OzVMX Forum
Clubroom => Tech Talk => Topic started by: John Orchard on May 11, 2017, 04:25:11 pm
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I had an issue with the shifting on my KDX400, occasionally if I shifted up into the next gear in a fast motion, the bike would immediately jump back to the gear I was in. Like, I shift into 4th and it would jump back to 3rd, then back to 4th again.
The feeling of the gear selection action with the engine not running did not feel definite, after internal inspection I find the shift-drum detent roller is quite large and doesn't drop into the gap between pins in the end of the shift drum very far.
I pulled a similar styled mechanism (KX250A5) from my boxes of spares to compare, it runs a much smaller detent roller, giving a more definite click when going into gear, plus more resistance to bouncing out of its detent.
So I got a spare detent roller and ground it down from 18mm diameter to 17mm, this has made it shift with much more definition and hasn't jumped between gears yet.
The pics below show the difference between the 250A5 and the 400/420/450 version for both the shift drum and the detent rollers.
(http://i1093.photobucket.com/albums/i423/JohnnyRacer89/Shift%20drums%20KX_zpso5llpjyj.jpg) (http://s1093.photobucket.com/user/JohnnyRacer89/media/Shift%20drums%20KX_zpso5llpjyj.jpg.html)
The difference between detent/pin spacing is 1mm less on the 250, the pins in the 250 drum are radially fitted closer to the centre of the drum, keeping correct alignment for the shift fork grooves.
(http://i1093.photobucket.com/albums/i423/JohnnyRacer89/Detent%20rollers%20KX_zpsgpxewyio.jpg) (http://s1093.photobucket.com/user/JohnnyRacer89/media/Detent%20rollers%20KX_zpsgpxewyio.jpg.html)
Because the gap between the pins was less on the 250 drum, I figured I'd not grind down to the 14.80mm of the 250 roller, but I may consider grinding another mill after further testing :-)
Not sure if this mod is applicable to other brands/models but something to think about :-)
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Thought about undercutting the dogs and slots in the gears?
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Thought about undercutting the dogs and slots in the gears?
I'd do it if it needs it, I guess they build in a detent mechanism for a reason, just making it work right. Harder to get neutral now though :-)
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the moto villa does that...will look at the gear selection mech when I strip her down
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you have a Moto Villa ? what year and size.
very rare (and way cool) bikes in OZ
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Would the 250 part not fit for testing?
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its a 1980 350 sm as far as I can tell. 2 were bought into the country, 1 was raced (I believe) by alan cunninghayme in NSW then a friend of mine and his mate bought the two bikes and rode them for a few years before the mate met the girl who didn't like bikes and it was relegated to some spot behind the shed for some time before my friend recovered it and stored it with the intention of restoring it with his son. his bike is running rider and I gave it a freshen up a few years ago.
https://youtu.be/Mm_xZ-snfa4
I started to strip mine down and here is a thread so far
http://www.cafehusky.com/threads/not-husky-moto-villa.86569/
apologies Geoff for the hijack...
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Would the 250 part not fit for testing?
250 shift drum is shorter so won't interchange.
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Thought about undercutting the dogs and slots in the gears?
I'd do it if it needs it, I guess they build in a detent mechanism for a reason, just making it work right. Harder to get neutral now though :-)
Only had one shift problem that undercut on the slots/dogs hasn't fixed.
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Would the 250 part not fit for testing?
250 shift drum is shorter so won't interchange.
I was thinking of the little arm with the detent wheel as they look much the same and thought it might allow you to try different size wheels without having to modify them
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Thought about undercutting the dogs and slots in the gears?
I'd do it if it needs it, I guess they build in a detent mechanism for a reason, just making it work right. Harder to get neutral now though :-)
Only had one shift problem that undercut on the slots/dogs hasn't fixed.
Where did you have the gears done?I want to undercut my XR600 gears on the drive face but want someone who knows what they are doing.
I want to try a detent roller for better shifts in this bike too.