1989 Yamaha YZ125 info.....

Hudweiser9
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Hudweiser9
Edited Date/Time 11/1/2021 12:07pm
I just recently picked up an '89 YZ125 project bike. Not that I needed another one, but the price was right (free, although I did give the guy $50 for it anyway). I'm looking for any information about it, good or bad. I have never owned a Yamaha motocross bike, always Suzuki and Honda's so any leads on resources for parts, plastics, upgrades with later model bike, etc... would be welcome. I posted it on the local VMX club page also (SSVMX), got a lot of great info there. Never can have too much info, IMHO.



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Dekon
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Dekon 3/11/2018 7:00am
3/11/2018 7:00am
I just rebuilt one, wished I started off with something that looks like yours. I haven't ridden it yet. Plastics, I got from UFO. Fork springs, I haven't found any due to 89-90 having 41mm forks. Supposedly the 91 forks(43mm and you can get springs for these) and triple clamps bolt right on and you can use your wheel, axle, and caliper. An upgrade would be to install a 91 or 92 outer clutch cover. The 89-90 are magnesium and flex making the clutch drag. 91-92 are aluminum and are stiffer. Speed and Sport Yamaha was a great help in locating those hard to find missing parts. Their website might not have a part listed, contact them, they might have it or they will try and find it. Like any 29Y.O. bike, some parts are NLA. It just takes a lot of searching to find what you need.
chuckie108
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chuckie108 3/11/2018 9:25am
3/11/2018 9:25am Edited Date/Time 3/11/2018 9:28am
Currently building the same bike! I concurre with everything Dekon has said. My bike is a roach so I have lots of research in on parts, so fire away if you have specific questions. One problem area on these bikes is the rear caliper. The caliper pins get badly corroded and are NLA through Yamaha. I’ve figured out late model KX85 is the same caliper and carrier and all the parts are available there.
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Dekon
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Dekon 3/11/2018 1:57pm
3/11/2018 1:57pm
chuckie108 wrote:
Currently building the same bike! I concurre with everything Dekon has said. My bike is a roach so I have lots of research in on parts...
Currently building the same bike! I concurre with everything Dekon has said. My bike is a roach so I have lots of research in on parts, so fire away if you have specific questions. One problem area on these bikes is the rear caliper. The caliper pins get badly corroded and are NLA through Yamaha. I’ve figured out late model KX85 is the same caliper and carrier and all the parts are available there.
Not to hijack, but Chuckie, what years KX85 caliper works? The only place I found that had a caliper rebuild kit was from the U.K. Cost almost as much to ship it as the kit was.

Another area with a limited parts availability is the clutch basket and inner hub. Was I knew if another year was able to swap in its place.

Also I've been looking and can not find the rear brake pedal spring, part 90506-14410-00. Right now I using a later model one, but it lifts the pedal a little to high for my liking. If you come across something that has a closer length to the original, please let me know.
chuckie108
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chuckie108 3/12/2018 1:56pm
3/12/2018 1:56pm
Dekon wrote:
Not to hijack, but Chuckie, what years KX85 caliper works? The only place I found that had a caliper rebuild kit was from the U.K. Cost...
Not to hijack, but Chuckie, what years KX85 caliper works? The only place I found that had a caliper rebuild kit was from the U.K. Cost almost as much to ship it as the kit was.

Another area with a limited parts availability is the clutch basket and inner hub. Was I knew if another year was able to swap in its place.

Also I've been looking and can not find the rear brake pedal spring, part 90506-14410-00. Right now I using a later model one, but it lifts the pedal a little to high for my liking. If you come across something that has a closer length to the original, please let me know.
2010 to current KX85, you can buy the carrier assembly, or you can buy the seals, pins, etc. seperately.

The clutch I haven't totally solved- yet. There are zero 89-90 hubs out there that I have seen. 89-90 is a six spring, 7 plate clutch. 91-92 is 5 Spring, 7 plate, and 93-05 is 5 spring 8 plate. If you want to run a 93 and newer combo, You need a 93 RT side center case. Im still figuring how to solve this. I know the inner hubs will work on our bikes(as far as inner and outer splines), but we will need a 5 spring basket to go with it, and that part I havent solved yet. I'll keep you posted. I'm sure there is a way to make newer components work, but I just havent gotten there yet. I'll keep you posted.

Brake pedal spring- I have no idea. There's gotte be a newer version out there that will work. Or maybe even look at Mcmaster-car for something that is workable.

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mark_swart
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mark_swart 3/12/2018 4:25pm
3/12/2018 4:25pm
I raced that bike from 89-90, and ended up with a 90 model for about a year a while back.

