Balancing the crank 1 hole or 3 hole method

[Wevil Kenevil]

Recently my friend acquired a drill press with some fancy clamps and vices so I decided to give balancing cranks a try.

I used the 3 hole method on the one I did and then saw the one hole method that puts the crank safely in the balanced zone. Like 90% 85% by drilling a half inch hole 15 mm deep directly between the two holes on both sides.

The guy has a bike shop and claims that's how he has always done them and never had anyone complain. He said it works on any type crank hi/low hole .

Has anyone tried this? If so what was your experience? Here's a good video I found on you tube about finding your balance weight is a good cheat sheet.

I am looking for the one hole method video so you can see it. Will post it when I do.

 

[Wevil Kenevil]

This...

 

[Wevil Kenevil]

I realize this isn't actually balancing a crank but still brings it into balance. I will tell you the results when I am done.

 

[EmCee]

Recently my friend acquired a drill press with some fancy clamps and vices so I decided to give balancing cranks a try.

I used the 3 hole method on the one I did and then saw the one hole method that puts the crank safely in the balanced zone. Like 90% 85% by drilling a half inch hole 15 mm deep directly between the two holes on both sides.

The guy has a bike shop and claims that's how he has always done them and never had anyone complain. He said it works on any type crank hi/low hole .

Has anyone tried this? If so what was your experience? Here's a good video I found on you tube about finding your balance weight is a good cheat sheet.

I am looking for the one hole method video so you can see it. Will post it when I do.

I just happened to be stumbling on here and figured I'd jump in.

What're my qualifications? Well, I coded the first crank balancing calculator that tells the people what everyone asks "How do I know how much material to drill, what size bits, how deep, how many holes, how many grams to go from one factor to a desired factor" I also can provide in detail math values for those interested and not make claims and when asked for proof/explanation I insist "bro just google it" Coding the calculator was an attempt to right the wrongs in MB society lol

The video is dangerous. I am aware of it and it's VERY inaccurate, almost can be classified as a work of fiction. First off, the "a crank has to be minimum 65% or it won't run" which is a quote from a video of his which is a statement pulled out of thin air. This false idea leads to what? People believing it needs to be 90% or 85%

·The Values in His Cheat Sheet are Impossible.

1) He claims a 12mm drill bit that is drilled 12mm deep will yield a 20g reduction. This is wrong and it is more like 10g. Density of steel is 7.85cm/3 but I'll fluff it in his favor to 8cm/3, it is impossible, including the other volume reductions provided.

Examples and Formula :

12mm drill bit radius = 6mm (0.6cm)
Area of 0.6cm radius = 1.13 cm2

20g ÷ 8cm/3 = 2.5cm2
2.5cm2 ÷ 1.13 cm2 = 2.21cm2
2.21cm2 ÷ 2 (holes) = 1.1cm
1.1cm to mm = 11mm
In order to remove 20g with 12mm drill bit, you must do two holes 11mm deep.
Through his cheat sheet, no, drilling 12mm deep w/ a 12mm bit will not remove 20g

By using a smaller bit diameter, we will need additional holes as it'll require more depth. Let's do only additional side holes (two more on each side and no center hole) with a 3/8" (9.5mm drill bit)

2.5cm2 ÷ 0.708cm2 = 3.53cm2
3.53cm2 ÷ 4 (holes) = 0.88cm2
0.88cm to mm = 8.8mm
Using a 3/8" bit to remove 20g, you would do four holes total (two on each side) 8.8mm deep

For it to be possible to remove 20g with a 12mm drill bit and drilling 12mm deep, the crank would need to have a density of 14.74/cm3 which is a density closer to uranium than steel.


2) 90% balance would be horrible. Cranks coming out of china are around 25%-30% (reciprocating mass plays a huge role, a crank that uses the reciprocating mass for a 47mm top end would have a higher factor than if you put a 52mm piston on it) I have seem them as low as 20% the more weight on the upper conrod, the more mass needs to be removed.

3) Balancing doesn’t make the engine smooth across all RPMs. For example, on my 372xp build (see photo), I used a crank at 44% balance, and it was perfect for cruising RPMs compared to a 53% balance. Balancing at 50%+ makes it smoother at high RPMs, not low. The common claim that "55% is best" is misleading; it depends on your typical RPM range. Balancing to 57% for cruising at 5,500 RPM is counterproductive.
3a) Anyone claiming "I balanced to 90%" didn't actually balance anything and drilled holes that someone else told you to do, therefor you don't know what you balanced it to. Sorry.


Going off of your comment on "any type of crank hi/low hole" that wouldn't be correlated. Whomever said repeated this, yikes.

1) Cranks cannot be low hole/high hole, only the pistons, and the pistons do not have a different weight based on low/high hole. Historically low hole pistons were paired with short rods (85mm) because a low hole piston on a long rod (89mm) would cause the piston crown to be way above the cylinder deck opening.

