No, it wouldn't. Norton tackled this problem with their Commando (I've read their patents, as well as Harley's). More important is maintaining alignment of the rear drive, so that the rear wheel pulley/sprocket moves in correct alignment relative to the transmission ditto. That is why the swingarm and rear wheel are mounted off the back of the trans and why the way Harley did things is similar to the Commando. The H-D solution is however superior to the Commando and benefits from Norton's experience.

Sorry about that! The H-D solution, as per Buells and Sportsters (why I own an example of both) is exquisite, from an engineering perspective.

 

I guess we"ll have to agree to disagree. The way I'm proposing to have made it would keep the swing arm and therefore rear wheel aligned with the frame and the transmission aligned as well. They would all still be aligned via the pivot bolt and only the transmission would be soft mounted over it's 4-9/16" mounting length. The pivot bolt would be held as is the steering neck bolt. And actually since the swing arm is only mounted to one 1" wide bearing on each side, the swing arm could be a forging at this pivot end and be only 1" wide allowing the vibration isolation on the transmission to be further apart or longer making it even more stable. Not rocket science.

 

The "rubbery cleave blocks" are silicone filled, have a metal core that when torqued to spec prevents sideways motion but not twisting moment. There's a very good diagram of them in my service manual. Basically you have metal to metal contact from one rubber frame isolator to the other, same as with the 2002-2008 and now 2009-2014 bikes.


All of the True Track type braces are trying to control the unwanted swing arm movement caused by the rubber isolators. It is a poor design.


If I had the $$$ I'd cast a new tranny housing and prove the design. I guaranty it would handle better and possibly have less vibration as I believe you could eliminate one or both of the front stabilizers depending whether the front of the motor had one or two vibration mounts (old or new chassis)

 

Are you saying maintaining pulley/sprocket alignment is more important than chassis alignment? What if you could have both? Wouldn't that be better?

 

I agree with you, and I would be too, but the FXR is said to handle and does it not have a very similar frame?

What are the differences ... the extended headstock, the weight and the rake?

Isn't it possible that certain circumstances make it flex when it pushed past the limits of the compressed rubber sandwich? Those mounts are pre-loaded quite a bit.

How tight should the pivot be in the transmission housing? A small looseness must translate to movement at the end of the rear fork/swing arm.

 

To better understand what you are dealing with here you really should read the Harley patent. The design is excellent, from an engineering perspective, poorly implemented by Harley on our Touring bikes. However I am repeating what I wrote in post #1, so please read that again. Any questions please ask!

If you use a True-Track stabiliser, you DO get both! All the hard work has been done for you. T-T were the first company to design and build a stabiliser that installs the rear stabiliser included in the original H-D patent and on all Buells etc. All other stabiliser kits are copies of the T-T. The swingarm is pivoted on the trans casing to maintain drive line alignment, the rubber mounting system with stabilisers (three of them) maintan alignment of that Assembly in the frame. It is really a very simple and elegant set-up!

 

I agree, the bushings and the shaft are what align the swing arm. If the bushings were as squashy and soft as many claim, I'd agree with you. They aren't though. They are actually darn hard and don't deform worth a darn. Play with one in a stout vice and you'll see what I mean. Now if the bushings are old and broken down, that's a different story. Then they would indeed allow wiggle of the swing arm.

The transmission hole that the swing arm bolt goes through is no different than that used by Yamaha and all the rest. It's a place to hang the rear of the engine, and a way to bring the transmission sprocket into rough alignment with the rear wheel sprocket. The turnbuckles for alignment let you more precisely align the sprockets without having to re-do it every time you replace the front motor mount and such. Bring it into alignment, lock the turnbuckles, and now let the rubber motor mounts do their thing to support the engine mass and isolate the vibration from it.

I suspect a lot of the vibration problem people have with their bikes stems from the misapplied attempt to alter the swing arm location via the engine alignment adjusters, the front motor mount turnbuckle in particular. They create such tension in the turnbuckle that it transmits the vibration the rubber front mount was intended to isolate.

The likes of most of the aftermarket wobble fix devices also end up doing this. They link the rear swing arm to the transmission, and attempt to have the engine mass hold the swing arm in place, via the front turnbuckle. This is a misapplication of forces in my opinion.

So where do I think bagger wobble lives? Two places.

One is the oem slop between the swing arm shaft and the swing arm inner bushing that I found on my bike. Well masked by belt tension. Wasn't wear on the old parts, the new replacement parts had the same slop. This oem slop lets the rear swing arm move side to side nearly 1/4" at the rear tire. But you can't detect it with any tension on the belt. I fixed it with shim stock, but a closer sized inner swing arm bushing would be a better fix. Frankly, I'm surprised there isn't a replacement bushing on the market now.

The second place is in the steering head. This is generic to all motorcycles and even bicycles, it isn't a Harley specific phenomena. It's inherent to the physics of having essentially two unicycles joined by a hinge. There will be wobbling. You can change the frequencies, you can make it better or worse, but you cannot make it go away as long as there is a hinge there. Damping of the hinge, bringing mass in closer to the hinge helps reduce the wobbling. Loosening the hinge, and moving mass out higher and away from the hinge makes it worse.

 

Good stuff

 

Graham,


I did read your first post. Car manufactures don't hard mount the engine to the suspension and then rubber mount the suspension to the chassis. Putting the isolation in the transmission housing but still having the pivot shaft pass thru it will keep all in alignment yet prevent misalignment.


This is only part of the problem as others have stated. If the front end is not correct it will exasperate the handling issues.

 

Car manufacturers use universal couplings in the drive-shafts between the engine/trans unit and the wheels! FWD vehicles use constant-velocity couplings, which are pretty darned clever devices. The engine can rock and roll however it pleases with no side effects, quite a different situation compared with a bike.