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KX125 ripping plating out?

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Ok so we finally pulled apart the recently purchased 2003 kx125 (more in this thread).

 

Unfortunately the plating is worn on this nearly brand new Athena cylinder as well (see top left exhaust port):

20140804_140612_zpsdda9f191.jpg

20140804_140758_zps5dbe2c87.jpg

20140804_140654_zps8c4ec8ed.jpg

 

The old one was worn at the exact same place, also notice that the power valve rubbed on the piston too:

20140804_140436_zps00317155.jpg

20140804_140508_zps6189eb19.jpg

 

Here's the Athena head and piston:

20140804_141446_zpsc0b9347b.jpg

20140804_141456_zps8ef0bde7.jpg

20140804_141729_zpse025133c.jpg

 

What could cause this twice? We found out the the carb's flat top gasket was ripped and had a gap but I don't know if that's enough to cause this kind of damage.

Edited by Crazyced

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All my bikes get a little scoring from the PV too.

 

My question is:

Did you or someone else attempt to hone that cylinder or is that the way it came from Athena. Those cross hatches are way too deep, rough and too slow of a pattern. 

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All my bikes get a little scoring from the PV too.

 

My question is:

Did you or someone else attempt to hone that cylinder or is that the way it came from Athena. Those cross hatches are way too deep, rough and too slow of a pattern. 

We honed them ourselves. The drill was a little too fast unfortunately but since both plating were trashed we didn't care too much.

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If that's a Nikasil type plating and you honed it with your basic engine cylinder hone with the basic stones or a ball hone less than 400 grit and no liberal lubrication....that's why!

 

The plating requires a special stone. The best way to to clean it is a green scratch pad or a 400 grit ball hone submersed in a solvent. If using a ball hone, only 4-6 swipes is all it takes to deglaze it.

 

Also, you vertical motion was entirely too slow.

 

As for the proper stones, you can get them from Lisle tools retail. Otherwise you must get them from a machine shop supply distributor.

 

Otherwise brake parts cleaner and a green pad does the trick. Re oil liberally with 2T oil.

 

But since you didn't care, then not much to say about it. 

Edited by SAPPERS

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If that's a Nikasil type plating and you honed it with your basic engine cylinder hone with the basic stones or a ball hone less than 400 grit and no liberal lubrication....that's why!

 

The plating requires a special stone. The best way to to clean it is a green scratch pad or a 400 grit ball hone submersed in a solvent. If using a ball hone, only 4-6 swipes is all it takes to deglaze it.

 

Also, you vertical motion was entirely to slow.

 

As for the proper stones, you can get them from Lisle tools retail. Otherwise you must get them from a machine shop supply distributor.

 

Otherwise brake parts cleaner and a green pad does the trick. Re oil liberally with 2T oil.

 

WD-40 was sprayed during the entire process. I do agree that the load was probably too tight. But it was my 1st time using this hone type and like I said, no proper technique would have brought back the holes in the plating so I wasn't too worried.

 

The point of this thread is, this bike ate 2 cylinders already. Why? And how can we make sure it won't eat a third one.

Edited by Crazyced

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What was your ring end gap set at?

And what was the piston to cylinder what clearance ?

 

Other then the bad hone job as Sappers said you don't ever need to hone a Nikasil bore it only needs de-glazing and WD-40 and a scotch bright pad by hand  will do. I don't see all that much on the new jug(pics not the best) that would worry me. Looks like the ring was trying to snag the edge of the port.

I like to chamfer the edges of the ports with a piece of 400-600 grit wet/dry + some WD-40 and use your finger or piece of wood doweling to round the edges, Go easy on it you're not wanting to take much off it just get it smooth and not a sharp angle, your finishing the surface not removing much material at all.  If it feels sharp to your finger it's going to feel the same way to the ring.

Edited by moose_338

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What was your ring end gap set at?

And what was the piston to cylinder what clearance ?

 

Other then the bad hone job as Sappers said you don't ever need to hone a Nikasil bore it only needs de-glazing and WD-40 and a scotch bright pad by hand  will do. I don't see all that much on the new jug(pics not the best) that would worry me. Looks like the ring was trying to snag the edge of the port.

I like to chamfer the edges of the ports with a piece of 400-600 grit wet/dry + some WD-40 and use your finger or piece of wood doweling to round the edges, Go easy on it you're not wanting to take much off it just get it smooth and not a sharp angle, your finishing the surface not removing much material at all.  If it feels sharp to your finger it's going to feel the same way to the ring.

 

The bike was just purchased so I don't know how the specs were when installed last year. I put the ring back in and the gap was significant but that's meaningless since it was worn out already. The plating itself is worn all the way through to the aluminum, I can get a nail underneath it.

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What about lubrication for break in? Was the piston heavily coated and a good amount of 2T oil in the holes to crank bearings and on the big end of rod. This extra oil makes it smoke like hell when first starting but is detrimental in the lubricating a new top or bottom end for break in.

 

Also, just for our info, what mix ratio and using what oil is being used?

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We JUST bough the bike, ran it 15min, realized it ran like crap and pulled it apart. That's ALL we know. That and the fact that the previous owner bought a brand new Athena cylinder kit (stock bore) to replace the worn stock one last year.

 

And for reference, here's the jetting we found in the carb:

400 main

6CHJ11-84 needle 3rd clip

35 pilot

Edited by Crazyced

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Agree with moose 338.

So where to go from here-

See if you can have the cylinder sleeved, get a new ring and piston. When installing check ring gap. Break in as suggested by manufacturer. Then ride the wheels off. Clean and repeat.

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There is some pretty serious wear at the top of the cylinder where the ring tops out.  That may be related to the problem you're having above the exhaust port.  It seems like a lube issue would be most likely assuming its not sucking a bunch of fine dirt.  What kind of premix are you using and at what ratio?  You are mixing oil with the gas right?

 

I'd send the factory cylinder out for a replate if you still have it.  With new plating and proper chamfering on the ports it'll be fine.

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