Adding Crank Weights for a Big Piston (KT100)

Burris Racing said:
Another myth that popped up on here is that "forgings are heavier" than castings. The truth of the matter is with equal mass (especially something like a piston) there is very little difference. The reason castings were lighter in many cases was the shape was more intricate but forged pistons have evolved to where they are near net shape and require very little machining and because of their strength and ductility can have thinnersections cast weaker less ductile castings. We have a forged replacement piston for the cast Rotax and it weighs 15 grams less!!
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Actually, for a given volume of material, forged aluminum IS heavier than cast aluminum. It is "denser", since the material and grain structure has been compressed in the forging process.

A better explanation (of piston weights) would be that a forged piston can be made lighter than a cast piston *IF* the design is optimized for forging.

PM
 
Sorry about that pete your right my actual growth was only.0001 at 378F differential temp, acording to your formula. So I must have gotten more shrinkage from the liquid nitrogen than I thought but that would only be another .0001 from your formula. I which i would have measured the plugs to actually see how much I did get. All I know is that the plugs went completly in with few light taps from a 10ounce hammer. I was in a hurry to install them while they were still at coldest point from their removal of the nitrogen. Maybe Jon will be able to get that info when he does his crank. I would like to know how the density of tungsten differs from steel in the actual amount of contraction. The pluges did vary .001 in diameter on the four of them i had and i used the smallest 2 of them. I thought that forged peices were heavier than cast if the same amount of material was used. The density of the compressed molacules is also what helps give the added strength to forgings. So for a forged piston the thickness of the dome and skirt must be much thinner to be as light as cast. I never have used cast anything in hi-proformance builds cranks or pistons. Thats why I like the strike pistons they have a very high Silacone (17)% content and are extremly hard, strong and heat resistant. They are very heavy but can be lightened quite a bit. Thats why I did this crank balancing project ,to use them. I assume that Yammi cranks are cast thought at least the flywheels are very soft. I guess they could nitrate the shaft parts or heat treat them for added strength dont know their process for manufactoring. I have sleeves on my cranks which I know are hardened and also increase the total diameter of the shaft at the bearing points. sleeves are used to reduce the wear on the shaft so it must not be very hard.Thanks for your info in the discussion Pete your knowledge is appreciated.
 
sundog said:
Great, nerds that are cyber bully experts. I guess the guy who trained me was wrong about that so I'm wrong too. You got me good so, maybe you guys can go high five each other. Anyway, now I'm jaded so, screw these forums, I'm never posting advise or projects again because apparently I'm an idiot. Post whatever after this, I ain't coming back.
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Well, I can't say that I'll miss you, but with an attitude like that, maybe it's best that you don't come back. A diversity of opinions, in my estimation, is the thing that makes Bob's such a great place to seek advice. I'm pretty sure nobody is disagreed with more than me, but I keep trying. In fact, I don't think anybody has more posts deleted than me. Just a guess.

Still, if you hold to your word, you won't read this anyway. lol
 
old but interesting topic.

Who's added weight to a crank with a 52.7-52.9 piston on it, how much did you add, what were the results? I think the piston weight on my 52.9 motor is 124 grams

Thanks,
 
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