1998 Yz125, Transmission? Or Clutch problem?

Dermestid

Member
Aug 2, 2010
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Okay so I just bought this Bike about a month ago, the previous owner just rebuilt the top end and the engine runs great! But I was riding it a week ago in first gear it just started to feel like a gear was catching on something and almost threw me off the bike, so I tried it again and it would just lock everything up and the only way to get it in neutral or any other gear would be to start it and pop the clutch real quick but it still wouldn't go, so I rolled it over to the pole barn and drained the transmission oil and took the clutch plates and basket off and now I think I need to get into the gears but before I do I was wondering if any of you guys had any idea what it could be. This is my first bike ever but I have worked on and own a few snowmobile so I know how two strokes work its just that transmissions are new to me, any help is greatly apprieceted, Thanks.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Either the kick starter is improperly installed and binding up the trans, or the shift drum and shift shaft are out of sync. Both installed with the marks lined up and in neutral, usually are a piece of cake. But? Vintage Bob
 

Dermestid

Member
Aug 2, 2010
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So can they get out of sync from riding it? because I rode it for three weeks and it ran fine. Also I take it if the shift shaft is the problem that I will have to split the cases to fix it?
 

whenfoxforks-ruled

Old MX Racer
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If the shaft somehow pushed over towards the right, less than 1/8th", it will disengage from the shift star, and the tranny will bind/not shift. Are the marks aligned?
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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The clutch cover is part of the method of holding the shaft in place. Some may need the clutch removed also, not impossible, just easier. Unless you have seen gear parts in the oil, that shaft is more than likely it. Some models use a piece of plastic between the shifter and the case, to hold the shifter in place?
 

Dermestid

Member
Aug 2, 2010
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Okay so I dug in to it a little more today and found that when I shift it with the clutch off just by turning the bolt inside the shift cam and spinning the rear wheel forward and just watching the stopper lever gets stuck on the cam inbetween gears and to get it in gear I just need to turn the mainshaft (the one the clutch goes on) and it pops right into gear, idk if that tells you anything or not but was just wondering...
 

Dermestid

Member
Aug 2, 2010
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0
Okay so I got it all put back together and tried riding it again, still the same thing, so I thought I would just try taking off in second gear and it works great, and I probably rode it for at least an hour today and every gear but first works fine, so is it okay to use it like this until I can crack the case open in the winter? Or should I not ride it like this? Also what do you think is wrong in there?
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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You have me there, I WOULD IMAGINE LEAVING IT ALONE AND RIDING IT WILL MAKE IT WORSE AND BREAK MORE? Sorry about the cap button. the problem is still likely in the shifting mechanism though. And, why do you seemingly want to take the transmission apart for? Vintage Bob
 

Dermestid

Member
Aug 2, 2010
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I guess I just assumed it is something in the transmission because I didnt see anything wrong when I had the clutch and right side cover off.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Something is not set correctly, or is not holding it in place very long. The shift star, 2 detents with springs or the shaft is not staying in place. Has the cases been split before?
 

Dermestid

Member
Aug 2, 2010
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0
Okay So I rode it around just to get it locked up so I could take it apart when it was locked up. Anyway I get it apart and it IS the kickstart gear catching! But the strange thing is it only does it in first gear! I need to go borrow and impact wrench again to get the clutch basket off before I can really get to it though.
 

pesky nz

Member
Sep 13, 2010
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We are all guessing a bit but the last time I had a similar problem it was a selector fork bent enough to engauge 2 gears at once. I believe the problem will get more expensive the more you ride the bike, but maybe the damage is already done. A total lock up is possible so I wouldn't venture further from the truck than I could walk.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Some kick starter gear and spring set ups are pre-loaded when you install them properly. When not installed properly they will bind up as described. And not break something else is lucky for sure! A shop manual is handy, is an under statement. A parts micro fiche will show sequence, not method.
 

Dermestid

Member
Aug 2, 2010
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Well I just bought a new return spring because I thought mabye the other was just worn and didnt have enough tenision and was just slipping out of the little hole. Well I installed the new spring and now when I bolt the right side cover on and just try to use the kick starter by hand to see if it works it will go down but not return back to the upright position but if I take out the one case bolt right under to the left of the kickstater it will work fine! Its like it is pinching the spring or something and so it cant work right when it is in? And I have had apart like 3 times trying to figure this sucker out! Ugh maybe I should just stick to snowmobiles I guess.
 

baxterj787

Member
Oct 4, 2001
36
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I built a YZ125 motor that did the kickstarter trick you are describing. The fix was pretty simple: Pull the kickstarter shaft all the way out. Take off the torsion spring and the white / tan nylon spring bushing. Clean all mating surfaces between the shaft, bushing and spring. Reassemeble the set and MAKE SURE you have the nylon bushing pushed all the way inboard onto the shaft. These spacers will sometimes get hung up on the inner diameter of the spring, causing the binding you described.

I also had to play with the rachet and return spring to get the two aligned properly and to set enough preload to pull the kickstarter back up. I cannot emphasize enough the need to make sure the bushing is seated all the way.
 

whenfoxforks-ruled

Old MX Racer
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Oct 19, 2006
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Merrillville,Indiana
baxterj787 said:
I also had to play with the rachet and return spring to get the two aligned properly and to set enough preload to pull the kickstarter back up. I cannot emphasize enough the need to make sure the bushing is seated all the way.
There you go.
 
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