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WHY WOULD U REDUCE CRANK COUNTER WEIGHTS #1160335 01/18/12 08:19 PM 01/18/12 08:19 PM
Joined: Apr 2005 Posts: 1,505 TN S SCATPACK 1 OP pro stock
SCATPACK 1 OP pro stock S Joined: Apr 2005 Posts: 1,505 TN	Have read a couple of post relating to reducing the outside diameter of a cranks counter weights. Why would u want to or need to do this Old Geezer Racing

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: SCATPACK 1] #1160336 01/18/12 08:26 PM 01/18/12 08:26 PM
Joined: Dec 2006 Posts: 3,395 Pa Hot 340 master
Hot 340 master Joined: Dec 2006 Posts: 3,395 Pa	to reduce rotational weight, and for short rod/low deck combos with long strokes for piston skirt clearance

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: SCATPACK 1] #1160337 01/18/12 08:35 PM 01/18/12 08:35 PM
Joined: Aug 2003 Posts: 43,180 Bend,OR USA C Cab_Burge I Win
Cab_Burge I Win C Joined: Aug 2003 Posts: 43,180 Bend,OR USA	It is usually done on Mopar BB or Hemi cranks being cut down to use in low deck blocks You cut the counterweights down to clear the main webs as well as cutting down the main sizes. Another reason to do this is to reduce rotational weight in the crank when your switching to ultra lightweight racing parts, rods, pistons and writs pins Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: SCATPACK 1] #1160338 01/18/12 09:02 PM 01/18/12 09:02 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	I do it to MOST of my cranks for 3 reasons... 1 to get the counter weight close for balancing... 2, move the weight in closer to the center line so it can accelerate quicker and 3, move it farther away from the oil

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: MR_P_BODY] #1160339 01/18/12 09:16 PM 01/18/12 09:16 PM
Joined: Apr 2005 Posts: 1,505 TN S SCATPACK 1 OP pro stock
SCATPACK 1 OP pro stock S Joined: Apr 2005 Posts: 1,505 TN	Ok. Makes good sense to me. Old Geezer Racing

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: MR_P_BODY] #1160340 01/18/12 09:47 PM 01/18/12 09:47 PM
Joined: Feb 2007 Posts: 970 Backwater, PA B bwdst6 Bob George Racing #1 Fan
bwdst6 Bob George Racing #1 Fan B Joined: Feb 2007 Posts: 970 Backwater, PA	Quote: I do it to MOST of my cranks for 3 reasons... 1 to get the counter weight close for balancing... 2, move the weight in closer to the center line so it can accelerate quicker and 3, move it farther away from the oil Number 1 and 2 contradict each other. This post is available in double vision where drunk.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: bwdst6] #1160341 01/18/12 09:59 PM 01/18/12 09:59 PM
Joined: Jan 2010 Posts: 588 Franklin, TN 23T Hemmee mopar
23T Hemmee mopar Joined: Jan 2010 Posts: 588 Franklin, TN	Not if you're balancing to a light rod/piston assembly. Ronny 6.789 @ 198.63 .956 Brand New 60'* 4.17@ 169 1/8th mile John 14:6 https://www.youtube.com/watch?v=TUku_hjYRh8

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: bwdst6] #1160342 01/18/12 10:00 PM 01/18/12 10:00 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	Quote: Quote: I do it to MOST of my cranks for 3 reasons... 1 to get the counter weight close for balancing... 2, move the weight in closer to the center line so it can accelerate quicker and 3, move it farther away from the oil Number 1 and 2 contradict each other. Not really.... if you run light parts you dont need all that weight out far from center line

