KTM 125 Rebuild Help

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3/10/2018 4:49 PM

Hey guys, thought today would be good to pop in a new top end. 2016 KTM 125SX. Just hit 80 hours. Rode yesterday, she runs great and sounds great...

Here are some problems I ran into and looking for advice:
Drained the oil and found these chips on the magnet-
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I drained the coolant and it looks almost grey. It was neon transparent green when put in-
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Here’s photo of my plug and piston(22 hours with c12/91)
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3/10/2018 5:17 PM
Edited Date/Time: 3/10/2018 5:19 PM

It's time to do a tear down and find where the pieces came from. My bet is that they are from a trans gear. I would also check the crank bearings.

Paw Paw

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3/10/2018 5:19 PM

Check your waterpump; only place I can think of where oil could leak into the coolant. What color was the oil?

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If you're not mixing gas, you're not haulin ass.

3/10/2018 5:48 PM

The oil looks good, clean. The water pump seal isn’t weaping. Any other ideas on that coolant color?

I pulled the clutch side cover and tried to use a magnet to find more pieces and nothing is coming out.

The crank has no vertical play.

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3/10/2018 6:01 PM

Certainly time to split the cases and do a major once-over sad

I believe the 2016's had some transmission issues, so inspect every gear thoroughly.

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3/10/2018 6:08 PM

Definitely check the trans. Upgrade to 2018 parts and you'll be good to go.

Coolant though, you got me on that one....

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3/10/2018 7:49 PM

MX915 wrote:

Definitely check the trans. Upgrade to 2018 parts and you'll be good to go.

Coolant though, you got me on that one....

Yeah it's time. She's gonna get rebuilt. I got a +1 from another guy about water pump seal letting oil into the coolant.

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3/11/2018 12:22 PM

I think it might be your head gasket leaking and letting burnt premix to your cooling system. The leak is probably caused by loose engine bolts you mentioned earlier. Your engine has been hanging from the cylinder head stays when your lower mounting bolts have been loose and caused excess stress on the cylinder head and made it leak.

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3/11/2018 9:08 PM

JMX82 wrote:

I think it might be your head gasket leaking and letting burnt premix to your cooling system. The leak is probably caused by ...more

That's actually pretty good detective work and could be a good explanation.

Back in the day, on 125s a lot of people used to oval the head stay holes to stop head problems

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3/12/2018 9:32 AM

JMX82 wrote:

I think it might be your head gasket leaking and letting burnt premix to your cooling system. The leak is probably caused by ...more

If the head gasket were leaking it would also pressurize the cooling system. Thus, it would be pushing coolant out of the overflow. Judging by how contaminated that coolant is, I would say it has to be coming from the transmission side.

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Tomac and/or Anderson for 2020.....

3/12/2018 9:49 AM

There is no pressure in transmission oil so I don't think it is possible to get transmission oil mixed in pressurized coolant. If there was such a leak transmission would be filled with coolant.

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3/12/2018 12:24 PM

JMX82 wrote:

There is no pressure in transmission oil so I don't think it is possible to get transmission oil mixed in pressurized coolant. ...more

Looks like we've got us a Mexican stand off

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Tomac and/or Anderson for 2020.....

3/12/2018 12:42 PM

BobPA wrote:

Looks like we've got us a Mexican stand off

Yeah I guess we have smile I have been riding 125 and 150 KTM's since 2005 and have been in similar situation what CarlinoJoeVideo has now.

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3/14/2018 8:18 AM

My guess would be one of the water pump seals is leaking and contaminating your coolant w/ gear oil because if it's like most other bikes it's got an inner and an outer water pump seal so it doesn't necessarily have to seep out the weep hole to leak. As for the metal pieces are they steel or aluminum? If they're steel and stick to a magnet then I would split cases, if it's aluminum then you could try and flush the bottom end with oil a few times because it could just be poor castings. If it were me, I'd split em..

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3/14/2018 8:50 AM

Thanks for keeping this alive. I pulled everything apart and it was the 3rd gear that chipped a tooth. Other than that it all looks good. I’m in the process of ordering a few bearings and all the seals.

The biggest problem is finding the gear, it’s on backorder so I gotta do some digging around...

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3/14/2018 10:51 AM

Try Munn Racing in Texas. If anybody has it, it would be them.

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3/14/2018 9:35 PM

CarlinoJoeVideo wrote:

Thanks for keeping this alive. I pulled everything apart and it was the 3rd gear that chipped a tooth. Other than that it all ...more

You'll be replacing with the updated 18' parts, yeah? Besides the AER switch in 2017, the updated gears were basically the best update the 125s/150s have seen since the new generation in 16'...

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3/14/2018 9:40 PM

CarlinoJoeVideo wrote:

Thanks for keeping this alive. I pulled everything apart and it was the 3rd gear that chipped a tooth. Other than that it all ...more

crc245 wrote:

You'll be replacing with the updated 18' parts, yeah? Besides the AER switch in 2017, the updated gears were basically the ...more

I should be dialed(cross my fingers). The KTM of Modesto In Nor Cal has 4 125 tranny conversation kits. Seems crazy that they have it, but if all goes as planned we will be back in business.

I’m sending my cylinder off to Millennium Tech and going to have the tranny micro polished at Yoshimura once the gears show up.

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3/15/2018 12:12 AM

Nice. On the transmission, have you considered WPC in lieu of the Yosh ISF treatment? I doubt you'd ever have a problem again with it again...

http://www.wpctreatment.com/index.htm

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3/15/2018 7:02 AM

crc245 wrote:

Nice. On the transmission, have you considered WPC in lieu of the Yosh ISF treatment? I doubt you'd ever have a problem again ...more

I was just going the Yosh route because I do some work with them and get a good deal.

I’ve been looking at the CryoHeat but I’d have to ship it and pay full price...
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3/15/2018 7:34 AM

Bummer but be glad you found that now with minimal damage! A few years agoI had 3rd gear shatter on a YZ 250 as I landed a jump at Pala and it smashed up 4 gears inside.

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3/18/2018 12:56 PM

Here’s a photo of the chipped 3rd gear. Got lucky it fell out and didn’t jam everything.
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Got the parts ready for ISF, just waiting in the new gear. I’ll post some after photos when they come back.
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