Engine discussion...Which And Why?? Busa? ZX10r? R1? Other?

[K-fab]

Originally Posted by Blownz28man

By "back cut" gears what do you mean? New to the bike world. And what about the "Dog ears" on the tranny??

The gears in a motorcycle transmission have "dogs" on them. Back cutting or undercutting them makes for a more positive engagement between gears.

The dogs are tabs that stick out from the side of the gears and are responsible for engagement as you shift.


Often these dogs slide into windows in the gear next to them.


The dogs may also slide up and engage another set of dogs on the adjacent gear instead of into windows.

As you can see, these dogs come out of the side of the gear at 90 degrees to the gear.

When under load the dogs on the gears can actually flex just ever so slightly; yielding a no-longer 90 degree contact. Because it's no longer perpendicular to the power being put through the gear, the dogs can slip away from each other letting the transmission pop out of gear (and this can lead to some serious damage if the other gears don't move in conjunction with the slipping gear - shift forks flex, things move - bad stuff happens.)

By undercutting the dogs on the gears ever so slightly, it effectively hooks the drive dogs together, eliminating the tendency of the gears to slip away from each other.


The site this pic came from is charging about $400 to do the work to a Busa transmission.

The trick, when undercutting, is to make sure that all the mating surfaces between the dogs and the gears have had exactly the same amount of material removed. If you were to leave one dog slightly "higher" than the rest (in contact area) you'll end up having one dog that tries to do the work of all the others and it usually won't last long.

It's a very precise modification and when done correctly helps make the transmission quite bullet proof.

The only downside to this is that if you're one that tends to shift the transmission while under power, the shift will take more effort and feel a bit notchy. Non-undercut transmissions usually shift under power quite easily and fairly slick (provided the transmission shifts smoothly from the start...)

[busasandrail]

Well put Fab...

[Gene]

Woof!

[El Toro]

Nice job...

[standfast]

99-07 Hayabusas are factory backcut in 3rd through 6th gear on upshift. 2nd gear has no undercut and will inevitably have problems in a buggy application unless you don't abuse the car at all. But whats the point in that? The factory backcut on the rest of the gears is useful but not optimized. The way the dog angles mate is not perfect so they can be optimized with a more precised matched backcut. 99-07 Hayabusas also have a small 25mm output shaft which has issues shearing. The metallurgy on the gen1 busa's output shaft is less than ideal do to issues with grain structure. Pitting/cancer is a VERY common issue with them. It is also common for engines with a lot of shift use to mushroom the shift fork pins causing poor/weak engagement.




08+ Hayabusas are factory backcut in 2nd through 6th gear on upshift. This takes care of the 2nd gear issue that the Gen1 busa is known for. All the gears are the same face width as the Gen1 busa but have a slightly different pitch to slow down gear wear. The Gen2 Busa output shaft is also less problematic and they increased it to 27mm. These improvements along with the additional HP from the compression ratio increase and dual injector setup make the GenII busa more desireable to use right off the bike without trans modifications. They also added titanium valves on the Gen2 so turbocharging this motor is not as appealing as it is the Gen1. It would need stainless valves and stiffer springs to deal with the boost along with the normal stuff like pistons/rods etc. This is obviously to run a significant amount of boost. There is gen1 and gen2 busas with stock motors out there that are turbocharged with low boost levels but the increased wear is still a factor and the motors tire out much faster than a stock one. Just a risk you take. There is some problems with the Gen2 shift forks pins wearing at an more rapid rate than the Gen1's so it is ideal to swap these out for the Gen1 units if you are ever that deep into the motor. They are a direct swap.


06+ ZX14s use no undercut on the gear dogs in any gear. Their solution was to have the gear dogs about twice as long as the Hayabusa so that they engage twice as deep to help keep them in place. The longer dog creates a much slower wear process. EVENTUALLY you can wear down these gears but it will take much more time and abuse. You can also backcut this transmission in the event that you do get to the point where the gear dogs aren't hanging in there anymore. The ZX14 has a 28mm output shaft for a point of comparison to the others.



It is a toss up whether the 08+ busa trans or the ZX14 transmission is best for our application in stock form. A undercut ZX14 tranny on upshift and downshift would be the most ideal setup of them all being it has so much larger dogs. The Gen1 Busa is the least appealing transmission in stock form but the weakpoints all have upgrades and can all be taken care of for about $400-600 or so if you pull the tranny out and ship it to a reputable company that knows what they are doing. That price difference can be a wash being you can generally get the gen1 busa engines cheaper. You just have to be able to break down the lower cases etc.

[Gene]

Nice comparison information. Very useful.

[Dezzrats]

Watch carefully when looking at wrecked ZX14 bikes. If they go down on the right side, or tumble, they tend to damage the engine case in the area of the timing pick-up (lower right). The cover is replaceable but week and the engine case itself is often damaged.