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Forged or cast??


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I know, i know this has been coverd alot, so im sorry! I'm gonna order a new top end and had heard pro's and con's of both. I have no problem warming my bike longer with a forged piston! Is that the only reason i shouldn't go with a forged unit. Also why are some people so sure that oem cast is better. It should be cut & dry, but there is such a debate on this issue!

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Cast pistons end up like mine did, Ive never had a forged piston shatter on me like that one did. I figured 45 hours would be a good time to change out since thats what I always changed my forged ones at but it fell short by about 5 hours and took my motor with it.

Im sorry that happend to you! I agree that the forging process is superior to cast, i just dont unstand why there is such a debate! Is wesico's neddle bearings and piston pin as good a oem?

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Why someone would use a cast piston when a forged unit is readily available for about the same money, I will never know. I pulled a grenaded cast piston out of a kwak 250 last week, and it was not pretty. While that case was obviously caused by neglect, the forged unit would have held up better. Wiseco all the way.

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I have often wondered how a forged piston could be swapped for a light weight cast piston and not negatively impact the engines longevity. Counterweights are sized to match a particular piston weight. At the rpm that these engines operate at even a small imbalance would seem to be damaging to the engine.

Mike

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I have often wondered how a forged piston could be swapped for a light weight cast piston and not negatively impact the engines longevity. Counterweights are sized to match a particular piston weight. At the rpm that these engines operate at even a small imbalance would seem to be damaging to the engine.

Mike

Thats a good point, and a valid one. Years back, the forged pistons were much heavier, but not today. Also, to calculate the weight, the bearing and pin need to be added in. Every Wiseco piston I have seen has a pin that has had some serious weight reduction happening inside. So even though the piston may be slightly heavier, by the time the bearing and pin are added in, the difference is none.

I remember my single ring Wiseco being quite a bit lighter than the oem cast piston.

I have a 295 forged piston in now. I know Eric did all he could to keep it light, but the thing is huge! The weight had to go up some. In reality, a person would need to measure the vibration difference with meters or something because the feel is very stock like. This leads me to believe that piston weight might not be as critical as we think.

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Thats a good point, and a valid one. Years back, the forged pistons were much heavier, but not today. Also, to calculate the weight, the bearing and pin need to be added in. Every Wiseco piston I have seen has a pin that has had some serious weight reduction happening inside. So even though the piston may be slightly heavier, by the time the bearing and pin are added in, the difference is none.

Cannon...What would you run(Wiseco or OEM) in your bike if it was a stock bore! Only mods to the motor are the ports are raised a little, and a high comp head. Also do you feel the bearing and pin from wiseco are up to par, being that their lighter?

Thanks.

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I remember the general consensus was that forged were heavier and that they don't rev as high or have as good engine response as cast.

This seems to be BS though.

One thing that has seemed to stick in the whole forge vs cast debate is that the forged needs to have a proper warm up to prevent cold siezure damage.

I chose my OEM piston because of this reason, too many times I have warmed the bike up for only 30 seconds and taken off to finish the warm up process. I'm impatient I suppose.

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Thats a good point, and a valid one. Years back, the forged pistons were much heavier, but not today. Also, to calculate the weight, the bearing and pin need to be added in. Every Wiseco piston I have seen has a pin that has had some serious weight reduction happening inside. So even though the piston may be slightly heavier, by the time the bearing and pin are added in, the difference is none.

Cannon...What would you run(Wiseco or OEM) in your bike if it was a stock bore! Only mods to the motor are the ports are raised a little, and a high comp head. Also do you feel the bearing and pin from wiseco are up to par, being that their lighter?

Thanks.

The best (most fun) piston I found for the stock bore was the single ring wiseco forged. Expensive, yes. Durable, yes. It was incredibly light and the bike reved like you cannot imagine. Instant rpm's. It felt more 125 like than 250 and made monster power.