The bike is surprisingly good for its age. 88-89 was really when the shape of modern bikes came into being with low boy layouts, USD forks and disc brakes. 89 had a punchy mid range motor and a comfortable layout. I raced and practiced on that bike, rode multiple times a week, and with regular maintenance (air filter, trans oil, top ends) the only thing that ever failed was the CDI box. I never had any issues with the clutch, and was a 125 B rider by the time I sold it.

I really hope to find another 89 at some point! Enjoy!!!

Yamaha also likes to share parts from model to model, so you will probably find a lot of things that cross over anywhere from 86 or 87 to the early 90s in that engine.
Hudweiser9
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Hudweiser9 3/19/2018 9:25pm
3/19/2018 9:25pm
This is the type of info I was looking for, thanks everyone! Please post any additional information on this bike you run across during your builds. Thanks again!
chuckie108
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chuckie108 4/1/2018 11:00pm
4/1/2018 11:00pm
Just to provide more specifics to the info already in this thread. I received the caliper carrier and seals this week. Here is a pic of the old parts next to the new parts along with the part number for each. That way if any '89 YZ owners stumble across this thread trying to find a solution to the sticky caliper which I have seen a few of on '89 YZ's.





Gene Frenkle 4/2/2018 9:48pm
4/2/2018 9:48pm
chuckie108 wrote:
Just to provide more specifics to the info already in this thread. I received the caliper carrier and seals this week. Here is a pic of...
Just to provide more specifics to the info already in this thread. I received the caliper carrier and seals this week. Here is a pic of the old parts next to the new parts along with the part number for each. That way if any '89 YZ owners stumble across this thread trying to find a solution to the sticky caliper which I have seen a few of on '89 YZ's.





Thanks Chuckie108 that's is super helpful.
Much appreciated.
MadMatt579 4/12/2018 4:02am
4/12/2018 4:02am
nice detective work there Chuck. i think that caliper mount might fit the 250 as well.
Jackbiggs22 7/9/2019 1:22pm
7/9/2019 1:22pm
Hey i have a 1990 yz125 i got for a $170 bucks but its a project bike it needs a new inner clutch hub and i cant find any at all do anyone no where i probably find one at or what other year inner clutch hub i could get to fix my problem please
Richard Tease II 7/9/2019 8:44pm
7/9/2019 8:44pm
I ran back in 89 a 1988 model fmf pipe and shorty style muffler. The 89 fmf wasn't good. The 88 model pipe made a huge difference and the shape was more like Bradshaws. If i remember the guy who did the motor had to weld some brackets different for it to fit though.
dcfitz
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dcfitz 7/10/2019 2:30pm
7/10/2019 2:30pm
DC Plastics has tons of vintage MX stuff.
Tuzzo123
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Tuzzo123 7/16/2019 10:05am
7/16/2019 10:05am

Just finished this 1990, the clutch was hell! I ordered a 91 cover for the clutch that is aluminum and used OEM plates and springs only. The Arm is key to have in the adjustment window on the cases. Make sure that it stays within the adjustment window ! I cant stress this enough!
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JMdirtrider 11/1/2021 12:07pm
11/1/2021 12:07pm
Hey Chuckie108 did you ever find a way around the NLA inner clutch hub on the 89-90? I just picked up a similar project and the hub has 2 broken studs/post's. Ive found some people are able to repair by welding or machining a new post and threading it in, but fitting a newer OEM hub would be nice
mace_bike
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mace_bike 3/4/2023 4:37pm
3/4/2023 4:37pm
Tuzzo123 wrote:
[img]https://p.vitalmx.com/photos/forums/2019/07/16/360564/s1200_4740.jpg[/img] Just finished this 1990, the clutch was hell! I ordered a 91 cover for the clutch that is aluminum and used OEM plates and springs...

Just finished this 1990, the clutch was hell! I ordered a 91 cover for the clutch that is aluminum and used OEM plates and springs only. The Arm is key to have in the adjustment window on the cases. Make sure that it stays within the adjustment window ! I cant stress this enough!

Do you have any info on the fmf pipe that’s on your bike? I’ve done a lot of researching and can’t find anything on that particular pipe, thinking it might’ve been a factory option?

mace_bike
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mace_bike 3/16/2023 10:44pm
3/16/2023 10:44pm
mace_bike wrote:
Do you have any info on the fmf pipe that’s on your bike? I’ve done a lot of researching and can’t find anything on that particular...

Do you have any info on the fmf pipe that’s on your bike? I’ve done a lot of researching and can’t find anything on that particular pipe, thinking it might’ve been a factory option?

And also wondering about the inner clutch hub spring? Part number (3JD-16383-00-00) I can’t find one anywhere, do I NEED this spring for my clutch system to work correctly?

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