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Small end movement TM125

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Hi guys new on this forum, will probably be posting a thread about my re-build soon.

 

Currently own a 2002 TM125, have a bit of concern rebuilding it. there seems to be a lot of top end movement because of the piston design.

 

14254542816_cf18dc9caf_z.jpg

 

Please excuse my crude drawing, this is the old piston and rod (new wossner piston is in the engine with head all back together), the red is where the walls of the new piston is, you can clearly see the gudgeon pin and the bearing can shift a little over half way out of the rod, the piston doesn't seem restrict the bearings horizontal movement along the gudgeon pin, just looking for input before I strip it back down tomorrow. the piston is the exact same dimensions otherwise, just curious to see whats stopping the bearing from moving? Cheers.

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Side to side movement (axially along the pin) of the rod's small end is perfectly normal( there should be a spec in your manual).  It's radial play in the rod end that's bad aka:up and down movement....

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That play between the piston and the rod won't hurt a thing. The bearing won't move around because it doesn't actually rotate, there's only a small amount of rocking motion.

 

The only two things you need to worry about with the rod are radial play as Fatty stated, and clearance between the rod and thrust washers. Your manual will have specs for both.

Edited by Chokey

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If that bearing can shift that far out of the piston bad things can happen imo. I understand what Chokey is getting at but it seems strange to me? I'll be interested to hear what you find out.

Edited by poldies4

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I agree with poldies, the pistons wrist pin is bigger compared to my old pistons, almost double the size. I'm aware slight axial movement is fine, there's no radial as it's a brand new bearing.

 

Just seems like the majority of the bearing could slide out while running, better be safe than sorry I'll return it to the shop wednesday.

 

Thanks a lot for your input guys!

Edited by smilie5768

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Please excuse my crude drawing, this is the old piston and rod 

 

 

If this is the old piston, then you already ran it with no trouble, did you not?

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Right here's a few pictures guys.

 

14302401833_6f81313bcb_z.jpg

 

Top end off / New piston.

14282217065_7095a3e7d5_z.jpg

New piston.

14259107496_ccd6e8be7c_z.jpg

New and old piston side by side, see how the bearing/rod would fit more snuggly in the old piston?

 

Looking at it now it doesn't seem too bad, think I was just over thinking things last night, better to be safe than sorry though! Cheers for any more info! And sorry for the double post.

 

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Right here's a few pictures guys.

 

14302401833_6f81313bcb_z.jpg

 

Top end off / New piston.

14282217065_7095a3e7d5_z.jpg

New piston.

14259107496_ccd6e8be7c_z.jpg

New and old piston side by side, see how the bearing/rod would fit more snuggly in the old piston?

 

Looking at it now it doesn't seem too bad, think I was just over thinking things last night, better to be safe than sorry though! Cheers for any more info! And sorry for the double post.

Do not run that motor like that!!!!!!!!!!!

You will destroy the top end bearing.

The pieces will go to the bottom and you will destroy the big end as well.

You might be lucky and destroy the cylinder at the same time.

I would return the piston and get the correct one.

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I took the piston back, as a few people said axial movement is fine, at the shop they told me it would be okay to run?! Very confused now with these mixed responses!

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Huh? Looks a little better than I was expecting. Still not sure I'd be totally comfortable running that. I bet it would be fine, but without a doubt an OEM piston would be the way to go. Is the original pic the OEM piston?

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Huh? Looks a little better than I was expecting. Still not sure I'd be totally comfortable running that. I bet it would be fine, but without a doubt an OEM piston would be the way to go. Is the original pic the OEM piston?

We're on the same page then! Don't feel comfortable but I can't get it replaced! A lot of the aftermarket pistons seem to look like this, I believe the original is an oem piston.

I bought the bike as a non runner but ended up changing the engine as the gearbox was blown.

Have a few days before I start it as I'm now waiting on a throttle cable, checked with various bike company's on Facebook and 3/3 said the piston would be fine. I'll send off a few more emails as I have time.

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I have owned a few TM 125s. Not one of the pistons I ever bought OEM or aftermarket looked like that. If you can't return it have alu spacers made up to make sure the small end bearing stays exactly central to the con rod. I can't guarantee you will not affect the piston or crank balance but a small vibration is better than a total failure. The spacers must be a tight fit so they don't rattle and wear. Clearance must be .5mm to 0.75mm.

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I have owned a few TM 125s. Not one of the pistons I ever bought OEM or aftermarket looked like that. If you can't return it have alu spacers made up to make sure the small end bearing stays exactly central to the con rod. I can't guarantee you will not affect the piston or crank balance but a small vibration is better than a total failure. The spacers must be a tight fit so they don't rattle and wear. Clearance must be .5mm to 0.75mm.

Took it to my local bike shop used a set of verniers and measured out the bearing movement, because the new piston walls are angled the bearing had the same movement, you can sort of see the slope on one of the pictures, it's perfectly fine to use. Cheers again guys!

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Took it to my local bike shop used a set of verniers and measured out the bearing movement, because the new piston walls are angled the bearing had the same movement, you can sort of see the slope on one of the pictures, it's perfectly fine to use. Cheers again guys!

 

OK second look at the photo, I can see it. DUH.

Which make piston is that? 

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OK second look at the photo, I can see it. DUH.

Which make piston is that?

It's a wössner piston, so I expect decent quality :)

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Ok .. I see what you mean .. Interesting

Took it to my local bike shop used a set of verniers and measured out the bearing movement, because the new piston walls are angled the bearing had the same movement, you can sort of see the slope on one of the pictures, it's perfectly fine to use. Cheers again guys!

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