Stihl 041 super
ArboristSite Operative
Which is better forged or machined pistons?
Which is better forged or machined?
- Thread starter Stihl 041 super
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shtoink
ArboristSite Member
It normaly depends on the material. If something is forged from saw a material like steel, then it will usually be tempered to add strength. Something that is machined may be tempered in the same manner and be strengthened as well. The process of forging steel aligns the molecules adding the ability to be stronger after the tempering. At least that is my understanding of it. I may have left something out.
There is a difference between cast and machined, though. Especially with aluminum. Cast aluminum isn't as strong as a part that is machined from a solid block. The reason for this is because the molecules in the amluminum are aligned in a more uniform manner and alow for a stronger part when machined. During the casting process, the aluminum has to assume the shape of the mold and goes through some contorions in the liquid phase to do so.
Someone correct me if I am wrong or have forgotten anything.
I hope that helps...
There is a difference between cast and machined, though. Especially with aluminum. Cast aluminum isn't as strong as a part that is machined from a solid block. The reason for this is because the molecules in the amluminum are aligned in a more uniform manner and alow for a stronger part when machined. During the casting process, the aluminum has to assume the shape of the mold and goes through some contorions in the liquid phase to do so.
Someone correct me if I am wrong or have forgotten anything.
I hope that helps...
By machined do you mean cast and machined, because they both would be machined. You could also machine out of solid billet. Forging forces the metal matrix into a tighter bond, which in turn creates a stronger piston. So forged are stronger.
GASoline71
Mr. Nice Guy
I agree with TimberMaster. I have never seen a "machined" piston. Granted all pistons are machined after the molding process to clean them up and make them true. Are you possibly refering to cast vs. forged vs. hyperutectic? All of which are different ways the metal is heated for strength and durability. I might be wrong though?
Gary
Gary
jensen 32000
ArboristSite Operative
Pistons
I have NOT seen any choices for chainsaw pistons, other than OE vs aftermarket. Are you saying you can get "Keith Black" pistons for chainsaws? Maybe Ed Herd can comment. Mike!
I have NOT seen any choices for chainsaw pistons, other than OE vs aftermarket. Are you saying you can get "Keith Black" pistons for chainsaws? Maybe Ed Herd can comment. Mike!
Al Smith
Addicted to ArboristSite
You do have a multitude of questions.I have never figured out how a person would forge an aluminum piston.Then again ,I haven't seen every thing having worked in the auto industry,in one form or another for over 30 years.I'm willing to learn,please enlighten.Stihl 041 super said:
GASoline71
Mr. Nice Guy
Sorry, I should have added that I was actually refering to Automobile type pistons. It would be cool if Kieth Black made chainsaw pistons. 
Hmm... By the way, Wiseco makes 2-stroke pistons, or are they just making pistons for dirt bikes?
Hmm... By the way, Wiseco makes 2-stroke pistons, or are they just making pistons for dirt bikes?
GASoline71
Mr. Nice Guy
Oh yeah, to answer the question.... Forged definately.
Gary
Gary
For high performance, forged pistons are the way to go. They are a lot stronger then a cast piston at high rpm and heavy load. For stock purpose the cast piston engine will live longer do to tighter clearence between the piston and cylinder wall to start with. The forged piston engine is set up with more clearance between the piston and cylinder wall to allow for the expansion of the forged piston. You do not have the expansion with the cast piston that you do with the forged piston. I would not say one is any better then the other. Each serves it's own purpose.
GASoline71
Mr. Nice Guy
Very good point.
Stihl 041 super
ArboristSite Operative
probably true.
Its probably true but ive seen so many forged wiseco pistons fall apart in high
performance race snowmobile engines. But ive never used cast pistons though.
Its probably true but ive seen so many forged wiseco pistons fall apart in high
performance race snowmobile engines. But ive never used cast pistons though.
andrethegiant70
Addicted to ArboristSite
Don't know lots about how pistons are made but I do know that the cold forging process (essentially "smashing" the part into shape) makes for some very hard material.... something about orienting the molecules.... So the logical sequence for creating the hardest parts would be to cold forge, THEN machine (if necessary). I think parts created from molten metal and "cast" are not particularly hard unless they undergo another process, such as heat treating. Raw billet that has been machined is very pretty, but is at the very weakest end of the strength spectrum.
Oh, and be careful when talking about "forged." "Cold forged" as described in the above paragraph is entirely different than the "cast from molten metal" process, which many also describe as "forged." I think the full terminology in this case is "drop forged." A part that is "drop forged" without a quality treating process afterwards makes for a junky part.
Oh, and be careful when talking about "forged." "Cold forged" as described in the above paragraph is entirely different than the "cast from molten metal" process, which many also describe as "forged." I think the full terminology in this case is "drop forged." A part that is "drop forged" without a quality treating process afterwards makes for a junky part.
Andre It seems these days that the best parts of a race engine are billet. Any casting or forging can be junk depending on the compesition of the metel and the method for forming it along with a good or bad heat treatment. The best of the best is billet along with a good heat treat. In pro ranks you will be hard pressed to find a twist forged crank. Forged rods are good, billet rods are better. Check prices for cast, forged and billet rods and pistons, cranks,heads and blocks. Billet is more expensive. Streangth wise billet is where its at. There is a lot more machine work in billet parts accounting for some of the higher cost but they dont go to all that extra work to end up with a weaker part.
