forged vs cast

[ktm868]

i am riding a 2008 ktm 250 xc. i am doing a top end rebuild and have been happy witht the oem piston made by vertex that is a cast piston. but i was looking into the wiseco pro lite piston but it is forged. is that an advantage?

or will it crack? i know alittle about the difference but need some help on the decision

[camman]

KTM knows what they are doing! They choose cast for a reason.

[adam728]

KTM knows what they are doing! They choose cast for a reason.

Yup, because it's cheaper! ?

Really though, there are decent arguments on both sides of the cast vs forged coin, and in a lot of threads those arguments get ugly. If you are someone that likes to run a lot of hours on a top end I would recomment forged, as cast pistons don't like to go past service life, they'll crack and drop a skirt. Forged pistons are much less likely to suffer a catastrophic failure like that (they'll just barrel-shape over time when ran with too much clearance, but still run).

[camman]

Aluminum is sold by the pound. The reason why yamaha,Honda,ktm,Suzuki , and Kawasaki use castings for two strokes is that the cylinder and piston are cast from the same material to keep the expansion rate the same during heat cycling. This allows much much tighter running clearance. This not only adds power but keeps noise down. As I said KTM knows what they are doing.

[adam728]

Forging processes cost much more than casting, even if raw material cost is the same. I do agree that a cast piston can be setup with tighter tolerances, although only slightly.

[Crosspower]

I BELIEVE in the stock Vertex pistons. They last forever. FYI I could have bought a Wossner or Weisco forged piston cheaper, but I put a Vertex back in my bike.

[KJ790]

Like said, Forged pistons are more expensive to produce due to the processes involved. Forged pistons tend to be stronger than cast pistons (less likely to break from fatigue), but there really isn't anything wrong with a cast piston. The downside to forged pistons is they have a slightly faster expansion rate, so you have to be a little more careful when warming your bike up that you don't cold seize it.

[cxcmoto]

We just had a big long discussion on cast vs forged over on the Kawi 2-stroke forum -- Wiseco ended up chiming in and pointing back to another post he had made --

Wiseco point of view

Kawisaki 2-stroke forum discussion on cast vs forged

[camman]

Forged piston certainly have their place like in a four stroke where they are definitely better than a casting. However, for two strokes it appears that all the oem engineers have settled on castings.

[KJ790]

Forged piston certainly have their place like in a four stroke where they are definitely better than a casting. However, for two strokes it appears that all the oem engineers have settled on castings.

All of the OEM manufacturers use castings for stock four stroke pistons as well. This isn't only in bikes, this is in pretty much every type of engine made. The reason is because cast pistons are much cheaper to produce in mass quantities. It's the same reason why most parts of an engine are cast.

[camman]

All oem high performance four stroke motorcycle pistons are forged.

[KJ790]

All oem high performance four stroke motorcycle pistons are forged.

I've never seen one... can you please tell me what bikes come with forged pistons stock? All 450's and 250F's I know of (as well as all 600cc and 1000cc crotch rockets I have seen) come with cast pistons.

[camman]

No all 250 and 450 motocross pistons are forged.

[grayracer513]

40 years ago, cast aluminum was brittle and weak, and forged aluminum couldn't be made with enough silicon to control thermal expansion. Since then, metallurgy has improved both materials and processes to the point where there is little or no practical difference in the two. Ultimately, a forged piston can be made with greater physical strength than a modern casting, but the advantage is much less than it was, and it's something that would only matter under the most extreme circumstances.

Most of the "forged is better, cast is junk" mentality is based on outdated information.

[dgcars]

No all 250 and 450 motocross pistons are forged.

Manufacturers do alter specs for the same bikes, depending on the country where they will be used. Iowa, obviously, gets forged pistons as stock.

[KJ790]

No all 250 and 450 motocross pistons are forged.

Do a little research, all 250F and 450 motocross bikes that I know of come with cast pistons. I know that all Honda, Yamaha, Suzuki, Kawasaki, and KTM four strokes come with cast pistons stock.

[camman]

The yamahas are using liquid forgings which squeeze the material under pressure to form the valve pockets and other details whiCh reduces machine work. Honda does this also. It is a high pressure technique that to the untrained eye looks like a casting.It is still a forging process as it requires high pressure and lower silicon content alumium alloys.

[camman]

The KTM oem supplier for the new 350cc is Vertex. I visit the Vertex factory quite often I can assure you it Is forging! As I said ALL 250F and 450F motocross pistons are forged.

[KJ790]

The yamahas are using liquid forgings which squeeze the material under pressure to form the valve pockets and other details whiCh reduces machine work. Honda does this also. It is a high pressure technique that to the untrained eye looks like a casting.It is still a forging process as it requires high pressure and lower silicon content alumium alloys.

A "Liquid forging" as you call it is a casting. They cast under pressure to reduce the porosity of the aluminum. Here's a nice little comparison between stock cast OEM four stroke pistons and forged four stroke pistons: http://www.motoxparts.co.nz/motocross.php?page=53

The KTM oem supplier for the new 350cc is Vertex. I visit the Vertex factory quite often I can assure you it Is forging! As I said ALL 250F and 450F motocross pistons are forged.

Straight from Vertex:

As the OE supplier of two-stroke pistons to KTM' date=' Vertex pistons has an outstanding reputation for quality and performance. Each [b']gravity cast[/b] piston is created with only premium aluminum alloys utilizing an 12-21% silicon content.

The silicon content in Vertex pistons is crucial to the quality of the piston. Silicon is critical in decreasing thermal expansion which, when an engine reaches normal operating temperatures, can change the geometry of the piston. Controlling this expansion means that a Vertex piston can be run at tighter tolerances for more power, less noise and a longer lifespan of the piston. Plus, the silicon content decreases wear on the piston skirt which also aids in the life of the piston.

In addition to the silicon, each Vertex piston utilizes a unique Molybdenum Disulphide (MOS2) coating which aids in the break-in process and reduces overall wear.

Vertex makes both forged and cast pistons.

[KJ790]

I can't find much info on the KTM 350SX-F, perhaps that does come with a forged piston, but the 250SX-F and the 450SX-F come with cast pistons. Here is a stock piston from a 250SX-F: