Piston And Rod Balancing New Post

[joed]

I HAVE A 2.4 WITH MERC STANDARD PISTONS AND ROD #636-8118
I WOULD LIKE TO GET SOME FEED BACK ON BALANCING MARGINS
PISTON TO PISTON, ROD TO ROD AND ENTIRE ASSEMBLY TO EACH
OTHER. THIS MOTOR HAS BEEN PORTED AND SHOULD TURN BETWEEN 7000 TO 7500. ALSO WERE TO TAKE THE WEIGHT FROM

[Jay Smith]

If you have a cast piston motor and I assume you do I would not get aggressive with the cuts on those pistons as they are VERY fragile. When we balance a piston , rod , wrist pin they are at "0" difference between the 6 assyemblies in grams.........Every combanation of rod , piston , and wrist pin weighs the exact as the other 5 assyemblies... Different people take off from different areas on different parts such as pistons and rods. The wrist pins are very hard and cannot be cutexcept with a boron tooling and a CNC lathe. You are undertaking one of those projects that when you get half way through you will be kicking your own ass for starting it and not having it done and done correctlywith out tooling and machinery its a time consuming nightmare !

just my opinion

[B.Leonard]

Forgive my Merc ignorance for a moment but...

I was talking to a guy the other day who has run quite a few Mercs (not on this board) and we were discussing that bobb weight issue. He was telling me that bobb weight is indeed a big issue and that counter weights must be turned down accordingly. He said that putting a 2.4 crank in a 2.5 motor is a good example and will cause the the crank to break due to the bobb weight being different. And vise versa 2.5 in a 2.4 motor.

Was I being fed genuine Bovine Surplus by this guy? :D

-BL

[Jay Smith]

Heavy weighted rotating objects such as turbine shafts, pump shafts , oh yea crankshafts with a small or narrow"throw"such as Mercurysthat have most of thier weight close to the center of the axis of rotation and has a VERY bad HARMONICS need weight to dampon this hi frec. harmonics. I have been a part of race teams that have the big $$$ lightened and knifed cranks and they are nortorious breakers and in my opinion a smoke show to raise the revinue of some of the companys peddling these services. I have seen SEVERAL of these pieces for sale on these boards as I suppose people are testing and seeing the adverse effects of these cranks to thier motors. Years back I took a Mercury crankshaft to a big $$$ race car shop in Houston that I respect as these guys make tons of power and had a crank bobweighted and guess what , the guy told me the cranks were TOO light that was the reason for the harmonics and for me to remove as much weight as I could from the end of the rod and that is what I have been doing the last several years and I might add have been successfull at it as high points championships and 10,850 rpms turning and living ( 2 years of trouble free racing ) motors has followed with this method.

I have seen 3 of these light weight cranks brake
all owned by the same customer , also the more material you remove from the chamber that is being compressed with the down draft of the piston to create crank case compression and AIR SPEED as more volume is created the lazier the motor becomes . Thats just common knowledge on 2 cycles.One can listen to 10 people and get 6 different answers and reasoning behind why they have reached any conclusion. My quanification is #1 winning and #2 longivity after all if your the fastest guy in the world in the first round or the first lap and if this motor comes unwound like a 2$ shirt its a mute point. Also one can get caught up in RE INVENTING the wheel so to speak , myself I haven't the time wondering if we really went to the moon, and if Elvis is really dead and who killed Kennedy and I really wonder about the guys sitting around wanting to discuss and debate those type of nonendingh time eating sillyness , the "what if " theory has made couch potatos out of alot of folks myself I am a do er I have too much work to do but I sometimes WISH I DID have that much free time on my hands to THINK and WONDER cause just thinking about it Oswald could'nt have acted alone or could he ???? LOL....................

just my opinion again...........

[Dave S]

Hole lot of shaking going on:) Raceman is realy Elvis,thats why he can buy all those toys. :D It seems Merc used the same crank in 150s and 200s with big and small rods, I don't think they used different cranks with all those combos. Ask 10 get 6 answers. What I used to do, is take all the weights and put the lite rods smallend with the heavy pisten. If you do the same with the big end,you could put heavy with lite to get a match in weight. The more it is out to start with, the better you can match balance.

[WATERWINGS]

AAAHHHH, don't you mean Jerry Lee??:eek: :D