XB12r gearbox parts.

[Aidan]

Hi all.
I am looking to source a new shifter drum and forks.
My 2008 XB12r (newer spec motor) jumps out of 3rd gear on occasion and i'm fairly sure it is down to a worn drum/fork combination.
Living in Ireland I am not exactly spoiled for choice on parts...
Does anybody here have the necessary parts or can you offer any advice on where I might source them?
I have been keeping an eye on EBAY but found nothing reasonable yet...

Thank you

Aidan

 

[Chicknstripn]

Try St.Paul, New Castle or Surdyk Harley Davidson. Look them up online and order new parts.

Prior to ordering new parts I would suggest disassembling the transmission. This requires pretty much disassembling the entire motor in order to split the cases. Once you’ve accomplished that inspect the transmission components. Chances are the shift drum is fine.

My bike had a slight skip in 3rd gear and after inspecting the transmission components I needed to replace 3rd gear, 5th gear, the shift forks and the associated shift dogs for the gears I was replacing. I think that’s exactly how it worked.

Download a service manual at www.buellmods.com and study the transmission section so you can see which gears and shift gods effect each other when engaged.

Good luck with the rebuild.

In your situation you might be better off finding a low mileage crashed bike and swapping motors.

 

[Aidan]

Thanks, great info there, much appreciated.
I had hoped to have all the parts necessary ready before beginning the tear down, but reading your comments probably best to wait til I assess the problem before ordering parts blind.
I was a motorbike mechanic for 15 years so I know what i'm getting myself in for. Also apart from the gearbox issue it is a good healthy low mileage motor.
With that in mind I can't justify just replacing it, especially given the price of shipping and taxes involved in bringing a complete motor in from the states. ( very little chance of finding a motor closer to home) Also who knows what problems may come with a second hand motor...
I think I'll go down the route of stripping her down and taking it from there.
Any more input is welcome too, especially in regard to options for parts once I have it stripped and checked.
I have found a place in Holland www.twinmotorcycles.nl who can supply parts too.
Keep it sunny side up.
Aidan

 

[Chicknstripn]

Twinmotos is a great place for anything Buell. They have A TON of helpful vids online and are a wealth of Buell knowledge.
I consider myself an absolute novice mechanic and I had no issues with tear down and rebuild of my engine. I went the rebuild route for almost the same reasons as you..... only thing I needed help with was using an arbor press and the necessary tooling to remove the transmission from the left crankcase(I think it was the left). Anyway, my local HD was pretty cool and pressed it out for me, free of charge.
Search the net as much as you can. I’m pretty sure some guys have gone DIY on pressing the transmission out of the crankcase.
Whatever you do, do not use impact tools to disassemble or assemble anything drivetrain/transmission related. That could cause additional damage.
Good luck.

 

[Cooter]

Good advise from Chicken (as usual )

Neither the shift drum nor the shift forks are meant to hold the trans in gear. The undercut in the dogs does that, so popping out of gear is typically worn dogs on the side of the gear and a pretty common problem for the 2-3 gears.

These guys are across the pond from you in Florida USA
https://www.yelp.com/biz/r-and-d-motorsports-clearwater.
1632 N Hercules Ave
Bldg G
Clearwater, FL 33765
Phone number (727) 447-4552
Business websiter-dmotorsports.com
They're super smart and can supply you what you need and even just re-machine the dogs on the gears you have if shipping (x2) is a better option than buying new stuff from sphdonline.com

 

[Outlaw]

Good video an explanation.

 

[rchuff]

Kevin has a lot of great vids on how motorcycles work.

 

[Silverrider]

Yes sir ^^^^

 

[Cooter]

{Quote Lunatic} "the correct spacing and shimming of the transmission gear shafts is what holds the gears in place during operation. undercuts????"

I'm not sure what you're trying to say here? Buells have the shafts pressed into one side of the case so theres no adjustment I know of? I'd love to know what you mean, you're a smart guy and dorking out on this stuff is fun!

Let me explain what I mean by "undercutting". The dog sets in the mating gear pairs (Kevin touches on them at 3:10) will be undercut anywhere from 1*-7* (Yes, because this is planet Earth... there are some odd exceptions at 0*). This little undercut:

holds the mating gears together under power so the trans doesn't slip out of gear because the shift forks are no where near strong enough to do that, nor are they designed for that stress, and also why motorcycle constant mesh transmissions have straight cut gears. Helical gears would be stronger and quieter, but helical gears would also side-load the shift forks under power trying to pop it out of gear.

In a constant mesh transmission that has worn dogs (typically 1-2, because it has the highest torque load/and highest ratio change) you'll see the shift forks blued from the heat of the gear trying to separate from its mated pair as well as a divot in the shift drum from the sideways pressure.
Like this Victory Drag bike (quit laughing, it was fun:black_eyed

The steeper the undercut, the stronger the gears hold together under power but it also makes it harder to shift, (to overcome the ramp angle of the undercut) as the gears are being twisted together. MFG's still play with the magic number for each type of bike every year.

The undercuts are exactly why you need to let off the throttle a little to reduce the pressure on the trans when clutches upshifting.







In My Opinion:angel:

 

[Aidan]

Thanks for all the replies folks.
As usual the true damage will probably be a mix of all the above.
I would just like to point out a few things.
Damage dogs are usually caused by incorrect shift drum action, whether due to worn or bent forks/drum or other issue.
This then results in power being transmitted through the dogs while only a small contact area has been achieved. Resulting in chipping or wearing of the dog surfaces.
My bike instantly pops back into gear after popping out and will then stay in while power is maintained indicating play in the drum and fork combo. ( with a lot of luck maybe the dogs are useable)
Also the Shifter pawl adjustment issues do not apply to this model firebolt as it does not have the adjustable earlier setup.
Hopefully in the next month i'll have time to get it stripped down and report back on the damage.
Thanks to all.

Aidan

 

[cossack84]

Aidan you need new parts not undercut gears. Undercutting is fixing a symptom not a problem. Replace drum, selector forks and selector fork shafts. in properly functional transmission there is no load on the gears side to side hence no need to undercut.
Here is a good explanation that I found helpful.

https://www.youtube.com/watch?v=GsgiaAMc7cM

 

[Cooter]

I have never held a Buell transmission in my hand, but I know for a fact other V-twins have undercut gears stock. Including the similar Harley XL (Sportster) transmissions (1-4* depending on gear and year), and can confidently assume that a similar engine built with considerably more torque (like Buell) has gears undercut stock. I'll do some research to find out definitively.

Gears with no undercut will work in light duty/ low-torque applications, but don't assume that's true of all transmissions. In high torque applications, the shift forks and drum are unable to control the sideways force of the gears from the gear shafts deflection. The slight undercut angle of the dogs makes sure to hold the gear pair together under high torque conditions. Too high an undercut (7*+) makes for hard shifting.

 

[cossack84]

The point of my post is to make sure folks dont go out of the way and send the gears to get them cut. Just replace with stock components and if there is still a problem with popping gears then undercutting should not be a solution. Rather look at the forks, fork shafts, drum or check make sure the input and output shafts are parallel. Those are the things that make, other wise perfectly functional transmission, miss behave.
There is very little to no side load during operation. Forks and drum do not hold gears in place. They are there to select which gear transmits power, they are not designed to hold gears in place, period.