Weighted cranks

So by that theory when you balance a tire you can just put the weghts wherever right?
 
nwpadmax said:
I think it's possible that from an engine balance and longevity standpoint, maybe the motor is happier with the mass in it.

But I don't see how the wheels know where all that twisting force is coming from. You could have two flywheels with the same exact rotational inertia....one from a dense material like iron that's small in diameter and long, versus an aluminum one that's bigger around and narrow.

It all just comes out to foot-lbs of energy storage, methinks. Work to accelerate = work to decelerate. You store up the energy on the line spooling it up, and you get it back at the end of the track when the sled goes *wham*.
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My feeble mind says it would be happier being supported betwixt the bearings, but on the flywheel it is betwixt the main and the pilot bearing. Granted if it is balanced it shouldn't matter, but then take into account any runout and assembly tolerance, you maybe able to get a better balance putting it on the crank, but maybe more beneficial on the large diameter of flywheel.
 
TheBigNasty said:
So by that theory when you balance a tire you can just put the weghts wherever right?
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We're talking apples and oranges.

In balancing, yes, you change the location and you have to change the weight too. Like adding weld versus Mallory....they don't use the same mass, it's different depending on where it is. If you could balance a tire by sticking the weight out on the tread, it would be a different mass than you would put on the rim.....but it would still be balanced.

What I was talking about is the energy you get back on the pulling track. Like the one fellow said, it "makes more torque".....well, the combustion part is not making more torque, but you get more work out of the heavy assembly when the sled loads you up.
 
zstroken said:
My feeble mind says it would be happier being supported betwixt the bearings, but on the flywheel it is betwixt the main and the pilot bearing. Granted if it is balanced it shouldn't matter, but then take into account any runout and assembly tolerance, you maybe able to get a better balance putting it on the crank, but maybe more beneficial on the large diameter of flywheel.
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This is my way of thinking! A heavy flywheel does more than put stress on just the rear main bearing. Think of it like this, you are bench pressing and the weight on one end of the bar is suddenly removed, the light end of the bar suddenly goes up in the air! Same thing applies in an engine with an extremely heavy flywheel, light end of crank goes up, now every time a cylinder fires the crank is being slammed down, it's only a small amount of movement but this creates torsional flex which in time will break the crank.
 
if it is just a heavier flywheel the weight would be balanced if the weight was consistant around the diameter.

I understand inertia, but seem to be stuck on leverage times added weight/inertia

My thoughts - 25lbs equally spaced around the curcumference of the crank which is lets say an 8" diameter will exert 4" x "x" amount of leverage on the driveline

whereas an extra 25 lbs added onto the last 4" of the diameter on a 24" flywheel would be 12" x (8"x mass) x "x" of total leverage

"x" being the addded weight

have i expressed this right?
 
zstroken said:
My feeble mind says it would be happier being supported betwixt the bearings, but on the flywheel it is betwixt the main and the pilot bearing. Granted if it is balanced it shouldn't matter, but then take into account any runout and assembly tolerance, you maybe able to get a better balance putting it on the crank, but maybe more beneficial on the large diameter of flywheel.
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I think you're right....if you put the mass on the flywheel, it had better run perfectly true or you'llhave all kinda vibration from it.

So you'd have to assemble it all and then put it on a lathe/grinder and turn it, keeping location marks and whatnot, then reassemble later with a real precision fit.

I agree, though, probably more effective inside the motor from a precision stanpoint.

All I'm saying is that I'm not sure the sled knows where the mass is. Just that there is a bunch of it somewhere that keeps it tooling along.
 
Weight between the throw's would significantly help dampen the hammering from combustion, with the added benefit of inertia for the heavy end.

Lowering the peak pulses between each throw, should net a higher max torque capability of the shaft.
 
Joesixpack said:
Weight between the throw's would significantly help dampen the hammering from combustion, with the added benefit of inertia for the heavy end.
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Yeah, I see what you're saying....the overall twist in the crank is less becuse the mass is closer to the point of application.

A big heavy flywheel would aborb the hammering too but there would lots of twist to the crank. Cylinder #1 pulse has to travel the length of the crank before the flywheel even sees it.
 
so best of both worlds would be a fully counterweighted crank for harmonics, plus a heavier flywheel for inertial increases
 
Heavyer rotating assembly will add low end torque.

Years ago I swap Mitsubishi 1.8TD engine to Mitsu Galant 4wd originally it was 2.0 Doch.
Because 4WD Galant needs different style I decide to use gas engine flywheel in my swap.
Gas engine flywheel will bolt on to diesel engine, but it is 5 kg lighter than diesel (7kg versus 12kg diesel)

After first test dive I found out, with very light rotating assembly you must keep rpm's very hight for normal driving and there is almost no low end torque,like normally diesel have.

I modiefied diesel flywheel and intalled, after flywhel swap low end torque was back and now was very easy to drive.
 
nwpadmax said:
Yeah, I see what you're saying....the overall twist in the crank is less becuse the mass is closer to the point of application.

A big heavy flywheel would aborb the hammering too but there would lots of twist to the crank. Cylinder #1 pulse has to travel the length of the crank before the flywheel even sees it.
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Now you have the idea! :Cheer:
 
stuckey_272002 said:
im not sure how much they add either. but they do it so the engine will make more torque adding weight has almost the same effect as stroking the engine but does not add any cid. and it makes the crank easier to ballance.
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What??

Adding weight to a crankshaft has absolutely zero effect on the torque output of an engine.

Added for balance...yes...

Added for more rotating mass for inertia...yes..
 
partsguy662 said:
What??

Adding weight to a crankshaft has absolutely zero effect on the torque output of an engine.
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That's kinda right, however; how would we measure the sustained inertia gained by beefing up the crankshaft? Hmmmmmm........

Charles?
 
partsguy662 said:
What??

Adding weight to a crankshaft has absolutely zero effect on the torque output of an engine.

Added for balance...yes...

Added for more rotating mass for inertia...yes..
Click to expand...

Snedge said:
That's kinda right, however; how would we measure the sustained inertia gained by beefing up the crankshaft? Hmmmmmm........

Charles?
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I think this thread is boiling down to how everything is phrased.

Increasing the mass of a rotating assembly will increase the energy storage within that system. In this case, the bottom line is when the sled hits, you will go further than an identical truck without a weighted crank. Why? Increased energy storage in the rotating assembly which will buy you a few more feet before the tires break traction or you fall under the turbo. It could be viewed as "adding torque" when in reality, the additional weight is just storing more energy.
 
Here is what I know based on my very limited knowledge.

Take a mid 80's Simplicity Garden tractor, 42" deck, 12hp Kolher Engine.

Now take a late 90's MTD, 38" deck, 12hp Briggs and Stratton.

Now the Simplicity has a 4" bigger deck but a cast iron flywheel. The MTD had a aluminum flywheel.

The Simplicity would mow all day (blades sharp on both) through 2.5' to 3' pasture (weeds, small trees, grass) and not bog down when going slow. The MTD would buck and bog going through stuff half as tall. Also the Simplicity when bogging, could get to a pretty low rpm before quitting.

Now the same old adage goes, there's no replacement for displacement.

We transplanted a 21hp V-twin into the MTD. The deck would float off the ground when engaged:charger:.
 
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