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Service Cylinder when changing piston?

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Hi, 

I am replacing my piston and it’s bearings and rings and the top end gadgets. So a top end I guess 🙂. It’s a ktm 250 2stroke (2016) and it’s has 300 hours. The piston has been changed before but not by me so I don’t know if any work was done to the cylinder. 
Now the bike didn’t blow up and I can’t feel or it see any horizontal scratches so I am good in that department. But do I have to hone or deglaze my cylinder? I hear a lot of people saying not to touch it like less is more and other people say you have to deglaze them or get them honed? What should I do? Or use scotch bright to make more criss cross hatching for the rings to seat better I guess that’s deglazing as well.  Or just keep running it as is since there are no scratches. Don’t know what to do. Any ideas? What do u guys do? 

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Aluminum oxide hone or scotchbrite to clean the glaze off ABOVE the top edge of the exhaust port. An old piston taped or jammed into the bore just at the portline makes a good seal and stop for honing. Over clean it afterwards. 

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1 minute ago, ossagp1 said:

Aluminum oxide hone or scotchbrite to clean the glaze off ABOVE the top edge of the exhaust port. An old piston taped or jammed into the bore just at the portline makes a good seal and stop for honing. Over clean it afterwards. 

What. I don’t understand. What should I do? Keep in mind that I don’t have scratches on the cylinder, the bike didn’t seize

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Your call. Your last question was "what do you guys do?" 

I just told you. If it sounds too complicated, maybe just see what a manual suggests for your model. If that seems too far for you to go, then a shop might be for you.

I did read your post and fully understand that you said it did not seize.

Good luck 

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2 hours ago, carbosam said:

I would just clean the cylinder with wd-40 and paper towel. Then just slap a new piston. Its not rocket science.

Thanks a lot. I’ll spray wd40 into the cylinder and clean it up with a paper towel

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I would deglaze your cylinder, either with a light hone, or with scotchbrite. These are easy things to do and will not remove any cylinder material. You do want a decent unglazed surface on the cylinder for the new ring to seat against. If the new ring starts its life running against a glazed surface it is unlikely to seal as well as it could. Once again just one mans opinion, but someone who has rebuilt a LOT of two stoke engines over his lifetime

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Just now, siswati said:

I would deglaze your cylinder, either with a light hone, or with scotchbrite. These are easy things to do and will not remove any cylinder material. You do want a decent unglazed surface on the cylinder for the new ring to seat against. If the new ring starts its life running against a glazed surface it is unlikely to seal as well as it could. Once again just one mans opinion, but someone who has rebuilt a LOT of two stoke engines over his lifetime

Thanks a lot, this sounds very reasonable. I don’t have a hono so I guess scotch bright it is. What scotch bright and how do I go about it so I don’t do too much or do it wrong what do I have to look out for? Sorry for the noob question but I have never done that before 😅.  Thanks!

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22 minutes ago, EnduroMX FOREVER said:

Thanks a lot, this sounds very reasonable. I don’t have a hono so I guess scotch bright it is. What scotch bright and how do I go about it so I don’t do too much or do it wrong what do I have to look out for? Sorry for the noob question but I have never done that before 😅.  Thanks!

The cylinder wall has a nikasel coating, which is very durable but also very thin. If your cylinder is clean, with no scratches and no built up areas of glaze or deposits, you might be able to get away with just thorough cleaning, and reassembly, but if there are slight scratches or build up of glaze on the wall covering any sign of the original cross hatching, then very light use of scotchbrite pad will help to remove the glaze and scratches. Remember LESS is MORE! Do not overdo this. Afterwards, make sure you clean thoroughly, first with contact cleaner, and then with NEW microfiber rags and WD40 until it is completely clean before reassembly 

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37 minutes ago, EnduroMX FOREVER said:

Thanks a lot, this sounds very reasonable. I don’t have a hono so I guess scotch bright it is. What scotch bright and how do I go about it so I don’t do too much or do it wrong what do I have to look out for? Sorry for the noob question but I have never done that before 😅.  Thanks!

I use green Scotchbrite pads. I use them with the cyl sitting in hot, soapy water (prefer Dawn dishwash detergent). I just work them more or less in a cross hatch pattern in both directions, from the top and bottom. Only looking to break any glaze loose. Then I rinse it off real good with water and blow it all dry with compressed air.

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3 hours ago, siswati said:

The cylinder wall has a nikasel coating, which is very durable but also very thin. If your cylinder is clean, with no scratches and no built up areas of glaze or deposits, you might be able to get away with just thorough cleaning, and reassembly, but if there are slight scratches or build up of glaze on the wall covering any sign of the original cross hatching, then very light use of scotchbrite pad will help to remove the glaze and scratches. Remember LESS is MORE! Do not overdo this. Afterwards, make sure you clean thoroughly, first with contact cleaner, and then with NEW microfiber rags and WD40 until it is completely clean before reassembly 

 

2 hours ago, jeb said:

I use green Scotchbrite pads. I use them with the cyl sitting in hot, soapy water (prefer Dawn dishwash detergent). I just work them more or less in a cross hatch pattern in both directions, from the top and bottom. Only looking to break any glaze loose. Then I rinse it off real good with water and blow it all dry with compressed air.

