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[jimamtay]

Thinking of trading springer for 10 Fatbob, really like unbalanced motor but never felt 110 unbalanced also like Dyna torque & growl. Anybody out there tried both??

[moscooter]

 
I have not tried both styles in the 110 displacement size,  but can only think of two real differences.

At a stop lite,  the B motor sits still and the A motor jumps around in it's rubber mounts.  The most critical other difference is RPM limitations on the B motor.  As I recall,  5800 RPMs or not much more is or was the upper limit elsewise the bearings in the balancers will come apart!!!!!   An unbalanced A motor can handle 6200-6300 or mayb more in RPMs..........Someone perhaps has the more specific limits of both,  but whatever the limit.........the A can rev higher.

[Heatwave]

My Fatboy 95" B motor has had a 6200 rpm rev limiter for the past 6 years. Routinely ran into higher rpms because I was running a se 258 cam. 102/108 motor. B motor will rev as high as an A motor. A motor produces slightly more hp/tq for the same displacement and engine setup because it doesn't have to spin the balancers.

[jimamtay]

Thanks guys for input, think the softail is higher on food chain BUT that Dyna sure is nice!

[FLSTFI Dave]

My Fatboy 95" B motor has had a 6200 rpm rev limiter for the past 6 years. Routinely ran into higher rpms because I was running a se 258 cam. 102/108 motor. B motor will rev as high as an A motor. A motor produces slightly more hp/tq for the same displacement and engine setup because it doesn't have to spin the balancers.

I agree.  My 03 Fatboy with the 95" big bore, 10.5:1 pistons and S&S 570 gear drive cam has a 6200 rpm red line.   I have 38K miles on the build with no troubles.  Still runs very strong.

[moscooter]

 

OK,  I accept you can take your B motor to 6200.....but you're getting close to granading it versus the higher revs capable on the A motor.   The lower (safe rev limitations) of the B motor versus the non-balanced A motor is a fairly known fact.

[jimamtay]

I agree w/ moscooter, my old fatbob would rev higher/longer than 110 springer, Fatbob was not a 110, but it was A motor. My 110 will rev past 4 but valve train does not like it.

[aka_Matt]

the 4" stroke "A" motors will spin to 7k, altho they won't last that long if u do it alot, plus u'd need the right internals/cam to make it even worth it... the "B" motors and the 4.375" stroke motors should not go over 6200... the "B" motors because of the balancers, the strokers, just because of the long stroke...

[bbrown]

the 4" stroke "A" motors will spin to 7k, altho they won't last that long if u do it alot, plus u'd need the right internals/cam to make it even worth it... the "B" motors and the 4.375" stroke motors should not go over 6200... the "B" motors because of the balancers, the strokers, just because of the long stroke...

Wow I did not know this

[skreminegul07]

Wow I did not know this

Being careful here but:

Stroked motors typically do not have the same longevity.  For each RPM, the stroked motor has to travel faster to traverse the same distance.  Simple science, distance + speed x time.  Therefore, more wear and tear.

[NA_Dude]

the 4" stroke "A" motors will spin to 7k, altho they won't last that long if u do it alot, plus u'd need the right internals/cam to make it even worth it... the "B" motors and the 4.375" stroke motors should not go over 6200... the "B" motors because of the balancers, the strokers, just because of the long stroke...

I did not know this either....  I have both... FXSDE & SEUC4. Both have D&D Fat Cat's with performance baffle. The diff is the SECU4 is running the quiet performance baffle. Both intakes have been upgraded, SERT & Dyno'd. Both make 90HP 110 TQ. That being said.

The Dyna will pull hard to 5200-5500 R's. The Ulra pulls to 4500-5000, then falls on it's face. Weight vs HP/Tq, I would guess is a factor.
The Dyna has more bark in the exhaust when I blip the throttle, and a sweeter sound through out the RPM range.
The Dyna w/o the counter balancer rocks on the mounts at idle.

[aka_Matt]

I did not know this either....  I have both... FXDSE & SEUC4.

both your bikes have the same engine, 110A, unbalanced... only softails have the B motor...

[mrmagloo]

Wait a sec...  Since when will an unbalanced motor be more stable and more safely achieve higher rpm's than a balanced motor?  Sounds very counter-intuitive to me??   

[moscooter]

 
It's quite simply actually.  You're taking the "unbalanced" comments out of context.  A V-twin motor with both rods/pistons riding up and down on the same crank pin are gonna shake.   The "balanced" (B motor) means that counter-balancers have been added to counter-act the inherent shaking that other-wise would take place.

The bearings in the balancer mechanism cannot sustain the higher rpms that the "A" motor......(that does not have counter-balancers in it) can handle.   

[mrmagloo]

While I understand the firing and rotational order of the Harley V-Twin, is not symetrical, if you have an unbalanced crank, how is that helpful to the bearings?  The entire objective of balancing a motor is to counter-balance the out of wack reciprocating assembly, which in turn should be easier on the bearings.