Aftermarket vs OEM piston?

Good topic. One of those polarizing discussions like premix or 2stroke vs 4 stroke. Seems to me that quality is pretty good on aftermarket choices these days. Can’t go wrong with OEM but my 2 strokes seem pretty happy on Vertex pistons. 

OEM pistons have come a long way and I have no problem running them. 

If it is performance one is after then there are plenty options with aftermarket. JE for example manufactures pistons for pro circuit which are a higher compression unit which allows a larger air/fuel mixture to be combusted.

For us normal folk a OEM unit will suffice and is probably way cheaper.

Vertex is the oem piston in a lot of bikes(Ktm group) and is my 1st choice if I can’t get oem yami top ends,unless you want more power oem makes the most sense , priced pretty well

As long as you're getting something which is genuinely good like Vertex, Wossner, JE, it'll be as good as OEM. Pays to be selective here so I understand people wanting to stick to OEM.

Are we talking about 2t or 4t pistons ?

This was my first thought too...

On a two stroke, I'm not interested in a cast piston so I go aftermarket and forged.
My reasoning is that if there's a failure, the forged piston is less likely to shatter, thus the cylinder and cases may survive.
I've had very good luck with forged pistons in two strokes.

I'm a new four stroke owner, but have worked on and ridden plenty.   
I would lean more toward OEM in a four stroke, especially on any brand of 450F or my new 350F.
Those bikes make plenty of power and the OEM parts last a long time if the maintenance is good.

I don't have any interest in owning a 250F. 
If I did and I wanted a higher compression setup, I would be very comfortable running a high quality aftermarket piston.

I have never broken or seized an OEM 2 stroke piston in 20 years with hundreds of hours of riding.  I figure Honda is going to put a quality part in their bike, why change?  

All the bikes on Craigslist have Namura pistons so they gotta be good. 

I always ran OEM in my Honda 125 just because they are dirt cheap and it’s Honda so you know it’ll be quality, my KTM two strokes have run OEM branded Vertex, Regular Vertexes, and A Wiseco a few times. I think the Wiseco I ran is discontinued now though, it was a really quality kit with TiN (Could be wrong on coating) coated rings and wrist pin. Lasted a long time and looked good when it came out. 

That made me chuckle. 

I've never tried anything from Namura, but I have the impression that it's "price-point" stuff for some reason.

I used namura once and it cost me a lot of money 😭, skirt snapped at 22hrs

OEM pistons run in my YZ250 2 strokes have been 100% dependable.  The one time I used a Wiseco (a dozen years ago) I had issues ... and yes, I do warm the engine up before riding.   Possibly Wiseco has changed things up in the last dozen years or so?  Have never tried a Vertex. 

Come to think of it...way back in the day, my 125 Hodaka didnt get along with Wiseco pistons either.

Depends on the brand no issues with the wiseco pistons I've run many. 

My favorite was the wiseco with they TiN ti nitrate coated rings. Lasted longer but they discontinued them in 2019 

I run OEM now, but I've had good luck with Vertex in the past. (2-strokes only, of course.) I understand Pro-X makes good stuff, too.

OEM or ProX only in my 2 strokes. OEM only in my 4 strokes.

Prox pistons used to be made by Art an oem supplier. They are not anymore now made in Taiwan and not as good as they used to be. They are owned by wiseco now. There's a lot of old stock floating around so you might get lucky and still get an Art made one. 

The rod kits are still made in Japan though. 

Good to know. OEM only now. Thanks

OEM stuff seems to be better quality than a lot of aftermarket crap that gets pushed in this motorsport. Took me awhile to figure out, but I try to use OEM whenever I can now. 

I've blown up a lot of Yz250's... Every time I've run a cast piston (Vertex, Namura, etc.) I've had to re-sleeve the cylinder. I think I've had to re-sleeve once with Wiseco. I've still blown them while using forged but there are typically fewer casualties. Wiseco is a winner for me! I'll likely go Wiseco or OEM for my 23 Yz450. It's nice to have a buddy that gets Wiseco for cost

OEM … if you keep your eye out sometimes RMATV will do sales on OEM parts. I will purchase my stuff then so i have the parts on hand when i do my two stroke top ends! 

Interesting hearing about forged 2t pistons causing less carnage if they die. How much of an issue is the warm up with a forged piston? Is waiting for the radiators to get warm enough?

I've ran them oem and all the aftermarket ones (no namuras and the likes) and did top ends on bike for people. I've also had every single one of them at some point have a failure. I've never seen one brand fail more then another. I've seen some user errors when it came to not letting the bike warm up enough. I've also seen 3 oem yz250 pistons disintegrate and end up in the pipe and bottom end with less then 5hrs on them. All 3 bike sufficiently warmed up before the moto.

Sometimes shit just happens.

It's a big deal. Back in the day, Wiseco had a really bad reputation for seizing. As it turns out, people weren't warming up their engines well enough, and when they rode, the piston expanded faster than the cylinder did... Presto! Instant cold seize. 

Wossner or oem

How do you know when it is warm enough?

There are many things to consider with this topic. For both 2 stroke and 4 stroke do you want the best reliability in a stock bike? In this case OEM is the best. You want lighter weight, aftermarket is the best. Now if you are talking 4 strokes only and you want lighter weight and higher compression, you cant beat aftermarket. 

I've always gone by the radiator. Once it's getting close to being too hot to touch the top of them then it's ready. Ive never had a cold seize even with the growing wiseco pistons. Slow revs and not to many throttle chops until then just enough to keep it from loading up. If it's a 2 stroke.

Some say wait until the top of the radiator is just warm to the touch. Which is fine for 4 strokes though.

I tried Namura once in a YZ125 and after just a few hours it started making noise. The holes for the pin were oval...

No bad experience so far with OEM, SRS, Vertex, Wössner or Meteor.

Try a Wossner, forged like the Wiseco.

I bet the guys scattering pistons always got the cleanest bikes at the track. Meticulously cleaned and shined $10k bike with $3k in accessories...100 hours on a $250 piston.