2021 husky tc250 new top end help

Usually theres a mark somewhere on the cylinder. If nothing else you can measure the piston thats in it and get your answer

You can go probably twice as much on that top end.

Usually the mark is on the back of the cylinder

Wouldn’t even waste your time on a top end yet. Keeping an eye on compression between new and 90 hours I only lost 14 psi.

If you still decide to do it measure the base gasket thickness so you can match the new ones.

I just took a look at the OEM parts catalogue and it looks like they sell Piston kit I and kit II,
I'm guessing kit I would be your first OEM kit, but 3bros Husqvarna would know best.
As AJ said, these bikes run a long time without top end service. I had a similar experience, replacing the first set of piston and rings in my 2017 KTM 250SX at 75hrs.

There should be a I or II stamped on the back of your cylinder. That corresponds to the piston kit you need. The piston sizes that fit I and II cylinders are listed in the service manual.

I've been wondering this same exact thing on my 2021 KTM 250SX. I am not exactly sure where these markings are? I see a stamp number on the top of the cylinder, is that it? I see the 0 *** 1 stamp raised higher.


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I'm at 75 hours, will probably pull/do top end at 90-100 hrs (C level rider).

I may be wrong, but I couldn't see a mark on mine ('19 250), but either way I wouldn't think it would be a cast number, as it's a manufacturing tolerance thing as to why piston size can change, I don't think they are intentionally making different sizes of the same stock cylinder.

On the last 300 I did for a friend I did see a mark though, it was kinda etched/scratched into the cylinder though.

I popped the plug out and head off and it said on top of the OEM piston. Measured the top.of the bore and ordered the same size again as it didn't seem to have changed (if I remember rightly, Vertex who are the OEM supplier did A, B and C on their aftermarket pistons instead of 1 and 2 though).

Double check any of this that sounds dubious or doesn't stack up, dont take it as fact, I've only been around bikes again recently and this is just what I've seen on mine, so I wouldn't want you put out by any oddities I've seen or mistakes I've made 👍

On KTM four strokes the cylinder size is stamped on the cam chain tensioner mount on later models. I believe on two strokes it is under the power valve cover. KTM does have two different cylinder sizes on the four strokes at least and is explained in the service manual. I believe the boring tool starts out slightly larger (size II) as it wears it bores slightly smaller holes (size I). This is only a guess. The difference in sizes is only one thousandth and either size should fit without any problem.

That's kinda what I always figured too, tooling degrading or heating/cooling variances though that seemed a stretch.

Good to know about the stamp inside the PV cover though.