He did ask people that know how to build/re-build cranks and he recieved straightfoward answers............

 

Yes, he did. Yes it was.

But a discussion on balance factors would be enlightening.

When R&R did a stock crank rebuild (with balancing), I ended up with a 52 balance factor. Engine was sooooo smooth. I would imagine any engine with the crank, etc all balanced would be similar. Just want to know more about 'balance factor'.

Kirby did an excellent job at describing the 'how to' for balancing a crank, BTW. Thanks.

 

You'll never get a v-twin crank to be smooth thru the entire rpm band, but rather place the vibration/pulsation point where your in/out of it without notice.
52-55% seems to be the numbers that folks use these days.
60% was always the number S&S reccomended.
We've found over the years just how far off the OEM balancing really is.
Not bad when removing material, but when you need to add weight,(tungsten, or also known as Mallory Metal) that is a bit more involved.
We've lightened, knife-edged, pork-chopped, reduced the diameters, etc, etc, to these cranks, and have built/rebuilt over 400 cranks to date, with completed S&S worksheets to prove it.
Our AHDRA racer's crank, was loaded to 450 ft.lbs on the crank pin nuts, and if someone has ever had to true those once torqued, you know that is no joy.
Nothing complex or hard to do once your tooled up to do it, and you have the hands-on experience to go along with the tooling.
Scott

 

This is all really informative. Thanks for all the responses. Right now Im still in the process of getting the bottom end out of the frame and I still want to take the cylinders to a shop and see if they need to be bored. If so, I believe I then need to get that done as well as get new pistons. Once I get that done, i will be looking to get this all balanced. It will still be some time before Im at that point, but was trying to get some info ahead of time so i knew what was going to happen next in the process and about how much to expect to spend. Thanks again.

 

flywheels that have been lightened or will see high RPM`s,we balance at 50-55%,but for most street stuff,60% still works best IMO.the balance factor is the percentage of the reciprocating weight (top half of rods,pistons,rings,w.pins & circlips).we found the motors seeing higher RPM`s will benefit from a slightly lower percentage (everybody seems to have their own opinion on this,but this is what we`ve found here,and we`ve balanced more flywheel sets that I could even begin to count).the rotating weight (lower half of rods,c. pin,bearings,nuts & cages) is balanced using 100% of the weight.theres also a lot of vibration that gets blaimed on the engine being out of balance,check all your motor mounts,prim chain adjusted and on the bikes with tapered main shafts,making sure the clutch hub isn't running out of true is a MAJOR cause for vibration on the earlier bikes

 

Great info guys!! Thank You!!

 

Bringing this back from the dead.

I have a new Low Rider S with a 117. I'm still breaking it in and haven't been revving it past 4000 rpm. At 3200 rpm, the motorcycle vibrates a lot. Below that, very little, and above that, very little. Does balancing help minimize that vibration, or is it a matter of lowering or raising the rpm point where you are feeling the engine out of balance?

Thanks,

Dave

 

Few things to note.

1. You cannot completely balance a 45 degree V twin. The rest is reference to the motor.

2. The vibration from the motor will increase with RPM not mater what so you really can't balance for RPMs.

3. Optimum balance factor really depends on how the the rest of the system, motorcycle chassis,everything that absorbs the imbalance that make a difference in felt vibrations. Obviously a lighter motorcycle will vibrate more than a heavy one.. The motorcycles as a system can have resonate frequencies so there is often an advantage to vectoring the imbalance.. Example.. 0% Imbalance will vector the imbalance vertically. 100% imbalance will vector the imbalance horizontally.


4. Selecting a balance factor around 50-53% reduces the overall imbalance but vectoring the imbalance in a direction where the center of mass can absorb it helps.

5. Reducing the reciprocating mass will reduce the vibrations.

6. Equalizing individual rods and pistons can help reduce vibrations.

7. Rubber mounted motors can resonate at certain frequencies making vibrations that cam become intolerable.

8. Twisted / Spread cranks throw off balance factors.

9. Stronger power pulses from a higher performance motor can cause motor vibration tho it's really not from imbalance.

In your case the bike is on the light side compared to a bagger. Pumping the motor up can make it vibrate more.. Exhaust is mounted to the tranny. It can can create a resonate frequency at certain RPMs. Sometimes lightening the exhaust or adding some flex to the exhaust mounts can help. Adding preload to the rubber mounts can help. Dynas have their own special issues so it's worth looking at the threads abbot vibration and asking questions over in the Dyna section.