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YZ250 2013 Piston Options
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Only $10 for all 2026 SX, MX, and SMX series.
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Anyone heard differently on this?
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Changing the piston at 20 hours on a 250 is pretty uncommon unless you are very fast and wringing it's neck. Good on you for doing good maintenance with an hour meter though...
If you run the cast pistons in a YZ250 for too long, the skirt will start cracking on each side of the intake skirt diagonally inward and up. Compression testing is not a good indicator of piston condition at all.
Personally I like to run the Wiseco forged, but that's not for everyone. They will not crack, but if you don't warm them up properly you can get some seize marks on the skirts. On the up-side, in a catastrophic engine failure there is a lower chance of piston fragments going through the engine. It can mean the difference between a simple melt-down and broken castings.
I know Vertex makes a good cast piston.
If you run a stock piston, Don't get too hung up on the bore tolerence codes. If you want the best fit you need to mic the cylinder bore properly and order the letter that fits. After a number of hours (depends on how you ride, what oil, jetting, other factors / etc) your bore isn't A or B or C or D any more. Often times there is enough initial wear to run a D piston in your used cylinder and still be in spec on piston clearance.
All of the good quality name-brand pistons will survive well beyond 20 hours without any trouble. I would suggest staying away from the Chinese and Tiawanese stuff like Namura. The casting quality is questionable and the $10 you saved might cost you a $400 cylinder or $500 crank-case.
Depending on how hard you ride, consider buying a wrist-pin & bearing for at least every-other piston. It will extend the life of your connecting rod.
I bought my '15 yz250 in the end of December. I hit 20hrs last weekend. I wring it out alot..
Just rings or piston kit?
Measure your cylinder & get the correct size. Also measure ring gap when installing, although never had to change it on any yam top end.
In my opinion, the pistons wear out long before the rings in these bikes; hence my comment above about compression being a bad indicator of top-end condition. The piston is garbage long before you lose compression.
Gaskets are cheap. Buy a spare PV linkage cover gasket and a spare cylinder base gasket when you get your next top-end kit. When you hit 20 hours, pull the cylinder and have someone who knows what they're doing mic the piston (with a micrometer, not a dial caliper). Have them mic the cylinder bore and you'll know where you're at for clearance.
If the engine is within service limits in the manual, put it back together (with your spare gaskets) and ride another 10 or 20 hours. Now check it all again.
You'll begin to figure out how much time you can put on a top end under YOUR conditions.
So many factors come into play in top-end life. What oil and ratio, what speed are you, where do you ride, how good are you about filter maintenance, etc.
A national level pro on a deep sand track with outboard oil at 50:1 might get 10 hours out of a piston/rings.
A beginner in tight single track at 32:1 might honestly get 200 hours out of a piston/rings while leaving an oil-spooge trail on the ground for miles.
The piston expands really quick and could get tight if the cylinder is still cold.
I did the tight piston in my bike all the time.
And I always used cast pistons,it is softer and wears instead of wearing the cylinder coating.
No hours idea,I just pull the pipe and look at the skirt and the port print left from wear to decide when to put in a fresh one.
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