Thanks a lot for the responses. I am not sure if I should get it wet since I have not disassembled my power valve. I have attached some pictures of the cylinder maybe this helps to see what has to be done. I would like to add that the cylinder feels very smooth inside and there are no scratches that you can feel at all

95B6E1AE-605E-4D81-9C52-948463BC22DA.jpeg

B3E28260-81D2-4C77-AE47-D9C8CD56DABF.jpeg

627D7714-FFEB-40DD-8912-4753ED8DBBD3.jpeg

19CB5249-CA88-4BE0-A378-76CE20864669.jpeg

DCBF3D5B-E800-4898-B81A-EFEBDDCB322A.jpeg

4352E4A6-E8E6-49A6-97B6-A9F771196635.jpeg

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Hi,

I am changing the piston on my 2016 ktm 250 2stroke. The bike has 300 hours and the piston was changed before however I don’t know if anything was done to the cylinder. I have attached pictures of the cylinder. My question is what I have to do to it? Leave it? Deglaze it (how?)? Hone(how?)? I would like to add that the cylinder feels very smooth and you can’t feel any scratches. Thanks 

68A9F04A-21D6-40E5-9EB2-6DD467F44C0C.jpeg

9EE5F530-095C-4F2D-A6DA-6F53DB67C38C.jpeg

23F26B9E-44B1-4A9B-A6C8-CF3BAC03BDBE.jpeg

5AB63F1E-B6DF-4F95-9872-3E551C046472.jpeg

D1FC6D63-25A8-4E5B-AEA7-E6B062BED0FF.jpeg

0EDBDAA6-9B0E-4860-894E-AECBE57EE8B6.jpeg

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You're over thinking it. Just clean, dry it and spay wd40 and that will take care of the water. Make sure with the scotch brite u go in a circular pattern around the cylender while going up and down to follow the crosshatch pattern. 

 

Wipe out the wd40 after and spray with carb cleaner after u are all done  cuz the wd40 eats oil

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1 minute ago, Ltlhondarida125 said:

You're over thinking it. Just clean, dry it and spay wd40 and that will take care of the water. Make sure with the scotch brite u go in a circular pattern around the cylender while going up and down to follow the crosshatch pattern. 

 

Wipe out the wd40 after and spray with carb cleaner after u are all done  cuz the wd40 eats oil

Ok so I will scotch bright in a circular motion then put wd40 to clean and then clean that with carb cleaner? Sorry for being stupid 😬😅

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You should clean the PV while you're in there. I've never done a topend w/o also doing the PV. I bet there's a bunch of carbon on the bottom of the flapper.

But getting the PV wet is not going to hurt anything. Just dry it off as best you can with compressed air.

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Just now, jeb said:

You should clean the PV while you're in there. I've never done a topend w/o also doing the PV. I bet there's a bunch of carbon on the bottom of the flapper.

But getting the PV wet is not going to hurt anything. Just dry it off as best you can with compressed air.

I can’t rebuild the pv because I don’t have the tool to set it so I though I’d leave it because it works fine

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13 minutes ago, EnduroMX FOREVER said:

Ok so I will scotch bright in a circular motion then put wd40 to clean and then clean that with carb cleaner? Sorry for being stupid 😬😅

Circular and up and down. Follow the crosshatch. Then use soapy water, rinse, dry, wd40 wipe off, carb cleaner. 

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That cylinder does show some wear.  Replating will be required soon, possibly with the next top end.

As far as cylinder preparation, I do absolutely nothing.  No scotch brite, absolutely no honing.  If you use a castor based premix I suppose you would want to clean the varnish off of the cylinder wall.  I don't, I just put it back together with fresh parts and run it.  There is nothing you can do to a worn bore short of replating that will improve it's condition in any way.  The less you do the better.

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6 minutes ago, EnduroMX FOREVER said:

I can’t rebuild the pv because I don’t have the tool to set it so I though I’d leave it because it works fine

You don't have to set anything if you don't loosen the adjuster bolt on the shifter side. But you will need some new orings and some sealant.

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Hot hot hot hot hot soapy water. Clean it. Then clean it again. Gotta get all the contaminants and carbon out before you reassemble. 

Once you've got it clean as can be - a scotch brite (the green one), and ATF. Follow the crosshatch with the pad. Good ol' elbow grease works the best. 

Rinse with hot hot hot soapy water. You don't want any fibers getting in to your new ring and piston job. Once you think it's clean, rinse it again.

See what other people think, but that's what I've done in the past! 

Edited by J-Pat

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