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Yz 125 can someone please help

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So I got this yz 125 the other day in pieces the guy told me he took it apart because it was making some "grinding" noise from the tranny I've never heard of that so I took it to my mechanic who's normally never wrong he said they never go out and all the bearings all seem fine. So he told me to just throw it back together and see what happens ? What could it be and should I just throw it back together?

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Hard to say man,if your mechanic says it's good than it may be,all the teeth look good,bearings are smooth,no wear marks on the gears or shafts,shift drum and forks are in good shape .I'd put it back togather in the right side case and rotate everything, make sure it shifts good and rotates.I used to only run enough oil that it came out the check bolt hole and seized a gear to the shaft,so they do break if not maintained correctly. What do ya have to lose,couple gaskets and time.

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Really depends on how much was taken apart before I would "throw it back together". Grinding noises come from many places, gears in transmission being the last to go bad (depending on how many hours are on the bike).

Inspect what is apart, then reassemble the bike and get it running. Maybe then, you will know what it needs. 

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Really depends on how much was taken apart before I would "throw it back together". Grinding noises come from many places, gears in transmission being the last to go bad (depending on how many hours are on the bike).
Inspect what is apart, then reassemble the bike and get it running. Maybe then, you will know what it needs. 

Yea I'm not sure it's completely torn appart cases split bearings out the bearings all seem fine though crank and piston are in great shape as well

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6 minutes ago, Kflight said:


Yea I'm not sure it's completely torn appart cases split bearings out the bearings all seem fine though crank and piston are in great shape as well

Have you not seen it!

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1 minute ago, Kflight said:


Yea I'm not sure it's completely torn appart cases split bearings out the bearings all seem fine though crank and piston are in great shape as well

Question: you want a machine to last you?

A) Complete engine rebuild yourself with a manual as your first tool. 

1) Make sure the crank is well within spec. or get a kit off ebay.

2) If it's within spec. order new main bearings, all seals, and gaskets. (There is a good gasket/seal/kit from RMATV, you need to purchase the main seals separate only)

3) Measure the bore, and inspect the cylinder to insure it has good plating, and get a new piston kit for it. (Make sure you get the upper bearing also)

4) Inspect all transmission bearings for anny excessive play, or binding.

5) Inspect shift forks and gears for abnormal wear.

6) Put a list of parts together, post any questions here, and add photos of anything you think is abnormal.

7) Ship entire engine to me, and I will rebuild it for 375. labor, you buy parts. I'll be in prescott next week until the 18th, then back in so cal for a month before returning. 

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12 minutes ago, P84ONE said:

Question: you want a machine to last you?

A) Complete engine rebuild yourself with a manual as your first tool. 

1) Make sure the crank is well within spec. or get a kit off ebay.

2) If it's within spec. order new main bearings, all seals, and gaskets. (There is a good gasket/seal/kit from RMATV, you need to purchase the main seals separate only)

3) Measure the bore, and inspect the cylinder to insure it has good plating, and get a new piston kit for it. (Make sure you get the upper bearing also)

4) Inspect all transmission bearings for anny excessive play, or binding.

5) Inspect shift forks and gears for abnormal wear.

6) Put a list of parts together, post any questions here, and add photos of anything you think is abnormal.

7) Ship entire engine to me, and I will rebuild it for 375. labor, you buy parts. I'll be in prescott next week until the 18th, then back in so cal for a month before returning. 

If you want proper, go for it! Good deal!

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If you want proper, go for it! Good deal!

I took it to my mechanic and he told me he couldn't see a problem at all with it at all no play in the bearings they don't feel crusty and everything is all in spec he said that the other guy could've put something in wrong and it may have been binding on something should I just clean everything up and feel it all then slap it together ?
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If your confident, go for it! All I was saying is p84one is the  most knowledgeable guy I know and will do a super  job! Worst case scenario is your in the same boat! Do it and you'll have p84one support and help i bet! Or motox will chime in

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Well she runs seems to run really good ! The only thing I notice I may here some time of chatter noise at high rpm in 5th gear but I may just be over thinking it.

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1 hour ago, Kflight said:

Well she runs seems to run really good ! The only thing I notice I may here some time of chatter noise at high rpm in 5th gear but I may just be over thinking it.

Chain slap.... 

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