Topic: Bwallers 6spd 350/550 gearbox mod.

[BomberMann650]

Excellent read,  but the pictures aren't loading.  And the thread stopped before he mentioned anything about actual speed gains.
I gathered something about a newly minted gearbox kit that handles hp better than salvage parts?
I'm turned on by the idea - but without pictures and a finished thread I'm at a loss.

If it's something simple (like crescent wrench and a 9lb hammer simple) I'd seriously consider that mod for my coming motor build.

[Scott S]

What is this mod you speak of? Link?

[BomberMann650]

http://forums.sohc4.net/index.php/topic,66355.0.html

I was lurking the stickies in the hipo forums

[BomberMann650]

The photos are loading today.  Dunno why I couldn't see them last night.

[chewbacca5000]

I would love a 6 speed for my K1 I am always looking for an extra gear.  Not sure I want to go through all that though.

[BomberMann650]

Bwaller did do quite a bit of modification to make it all work.  Shorten this, bore that, hang these, etc.

And he still burned up a few gearboxes in the process!

1 down 5 up remains a bit of a fantasy it seems.

[bwaller]

My ears were burning! 

Actually the 6spd worked great from the start in my CB550 but there was a lot of machining involved. Ultimately though what makes it such a great gearbox is the work Ellis at Moore Performance Engineering did for me. I worked out on paper different gear tooth counts to create much closer ratios which pays dividends on the race track. Ellis made a new mainshaft with an extra tooth 1st plus five other gears.

Closer ratios aren't necessary though because Jerry Kooistra from Australia used stock CB360 gearboxes in his very successful CB77 based racebikes. Once my engine produced over 65 RWHP we twice experienced broken teeth on the stock 360 (twin module) sliding gears. Considering this CB360 gearbox was engineered to mate with an engine producing 30 HP it did very well. The gears Ellis made were of higher grade material with newer, better machining capability. Last winter we replaced three more of those 360 gears and now that the engine is producing 75HP I feel comfortable the gearbox will continue to be reliable.

Every effort was made to fine tune this transmission including adjusting the lever "throw" to match dog engagement, using different spring tensions, trying different detent roller diameters, switching the detent rollers to bearings and polishing every surface besides undercutting upshift dogs/grooves. I've upgraded the clutch to use an extra plate/disc, all stock parts.  It is the smoothest shifting gearbox I've ever had.

[scottly]

Brent, how did you adjust the "throw" to match dog engagement? Weld/grind the slots in the shift drum?

[bwaller]

I took a simpler approach Scottly, just made a sleeve the correct OD & welded it over the return spring pin to limit the travel of the shifter shaft.

[BomberMann650]

Bwaller!!!! THANK YOU for stopping by.

You're onto some next level sh!t for this farm boy to try and understand (*see cowvatar)

It is awesome what you were able to accomplish.  But the burning question still remains;
Did the bike break the 105mph mark with that extra power and gearing?

Furthermore, any practical reason for backwoods riders to go through the modification?

Thank you!

[Bankerdanny]

At 75hp I would hope he can crush 105 mph.

[BomberMann650]

At 75hp I would hope he can crush 105 mph.

Or he can charge thru all the gears and get to 105 faster than everybody else!

[bwaller]

Well BM650, I'm a farmboy too so that has nothing to do with much. It's a racebike and at 322lbs it does surpass 105 mph,  never had anyone point a radar gun at me on the end of a straight anywhere!

Was it worth it? Yes. Would I duplicate it? Not as it is, I would probably either buy a gearbox from Nova Racing in the UK or start with all new fabricated parts. The effort was part of my racebike project and I had a goal in mind. I calculated the HP difference dropping far fewer rpm's (with a close ratio 6spd) while shifting at redline. This based on the engine dyno charts. In every case 350-800 greater rpms  after a shift translated into 2.5 to 10HP advantage. Not earth shattering, but no small deal either. 

So long story short a 6 speed gearbox is available as a drop in. (mostly) It is designed as a race transmission. The Nova first gear ratio is 2.00:1, whereas mine is 2.125:1 and a stocker is 2.353:1. It will be a little harder to launch from a stop, but not impossible. I think you lose the kickstarter as well. Price was $2500 at one time, and that's cheap compared to what I went through!

As an aside my all time favorite motorcycle racer is Steve Baker who's a ways upstate from you. He often came up to Westwood race track (1976 ish) in BC to practice/race with us and I remember him fondly as a very nice guy. Hopefuly he is doing well.

[BomberMann650]

thanks for the writeuo Bwaller