2) His cheat sheet is way off for connector rods.

2a) He posts the total weight of the connector rod. This is once again VERY wrong. You only measure one side of it because its the reciprocating mass. You can't even manipulate the math to make that work.

2b) Doing a "mock balance factor formula"

·Reciprocating Mass = 140g
·Hung weight = 50g
·End of conrod = 38g
·Balance Factor = 49.5%
If I used 85g as he claims, it would now be 60%

People can argue "he's reliable, everyone does this, you're wrong," but that doesn't change how math works. I had to engage in a frustrating debate on YouTube because someone claimed the port timing formula for exhaust/transfer was (Opening degree ATDC x 2 = duration), which is mathematically impossible. Viewers kept repeating the incorrect formula without providing any numbers to prove or disprove it. I respect @Wevil Kenevil for saying, "Here are the resources, let's figure this out"—a rare and commendable approach.

The calculator I referred to coding is listed below.

Any questions or clarification of what I have mentioned, please ask. Your question may be someone elses in ten years. This forum is a vault of information from 2008 that I still find valuable today.

Note : Google scripts won't open if you use an ad-blocker, I have no clue why but thanks big tech

Sign in - Google Accounts

 

[Wevil Kenevil]

Wow!!! You definitely are the end to beat all! Thank you so much for adding to my post!

It's people like you that make life easier! You humble me sir! You've totally clarified this to the smallest degree!

I can't thank you enough sir!!!

You rock big dawg!!!!

 

[Wevil Kenevil]

I am an artisan and I work in an art foundry building bronze sculptures so spatial orientation is my strong suit and math unfortunately eludes me. Is there a way that we can make a cheat sheet / quick reference sheet. For this?

Example: the standard crank weighs (xxx) and a list of connecting rod weights so that drilling this size hole in these spots will give you approximately this percentage of balance?

Sorry if this sounds like a lazy or a stupid question but I am not blessed like you.

This is my where my strength lays...

As you can see I work more by sight than mathematical calculations.

Again thank you for your reply

 

[Wevil Kenevil]

I just happened to be stumbling on here and figured I'd jump in.

What're my qualifications? Well, I coded the first crank balancing calculator that tells the people what everyone asks "How do I know how much material to drill, what size bits, how deep, how many holes, how many grams to go from one factor to a desired factor" I also can provide in detail math values for those interested and not make claims and when asked for proof/explanation I insist "bro just google it" Coding the calculator was an attempt to right the wrongs in MB society lol

The video is dangerous. I am aware of it and it's VERY inaccurate, almost can be classified as a work of fiction. First off, the "a crank has to be minimum 65% or it won't run" which is a quote from a video of his which is a statement pulled out of thin air. This false idea leads to what? People believing it needs to be 90% or 85%

·The Values in His Cheat Sheet are Impossible.

1) He claims a 12mm drill bit that is drilled 12mm deep will yield a 20g reduction. This is wrong and it is more like 10g. Density of steel is 7.85cm/3 but I'll fluff it in his favor to 8cm/3, it is impossible, including the other volume reductions provided.

Examples and Formula :

12mm drill bit radius = 6mm (0.6cm)
Area of 0.6cm radius = 1.13 cm2

20g ÷ 8cm/3 = 2.5cm2
2.5cm2 ÷ 1.13 cm2 = 2.21cm2
2.21cm2 ÷ 2 (holes) = 1.1cm
1.1cm to mm = 11mm
In order to remove 20g with 12mm drill bit, you must do two holes 11mm deep.
Through his cheat sheet, no, drilling 12mm deep w/ a 12mm bit will not remove 20g

By using a smaller bit diameter, we will need additional holes as it'll require more depth. Let's do only additional side holes (two more on each side and no center hole) with a 3/8" (9.5mm drill bit)

2.5cm2 ÷ 0.708cm2 = 3.53cm2
3.53cm2 ÷ 4 (holes) = 0.88cm2
0.88cm to mm = 8.8mm
Using a 3/8" bit to remove 20g, you would do four holes total (two on each side) 8.8mm deep

For it to be possible to remove 20g with a 12mm drill bit and drilling 12mm deep, the crank would need to have a density of 14.74/cm3 which is a density closer to uranium than steel.


2) 90% balance would be horrible. Cranks coming out of china are around 25%-30% (reciprocating mass plays a huge role, a crank that uses the reciprocating mass for a 47mm top end would have a higher factor than if you put a 52mm piston on it) I have seem them as low as 20% the more weight on the upper conrod, the more mass needs to be removed.

3) Balancing doesn’t make the engine smooth across all RPMs. For example, on my 372xp build (see photo), I used a crank at 44% balance, and it was perfect for cruising RPMs compared to a 53% balance. Balancing at 50%+ makes it smoother at high RPMs, not low. The common claim that "55% is best" is misleading; it depends on your typical RPM range. Balancing to 57% for cruising at 5,500 RPM is counterproductive.
3a) Anyone claiming "I balanced to 90%" didn't actually balance anything and drilled holes that someone else told you to do, therefor you don't know what you balanced it to. Sorry.


