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Discussion Starter · #1 ·
What does it mean when it states the tranny was undercut?

Thanks guys and gals

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Found this article here http://www.alphalink.com.au/~asg/tips/tip3.htm

It's about motocross tranny's but applies to street bike tranny's too. I beleive racers will undercut their transmission's to allow better shifts at the extreme conditions that they run their engines at.(most likely someone else can elaborate)

Technical Tip - Undercut Transmission Gears

Most motocross transmissions have straight cut transmission gears that use engagement "dogs" - which are lugs that protrude from the gear and lock into a female matching gear. These dogs are relied on to enguage the two gears when the selector fork pushes the gears together. This gives the drive from transmission to output.

Worn or rounded dogs can cause gears to repel each other when they should be locked together. RM400s quite often round off dogs on the third gear, causing the bike to jump out of gear just after third gear is engaged.


So if your trans is getting old, and the transmission is not holding gear selections, the dogs may be worn. Specialist automotive machine shops can take the transmission gears and shafts, and undercut the dogs on the gears to improve the engagement. This is done by sharpening the original angles (undercuts) on the dogs, and allows the male gear to "hold on" when the dogs are engaged.

The effectiveness of this refurbishment is dependent on the angles cut into the faces of the male dogs, and the condition of the female mating gear. We have achieved huge improvements in shifting reliability by constant inspection and repair of the dogs.
 

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yup, thats correct. for a long time, i didn't know exactly what it meant either, so i asked a pretty notable tuner/racer about it and he indicated it applied mostly to older design transmissions... for all modern one's are already designed and produced (chamfered) that way. or of course, if your modern tranny is "extremely" old and worn. were talking worn as in 25k-50k hard miles.
 

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The other post is correct. I had undercutting performed last year due to engagement problems. Some people only have one side undercut (upshifts only), but I had both sides done because hard deceleration is hard on the tranny too! Makes a huge difference in engagement and I have not missed a shift or had it pop out of gear since the work was done. The only down side is that to perform the work on most bikes the engine has to be torn apart to get to the tranny and remove it. Depending on how much wear you have to the gears (some gears may be beyond machining) your looking at about 1500 - 2000.00 with labor. I was lucky and did not need to replace any of the gears - that would add a fair amount to the cost!

WMRRA #961
98' CBR900RR
 

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Discussion Starter · #5 ·
I'm replacing my tranny soon anyway...I'm going to drop the engine and just bring that in. I'm getting a new "used" tranny in there...slightly used tranny on a dead bike. So, how much extra would it cost, approx. and could the local shop do it, or does it have to be a machine shop?

Thanks guys.../images/icons/smile.gif

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When I had to deal with my tranny problems last year I ended up just getting a new "used" engine. I found a 2001 engine for my bike that was the same price as the parts to fix my worn out second gear. I saved a ton of cash because I was able to swap the engine myself and didn't have to involve the shop at all. From what I was told by some experts on this board fixing a gear can run you $700-$1200 in labour /images/icons/frown.gif

Is a 97 engine compatible with your 95 bike? Have you gotten a quote for fixing your tranny?

http://cgi.ebay.com/ebaymotors/ws/ebayISAPI.dll?ViewItem&item=1813407075&r=0&t=0

Here's a 95 that's had everything fixed up on it...

http://cgi.ebay.com/ebaymotors/ws/ebayISAPI.dll?ViewItem&item=1812997438&r=0&t=0
 

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Discussion Starter · #7 ·
Cost for the new tranny $275...labor with the engine out $275. Labor for a new Honda tranny, about $250 per gear...geez! So, I'm looking at about $650-700 with all the gaskets and fresh oil/filter. Not too bad.
I saw the link for the 95 engine, I just don't have that kind of money for an engine, plus then I still have an extra engine...and then if I get that fixed, I'd have to buy a whole new bike just to use the engine...you get the idea.

Thanks though! /images/icons/smile.gif

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When I had my tranny undercut, my mechanic said that there are only a few people who do it. I can't remember off hand where it was sent, I think east coast? I think just the labor cost on undercutting was 700 - 1000.00. If you want to know any specifics - email me and I will give you name and number.

WMRRA #961
98' CBR900RR
 
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