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Hi, here goes my first thread as well as my first post on here! Name is Matt. Been a reader for quite a while and have learned a ton from these forums.

 Anyways, i'm 24, and have liked motocross bikes since I was 6, my uncle was an mx rider here in the northeastern ohio and shoot mainly all over ohio (greg urban, 803, rode hondas say something if you know him lol) but ever since I was a young gun i was in love with bikes but never had one of my own, just a 90cc dinli 2 stroke quad my gramps got me in mansfield on the farm when i was about 12, lol! That thing and that farm are long gone, they didnt pay taxes and ended up gettin screwed for it, lost everything, all the toys, boats, quads, golf carts, had to sell it and move to somewhere much more affordable. My family isnt the smartest but theyre pretty cool. 

 ANYWAYS. I am 24 now and just recently had the chance to grab a bike to work on, ive spent my live doing other things like skateboarding, going to school, working full time, moving in with a girl etc. So I just found a 1990 yz125 on offerup for 200 bucks. I was dead broke at the time paying court costs n whatnot but I pulled together 100 bucks and made a deal with the guy to pay him 50 a week for the rest, since I had practically nothing and had literally just started a new job. So he was down and we met up and I got the bike.

(QUESTION: Can i post any sort of htm image codes so I can post these pics throughought the thread? Cause if so im gonna edit the heck out of this thread and make it way more organized.)

 I brought her home. The reason it was so cheap is because the crankshaft was seized. The piston is in good condition, the cyclinder as well, no scratching or chipping, leading me to believe the issue could be in the main crank bearing. The guy I bought it off of has been in close contact, i see him once a week or so and we talk bikes and about the parts i'll need and whatnot. So my next step is to grab my next paycheck, finish paying him and bring the engine back over, split it open with him, and see if its just the bearing or whole crank assembly. Either way, pretty stoked about the deal, and the piston and cylinder being in such great shape.

 Im gonna attatch the pics of the bike and the engine! The cylinder head is taken off as well as the pipe and kickstart but here she is. 

 Any input is appreciated! This is my FIRST bike and if anyone has any pointers about working on 2 strokes this old, I would REALLY appreciate it!

Thanks yall

Also if anyone notices anything that I am not saying, please do say something! Or if there is anything super critical to check. I plan om getting a manual when I find one and literally checking every single thing that can be loosened and tightened on it.

Matt

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Edited by firebreathinCR
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5 minutes ago, firebreathinCR said:

Hi, here goes my first thread as well as my first post on here! Name is Matt. Been a reader for quite a while and have learned a ton from these forums.

 Anyways, i'm 24, and have liked motocross bikes since I was 6, my uncle was an mx rider here in the northeastern ohio and shoot mainly all over ohio (greg urban, 803, rode hondas say something if you know him lol) but ever since I was a young gun i was in love with bikes but never had one of my own, just a 90cc dinli 2 stroke quad my gramps got me in mansfield on the farm when i was about 12, lol! That thing and that farm are long gone, they didnt pay taxes and ended up gettin screwed for it, lost everything, all the toys, boats, quads, golf carts, had to sell it and move to somewhere much more affordable. My family isnt the smartest but theyre pretty cool. 

 ANYWAYS. I am 24 now and just recently had the chance to grab a bike to work on, ive spent my live doing other things like skateboarding, going to school, working full time, moving in with a girl etc. So I just found a 1990 yz125 on offerup for 200 bucks. I was dead broke at the time paying court costs n whatnot but I pulled together 100 bucks and made a deal with the guy to pay him 50 a week for the rest, since I had practically nothing and had literally just started a new job. So he was down and we met up and I got the bike.

(QUESTION: Can i post any sort of htm image codes so I can post these pics throughought the thread? Cause if so im gonna edit the heck out of this thread and make it way more organized.)

 I brought her home. The reason it was so cheap is because the crankshaft was seized. The piston is in good condition, the cyclinder as well, no scratching or chipping, leading me to believe the issue could be in the main crank bearing. The guy I bought it off of has been in close contact, i see him once a week or so and we talk bikes and about the parts i'll need and whatnot. So my next step is to grab my next paycheck, finish paying him and bring the engine back over, split it open with him, and see if its just the bearing or whole crank assembly. Either way, pretty stoked about the deal, and the piston and cylinder being in such great shape.

 Im gonna attatch the pics of the bike and the engine! The cylinder head is taken off as well as the pipe and kickstart but here she is. 

 Any input is appreciated! This is my FIRST bike and if anyone has any pointers about working on 2 strokes this old, I would REALLY appreciate it!