Going off of your comment on "any type of crank hi/low hole" that wouldn't be correlated. Whomever said repeated this, yikes.

1) Cranks cannot be low hole/high hole, only the pistons, and the pistons do not have a different weight based on low/high hole. Historically low hole pistons were paired with short rods (85mm) because a low hole piston on a long rod (89mm) would cause the piston crown to be way above the cylinder deck opening.

2) His cheat sheet is way off for connector rods.

2a) He posts the total weight of the connector rod. This is once again VERY wrong. You only measure one side of it because its the reciprocating mass. You can't even manipulate the math to make that work.

2b) Doing a "mock balance factor formula"

·Reciprocating Mass = 140g
·Hung weight = 50g
·End of conrod = 38g
·Balance Factor = 49.5%
If I used 85g as he claims, it would now be 60%

People can argue "he's reliable, everyone does this, you're wrong," but that doesn't change how math works. I had to engage in a frustrating debate on YouTube because someone claimed the port timing formula for exhaust/transfer was (Opening degree ATDC x 2 = duration), which is mathematically impossible. Viewers kept repeating the incorrect formula without providing any numbers to prove or disprove it. I respect @Wevil Kenevil for saying, "Here are the resources, let's figure this out"—a rare and commendable approach.

The calculator I referred to coding is listed below.

Any questions or clarification of what I have mentioned, please ask. Your question may be someone elses in ten years. This forum is a vault of information from 2008 that I still find valuable today.

Note : Google scripts won't open if you use an ad-blocker, I have no clue why but thanks big tech

Sign in - Google Accounts

That calculator you made is crazy GENIUS, god I wish I could do math like you. That's amazing...

 

[EmCee]

I am an artisan and I work in an art foundry building bronze sculptures so spatial orientation is my strong suit and math unfortunately eludes me. Is there a way that we can make a cheat sheet / quick reference sheet. For this?

Example: the standard crank weighs (xxx) and a list of connecting rod weights so that drilling this size hole in these spots will give you approximately this percentage of balance?

Sorry if this sounds like a lazy or a stupid question but I am not blessed like you.

This is my where my strength lays...

As you can see I work more by sight than mathematical calculations.

Again thank you for your reply

So I understand your question The problem is there's no minimum balance factor coming out of the factory. If all cranks were 35% it would be easy to say "drill X holes, X diameter, X depth and you should get X percentage. If you drill your hole too high or too low that will affect it. Even with knowing the crank weight, there still wouldn't be a way to take the mass from that (1500g lets say) and convert it into a potential balance factor. I understand your question but unfortunately, it's not realistic due to the fact that we don't have a guaranteed minimum balance factor to then create a chart of what to do to go from 25% to 45% or 25% to 55%

 

[Wevil Kenevil]

Thank you sir, I appreciate your consideration. I was looking around and found yet another hole configuration from cdh.

It's for the 52 mm piston or the "85"cc motor they sell. It's like the three hole but skip the one dead center. What do you make of that ?

Now I've seen it all... Smh

 

[EmCee]

Thank you sir, I appreciate your consideration. I was looking around and found yet another hole configuration from cdh.

It's for the 52 mm piston or the "85"cc motor they sell. It's like the three hole but skip the one dead center. What do you make of that ?

Now I've seen it all... Smh

I purchased one of these for my 372xp build I did. Note - Its supposed to be a 40mm stroke, but mine was around 38.5mm which for my case was perfect

It's more mass removed which is good. If one needs a 12mm pin crank (it's not a 10mm) and plans on removing more mass, it would be a cheap and efficient way to get there.

Here are two photos that tie into this

1) Crank (w/ blue spring ) is around 57%
2) Crank is around 50%

The 50% crank required more material to be removed than the 57% one because of how bad the original balance factor was.

I THINK the Avenger 85 crank (thats the photo you posted, CDH once again re-branding already existing parts) is supposed to be in the neighborhood of 40%-45%

 

[Wevil Kenevil]

I purchased one of these for my 372xp build I did. Note - Its supposed to be a 40mm stroke, but mine was around 38.5mm which for my case was perfect

It's more mass removed which is good. If one needs a 12mm pin crank (it's not a 10mm) and plans on removing more mass, it would be a cheap and efficient way to get there.

Here are two photos that tie into this

1) Crank (w/ blue spring ) is around 57%
2) Crank is around 50%

The 50% crank required more material to be removed than the 57% one because of how bad the original balance factor was.

I THINK the Avenger 85 crank (thats the photo you posted, CDH once again re-branding already existing parts) is supposed to be in the neighborhood of 40%-45%

Exactly sir!