close...??
 
Marty,

If our engines were designed like Ed Kalfus' .90 cu in boat engine we could use Sir Harry Ricardo's formula for balancing single cylinder engines. Ed used 1/2 the total reciprocating weight plus the total rotating weight on the crank counter balance. His engines ran very smooth in all RPM ranges from 8,000 to 26,000. This doesn't work in our engines because there is no hanger piston & no windows in the piston to make the reciprocating weight very low.

I had to also add 2, 5/16 dia, carbide slugs to my crank counter balance to give 1/3 of the total weight of the piston & connecting rod assembly on the crank counter balance. My engines run very smoothly in the 15,000 to 35,000 RPM range. My engines also have a very long connecting rod. This greatly reduces any piston slap as the piston rocks from side to side in the bore. Ed's engine had the longest connecting rod possible because of the hanger piston.

Jim Allen
 
Marty,

If our engines were designed like Ed Kalfus' .90 cu in boat engine we could use Sir Harry Ricardo's formula for balancing single cylinder engines. Ed used 1/2 the total reciprocating weight plus the total rotating weight on the crank counter balance. His engines ran very smooth in all RPM ranges from 8,000 to 26,000. This doesn't work in our engines because there is no hanger piston & no windows in the piston to make the reciprocating weight very low.

I had to also add 2, 5/16 dia, carbide slugs to my crank counter balance to give 1/3 of the total weight of the piston & connecting rod assembly on the crank counter balance. My engines run very smoothly in the 15,000 to 35,000 RPM range. My engines also have a very long connecting rod. This greatly reduces any piston slap as the piston rocks from side to side in the bore. Ed's engine had the longest connecting rod possible because of the hanger piston.

Jim Allen
Jim:

So, what you are saying is that you make a Bobb Weight to place on the crank pin that is 33% of the total of Rod, Wrist Pin, Clips and Piston?
 
Marty,

If our engines were designed like Ed Kalfus' .90 cu in boat engine we could use Sir Harry Ricardo's formula for balancing single cylinder engines. Ed used 1/2 the total reciprocating weight plus the total rotating weight on the crank counter balance. His engines ran very smooth in all RPM ranges from 8,000 to 26,000. This doesn't work in our engines because there is no hanger piston & no windows in the piston to make the reciprocating weight very low.

I had to also add 2, 5/16 dia, carbide slugs to my crank counter balance to give 1/3 of the total weight of the piston & connecting rod assembly on the crank counter balance. My engines run very smoothly in the 15,000 to 35,000 RPM range. My engines also have a very long connecting rod. This greatly reduces any piston slap as the piston rocks from side to side in the bore. Ed's engine had the longest connecting rod possible because of the hanger piston.

Jim Allen
Jim:

So, what you are saying is that you make a Bobb Weight to place on the crank pin that is 33% of the total of Rod, Wrist Pin, Clips and Piston?

Marty,Jim.....

This is what I have used for over 30 years with great success........

I weigh the piston & wristpin ........I then weigh the connecting rod and divide the weight of the rod by 2.......I do all this on a triple beam lab gram scale.....

Add together the weight of the piston + wristpin and 1/2 the weight of the rod and multiply that total weight times .6 [or 60%] for the weight of the bob weight....

IMPORTANT>>>>>>Make sure you don't make the bobb weight any larger in diameter than the O.D. of the bottom of the rod......

The bob weight can be as long as you want just no larger in diameter than the bottom of the rod.....

I have tried several multipliers I.E. .....55 & 60 & 65% and haven't seen any difference in performance.....

Generally what happens is I have needed to lighten the piston to obtain the correct balance......

Since I am not a big fan of skirting pistons,I generally remove material from the piston crown from underneath the crown with a endmill up between the pin bosses.....I don't go any thinner than .060" piston crown...

I turn a bobb weight , put it on the crankpin and and put the crank on a fixture very similar to a hi-point balancer.......Depending on what it needs I either add tungsten to the counterbalance or remove piston crown material...

I am not saying this is the only way to balance but this is the way I was taught and it has always worked very well for me......

PS:I looked for my balancing fixture to post a photo,but I think I may have given it to Truex......If he has it maybe he can take a photo of it when he gets home from Pocono and post it if you want to see it.....

