anyone back-cut their dogs?

alex.s · June 29th, 2012, 12:49 PM

going to have the box apart and the transmission has really been slipping lately. dogs feel worn, so i'm going to back-cut them. has anyone done it on a 250 transmission? what kind of disk did you use to do the actually grinding?

Gorilla25 · June 29th, 2012, 06:15 PM

interesting....ive heard of cutting them back for drag or race applications, but never to "re-tighten" the gears because the transmission is slipping. assuming you already made sure the clutch is still good, wouldn't you need to replace the dogs rather then cut them back?

Kevin2109 · June 29th, 2012, 07:30 PM

Subbed

I want to do this to the 636 some day

alex.s · June 30th, 2012, 12:46 AM

stock 250 dogs are flat. back cutting them gives them an angle so any sliding they do will just lock them harder

Motofool · June 30th, 2012, 05:19 AM

Repeated clutch-less shifting tends to round the edges of the dogs.
When too pronounced, that can make the gear try to self-disengage putting some force on the selector fork and mechanism.
Replacement is better once dogs reach that condition.

The designed square edges make the forces on the shifting mechanism neutral.
Any positive angle would make clutch-less disengagement much more difficult, in my opinion.

Out of necessity, I brought back to square some worn bones of a classic German motorcycle (lower HP's and rpm's).
I worked in a machine shop back then and I was able to use the milling machine for making the cuts at precise angles and equally distributed.
As a cutting tool, I used an abrasive cutting disc, since the teeth of the dogs are very hard for a regular steel tool.
I was very careful of providing abundant fluid (mix of lubricant and cooler used in milling machines) during the cuts, because the hardness of the dogs would be compromised if allowed to get too hot.
I believe that the machine is still working properly.

Doing it by hand may introduce errors in angle and radial distribution that may put all the stress on one tooth, compromising the sliding of the dog over the shaft; hence, I don't recommend it.
I have been wrong before, and I may be again now.

LoneRonin · June 30th, 2012, 10:22 AM

what the hell is a dog in reference to bikes??

Gorilla25 · June 30th, 2012, 11:03 AM

Quote:

Originally Posted by LoneRonin

what the hell is a dog in reference to bikes??

we're referring to the transmission gears. the ones in our bikes are called dog gears.

Motofool · June 30th, 2012, 12:24 PM

Quote:

Originally Posted by LoneRonin

what the hell is a dog in reference to bikes??

See "Crash gearboxes or dog boxes" here:

http://www.carbibles.com/transmission_bible.html

alex.s · June 30th, 2012, 12:25 PM

yeah hernan. you mentioned everything i was worried about. last night i did some work on the bike and reconfigured my external shift lever mechanism to have more torque to turn the shift bar thing and more clearance. it solved a good portion of my problems. last time i had the transmission out the dogs looked flawless so it surprised me when it started slipping out. i will have the engine apart soon and will update with photos of the condition

June 29th, 2012, 12:49 PM	#1
alex.s wat Name: wat Location: tustin/long beach Join Date: Sep 2009 Motorcycle(s): wat Posts: Too much. Blog Entries: 5 MOTM - Oct '12, Feb '14	anyone back-cut their dogs? going to have the box apart and the transmission has really been slipping lately. dogs feel worn, so i'm going to back-cut them. has anyone done it on a 250 transmission? what kind of disk did you use to do the actually grinding? __________________________________________________

June 29th, 2012, 07:30 PM	#3
Kevin2109 KThanksBye Name: Kevin Location: Orange County Join Date: Mar 2011 Motorcycle(s): 2006 zx636r Posts: A lot.	Subbed I want to do this to the 636 some day __________________________________________________ ----> My Youtube! <---- Unregistered, watch my youtube page!

June 30th, 2012, 12:46 AM	#4
alex.s wat Name: wat Location: tustin/long beach Join Date: Sep 2009 Motorcycle(s): wat Posts: Too much. Blog Entries: 5 MOTM - Oct '12, Feb '14	stock 250 dogs are flat. back cutting them gives them an angle so any sliding they do will just lock them harder __________________________________________________

June 30th, 2012, 05:19 AM	#5
Motofool Daily Ninjette rider Name: Hernan Location: Florida Join Date: Mar 2011 Motorcycle(s): 2007 Ninja 250 Posts: A lot. MOTY - 2016, MOTM - Dec '12, Jan '14, Jan '15, May '16	Repeated clutch-less shifting tends to round the edges of the dogs. When too pronounced, that can make the gear try to self-disengage putting some force on the selector fork and mechanism. Replacement is better once dogs reach that condition. The designed square edges make the forces on the shifting mechanism neutral. Any positive angle would make clutch-less disengagement much more difficult, in my opinion. Out of necessity, I brought back to square some worn bones of a classic German motorcycle (lower HP's and rpm's). I worked in a machine shop back then and I was able to use the milling machine for making the cuts at precise angles and equally distributed. As a cutting tool, I used an abrasive cutting disc, since the teeth of the dogs are very hard for a regular steel tool. I was very careful of providing abundant fluid (mix of lubricant and cooler used in milling machines) during the cuts, because the hardness of the dogs would be compromised if allowed to get too hot. I believe that the machine is still working properly. Doing it by hand may introduce errors in angle and radial distribution that may put all the stress on one tooth, compromising the sliding of the dog over the shaft; hence, I don't recommend it. I have been wrong before, and I may be again now. __________________________________________________ *Motofool* *.................................Never ride faster than your guardian angel can fly* "Mankind is composed of two sorts of men — those who love and create, and those who hate and destroy. Love is the bond between men, the way to teach and the center of the world." - José Martí

June 30th, 2012, 10:22 AM	#6
LoneRonin ninjette.org sage Name: Jason Location: Mississauga Join Date: Mar 2011 Motorcycle(s): 09 Ninja 250r Posts: 634	what the hell is a dog in reference to bikes?? __________________________________________________ ”Any man dies with a clean sword, I’ll rape his f*ing corpse!”- The Hound

June 29th, 2012, 06:15 PM	#2
Gorilla25 Dakine... Name: AJ Location: DFW Join Date: Jun 2011 Motorcycle(s): 2009 Ninja 250R (Sold) \| 636 (hopefully soon) Posts: A lot. Blog Entries: 5	interesting....ive heard of cutting them back for drag or race applications, but never to "re-tighten" the gears because the transmission is slipping. assuming you already made sure the clutch is still good, wouldn't you need to replace the dogs rather then cut them back?

June 30th, 2012, 12:25 PM	#9
alex.s wat Name: wat Location: tustin/long beach Join Date: Sep 2009 Motorcycle(s): wat Posts: Too much. Blog Entries: 5 MOTM - Oct '12, Feb '14	yeah hernan. you mentioned everything i was worried about. last night i did some work on the bike and reconfigured my external shift lever mechanism to have more torque to turn the shift bar thing and more clearance. it solved a good portion of my problems. last time i had the transmission out the dogs looked flawless so it surprised me when it started slipping out. i will have the engine apart soon and will update with photos of the condition __________________________________________________

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