KTM SX 250 2015 - 25 Hours since last rebuild.

Owen2020
Profile picture for user Owen2020
Posts
36
Joined
4/19/2020
Location
GB
Owen2020
Edited Date/Time 4/20/2020 12:20pm
Hello guys, new to here. Looking at the photos would you say I need to change my piston? Bike has been absolutely fine no issues, I don’t ride it hard but always like to keep my bike highly maintained. Thanks!


|
2F4A
Profile picture for user 2F4A
Posts
137
Joined
5/17/2019
Location
NL
2F4A 4/19/2020 3:02pm
4/19/2020 3:02pm
Can't tell by these pictures. Looks like it runs clean which is good. Inspect piston, take measurements of cylinder and piston.
1
Owen2020
Profile picture for user Owen2020
Posts
36
Joined
4/19/2020
Location
GB
Owen2020 4/19/2020 3:08pm
4/19/2020 3:08pm
2F4A wrote:
Can't tell by these pictures. Looks like it runs clean which is good. Inspect piston, take measurements of cylinder and piston.
Thanks for the reply! I’ve had a look through the exhaust manifold and the piston does look like it has light scoring? Yeah it’s currently fitted with a 66.34, without measuring the cylinder can you just run again with a 66.34? Or next one up 66.35? Thanks
2F4A
Profile picture for user 2F4A
Posts
137
Joined
5/17/2019
Location
NL
2F4A 4/19/2020 4:17pm
4/19/2020 4:17pm
2F4A wrote:
Can't tell by these pictures. Looks like it runs clean which is good. Inspect piston, take measurements of cylinder and piston.
Owen2020 wrote:
Thanks for the reply! I’ve had a look through the exhaust manifold and the piston does look like it has light scoring? Yeah it’s currently fitted...
Thanks for the reply! I’ve had a look through the exhaust manifold and the piston does look like it has light scoring? Yeah it’s currently fitted with a 66.34, without measuring the cylinder can you just run again with a 66.34? Or next one up 66.35? Thanks
I would pull the cylinder and inspect the whole piston. I would check the cylinder wall, if in good shape take measurements and order the appropriate piston. also make sure the crosshatching is sufficient. You can't just guess which piston you need, If you don't have the tools to measure the cylinder you should bring it to somebody / shop who can.

good luck!
YZed250
Profile picture for user YZed250
Posts
1053
Joined
11/9/2014
Location
Costa Mesa, CA US
YZed250 4/20/2020 11:37am
4/20/2020 11:37am
Any idea of hours on this topend/bike?
If in doubt/unknown, replace and install an hour meter.
For your info, these motors are extremely durable and can run hundreds of hours under 'normal' conditions with quality 2-stroke lube and clean intake.
Measuring piston clearance is not an easy job and is best left to the pros. The tolerances are so small, it can be difficult to do this accurately.

I usually go off compression reading and hours to make this decision to replace piston. For the price/headache, if you're not sure, put a new piston and rings in it.
2

The Shop

See All »
Matt_B_#57
Profile picture for user Matt_B_#57
Posts
10
Joined
4/16/2020
Location
Douglasville, PA US
Matt_B_#57 4/20/2020 12:20pm
4/20/2020 12:20pm
As mentioned above, I think a compression test would be a good idea but since you're already there, pull the cylinder and see what you have going on. How's the piston skirt wear? Cross hatching? You can pull your compression ring off the piston and put it back in the cylinder to check your ring gap as well. Check your crank for up/down play while you're at it (shouldn't have any).
2
Owen2020
Profile picture for user Owen2020
Posts
36
Joined
4/19/2020
Location
GB
Owen2020 4/26/2020 12:21pm
4/26/2020 12:21pm
Matt_B_#57 wrote:
As mentioned above, I think a compression test would be a good idea but since you're already there, pull the cylinder and see what you have...
As mentioned above, I think a compression test would be a good idea but since you're already there, pull the cylinder and see what you have going on. How's the piston skirt wear? Cross hatching? You can pull your compression ring off the piston and put it back in the cylinder to check your ring gap as well. Check your crank for up/down play while you're at it (shouldn't have any).
Thanks guys! Still haven’t taken the cylinder off, at first I just wanted to inspect. Bike had a full engine rebuild at 90 hours. Bike has done 108 hours.
Piston size is 66.34 as I’m this far I might aswel change the piston etc, would it be fine to just replace the piston with the same 66.34?
LuiesMaes
Profile picture for user LuiesMaes
Posts
79
Joined
9/1/2020
Location
Pueblo, CO US
LuiesMaes 9/14/2020 3:13am
9/14/2020 3:13am
Do a light hone and use the stock size piston, you'll be fine. Also inspect the piston, I replaced my piston on my 15 as preventative maintenance and when I got the cylinder off a piece of the piston had broke off the exhaust side. Also check your engine mounts on the frame and make sure the mounting bolt is tight mine went loose and rubbed through both bottom mounts. I had to weld new engine mounts on.

Post a reply to: KTM SX 250 2015 - 25 Hours since last rebuild.