11:29:33pm, Saturday, May 11, 2024
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counter balanced crank
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666 Red
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What does it mean to have a crank counterbalanced and what does it involve? Can you run a diff piston and rod weight after you have a crank counterbalanced or if you change from a diesel setup to alcohol? What does it cost to have an IH shaft done? Thanks 666 Red |
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Re: counter balanced crank
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John Hoffman
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Talk to Terry Blackbourn he does a great job on these cranks , I had a 300 series motor with 10 years on the same bearings , His phone # is 608-574-2173 |
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Re: counter balanced crank
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Posts: 347 |
So counterweighting a crank dramatically improves bearing life?? How hard were you turning this 300 series?? |
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Re: counter balanced crank
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Kevin Campbell
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John,
Good luck with the new tractor. I am sure it will be nice. Kevin |
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Re: counter balanced crank
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puller1234
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Greatly increases your rpms. You weld counter balance back on your crank(rod side) allows you to run lighter pistons and rods. need less counter balance because of the decreased weight . Engine gains rpms easier , less vibration and better bearing life!!! Call "Illinois crank shaft" a stock shaft will cost you $3500 to have balanced . |
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Re: counter balanced crank
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666 red
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so is the crank counterbalanced to a specific rod and piston weight? If it were set up for diesel and you went with a light forged alum for alky would you have to have the crank re counterbalanced? Thanks 666 red |
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Re: counter balanced crank
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Registered: 03/31/2008 Posts: 762 |
My opinion is that puller1234 is way off. First, the counterweight is added OPPOSITE the rod journal to compensate for the journal weight & a percentage of the rod/piston weight. Many ag diesels (including I believe the 359 IH) have NO counterweight opposite the journal from the factory. I've been told (by So Ill Crank) that you can't fit enought counterweight between the pan rails on most or all Ag applications. You may be able to get enought counterweight on a short stroke alky motor with aluminum pistons & rods but that's about it.
Tie something heavy to an end of rope & swing it in a circle. Notice how it pulls you hand/shoulder towards the weight as it goes around? That's whats happening to your crank & the bearings have to take the load your hand/shoulder takes. If you can keep another rope wiht a weight directly opposite the first one it quits pulling on your hand/shoulder as one weight counteracts the other. If the rope is longer the counterweight can be smaller & this is what racers try to do since more mass takes more power to accelerate & decelerate. Pullers in turbocharged classes tend to come off the line at max RPM's so extra mass in the flywheel & crank help more than hurt. Balancing does little to change the motor RPM directly, it mostly allows bearings to live at the RPM's you're trying to run. That weight on the rope starts to pull harder the faster you swing it, that's why these cranks are fine at 2500 RPM but take out bearings at 5000. With a 6 cylinder it will start with the center main because #3 & 4 are on the same side of the crank so the imbalance at that journal is the highest. 666 Red - So Ill Crank (or whoever you're going to have do your work) should be able to tell you for sure but I don't think either the alky or smoker will be completely neutral so you should be able to switch as long as both sets of rods & pistons are balanced within each set. |
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Re: counter balanced crank
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Key Board
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most modern engines have counter wieghts, not sure what 359 your talkin bout. IH had a 358 german that had removeable wieghts. you have a point.... but not sure if you know what your talkin about. lol |
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Re: counter balanced crank
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Posts: 508 |
Have seen crank counterweights drilled and heavier material pressed into the holes! makes more sense to lose weight in the piston and rod end of things! no sense turning your crankshaft into a second flywheel. |
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Re: counter balanced crank
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666 red
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I found a counterbalanced crank for a 300 series IH that was set up for disel light lim pro. Do you think the counterbalance would be close enough if I juat changed pistons for an alky setup? thanks again Red |
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Re: counter balanced crank
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Anonymous User
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new pistons equals new balance job unless you know the weights of the pistons and rods the crank was balanced to and can match these weights.i balance my pistons and rods myself on a set of automotive paint scales as they will weigh grams.then send my crank to the shop with the weight numbers so they can add or remove weight as needed.doing the rods and pistons yourself saves a lot of money since most shops charge by the hour and you are working with grams.your engine will live a lot longer and it will be money well spent.if you are off just a few grams,at 6 or 7000 rpms how many pounds do those 1 or 2 grams turn into? |
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Re: counter balanced crank
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TJ
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Disconnect the rods from a crankshaft and the crankshaft itself should be pretty close to being balanced. That being said why try to counter balance it? The balancing should be done with the rods and pistons you put in. All rods with end caps, bolts, and bearings should weigh the same, all pistons with bearings, wrist pins, and rings should weigh the same. If not shave some weight off to match the lightest weight reading you have. Thats my opinion. |
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Re: counter balanced crank
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for real engine engineer
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Simple answer...if the diesel crank was counterweighted correctly for the diesel pistons/pin/rings/small end rod (50% balance factor), and if you go to a lower CR than diesel, you can assume your piston will be lighter if the rod length and wrist pin comp height are the same. So for the same 50% BF you can drill out the counterweights vs. adding a heavy metal to the counterweights.
