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Balance factor -65 XLCH?

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Post Tue Jan 12, 2010 12:12 pm

Posts: 188
Location: sweden
I've been told that it's "common practice" to go with a 50% balance factor. but are there any factory specs that verifies this?
Thanks Stefan.

Post Thu Jan 14, 2010 4:08 pm

Posts: 587
Location: Crewe, Great Britain

Hi Epinut,

No, the Harley's factory balance for street is not 50% and despite looking for the info, I haven't found it so far...

The race shop did balance their racers at 50% up to sometime in the life of the alloy XR.

I have done all my XL/K balancing with the 50% factor and the experienced guy that does it for me always querries it, saying all V Twins should be around 60%...

Patrick

Post Fri Jan 15, 2010 2:43 pm

Posts: 188
Location: sweden
Thanks for the input Patrick. Can't help wondering why any factory recommendations seems so unobtainable?
Stefan.

Post Sat Jan 16, 2010 4:19 pm

Posts: 150
Location: Carver, MN

Sometime back in the 1980s I attended a factory service school. The figures that they gave as production balance factors were 50% for Shovel and Pan 1200, 50 to 55% for XR, and 62% for XL1000. They even went as high as 69% on the XL1100. I never noticed until now that they didn't give a figure for the XL900.

S&S did some testing a few years back and concluded that there was more to be gained in smoothness by getting the weight of the connecting rod small ends close to matching each other than by changing balance factors. S&S changed their rod forgings to address this. This was covered in the November 2003 issue of S&S "Dealer Focus" (I just happen to have it in my notebook along with the balance factors)

Post Sat Jan 16, 2010 6:51 pm

Posts: 587
Location: Crewe, Great Britain

Thanks for the info, Lee.

But what is the 900 balance factor????!!!!

Patrick

Post Tue Aug 10, 2010 8:04 pm

Posts: 328
Location: north central Ma.
Give Mike or Zint an e-mail they'll tell you want the books say and what feels the best based on 50+ years of customer feedback.

http://lindskog.com/contact.php
"Smok'in the competition NOT Tobacco"
"Transplant organs, Don't bury them!"
Why dwarf? 5/8 scale race cars! http://www.dwarfcarracing.com

Post Fri Dec 10, 2010 7:49 am

Posts: 3060
Location: Central Illinois, USA
Lee W wrote:
Sometime back in the 1980s I attended a factory service school. The figures that they gave as production balance factors were 50% for Shovel and Pan 1200, 50 to 55% for XR, and 62% for XL1000. They even went as high as 69% on the XL1100. I never noticed until now that they didn't give a figure for the XL900.

S&S did some testing a few years back and concluded that there was more to be gained in smoothness by getting the weight of the connecting rod small ends close to matching each other than by changing balance factors. S&S changed their rod forgings to address this. This was covered in the November 2003 issue of S&S "Dealer Focus" (I just happen to have it in my notebook along with the balance factors)


Sorry to get into this late folks,
But by back-calculating a Factory Pan, I found it to be about 57%, so I suspect the "factory service school" was making it up as they went.

And "getting the weight of the connecting rod small ends close to matching each other" sure sounds good.
The problem is that the top ends can never weigh the same, unless you use two male rods!

The female rod top will always be heavier than the male top because it is half of a heavier rod.
That's why there is only one reciprocating weight in the equation: all of it.

The incredible range of expert's preferred factors only proves how arbitrary balancing of a v-twin actually is, and how gullible the masses are!

....Cotten

Post Fri Dec 10, 2010 12:02 pm

Posts: 2683
Location: Los Angeles, CA
All I know is that if I balance correctly I won't fall down. :D

Post Mon Dec 13, 2010 7:04 pm

Posts: 150
Location: Carver, MN

Cotten wrote: But by back-calculating a Factory Pan, I found it to be about 57%, so I suspect the "factory service school" was making it up as they went.
And "getting the weight of the connecting rod small ends close to matching each other" sure sounds good.
The problem is that the top ends can never weigh the same, unless you use two male rods!


Hey Cotten, I don't really disagree, but the 57% factor you found does beg the question, Did the engineers specify 50% and poor quality control resulted in 57%, or did poor record keeping over the years result in the claimed 50% figure? The reason that I gave all of those figures was to illustrate exactly the point that you make; that balance factors are somewhat arbitrary.

As to the issue of getting the reciprocating weight close between front and rear cylinders, of course you are right that there is nothing you can do with stock rods. Still, S&S felt it was worth retooling their rods to get closer, so I have to think that it is a legitimate issue. Of course, I believe their ulterior motive was to allow them to use several different piston weights without changing the actual balance of the flywheels.