That was the saddest part in going to the 300 kit. Losing that piston. It was nothing I needed and did not help me at all. But people who rode it came back laughing after they came close to looping it. If you used that single ring piston with a port job, it woudl be works level power.

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Another nice thing is the Forged pistons tend to lose power in a noticable way letting you know its time to re ring, then change the piston. Casts seem to hold power pretty steadily until they fail completely.

Is there a reason for this?

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Is there a reason for this?

IM not entirely sure about it, my CR would be feeling noticeably weaker if I went more than 25 hours on the rings, so Id re ring at that point and then the second re ring would lead to me changing out the whole top end. My Cast piston felt almost new level right up until it catastrophically failed.

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I like to run the Wiseco forged pistons. I have never seen one crack under normal use, however I have seen stock pistons crack and shatter when they reach the end of their service life. The pieces from a shattered cast piston can wreak havoc on your cylinder and if they get down in the bottom end, they can destroy a set of center cases.

1999 and up YZ250 pistons like to crack on the rear skirt near the intake port.

Regarding balance issues, small changes in reciprocating mass will not make a huge difference in felt vibration. Think about that carbon that builds up on 2T pistons during their service life, that's got to add some amount of mass.

Automotive engine builders often balance to 100% of the rotating mass and 50% of the reciprocating mass.

What's that mean? You weigh the crank pin, rod bearing, thrust washers, and the big end of the rod on a scale to get the rotating mass.

You then weigh the piston, rings, pin, bearing, clips, and the small end of the rod to get the reciprocating mass.

Now add half of the reciprocating mass to the rotating mass and attach that much mass to the crank where the crank pin goes in. Now run the crank through a balancing machine, or use a v-block setup with some new main bearings and check the balance.

You will never get perfection:

If you balance out all of the reciprocating mass, now you have that huge counterweight mass on the crank adding a new vibration with it's peak amplitude somewhere around 90 degrees to the cylinder bore.

If you fail to balance out any of the reciprocating mass, you will have a vibration caused by that mass changing direction twice every revolution with peak amplitude parallel to the cylinder bore.

The 100% + 50% formula above gives you a happy medium between those two extremes.

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I have often wondered how a forged piston could be swapped for a light weight cast piston and not negatively impact the engines longevity. Counterweights are sized to match a particular piston weight. At the rpm that these engines operate at even a small imbalance would seem to be damaging to the engine.

Mike

There is no such thing as a "perfectly balanced" single cylinder engine. The counter-weights are not equal to the piston weight, not even close. If the crank weights perfectly countered the piston's weight, the engine would be perfectly smooth in the vertical plane but would shake like an out-of-balance washing machine in the fore-aft plane. Single-cylinder engines typically use balance factors of around 60%-65% to make them as reasonably smooth as is feasible in all planes within the typical operating range the engine will be used in. So changing the balance factor by adding or reducing reciprocating weight will change the rpm range in which vibration occurs, but won't significantly change the vibration levels unless a LARGE amount of weight is added or subtracted.

In most cases, the complete Wiseco assembly is very close to OEM and often slightly lighter. But a difference of a few grams will be hardly noticeable in terms of vibration.

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The counter-weights are not equal to the piston weight, not even close. .

Perhaps it would have been easier to understand if I had said a particular sized counterweight is used for a particular piston weight. They are in fact matched to each other but they are not equal.

Mike

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Im always wondering about things like this also but no one has mentioned where the weight of the piston is at. Piston goes up and down and id think as long as the piston itself is balanced then only the centrifugal force may be affected.

Id prefer Forged over cast anyday just because of the catastrophic failure rate.

Also who just fires their 4 stroke up and rides away ? . I Dont see why forged would take a substantial amount of time to warm up, theres too many variables to consider (Temperature, Idle Rpm,Fuel,Jetting,Ring Gap Clearence, Piston/Bore Clearence And probably more.

🙂 If your one of the guys who starts it and instantly makes sure you rev limiter is working.

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