Most likely though, the stock diesel crank with added counterweight is less than 50% BF. Diesel pistons have huge top ring lands and comp heights which equal heavy mass, so packaging that much counterweight is not possible between the pan rails or between the crank webs. So the lower alcohol piston mass will help get the BF closer to 50% and you should be safe with running the same crank untouched. |
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Re: counter balanced crank
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for real engine engineer
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I'll attempt to give you a simplified answer to a complex engineering issue. Counterweighting a crank is simply adding bob weights 180 degrees from each crank pin. That's it really.
Why counterweights are needed: on 6 cylinders, they aren't needed at all for shaking force suppression. In an inline 6 cylinder, the first and second order shaking forces are canceled completely. This is why 6 cylinder inline engines appear to be smooth running and have low vibration to the chassis and operator. However internal to the engine is a different story. Typically each cylinder on a crank is balanced to 100% of the rotating mass (rod big end, crankpin) and 50% of the reciprocating mass (piston/pin/rings/small end of rod). This offers the best compromise to packaging weights on the crank and acceptable reliablity of the crank itself. The purpose of the counterweights is to cancel the centrifugal force of the pin and big end of the rod, and that takes load off the bearing shells. Ultimately if a crank is counterweighted correctly, main bearing life is extended due to less deflection of the crank, due to less centrifugal load. And the centrifugal force goes up with the square of the RPM.....so a crank that was designed to turn a corn picker all day at 1800 RPM, will have high bending (meaning high deflection especially in the center mains) and low bearing life at 5000 RPM. Older stock tractor cranks were not counterweighted since the RPM was low (meaning centrifugal force was low enough that it didn't effect main bearing life), and main pins and crank pins were very large making the crank stiff enough so bending and torsional modes were completely out of the operating RPM range. There are really 2 main issues with adding counterweights to a stock inline 6 tractor crank. The first is that any mass added to the crank will lower the natural frequency of the crank in torsion and bending. It could lower it enough that it occurs in the operating RPM range of the engine. If the engine RPM and the natural frequency line up on each other, the deflection is greatest and could destroy the crank and main bearings quickly. A simple analogy: pay attention to your refrigerator compressor as it turns on and off......within the 1st second of start up, it vibrates heavily and then smooths out and vice versa on shut down. The natural frequency of the motor/compressor is within the operating range. The reason for this is that the motor/compressor is on very soft mounts, so the natural frequency is very low. This is acceptable as the vibration magnitude is low. However on a crankshaft, the design goal is to get all bending and torsional natural frequency modes at least 1.4 times the operating range of the engine. And dampers on the front of the crank are important to limit the torsional deflections of the crank. To be honest, for the cost of counterweighting a stock crank, it pays to go with a fresh billet. Counterweighting a stock crank adds stress risers everywhere which only means many more places for cracks to start propagating. |
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Re: counter balanced crank
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Registered: 06/03/2008 Posts: 44 |
WOW! Lots of good detailed information. I had to read it a couple of times, just to get it all to sink in. Where did you learn all of that? |
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Re: counter balanced crank
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Posts: 508 |
Thanks very informative! maybe you can expand my limited knowledge in regards to harmonics in horizontally opposed engines. most if not all 4 cly. aircraft engines have no crank counter weight, but they do have a large flywheel,as in a 72" plus propeller on it's end.also some models have a general admonishment not operate at roughly 1500-1900 rpm.I may be wrong on the exact number as I dispersed my cessna years ago. Anyways my question is in regards to the larger 6 cly. eg. the 540 Llycoming and 550 Continental, both have swinging counterweights at centre of the crank assembly,would these weights be strictly for controlling balance and harmonics of centre cylinders or would they benefit the whole assembly? one issue with these weights,if sudden engine stoppage they will crash into the crank! thanks again and keep the lessons coming! |
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Re: counter balanced crank
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Registered: 03/01/2009 Posts: 133 |
I went to a counterwieghted crank half way through the season and found that it ran smoother as in less vibration. We run a 300 series motor. I had to change the length of the piston for the counterwieghts. Also had to do alot of grinding in the block for clearance of the counterwieght. Overall I'd do it again less vibration. We are a diesel lss. Tryin to run between 4500 - 5000 rpms down the track. Hope that helps. Edited 1 time(s). Last edit at 11/14/2009 12:09AM by IHC686. |
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Re: counter balanced crank
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mike sandefur
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Sandefur performance can counterbalance any 6 cylinder crankshaft. most between $1500 and $1800. diesel or alchohol. call 812 371 3677 |
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Re: counter balanced crank
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for real engine engineer
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These are pendulum weights and I have no experience with them. But this is a paragraph directly out of a text that I reference once in a while on balancing:
"In some engines where the weight penalty involved in the use of counterweights is considered a serious disadvantage a device known as a pendulum damper has been used successfully. This damping system consists of suitable massess which are attached to selected crank webs in a matter which permits limited movement. When the shaft tends to accelerate under the action of cyclic torque fluctuations the pendulum bobs lag behind and absorb some of the energy imparted by the increased torque only to give it back again to the system when the torque drops below the mean value established at the driving end of the shaft." |
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Re: counter balanced crank
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666 red
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Thanks for all the input. Question, How are the counterweights fastened normally? |
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Re: counter balanced crank
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Registered: 03/01/2009 Posts: 133 |
There welded |
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