How about this. Since the reciprocating weight includes not only the wrist pin end of the rod, but also the piston assembly, what if a guy were to use a lighter wrist pin in the rear piston? I just went back in my records and found 5 XA rod sets that had differences in front and rear reciprocating weights that ranged from 5 to 21 grams (rods only: not including pistons). A stock wrist pin weighs about 93 grams (probably some variation there too). Axtell used to sell taper wall pins that weighed 83 grams and they still carry tool steel straight wall pins that weigh 67 grams. Looks to me that it may be possible to get those total reciprocating weights pretty close in some situations. Would it be worth it? I don't know, but it would be interesting to find out.

Post Mon Dec 13, 2010 7:47 pm

Posts: 328
Location: north central Ma.
The place i used to work at would use alum slug in the wrist pins when needed.

44
"Smok'in the competition NOT Tobacco"
"Transplant organs, Don't bury them!"
Why dwarf? 5/8 scale race cars! http://www.dwarfcarracing.com

Post Tue Dec 14, 2010 9:20 pm

Posts: 3060
Location: Central Illinois, USA
Lee!

I am yet to be convinced that 50% was the MOCO spec.
Seven percentage points difference is enormous.

Using lighter pins to raise the factor, or slugging the pins to lower it are both tricks of the trade.
I installed many an Axtell pin!
Drilling the wheels is somewhat permanent, whereas the top end is always temporary.
Placing such a pin in either the rear or front makes little difference, as there is only one reciprocating mass in a V-twin.
It usually takes two light pins to make any significant difference in factor anyway.

....Cotten

Post Wed Dec 15, 2010 4:50 am
jib

Posts: 575
Location: devon,england
would drilling the female rod and leaving the male rode give them nearer comparative weights?
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

Post Wed Dec 15, 2010 7:06 am

Posts: 3060
Location: Central Illinois, USA
Jib!

You could, at risk of course, but why?

These notions that the individual portions of the reciprocating mass must be equal are only important to motors with multiple throws on their crank, with portions of their mass moving in different directions.

Our V-twins do not even know they have two rods or two pistons, as they move as one mass.

Attempts to approach a mythical ideal may make you sleep better, but it is not even part of the balancing equation.

....Cotten

Post Wed Dec 15, 2010 5:36 pm

Posts: 150
Location: Carver, MN

This quotation is from the November 2003 S&S Dealer Focus regarding why they redesigned their connecting rods:

"...Our test have shown that matching small end weights has a greater effect on balancing than the overall balance factor. ...What we found was that when we made small changes in the overall balance to mimic different piston weights on a given flywheel assembly, the effect was small. It took big changes in the balance factor, from say , 40% to 60% before producing a change in seat of the pants engine smoothness. At the same time, changing the connecting rod small end weight relationship from the front rod to the rear rod made a noticeable difference in the amount of engine vibration at any given balance factor. When the test engine was run with front and rear rod end weights that were different, there was a noticeable change in seat of the pants smoothness. When the engine was run with rod end weights that were close to the same, it ran smoother with less vibration. Results of the tests indicate that the small end rod weights have more influence on engine balance than the overall balance ratio."

Post Wed Dec 15, 2010 6:51 pm
Pa Site Admin

Posts: 5668
Location: Ohio USA

Isn't this balancing delema the reason for inventing the rotary engine ?

Post Wed Dec 15, 2010 7:55 pm

Posts: 3060
Location: Central Illinois, USA
Motors are not balanced for the seat of the rider's pants.
They are balanced to keep from tearing themselves apart.

The reciprocating half of two rods that do not weigh the same cannot be equal.

Who wrote that crap?

....Cotten

Post Wed Dec 15, 2010 8:33 pm

Posts: 150
Location: Carver, MN

The reciprocating half of two rods that do not weigh the same cannot be equal.



But, as I pointed out earlier in this thread (perhaps not very clearly) it is possible to make the reciprocating weight equal between front and rear cylinders. Reciprocating weight is the combination of the weight of the wrist pin end of the rod and the weight of the piston assembly. That is why I suggested the possibility of using wrist pins of two different weights to equalize the front and rear reciprocating weight.

The fact that S&S spent the time and money to build a test engine, and then spent the time and money to redesign their rods because of their findings, tell me that there might be some chance that the concept is worth at least considering.

Post Thu Dec 16, 2010 4:37 am
jib

Posts: 575
Location: devon,england
Cotten wrote:
Motors are not balanced for the seat of the rider's pants.
They are balanced to keep from tearing themselves apart.

The reciprocating half of two rods that do not weigh the same cannot be equal.

Who wrote that crap?

....Cotten



cotten are you ok? not suffering from 'panicitus' :roll: :roll: :lol: :lol:
Dude, check out that jibhead, he's crazy. Hasn't been sober for 40 years

Post Thu Dec 16, 2010 8:04 am
Pa Site Admin

Posts: 5668
Location: Ohio USA

Everyone on the web seems on the bit edgy side lately. :shock:


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