Thanks guys!!!!! 

Matt

20171129_161755.jpg

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20171205_182246.jpg

20171205_182142.jpg

20171205_182205.jpg

20171205_182150.jpg

20171205_182258.jpg

20171205_182313.jpg

One heck of a deal right there man looks pretty good and got potential.  Best thing is to take bottom end out split it down id suggest getting that crank rebuilt with new rod kit and crank bearings and seals. Good thong is you day cylinder is ok so teats good. Be more than happy to help you as needed and other guys will help as well.  Someone loved it up already looks great for 200

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Thanks a lot man!! Gets me even more stoked to hear that. I don't have the tool to split the case so i am a bit nervous to do that and am not sure if there are other ways, but the guy I got it from says hes got the tool and to bring it over once i get a whole new crankshaft assembly which I plan on doing and we will put it together. Only about 100 bucks for the whole thing.

 Also a side note i saw the cylinder in person and it truly is perfect inside! He had a cr125 for sale as well, 2001 i believe and he showed me the cylinder of that, or maybe it was a newer yz125, and noted that mine being older (1990) actually is a few CC's larger. Thought that was pretty cool. 

 I'm so stoked to get this thing running.

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Got sort of a question for now, feels like it may have a hard time shifting all the way down to neutral, the shifter peg works fine, i can shift up and down, definitely doesnt seem to go a full 6 clicks however, regardless, at times i will shift all the way down and the wheel will still not roll. So i roll it back and forth, shift up and down a few times and it will usually get rolling after some messing with. Not sure if this is normal for a bike with an engine that isnt all the way put together, and keep in mind my crank is currently seized so im not sure if this is normal or what it means. Main question I'm looking for help with out of that paragraph^^^:

- Is it normal for a not-all the-way-assembled-engine to not shift normally, or through all the gears when being rolled? Not all-the-way as in the cylinder & exhaust are taken off as seen in pics OR is this an issue i shouldn't be having? (Note: i have not yet had the bike raised high enough to have the rear tire spinning so if that has anything to do with it, please let me know lol. Remember to have mercy, i am here to learn.)

 

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11 hours ago, firebreathinCR said:

Got sort of a question for now, feels like it may have a hard time shifting all the way down to neutral, the shifter peg works fine, i can shift up and down, definitely doesnt seem to go a full 6 clicks however, regardless, at times i will shift all the way down and the wheel will still not roll. So i roll it back and forth, shift up and down a few times and it will usually get rolling after some messing with. Not sure if this is normal for a bike with an engine that isnt all the way put together, and keep in mind my crank is currently seized so im not sure if this is normal or what it means. Main question I'm looking for help with out of that paragraph^^^:

- Is it normal for a not-all the-way-assembled-engine to not shift normally, or through all the gears when being rolled? Not all-the-way as in the cylinder & exhaust are taken off as seen in pics OR is this an issue i shouldn't be having? (Note: i have not yet had the bike raised high enough to have the rear tire spinning so if that has anything to do with it, please let me know lol. Remember to have mercy, i am here to learn.)

 

Shifting will always seem notchy and inconsistent when the bike is sitting. With the engine running it will get easier.

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Yes, don't worry about the bike not shifting nice when the engine isn't running.

When you get it running again, and its not shifting right....then you do have a problem but I highly doubt that will happen so your good.

Make sure your careful as you take it apart to keep all the parts organized and safe from dirt etc.  But the parts into boxes, label, take pictures because its EASY to forget where things go.

Sorry to tell you this but you probably won't have it running for quite a while...Especially if money is a problem.  So keep good track of all the parts you take off the engine.

Ok...So when you split the two cases with the case splitter your friend has to get the crankshaft out; make sure you split it evenly... make sure it's coming apart evenly.   idk how easy those yamaha's cases come apart if its anything like my 01 cr125 you'l have trouble i;m sure.  So be patient, use a rubber mallet to tap it apart, and TAKE YOUR TIME.

Let us know your progress and if you have ANY more questions please let us know.   Better to ask than to try and do it yourself and break something that will cost you hundreds of $$$. 

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12 hours ago, firebreathinCR said:

Thanks a lot man!! Gets me even more stoked to hear that. I don't have the tool to split the case so i am a bit nervous to do that and am not sure if there are other ways, but the guy I got it from says hes got the tool and to bring it over once i get a whole new crankshaft assembly which I plan on doing and we will put it together. Only about 100 bucks for the whole thing.