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: 23T Hemmee] #1160343 01/18/12 10:07 PM 01/18/12 10:07 PM
Joined: Feb 2007 Posts: 970 Backwater, PA B bwdst6 Bob George Racing #1 Fan
bwdst6 Bob George Racing #1 Fan B Joined: Feb 2007 Posts: 970 Backwater, PA	Quote: Not if you're balancing to a light rod/piston assembly. the absolute value to counterbalance is irrelevant. Whatever the number you determine to balance will result in the same rotational inertia regardless of diameter. If you want the weight on a smaller diameter you will add more of it! This post is available in double vision where drunk.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: bwdst6] #1160344 01/18/12 10:26 PM 01/18/12 10:26 PM
Joined: Nov 2004 Posts: 4,330 Lynchburg, VA Leon441 master
Leon441 master Joined: Nov 2004 Posts: 4,330 Lynchburg, VA	If you find your crank is heavy for your parts. You have a choice either cut holes on every counterweight to get in balance or simply trim the counterweights until you get close. Career best 8.02 @ 169 at 3050# and 10" tires small block power.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: bwdst6] #1160345 01/18/12 10:27 PM 01/18/12 10:27 PM
Joined: Jan 2003 Posts: 5,894 Florida Locomotion master
Locomotion master Joined: Jan 2003 Posts: 5,894 Florida	Quote: Quote: Not if you're balancing to a light rod/piston assembly. the absolute value to counterbalance is irrelevant. Whatever the number you determine to balance will result in the same rotational inertia regardless of diameter. If you want the weight on a smaller diameter you will add more of it! Basically, it is much more efficient to cut down the overall diameter of the counterweights to eliminate the unneeded weight to balance rather than keep the overall diameter the same and drill them full of holes to reduce the weight. The smaller radius will allow for faster accelleration as well as reduced windage. I believe it will also reduce the stress/flex the crank experiences. Last edited by Locomotion; 01/18/12 10:29 PM.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: Leon441] #1160346 01/18/12 10:32 PM 01/18/12 10:32 PM
Joined: Jun 2003 Posts: 52,972 Romeo MI MR_P_BODY Master
MR_P_BODY Master Joined: Jun 2003 Posts: 52,972 Romeo MI	Quote: If you find your crank is heavy for your parts. You have a choice either cut holes on every counterweight to get in balance or simply trim the counterweights until you get close. Yep... if you need to drill... turn it down more... but alot of the guys that balance find it easier to drill

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: MR_P_BODY] #1160347 01/18/12 10:36 PM 01/18/12 10:36 PM
Joined: Jan 2003 Posts: 31,035 Oregon A AndyF I Win
AndyF I Win A Joined: Jan 2003 Posts: 31,035 Oregon	You have to do a little bit of math to figure out how much material to remove in order to balance the crank when turning. I usually try to get the crank within 50 grams on the lathe and then let the balance guy finish the job on the balance machine.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: Locomotion] #1160348 01/18/12 11:15 PM 01/18/12 11:15 PM
Joined: Feb 2007 Posts: 970 Backwater, PA B bwdst6 Bob George Racing #1 Fan
bwdst6 Bob George Racing #1 Fan B Joined: Feb 2007 Posts: 970 Backwater, PA	Quote: Basically, it is much more efficient to cut down the overall diameter of the counterweights to eliminate the unneeded weight to balance rather than keep the overall diameter the same and drill them full of holes to reduce the weight. The smaller radius will allow for faster accelleration as well as reduced windage. I believe it will also reduce the stress/flex the crank experiences. this is true only if you need to lose weight! Also, the smaller diameter does reduce Windage but does not effect acceleration. Rotational inertia effects acceleration which like I said remains constant per your desired weight to counterbalance. Ditto with flex/stess. This post is available in double vision where drunk.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: bwdst6] #1160349 01/19/12 12:15 AM 01/19/12 12:15 AM
Joined: Jan 2003 Posts: 5,894 Florida Locomotion master
Locomotion master Joined: Jan 2003 Posts: 5,894 Florida	Quote: Quote: Basically, it is much more efficient to cut down the overall diameter of the counterweights to eliminate the unneeded weight to balance rather than keep the overall diameter the same and drill them full of holes to reduce the weight. The smaller radius will allow for faster accelleration as well as reduced windage. I believe it will also reduce the stress/flex the crank experiences. this is true only if you need to lose weight! Also, the smaller diameter does reduce Windage but does not effect acceleration. Rotational inertia effects acceleration which like I said remains constant per your desired weight to counterbalance. Ditto with flex/stess. Let me present my theory/question in a simpler form; You're saying that a 10 lb 5" diameter wheel is not easier to accellerate than a 10 lb 10" wheel??? (Representing short cut counterweight vs tall drilled counterweight to achieve the same balance.) Despite the similar weight, wouldn't the larger wheel with weight further out be a little more difficult to accellerate? After all, the larger diameter has further to travel than the smaller diameter. I said "similar" because less weight would be required to balance as the counterweight is moved further out. But the extended travel radius would have to be a hinderance. Am I getting in over my head and/or would this require some complicated mathamatical formulas to prove or disprove? Last edited by Locomotion; 01/19/12 12:17 AM.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: Locomotion] #1160350 01/19/12 12:27 AM 01/19/12 12:27 AM
Joined: Jul 2010 Posts: 2,091 Delray beach, Florida P Performance Only top fuel
Performance Only top fuel P Joined: Jul 2010 Posts: 2,091 Delray beach, Florida	if you have two crankshafts with identical weights, but crank # 1 has a circumference of 8" and crank # 2 has a circumference of 6", crank # 2 will need less force to accelerate because the mass is closer to the center of mass. simple way to prove it to yourself. tie a 1 lb weight on a string 3 feet long, make up another one with a string 1 foot long. twirl them both and see which one is easier. keep in mind that a crankshaft in a practical application still needs to overcome the forces working against it outside of the engine such as more rotating mass, vehicle weight, etc. in some cases a heavier rotating assembly can be more beneficial to overall performance. i.e. heavy vehicle with a high reving, low torque small CID engine. Last edited by Performance Only; 01/19/12 12:33 AM. machine shop owner and engine builder

