What causes this kind of damage to a cylinder?

[_MountainRider_]

maybe 20 hours on a complete engine build with a cylinder works 365 kit

[BDubb106]

Looks like material from the rings as I can still see cross hatching in most areas of the damage. Can you feel the marks with your finger nail?

[_MountainRider_]

Looks like material from the rings as I can still see cross hatching in most areas of the damage. Can you feel the marks with your finger nail?

Very slightly yes

[BDubb106]

The only thing that would cause marks like that then is dirt or dust unless the rings are not seated correctly in that area.

[_MountainRider_]

The only thing that would cause marks like that then is dirt or dust unless the rings are not seated correctly in that area.

I don’t really like how to boot seals to the airbox it seems you just slide it in? Should I be adding gasket maker or something?

[BDubb106]

I use grease at the connection and between the filter and housing. Catches the dust and cleans up easily with contact cleaner.

[_MountainRider_]

I use grease at the connection and between the filter and housing. Catches the dust and cleans up easily with contact cleaner.

It’s an 2011 ktm 350sxf and the air boot literally slips into the plastic airbox and it doesn’t seem like it would seal good

[Spud786]

7 hours ago, _MountainRider_ said:

It’s an 2011 ktm 350sxf and the air boot literally slips into the plastic airbox and it doesn’t seem like it would seal good

Air box seal is not a huge issue(cause boots just slips through and there's open holes all around the airbox), but seals the filter fine (its a one piece boot).   The airfilter itself is your weakest link , you can grease the base(it will only help if you have a poor mechanical seal), but its the filter itself is the weakest link, its very porous and takes the strongest of filter oils to hold back dirt.

If you've sucked dirt, the venturi of your throttle body should also show evidence too.  

your piston crown looks too clean, may also be running too lean

[yzrider53]

Not enough ring end-gap when you put it together?

[_MountainRider_]

Air box seal is not a huge issue(cause boots just slips through and there's open holes all around the airbox), but seals the filter fine (its a one piece boot).   The airfilter itself is your weakest link , you can grease the base(it will only help if you have a poor mechanical seal), but its the filter itself is the weakest link, its very porous and takes the strongest of filter oils to hold back dirt.
If you've sucked dirt, the venturi of your throttle body should also show evidence too.  
your piston crown looks too clean, may also be running too lean

I suspected the lean condition aswell and yes the throttle body did have some little scratches from sand and dirt so I’ll be ordering up a new filter. How do I change the fuel mixture on it. I’m new to the efi system

[mbw479]

2 hours ago, _MountainRider_ said:

I suspected the lean condition aswell and yes the throttle body did have some little scratches from sand and dirt so I’ll be ordering up a new filter. How do I change the fuel mixture on it. I’m new to the efi system

Big bore kit will cause it to run lean, unfortunately I know because I had the same problem. For the 365 kit you can send your efi to tokyo mods, they can install a 365 map for you. Thats probably the cheapest option

 

[_MountainRider_]

Big bore kit will cause it to run lean, unfortunately I know because I had the same problem. For the 365 kit you can send your efi to tokyo mods, they can install a 365 map for you. Thats probably the cheapest option
 

I ordered an oem cylinder and wiseco piston do you thing it will run okay?

I ordered an oem cylinder and wiseco piston do you thing it will run okay?

Think*

[mbw479]

Just now, _MountainRider_ said:

I ordered an oem cylinder and wiseco piston do you thing it will run okay?
Think*

Yeah it should be fine if you go back to stock, change the oil and filter and check your valve seats don't have any marks. But yeah you should be fine.

[_MountainRider_]

Yeah it should be fine if you go back to stock, change the oil and filter and check your valve seats don't have any marks. But yeah you should be fine.

Everything else is perfect although I do have a question. My shift shaft has some play in it and I’m not sure if that’s usual or not

[_MountainRider_]

Like my 17 yz is super tight along with my 02 Cr and 13 yz but my brand new Trx250 has about the same amount of play so I’m curious

[Jackrides]

Not enough ring end gap or the piston may have been a little tight. Pull the jug and have the cylinder honed and cleaned. Remove the piston and sand off vertical marks with horizontal motion. Use 320 -400 grit with water. Yes replace the rings and removed circlip. Check the end gap of the new rings and file if necessary. Ask if you need more detail.

[Spud786]

3 hours ago, _MountainRider_ said:

I suspected the lean condition aswell and yes the throttle body did have some little scratches from sand and dirt so I’ll be ordering up a new filter. How do I change the fuel mixture on it. I’m new to the efi system

See if JD jetting makes a tuner for that original model, it would be the easiest way, The preset settings would be off, and can be adjusted, but call him, it can be a week email.

[gberry50]

I had similar damage didn't clock ring end gaps at 120 degrees 

[InRoostWeTrust]

If this is on the exhaust side you could have a failing lower connecting rod. Any metal on the crank screen?

[Jace Perez]

The newer Ktms air box designs have a huge problem with dirt getting pas because of bad cage and air box seal. Take the Air filter off and just install the cage and you will see the gaps that occur on the edges of contact points. Buy a metal cage like the two air power flow kit, it will fix all of your issues with dirt getting past, also what oil are you using on your filters and did you disassemble you air box and boot and re seal the air bike to the air boot with gasket maker?