Balanced Crank?

[Street Ryderz]

I guess I need to make a video showing how non-universal that old method is

LOL gee the tittle says how to find your balance factor and that's what is demonstrated.And I'll gaurantee that it works perfectly! Again I guess all the builders that use this method and have engines that way out spin and perform anything you've done are wrong right? LOL keep trying though!

 

[Street Ryderz]

Oh what happened there? you posted that I posted a video that had nothing to do with balance factor,so I replyied the above post now your back peddaling LOL.

 

[Deleted member 12676]

SR, please look at this drawing and tell me if you would enlarge or shrink the balance holes and by how much.

 

[Street Ryderz]

SR, please look at this drawing and tell me if you would enlarge or shrink the balance holes and by how much.

I would lose the 9mm holes all together since it's to heavy at the rod and we dont want a static or under balance they dont work! you need the rotational mass! I dont balance this way above I physicaly do it so that's it's right there infront of me on the stand! I weigh the piston,pin,bearing,clips along with the little end,then hang weight from the rod until it staticly balances and divide that weight into the recip mass and you have the balance factor not a perfect balance there's no such thing! and if you can get 40% balance factor it will spin smoothly this is fact!Like I said just because I perfer this easier method of achiving the same results along with many others whom also do it this way doesn't make it wrong because that's not how you do it! Sorry but in the time it would take to input and pay with the figures my crank would be done.

 

[Deleted member 12676]

OK thanks for responding.
If the weight of the small end of the conrod (horizontal with it resting on the scale) is 41 grams and the engine revs to 9000 RPM then what would you do to balance this crank?
This is your chance to prove that your method is correct and put egg on my face.
If the reciprocating mass is piston assembly + weight of the small end of conrod then that is 115 grams.
You can see by the drawing that the static balance weight hanging from the conrod is 80 grams.

 

[Street Ryderz]

OK thanks for responding.
If the weight of the small end of the conrod (horizontal with it resting on the scale) is 41 grams and the engine revs to 9000 RPM then what would you do to balance this crank?
This is your chance to prove that your method is correct and put egg on my face.
If the reciprocating mass is piston assembly + weight of the small end of conrod then that is 115 grams.
You can see by the drawing that the static balance weight hanging from the conrod is 80 grams.

In this the piston is very light compared to the rod and it allready has a very high balance factor of 70%.I know your used to smaller piston's but on average for a 66cc the piston assembly and little end weigh 135 g combined and if 80g was hung from rod for static balance the factor would be 60% and this is hard to achive since most cranks after drilling holes only require 28-30 g hung from rod to get the static balance witch means the factor is only 22%.

 

[Deleted member 12676]

Correction to drawing: Balancing bob weight is 69 grams (sorry but I made that very late at night)

Actually I am unconcerned about the hypothetical balance factor. (that's your baby. I don't subscribe to that theory)
The engine is 60cc with a lighter weight motorcycle piston.
Just tell me what exactly you would do to this crank to balance it using your method.

 

[Deleted member 12676]

from http://www.onallcylinders.com/2016/03/17/the-basics-of-crankshaft-balancing/

Machinists and engine builders have long been taught that, when balancing a crankshaft, its counterweights should equal the weight of the rotating mass, and equal half the weight of the reciprocating mass. Machinists have used this formula to calculate bobweight for decades.
While this technique works extremely well for most street and race 90-degree V8 engines, the truth is it’s nearly impossible to balance a crankshaft perfectly. That’s because the balancer cannot account for variables like cylinder pressure, ring drag, rod length, counterweight phasing, engine rpm, stroke length, bearing friction, secondary vibrations, rocking couples, and static mass.
All of those factors play a major role in engine balance, yet the traditional mathematical formula used for calculating bobweight completely ignores them. Instead, calculating bobweight is based strictly on measuring rotating weight and reciprocating weight, which is a gross oversimplification of the actual dynamic forces at play inside an engine that affect balancing.
In other words, the traditional method of balancing a crank is, at best, an imperfect science. In fact, it’s not based on any real science or mathematics at all. It’s simply a technique based on trial and error that happens to work well in most 90-degree, cross-plane V8s.

 

[Deleted member 12676]

That old method was devised for V8 engines. I did a comparison of that method to my spreadsheet calculator and the old method recommended a larger balance hole that provided 50% more weight removed. In other words way too much counter-balance for a single cylinder. But for a V8 I can see how that would work since you're having to balance for a large percentage of two pistons.

C'mon Sleez Rider, give me an answer to the proposed balancing problem.
Back up your method! You're so F'ing sure its the best way, right?
C'mon man, I'm waiting. (rope-a-dope)

 

[Deleted member 12676]

Just as I thought.
That crank is mine and is balanced.
Now I will answer the question for you as to what to do using your model T Ford method.
115 grams is the reciprocating weight and so .6 (a typical balance factor) times that is 69 grams.
So with a bob weight of 69 grams hanging from the hanging con rod the 9mm hole would need to be bored out to 13.6mm to have a static balance.
That is basically 16.6 grams needlessly removed.
Both too little and too much causes vibration.
Using this stupid method designed for 90 degree V8's the engine would end up with needless vibration.

If any of you all want to rescue yourself from any of your idiot predecessors and become truly informed just go to my site and read up on this subject as well as many others. Beware all the con artists like Sleezy Rider (Street Riderz). They have a low IQ and have a dangerous amount of knowledge, not much but just enough to inflate their corrupt ego's. Just as I destroyed his crude beliefs about crank balancing I can do the same about porting, compression, squish bands, ignition timing, expansion chambers, carburetion, etc.
Here's why I infrequently visit this forum or any other: http://www.dragonfly75.com/motorbike/forums.html