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I ride with all KTMs; I'm the sole member of team green (kinda like that!) I broke in a new Wiseco piston on an 18 mile ride yesterday. When we got back to the trucks I mentioned that I had just stuck a Wiseco in my bike.

You could have heard a pin drop. "Oh Wiseco huh... oh that's cool." They had a look on their faces like I stuck a wet sponge in there instead of a piston. WTF?

The senior guy said, "Yeah we stick with OEM in our bikes."

It seems everyone here plunks Wisecos in. So that's what I did.

Is there an issue with Wiseco? Wiseco and KTM? Or are they just orange snobs?

Many old timers have some bad memories regarding forged pistons, and wiseco specifically. Mostly cold seizures. Forged pistons expand differently and slightly more than their cast counterparts. This is why wiseco recommends a slightly larger clearance than OEM in most cases. If you take a brand new OEM cylinder and slap a standard wiseco piston in there it's likely to have some clearance issues. By the time the OEM piston is worn and needs replacing, the additional .001" of clearance needed for the wiseco is usually there.

All that said, things are quite a bit different than they were 20 years ago. Forged pistons are lighter than they used to be, and have a more uniform rate of expansion. I'm still on the fence about forged vs. cast, as I feel both have their place.

Don't worry, the wiseco piston is just fine if installed with proper clearance. In fact it's a necessity if you have a 220. The OEM 220 piston has some issues, as we all know. The main things to watch out for with a forged piston are proper clearance, and ALWAYS giving the bike a fair amount of time to warm up before riding. The forged piston will expand more, and more slowly, so it needs to come fully up to temp before you wring on it.

Wiseco has been around for a long, long time and they know how to make a quality piston. There no problems with running their pistons. I ran them reliably in my RD's for years and I abused the hell out of all of them. When it comes time for my KDX to get a new piston it will be a Wiseco.

My vote is that they are snobs. Not necessarily "KTM" snobs but "OEM" snobs.

They probably don't even work on their own bikes

Most punkin riders I know trade up every couple years

Find a new crowd ....

Mr. Wibbens wrote:They probably don't even work on their own bikes

Most punkin riders I know trade up every couple years

I agree. It's six KTMs and me. Two of them have two!

Oh you should hear the crap I take. I've done the fork mods and RB carb and head and I get, "It's still a KDX".

Fun part is... four of them are always behind me, so I can talk smack too!

Varmint wrote:Oh you should hear the crap I take. I've done the fork mods and RB carb and head and I get, "It's still a KDX".

That's when I would say... "Yeah... that's the great part!"

Bet you have more BEER money

Mr. Wibbens wrote:They probably don't even work on their own bikes

Most punkin riders I know trade up every couple years

He's right.
This is a decidedly DIY crowd.
However... the real story is, this is the only bike I've ever owned that has a well known piston defect problem, and aftermarket is really the only sensible option. I feel completely comfortable using OEM in my RM, or KLX, and so should your buddies with their KTM's.

Mr. Wibbens wrote:Bet you have more BEER money

Correct! One of them just spent $75 (no lie) on a spark plug wrench!

If you take a brand new OEM cylinder and slap a standard wiseco piston in there it's likely to have some clearance issues.

Not true, but it would be on the tight side. Wiseco makes one piston. Pro-x (OEM)makes like 6 (A,B,C,D,E,F). Wiseco is like an F. An F piston in an A cylinder is still within spec...Just on the tight side. Just make sure it's WARMED UP before flogging it to avoid cold siesure....Not that it would, but if it's gonna it's going to be because it was cold...This is always recommended, IMHO. These differences are something like .00001" in between the sizes BTW.

"We use OEM" KTM doesn't make their pistons...Most all OEM's don't. Can they answer what the brand is actually in their bike? In this case I'd trust anyone but Pro-X/OEM for the KDX, and that's only for the 220.

F piston in an A cylinder is still within spec...Just on the tight side.

Yeah, and then add in the extra .001 that wiseco recommends and you have trouble.

Anyway, "a little tight" with a forged piston is a bad idea. I assure you this is true. I just finished participating in a very very long discussion on forged vs. cast pistons. I have a very inofrmative email message from Wiseco to back this statement up. If you do not observe proper clearance, break in, and warm up when running a Wiseco piston, you're begging for trouble.

You'll notice lots of folks complain about the Wiseco pistons rattling in the bore before they warm up. That's because the forged piston has to have a larger cold clearance. The piston expands more than cast, and clearance at operating temp well be equal to or tighter than OEM.

By the way, the difference in A,B,C OEM pistons is .01 mm, or roughly .0004"

Stock KTM pistons are manufactured by Vertex btw. They may be forged or cast depending on the model. Either way it's a quality part.

Also... good luck specifying what spec piston you want from any Pro-X dealer. They will send you what they have in stock. So it is kinda pointless to have those designations.

When they order from the distributor (Tucker Mountain I believe) they have no way of designating which spec piston to order. So, here is the problem.

Good point Inda. If you order OEM from a shop for a KDX, you get whatever you get. There are a good many resellers who offer each size up though.

FWIW, my pro-tru piston from Wiseco measured at 65.96 (same as pro-x C)

Cylinder bore diameter per my manual is 66.016 - 66.031

If my bore were at the low end of spec I would have .056 piston to cylinder clearance. Considerably less than the factory recommended .072 - .092 clearance.

Wiseco recommends an additional .001" clearance. That's .0254 mm. According to Wiseco I need at least .097 piston to cylinder clearance. See a problem here? .056 actual vs .097 recommended

Anyway, my point is you can't just slap a forged piston in any old cylinder without checking clearance very carefully. If your cylinder is on the low end of spec, you could very well find out for yourself why Wiseco earned the name Seizico back in the 70's/80's.

Please don't get me wrong, I hold Wiseco pistons in high regard myself, and am perfectly comfortable using them. For the average joe who just wants to slap it together without measuring anything, yank it out of the truck, kick it, and pin the throttle while it's cold to "clear it out", a cast piston will be a better choice, lol.

If you do not observe proper clearance, break in, and warm up when running a Wiseco piston, you're begging for trouble.

Agreed. Warm-up being the most important in this case. You can't set the clearance on these so like you posted you just end up with what you get. Clearance can be set at the time of plating.

yank it out of the truck, kick it, and pin the throttle while it's cold to "clear it out", a cast piston will be a better choice, lol.

YES! Does Athena, Vertex, etc make a 220 piston?

lol

fuzzy wrote:

Can they answer what the brand is actually in their bike?

I know the last guy to change the piston in his KTM used an Athena kit.