 Also a side note i saw the cylinder in person and it truly is perfect inside! He had a cr125 for sale as well, 2001 i believe and he showed me the cylinder of that, or maybe it was a newer yz125, and noted that mine being older (1990) actually is a few CC's larger. Thought that was pretty cool. 

 I'm so stoked to get this thing running.

You can split the case without the tool. Break it all down, Flywheel gone, magnito, water pump, reed cage, clutch, etc. The use a plastic or rubber mallet and hit the crankshaft on the clutch side. You should see it slowly start to separate. DONT pry it anywhere, just use your fingers and hit the crankshaft. If you HAVE TOO, wrap a tool in a towel for leverage proposes. I have broken down many motors like this. The only too that I feel I MUST have is a clutch tool to get the nut off of the crankshaft. Also, piston looks OK, but I would put another in it before you button everything up, as well as all the gaskets and bearings. If you are going to have it stripped down naked, you misewell considering the age and you not fully knowing the history of the bike. I would absolutely put all new internals in. Its only maybe 200 bucks total. Prevents you from tearing it back down in two months after rebuild.... 

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6 hours ago, TeamGreenPilot said:

That’s a 1987 YZ, not a 1990

IMG_3067.jpg
1990 Model

IMG_3068.jpg
1987

Yep, I was about to say the same thing ---  would really help to know the right model year before ordering up a bunch of parts.   I ran Yamahas between '88 and mid '91 then switched to Suzi ---  the '88 125 looked just like this one, but had a disc brake in back and some significant motor differences from the '87.     In '89 the bodywork changed completely and the bikes looked like the '90 posted above 

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Oh and I almost forgot to mention...

I noticed in a couple of the pictures you posted that the rear tire shock mud guard is snapped off.

When you order all your parts MAKE SURE you get a new one.  If not, after a little while of riding, dirt will undoubtedly get thrown on to that shock cylinder.  It will score it and your rear shock will seize up....and.....yeah.  

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I'd wait to order all of your parts for it before you split the cases. That way you can put the new crank assembly in right away after you get everything cleaned up and gone through. I split my cases without the special tools, it isn't hard. YouTube and an owners manual are your best friends. Use them.

 

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16 hours ago, TeamGreenPilot said:

That’s a 1987 YZ, not a 1990

IMG_3067.jpg
1990 Model

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1987

Well I thank you for that, this is something I absolutely needed to know, the guy must have had no idea himself, selling it as a 1990. I always noticed when I googled 1990 yz125 the forks looked different than mine.

5 hours ago, Slicing-Air said:

Okay..Have you read the above comments Matt?

Don't go order a bunch of parts until you know what year your bike is! 

These guys know what there talking about.... If you now think its a 87 do some more research and make sure. 

Yes, I have read everything and you guys have just saved me a lot of time and money. I will be keeping you all posted as I go so you will know the parts I'm ordering and when! 

 Also, I may end up opening it myself, but i'm not in a huge hurry so i'm trying to have someone experienced here with me. But I will be posting all about it and asking a million questions if I decide to open it and check it out myself.

 Thank you all so much, all of the advice and kindness is overhwhelming, this is a great community!!

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12 hours ago, emperialwizzard said:

You can split the case without the tool. Break it all down, Flywheel gone, magnito, water pump, reed cage, clutch, etc. The use a plastic or rubber mallet and hit the crankshaft on the clutch side. You should see it slowly start to separate. DONT pry it anywhere, just use your fingers and hit the crankshaft. If you HAVE TOO, wrap a tool in a towel for leverage proposes. I have broken down many motors like this. The only too that I feel I MUST have is a clutch tool to get the nut off of the crankshaft. Also, piston looks OK, but I would put another in it before you button everything up, as well as all the gaskets and bearings. If you are going to have it stripped down naked, you misewell considering the age and you not fully knowing the history of the bike. I would absolutely put all new internals in. Its only maybe 200 bucks total. Prevents you from tearing it back down in two months after rebuild.... 

I would love to have all new internals before trying to fire it up so that is a goal....might regret not having it pristine inside being 30 years old 

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11 hours ago, firebreathinCR said:

I would love to have all new internals before trying to fire it up so that is a goal....might regret not having it pristine inside being 30 years old 

Yes, especially if the bike has sat at all over the years. When things stop moving for awhile, and then get put into motion again it can be painful for you and the bike.. haha so new internals would be great! Its kinda like asking your grandma to run a marathon after she is wheelchair bound. She isnt moving without new hips! lol ok so maybe that was a messed up analogy, but you get the point 🙂  Where are you located? Ill come help if your in Ga, east Alabama, or southern Tenn.. hahaha

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