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Only $10 for all 2026 SX, MX, and SMX series.
No, I actually bought it for the 300 kit I plan to install soon on my TC250. The Vertex in the pic is from the kit.
I'm short shifting my 300SX which works fine, and will get another Wossner when it's time for a top end.
I’ll have some updated info on this shortly, I have mine apart as I wanted to get to the bottom of this. So numerous hours and measurements and some modeling clay later I have some answers. And they are not what most suspect.
For starters, of course the piston hits the crank when the cylinder is not installed and at BDC. I don’t even know why someone found that alarming, the piston will never have that much lateral movement at the skirt with the cyl on so that’s a mute point.
The area I suspected of being the closest to hitting the crank does appear to be the case, but so far there is still plenty of clearance. I am gonna check a few more things and get a few more measurements and will share once I am finished.
Thanks for sharing your findings.
If yours hasn’t happened yet, you may be one of the lucky ones.
There are many people who suffered major engine failures due to it hitting with the engine assembled.
Not shown in this video but in pics was the underside of the piston after it was started and run for start up with the piston hitting and the marks to prove it.
There is a reason why Wossner and other piston mfgs made production changes to make the skirt shorter.
Wossners skirt isn’t shorter, I have one on my bench.
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This would mean that the stocker piston you have is good and made right, as with the Wossner, it is made right...many KTM spec Vertex pistons that were made wrong, made it into the production line. So if you ordered one direct from Vertex it would be correct.
KTM had hundreds if not more, old stock 300 KTM spec pistons that were made wrong, boxed, and shipped to the assembly warehouse where they were stocked with other ones that were made correctly.
This has been well documented already.
Here are some pictures of both the stock piston with clay to demonstrate what the closest area is for interference. The wossner had the same clearance in the same area. .032-.040 depending
the clay was rounded and you can see where the crank flat spotted it
Where are you guys getting gaskets? I'm trying to rebuild my 23 250SX and can't find any microfiches on any websites. I've found a pro X piston kit on Rocky Mountain, but can't find base gaskets or vertex pistons anywhere.
Both Vertex A and B pistons are in stock with PU. Any PU dealer can order them.
Top line is the PU part number. Bottom is Vertex number.
I have (9) complete top end gasket sets left, just got them in today from the UK..$59 shipped.
Are you on FB?
Join my page!!
https://www.facebook.com/groups/709915283880183
Try this for the PNs. They have 2024 and older fiches. There are similar sites for Gasgas and Husky.
https://sparepartsfinder.ktm.com/
Ktm is going down hill in ever since Covid response measures. They still havent come back from that.
Are you sure that these pistons are for the 23? When looking up those numbers it's for the older 250's, just wanted to confirm that the same piston is used in the new model. Thanks for your help so far.
23 uses the same pistons as the old-gen bikes for the 250 (and the 300's). I double checked on both the Vertex website and the OEM part numbers. You can double check the Vertex numbers here. They have the 2023 listed. https://www.allballsracinggroup.com/vertex
Thanks for the help. Got the piston on order and got the gaskets from Jbone. Will probably map the bike soon, hopefully get a little more hit so it pulls second better and doesn't bog out shifting to third on tilled starts. It pulls smooth and long in second, but in tight corners I feel it needs a bit more punch.
Some more info to add to this 300 piston discussion.
OEM 300 piston size is A-71.925mm and B-71.935
Both aftermarket Vertex and Wossner are
A 71.94
B 71.95
C 71.96
So, all aftermarket pistons are bigger than both OEM sizes with less clearance. Anyone think the extra clearance on the stock pistons might contribute to potential to contact the crank? Likewise, when putting in an aftermarket piston to correct the issue, perhaps it's as much about reducing clearance and piston rock as it is about the skirt length or thickness.
Good point, from what I have seen, it is the skirt issues more than the larger bore size.
If my math is correct, the .005mm diff between the 71.935 and 71.94mm is just under .002” which is measured at the outside of the skirt diameter and such a small number and it seems to be hitting on the bottom of the skirt from what I have seen.
Yes, the belief is the skirt is contacting the crank on the intake side. The point I am making is that the larger the piston to bore clearance is, the more piston "tilt" you get which will dynamically decrease whatever static clearance you have between the skirt and crank, which is very tight to begin with. The difference between the OEM and aftermarket pistons may seem insignificant, but when you have extremely tight skirt to crank clearance, that extra little bit of piston tilt may suddenly matter.
To add to this, I've been wondering if the rev limiter on the TBI bikes may play into this. Carb bikes don't have a rev limiter. What happens on a TBI bike when the bike is at max rpm and suddenly the ignition or fuel cuts and introduces new harmonics in the rotating assembly?
I see what your saying but I thought it was the oem pistons that were hitting?
Pit Row
Yes, exactly. OEM pistons have a smaller diameter, therefore more cylinder clearance, therefore can "tilt" more, therefore decrease the already minimal skirt to crank clearance.
I am surprised a bike can go to the rev limiter for a fraction of a second if the piston can hit the crank let alone a few hours.
Hey guys!
I have a 2024 TX300 and I came across this discussion. Any more info? Should I be ordering a top end kit to protect my bike?
Thanks
If you get a piston, (Wossner), I would still trim the skirt a little bit. I have heard but not seen, that there still may be contact with the crank regardless of the piston. If it does happen with the Wossner, it is a forged piston so it can withstand some kisses off the crank and not explode.
Just an FYI.
I’m very curious about this too. I put many hours on my 2020 300xc, now have about 15 on my 2023 300. Love the bike and i pin it on my straight aways. Man, i would hate a grenaded engine and I’m lazy to pull piston for a maybe possible issue.
Not sure how slavens goes over here but i commented to Jeff about this issue and he is going to be doing a vid on it. He did say there were some bad pistons but the affected engines had obvious ticking.
I don't agree with that take and the idea that if the piston is going to hit, it's going to hit immediately, not after 40 hrs or whatever. I believe there's a difference between "static clearance" and "dynamic clearance". In other words, if you could get in a brand new engine, all cold, and measure the skirt to crank clearance, there might be some clearance there, so no ticking. But when the parts get older, worn, looser, warmed up and expanded, and you rev it to the limiter and the piston is tilting to it's max in the cylinder, and maybe there's even a hint of deformation... then you might get contact. Kind of like how you can set up an engine with a very tight squish, so clearance when measured cold, but then get piston to head contact on down the road. There are plenty of posts from guys on the TBI forums with grenaded engines who never mention hearing a ticking before the explosion.
Off topic but just watched a video on the sr-71 blackbird engine. It expands 6” in overall length at full cruising altitude and speed, that’s insane.
if the pistons on these bikes are expanding just enough and the clearance is already so little it’s possible the piston wouldn’t hit when cold but under extreme heat it could.
Does this affect the 250 as well?
I have seen a few 250’s but not as much as the 300.
Saw one of those when I was in the Air Force in the 70s. It would have multiple hydraulic leaks when not in flight because of that!
Anymore updates on piston issues?
Post a reply to: 2023 KTM 300sx potential issue (pics and video)