cast vs forged pistons

[expansion chamber]

Cast are lighter, forged are heavier. Which is better? I have a bored out yz 250 and have a wiseco in there now but have always been a fan of Pro-x pistons. Im going to continue with the wiseco for awhile longer but was considering getting a pro x one next and was just curious what you guys have ran into for expirence with both.

 

[Rich Rohrich]

Cast are lighter, forged are heavier.

Not necessarily.

Which is better?

Define "better" in this case.

 

[whenfoxforks-ruled]

The pro x? Isn't that the cheaper product line, offered by Wiseco? The cast is worth 50 dollars less than the forged, Wiseco said so! How on Earth can their cast be "better" than their forged? You do get what you pay for, generally. Vintage Bob

 

[RM_guy]

Do a search. There is tons of info on this topic.

 

[expansion chamber]

I was referring to better as in, is cast more reliable than forged? do forged pistons offer more performance? visa versa. what else would someone ask for? looks? no. Ive ran both kinds of pistons. Ive used more Pro-X pistons than Wiseco and had good luck with Prox.. I was just asking for other peoples expirence on using the two different types of pistons.

I have a little over 30 hours of time on the wiseco and the skirt coating is all worn off.

I run SPI cast pistons on my 700RMK sled, they are ceramic coated and they seem to hold up really well for having over 150 hours on them. Seems like the forged pistons dont hold the coating as well as the cast pistons. IMO

 

[whenfoxforks-ruled]

You are complaining that you only got 3 times the life out of a piston? How many re-rings went on it? I am not in the kdx forum again? Vintage Bob

 

[expansion chamber]

I never re-ringed the wiseco piston. Ive ran my yz when it was stock with stock piston in it for 3 years before rebuilding it. And I put alot of time on the engine each year.

 

[expansion chamber]

You are complaining that you only got 3 times the life out of a piston? How many re-rings went on it? I am not in the kdx forum again? Vintage Bob

You misunderstood me. I have ran more Pro X pistons in my life time than Wiseco. Im trying out wiseco a little more to see how they compare to Pro X. Shouting out for some friendly knowledge about other personal expirence with them and Im just getting questioned.

 

[whenfoxforks-ruled]

I never hit the capitol or entry keys hard? I was just clarifying something. If you can run a piston that long, you could run probably any piston made. A lot can be said for air filter maintenance, and how heavy handed you are, for it to last that long. And I would be real watchful of the bore staying true. Sleeve or coated bore? What were the skirt and ring gaps? I have heard all kinds of long stories on my 480, but around 10 hours the top ends coming off to see how its wearing, and put new rings in her. Vintage Bob

 

[_JOE_]

I've always used Wiseco. I've never run one more than around 75 hours or so. The 250f is my first bike that really shows any skirt wear after 30 or so. The wear on the skirt is allowing the piston to rock in the bore and can lead to the skirt cracking and breaking off as well as an ovaled bore. But at least the broken piston will do enough damage you'll need to oversize the bore anyway......

I know several guys who run Pro-X with good results as well. They all take good care of thier bikes though.

 

[plynn41]

Hey,
Don't know about the YZ hardware, but there seems to be a consensus with CR500 riders (cr500riders.com and bannedcr500riders.com) that Pro-X pistons are to be avoided due to poor architecture--the sides of the pistons are open to the exhaust port, allowing the transfer charge to blow straight out when the exhaust port should be sealed. Also, alot of those guys are getting away from Wiseco forged pistons because they seem to seize easier--the forged aluminum is apparently stickier than cast.
That's why I'm putting a Vertex cast piston in my '85 CR500. All reports I have gotten is that reliability is similar to OEM.
Hope this helps!

 

[whenfoxforks-ruled]

Geez, are we going down the crapper? What next, testimonials for namura and magnum brands? Forged are Stickier, really? And to think of the money I could have saved, never changing my oil in a car with over 200,000 miles on it???? Is that a sign of quality, or dumb luck? I would rather believe its how the engine is getting used/abused. Doing a search seemingly did not work, we will now roll over and be another hear say site? Anybody else up for hear say talk, or dig up the facts, forged are miles better than cast. Stickier? Some new engineering word? Vintage Bob

 

[ellandoh]

im going with cast since i work in a foundry

anybody have a pattern for a piston I'd like to pour my own out of waspaloy :boss:

http://en.wikipedia.org/wiki/Waspaloy

 

[holeshot]

Forged pistons are generally used in high perfromance applications because of their greater strength over cast The grain structure of forged metal tends to follow the shape of the piston (because it was hammered into shape) and the cast grain structure follows one line. Forged pistons expand more than cast when heated, so they need slightly looser tolerances when cold (which can cause the forged piston to rattle a bit more at start up).

Regardless of which method is used, it still depends on the manufacturer to create a quality product and the installer to intall it correctly.

 

[plynn41]

Did you have a bad Easter weekend Bob?
If my comments aren't useful, then disregard them.

