Crank Balancing

[ClayGlover]

eric perez, i need some advice and i know you've got lots of mod experience with car motors. i picked up a never started rear exhaust NR .12 that has a "turbo cut" hand done to the crank. it looks clean like whoever did it knew what they were doing, but my question is will this throw off the cranks counter-balance? :- thanks bud

 

[TimD]

Re:? for rigger dance perez

Clay,

Check the crank balance! you will get more performance from a properly balanced crank than you would from a turbo cut.....

 

[ClayGlover]

Re:? for rigger dance perez

i hear that! thanks tim

 

[ClayGlover]

Re:? for rigger dance perez

oh, how the heck do you balance a crank? make some kind of bearing for it to spin in/on and hang the rod and piston on it? then spin and then remove material where needed? ??? lol, don't worry, i know where i shouldn't cut ... thanks

 

[ClayGlover]

Re:? for rigger dance perez

ok, i did some searching and found this info for those interested in this-

http://www.prestwich.ndirect.co.uk/technic...l_balancing.htm

http://www.rcboat.com/cgi-bin/yabb/YaBB.pl...312040;start=16

hmmm, well i'll just have to fire it up and see what happens i guess. ;D

 

[TimD]

Yep,

that is how it's done........ Can really change an engine's behavior.

 

[Eric Perez]

The short article is not too far off the mark. The problem with balancing act is that you cannot balance the crank statically (like a prop or air-plane spiner). The engine will have a different balance point at different RPMS. Also the stress of a slightly "unbalanced" crank is not going to be worst than the stress of the combustion pulses on the crankshaft assembly.

I have yet to see any negative effects of cutting cranks, knife-edging connecting rods or removing portion of the piston skirt on engine operation.

My theory is that the counter-weight on the crank-shaft is more important for reducing the requirements on the fly-wheel (less inertia) than anything else.

I'm having problems finding the book with the actual formula for engine counter weight design. I will continue to search -It's just a matter of time until the book turns out...