Rod Geraghty
 
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I have always bin under the assumption that the rod should be weighed at the small end balancing the big end.

IE small end weight.

David
 
I have always bin under the assumption that the rod should be weighed at the small end balancing the big end.

IE small end weight.

David
In a perfect world I believe you are probably right.......I have heard that also....

That is very difficult to do on a 1-1/2" rod......All I am doing is telling you what has worked for me......:)
 
Rod,

I also saw little difference when I tried different amounts of weight. But when I used a strobe on the front end of the engine I found the least amount of oscillations with the 1/3 amount. The use of a full hardened steel front end almost eliminated those oscillations. It was impossible to put a mounting lug on the front end.

Jim Allen

Note: In fact I remember now that the brass gasket between the crankcase & the front end would show signs of fretting erosion before I got the balance right.
 
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Marty,

If our engines were designed like Ed Kalfus' .90 cu in boat engine we could use Sir Harry Ricardo's formula for balancing single cylinder engines. Ed used 1/2 the total reciprocating weight plus the total rotating weight on the crank counter balance. His engines ran very smooth in all RPM ranges from 8,000 to 26,000. This doesn't work in our engines because there is no hanger piston & no windows in the piston to make the reciprocating weight very low.

I had to also add 2, 5/16 dia, carbide slugs to my crank counter balance to give 1/3 of the total weight of the piston & connecting rod assembly on the crank counter balance. My engines run very smoothly in the 15,000 to 35,000 RPM range. My engines also have a very long connecting rod. This greatly reduces any piston slap as the piston rocks from side to side in the bore. Ed's engine had the longest connecting rod possible because of the hanger piston.

Jim Allen
Jim:

So, what you are saying is that you make a Bobb Weight to place on the crank pin that is 33% of the total of Rod, Wrist Pin, Clips and Piston?

Marty,Jim.....

This is what I have used for over 30 years with great success........

I weigh the piston & wristpin ........I then weigh the connecting rod and divide the weight of the rod by 2.......I do all this on a triple beam lab gram scale.....

Add together the weight of the piston + wristpin and 1/2 the weight of the rod and multiply that total weight times .6 [or 60%] for the weight of the bob weight....

IMPORTANT>>>>>>Make sure you don't make the bobb weight any larger in diameter than the O.D. of the bottom of the rod......

The bob weight can be as long as you want just no larger in diameter than the bottom of the rod.....

I have tried several multipliers I.E. .....55 & 60 & 65% and haven't seen any difference in performance.....

Generally what happens is I have needed to lighten the piston to obtain the correct balance......

Since I am not a big fan of skirting pistons,I generally remove material from the piston crown from underneath the crown with a endmill up between the pin bosses.....I don't go any thinner than .060" piston crown...

I turn a bobb weight , put it on the crankpin and and put the crank on a fixture very similar to a hi-point balancer.......Depending on what it needs I either add tungsten to the counterbalance or remove piston crown material...

I am not saying this is the only way to balance but this is the way I was taught and it has always worked very well for me......

PS:I looked for my balancing fixture to post a photo,but I think I may have given it to Truex......If he has it maybe he can take a photo of it when he gets home from Pocono and post it if you want to see it.....

Rod Geraghty
Thanks Rod!!! An area I have yet to even look at!!
 
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Picture_005.jpg
 
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; 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
 
I can't seem to find it Jack. Are you going to tell us, or is this proprietary information? I don't run a tether car.

Jim Allen
 
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Jack,

Two more question please? Are you still using the bell valve? Have you made any changes to the timing numbers?

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
 
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I can't seem to find it Jack. Are you going to tell us, or is this proprietary information? I don't run a tether car.

Jim Allen
http://www.prestwich...l_balancing.htm

So where do you differ from the way Dave dose it Jack.
The amount of counterbalance that I use is for engines operating from 15,000 to 32,000 RPM range. As Dave clearly stated the 55% factor is good for 15,000 RPM. However what he said about the reciprocating weight being as low as possible is definitely true. This is one of the reason the hardened steel connecting rods used in my engines have no bushing in the top end.

Jim Allen
 
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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
 
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