 

[RM_guy]

Here's a good thread on forged vs cast. It's amazing how search works ;)
http://www.dirtrider.net/forums3/showthread.php?s=&threadid=35945

 

[expansion chamber]

but does a harder piston (forged) wear the nikasil coating quicker than a cast piston?

 

[whenfoxforks-ruled]

but does a harder piston (forged) wear the nikasil coating quicker than a cast piston?

I highly doubt an aluminum piston, whatever can be done to it, could EVER wear a harder plating out. Running a loose piston has the effect of pushing the material behind the plating out of round. I doubt it would on a sleeve though, thats why I asked. Loose a bearing, ring or cir clip and say good bye to the bore. Most of the seemingly horrible looking bores, thats just aluminum flashing rubbed onto the plating. A scotch brite pad and oven cleaner takes it right off, back to the original hash mark. If a guy wants to run long, put the sleeve in, they even claim to have chrome and some alloy sleeves, and they can plate sleeves. Only 1 issue, they still wear quicker than oem or better plated aluminum. The heat dissipation and expanding and contracting differences. 3 races or 7.5 hours, thats what my 97 CR250 suggests. I know darn good and well that I can go longer, minus any debris catastrophes getting by the carb. I also know that James Stewart could NEVER get that much time out of a top end. His would do well to last 30 minutes plus 2 laps. Wiseco, namura, vertex what ever, they are not going to tell you much longer than the manual. 5 to 10 hours on a 250, the rings are gone, less for the smaller bores. And that is running 32 to 20:1 premix ratios! My recent experience with used dirt bikes has pushed the limit on what gets said about how long parts last Plynn 41, proper maintenance and these bikes would last a lot longer, and be a lot cheaper in the long run. Abusing the maintenance schedules, I sure do not want to buy a bike from someone like this again! Not too many 2 stroke ex-racer bikes around anymore. Vintage Bob

 

[RM_guy]

Whether it's a forged or cast piston it's going to wear the same. They are both aluminium and one is not harder...or softer than the other. They both will wear out long before the plating.

 

[In come tacks]

Seems like the forged doesn't grenade, and I hate installing crankshafts! I think the one guy had it right, if you're not changing your cast piston after every hard long run, then forged would last longer.

 

[julien_d]

Cast pistons - less expensive, can run tighter tolerance, good enough for most riders, more forgiving for the noob that want's to pin the bike right after it starts to "clean it out". Requires very little warm up time.

forged pistons - stronger, longer service life, less forgiving to the idiot that tries to cold seize the bike, needs a larger cold clearance, and yes, that additional cold clearance can cause piston slap at startup and wear the bore quicker (but only for that same idiot who pins it when the piston is still cold). You can also build up some incredible hot spots this year, and seize a forged piston in the bore right quick. This is probably what earned wiseco the name siezico back in the day. Proper warm up is imperative with a forged piston.

Certain bikes really need to avoid pro-x pistons to prevent shattered skirts. KDX220 is one that comes to mind. Some models of the yz250 seem to have issues with the pro-x piston as well.

A forged piston will last longer, yes. Either piston run too long will cause problems though. While the cast might drop it's skirts from fatigue, the forged will continue to wear down and cause piston slap eating up the plating or forcing the bore out of round. Either way you go you need to service the top end like you should!

 

[whenfoxforks-ruled]

Julien, I do think the seizco thing, was running too tight a bore, and the cold seizures for sure. I was 1 of them, used to be skeptics on new fangled products. I was oem Bob! On the 4 strokes, 06 to present, the oem never saw me! The 2 smoke rebuilds, we are friends again. NOT ON THE PISTON THOUGH! Racing MX, I need it, especially if my children ride my bike. Never enough insurance, for the real heavy handed. Except for the 1 hour rebuilds, and I truly wish I was financially secure enough to do the 1 hour rebuilds! Double the piston life indeed? I really do not enjoy tossing cranks, doing the crankcase flush at the track, NOOOOOO! Not again, been there and done that, some good, some bad$$$$. Yes, it can get 4 digits of misery/fun. And for what, a 30 dollar re-ring and inspection? Vintage Bob

 

[julien_d]

I'm with you Bob. Cast pistons have their place still, and I'll use one in a pinch, or even just because I got a deal on a pro-x for $50 on ebay. I keep a closer eye on piston wear if using a cast as a general rule. I feel more comfortable running a wiseco, for sure.

That cold clearance and proper warm up is extremely important with a forged piston! If you're too lazy to measure clearances, break-in properly, and properly warm up the bike before you ride, then stick with OEM.

 

[FatBiker]

I'm "new", been away for many years, to this so my question may be a bit silly. What about hyper eutectic pistons? Are they automobile only things? I know for years, even now, hyper eutectic pistons are the cat's pajamas. They can be run tighter because they are more thermally stable. In essence, you get the best of both worlds. Are they not offered for dirt bikes? :think:

 

[ellandoh]

im not positive but i would venture a guess that there is silicon in the makeup of the pistons in dirtbikes also. i dont have one laying around here but next top end i will put mine into our spectrometer to see the % of silicon in it . probably wont be as im running a forged piston now, if i can find someone with a cast piston ill use that