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: Locomotion] #1160351 01/19/12 12:47 AM 01/19/12 12:47 AM
Joined: Feb 2007 Posts: 970 Backwater, PA B bwdst6 Bob George Racing #1 Fan
bwdst6 Bob George Racing #1 Fan B Joined: Feb 2007 Posts: 970 Backwater, PA	Quote: Let me present my theory/question in a simpler form; You're saying that a 10 lb 5" diameter wheel is not easier to accellerate than a 10 lb 10" wheel??? No, obviously not. First of all that assumes a homogeneous disk with one material. Real cranks have mallery (spelling?) possibly, undercut counterweights sometimes and somtimes holes on the OD. When one goes to balance a crank the weight of the pistons, rods, underbalance/overbalance gives you a bob weight. That tells you a rotation mass you need to counter balance. That's set!!! To counterbalance it you either need to put less mass on a large diameter or more mass on a small diameter. But it will be the same rotational mass. And will be the same to accelerate! F=ma. In a rotational system. If F remains constant and m (rotational mass) remains constant then a remains constant. This post is available in double vision where drunk.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: bwdst6] #1160352 01/19/12 01:16 AM 01/19/12 01:16 AM
Joined: Nov 2009 Posts: 2,177 ill D dennismopar73 top fuel
dennismopar73 top fuel D Joined: Nov 2009 Posts: 2,177 ill	I think every one is right ! Lite weight is always good, can be less bearing fatigue, mains can see longer use, increase in rpm range. Thus more harmonics the block has to endure, Loss of 'initial hit' over come by increase in tq rate of stahl, thus increasing thrust bearing issues? OO the domino effect, Ain't it great!! I will do it to clear the block,other wise I don't worry about it.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: bwdst6] #1160353 01/19/12 01:24 AM 01/19/12 01:24 AM
Joined: Jan 2003 Posts: 5,894 Florida Locomotion master
Locomotion master Joined: Jan 2003 Posts: 5,894 Florida	I understand the "set" amount of rotational mass required to balance a rotating assembly. We're just saying that the distribution of that mass away from the centerline will affect how quickly the rotating assembly can be accelerated. I'm tired, gotta work early tomorrow & all this thinking is giving me a headache! G'nite.

Re: WHY WOULD U REDUCE CRANK COUNTER WEIGHTS [Re: Performance Only] #1160354 01/19/12 01:25 AM 01/19/12 01:25 AM
Joined: Dec 2008 Posts: 415 Peru cbarracuda mopar
cbarracuda mopar Joined: Dec 2008 Posts: 415 Peru	Quote: if you have two crankshafts with identical weights, but crank # 1 has a circumference of 8" and crank # 2 has a circumference of 6", crank # 2 will need less force to accelerate because the mass is closer to the center of mass. Nunber 2 will meed more weigts because tre mass is closer

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