Mange
Addicted to ArboristSite
I think you should try and fint out what types are availeble and see how much the costs differ, then show the resoults here, I am not sure if there is other types, I have only seen casted for chainsaws / small engins.
andrethegiant70
Addicted to ArboristSite
I do see what you mean, eric, thought it may simply not be reasonable for limited production parts to be cold forged, which takes a massive machine and stamps which are good for THAT part only. A cold forged part is a VERY high effort, resource intensive part and you need to make and sell many parts to justify the cost. And if the part doesn't come out right, there's no easy way to go back and retool. All "billet" parts are all made from the same CNC (computer numeric control) machine and are "programmed." VERY easy to make a one-of-a-kind-part.... if you can think it, you can cut one out! If the part doesn't work, reprogram the machine and zap out another one! If the parts are to be used under stress, THEN I think they go the extra mile and use a heat treatment process.
I remember when the cold war drew to a close and many ex-aerospace CNC guys got jobs making high-tech bike parts... some incredible parts came out of the process, very pretty... fork crowns, cranks, brakes, etc. It didn't take long, however, until people began to realize that the billet parts, as pretty as they were, were no match for the cold forged stuff. Fact is, cold forging can ONLY be practical if you're a large shop and you're turning out a LOT of the same parts. Some of the lightest and most durable parts are still the boring ones (cold forged) made by the likes of Shimano and Cannondale.... This fact is very frustrating to many cyclists, many of whom have the money to pay for high quality, but who'd rather not give their money to the big guy on the block. Think Microsoft.. many people are frustrated with the "monster" but it's still the best game going.
Lets face it, there's a zillion different types of engines and components, and lots of little guys with limited resources are zipping out parts using the CNC process (because that's their only economically reasonable method for doing it.) I'm guessing they make up for using billet by overbuilding the part and heat treating in some way. Seen the Orange County Chopper guys lately? They bought a cheeseball CNC machine and they're knocking out CNC parts too! Provided the parts are well designed and there is enough material, the parts will hold up.... but billet is a bit like milling something out of a bar of soap... the material is in its softest state, it's EASY, and that's why its done.
Having said all that, Al is right, I don't know if you could cold forge a piston. Just a bad shape. I think you'd HAVE to either pour metal into a mold (drop forge) or CNC it. But why go to the trouble of making a big old complicated mold for a few racing pistons? Just get poindexter over there to program the CNC machine! My guess is that the most important difference in the resulting piston from each of the respective processes is the quality (and suitability) of the alloy used and the quality of the heat treament process.
I remember when the cold war drew to a close and many ex-aerospace CNC guys got jobs making high-tech bike parts... some incredible parts came out of the process, very pretty... fork crowns, cranks, brakes, etc. It didn't take long, however, until people began to realize that the billet parts, as pretty as they were, were no match for the cold forged stuff. Fact is, cold forging can ONLY be practical if you're a large shop and you're turning out a LOT of the same parts. Some of the lightest and most durable parts are still the boring ones (cold forged) made by the likes of Shimano and Cannondale.... This fact is very frustrating to many cyclists, many of whom have the money to pay for high quality, but who'd rather not give their money to the big guy on the block. Think Microsoft.. many people are frustrated with the "monster" but it's still the best game going.
Lets face it, there's a zillion different types of engines and components, and lots of little guys with limited resources are zipping out parts using the CNC process (because that's their only economically reasonable method for doing it.) I'm guessing they make up for using billet by overbuilding the part and heat treating in some way. Seen the Orange County Chopper guys lately? They bought a cheeseball CNC machine and they're knocking out CNC parts too! Provided the parts are well designed and there is enough material, the parts will hold up.... but billet is a bit like milling something out of a bar of soap... the material is in its softest state, it's EASY, and that's why its done.
Having said all that, Al is right, I don't know if you could cold forge a piston. Just a bad shape. I think you'd HAVE to either pour metal into a mold (drop forge) or CNC it. But why go to the trouble of making a big old complicated mold for a few racing pistons? Just get poindexter over there to program the CNC machine! My guess is that the most important difference in the resulting piston from each of the respective processes is the quality (and suitability) of the alloy used and the quality of the heat treament process.
andrethegiant70
Addicted to ArboristSite
Sheesh!
Good Lord, what a brain dump I just did. Feel free to ignore me.
Good Lord, what a brain dump I just did. Feel free to ignore me.
Mange Im speaking purely automotive. I have not seen any after market billet parts for chainsaws and not saying you can't get them cause if the price is right you can have anything made. As much as some people like to speed their saws up, the billet parts would be a real +. Im sure sometime back I read where billet crankshafts were being used now by J reds but could have been another brand. Not for sure on that. Im to lazy to show links but trust me if you were building a high performance street engine and you started priceing cast, forged and billet rods and pistons, the price of the forged rods and pistons would look a lot better then the price of the billet rods and pistons.
Andra you are probly right on the over building part of it but at the same time when you can buy 4340 billet steel and heat treat it for rods and cranks is there a forged crank any better? You got me thinking now. 
