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Author Topic: Flywheel balancing question  (Read 31375 times)

Fairmountvewe

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Flywheel balancing question
« on: October 18, 2013, 03:32:28 AM »
Hi all.  I have a question, but first a little background.  A bunch of years ago, thanks in no small part to Rocketboy F1's excellent website, and a loving and understanding wife, I found myself in possession of a 12/2 engine.  Now here is where the fun starts.  The engine is internally counterbalanced.  The flywheels are the 6/1 counterbalanced type.  It seems to me that I need to "un" counterbalance my flywheels.  I have toyed with the idea of buying new ones, but a big part of me wants to solve this problem.  I have debated using an angle grinder to grind out the weight, but from all that I have been able to gather that is a messy, time consuming, fraught with potential failure kind of idea.  My son (a MatTech in the CF) gave me an idea. What would stop me from putting a bunch of lead opposite the counterbalance and effectively oppose the generated forces?  I really don't know.  What say ye?
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Horsepoor

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Re: Flywheel balancing question
« Reply #1 on: October 18, 2013, 06:37:05 AM »
I recommend a two-step process. First remove both flywheels: Construct a basic device out of scrap 2 X 4 piece about two feet above the flywheel laying flat on the ground. Through the center of the hub, you will run a cable or rope down from the 2 X 4 support above. If carefully positioned in the center of the hub, the heavier side will lean down. Apply stick on wheel weights to the opposite side until the suspended flywheel is level. The most difficult part is constructing a plug in the center of the flywheel hub to precisely center the lifting cable. CUJET had a cone which we drilled a hole through the center and threated the cable through. I think Home Depot sells wooded cones in the wood finishing section, if not, make something out of scrap metal.

Step one will get you very close assuming the internal balance weights are correct. Now for step two. Install your flywheels back on the engine and see how they run. Perhaps you are done. If not, do you own an iPhone? Then down load from the apple store this $4.99 application.

https://itunes.apple.com/us/app/vibration/id301097580

This program uses the iPhone internal accelerometer which runs at 100 Hz. You can measure and graph vibration in the X, Y, & Z planes. It does a really good job on low frequency vibration and only costs $5. You are only interested in the X & Y planes on a single cylinder. Check the graph, how much vertical vibration / acceleration do you have? Remember there is a power pulse on the piston. Try adding weight at a point on the flywheel. Did the vibration get worst or better? Repeat until you fine tune the rotation. You will never get it perfect, but you can measure your progress with each trial run and engine start. Keep a log book, divide you flywheels into at least six (6) 60 degree slices, twelve would be better, masking tape works well, and number them, 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, 330, 360. This is a time consuming process to fine tune your flywheels. You might get satisfactory results after step one, but if you need to go to step two, you can apply a lot of lip stick to a pig as I have done.
« Last Edit: October 18, 2013, 09:03:06 AM by Horsepoor »
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M61hops

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Re: Flywheel balancing question
« Reply #2 on: October 18, 2013, 06:42:36 AM »
I would add weight to balance the flywheels if it was mine.  To balance my 6-1 I made weights out of channel steel that straddled the ridge between the spokes.  Held in place with set screws and spray foam to try to avoid causing stress points.          Leland
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millman56

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Re: Flywheel balancing question
« Reply #3 on: October 18, 2013, 08:01:37 AM »
 Never tried equalising the mass of a Lister spoked flywheel but if I did I would maybe try removing the gib key, lubricating the shaft, adding a weight opposite the counterweight at the same radius and spinning the flywheel on the shaft several times and noting where the flywheel comes to rest each time,  adding weights until a random stopping point was acheived.     It would be a quick job to then fit the key and test the results on a running engine,   probably far to much friction on the shaft /flywheel  to be anything like as accurate as Horsepoors teetering rig  but I have noticed that the flywheels spin quite freely with oil sans key.     

The posts on flywheel balancing are interesting and very informative but to be fair I`ve never had one  (never had an Indian clone, thank the Lord !!)  that I thought was a problem and after all ,  these engines are state of the art 1930s diesel technology not gas turbines ;D

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38ac

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Re: Flywheel balancing question
« Reply #4 on: October 18, 2013, 01:05:50 PM »
Never ceases to amaze me what the Indians will throw together  gesh.  ???

No, you should not have both internal counter weights and weighted flywheels. Have you had this thing running?  I don't believe that Lister ever used internal weights? If so I have yet to see one. The Lister 12/2s and 16/2s that I have laid my eyes on both used off-set weight in the flywheels for balance and you have to pay attention to which side they are on because the heavy side is 180 opposite the keyway on one side and inline with it for the other side.  I would equalize the flywheels with weight opposite the cast in weight as a first attempt,,, if it were mine.
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Fairmountvewe

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Re: Flywheel balancing question
« Reply #5 on: October 18, 2013, 01:19:28 PM »
Thanks for all the replies, and thanks for the app info.  I will be looking into those.  I have a seismograph app on my iphone, but it is pretty simple (read free).  So it looks like the general consensus is to add weight, not to try and remove it.  Well it looks like my weekend plans are being arranged as I type.
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Tom

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Re: Flywheel balancing question
« Reply #6 on: October 18, 2013, 07:36:12 PM »
Well before adding that much weight please allow me to be the contrarian here and express a concern that concentrating that much weight on the far side of the flywheel may cause catastrophic disassembly. The counter balance weight that is cast into the flywheel is also a structural member of the flywheel. If this was my engine I would be inclined to follow your initial idea and grind off the counter balance weights to match the contour of the rest of the flywheel and then add lead weights to balance from there.

Can you confirm that there is indeed additional counter balance weights bolted to the crankshaft on your engine? If so those will need to be removed and the holes filled, perhaps by bottoming a bolt in the hole and grinding the head off.

A picture of the crank would also be interesting to see too.
Tom
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cgwymp

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Re: Flywheel balancing question
« Reply #7 on: October 18, 2013, 09:51:01 PM »
Well before adding that much weight please allow me to be the contrarian here and express a concern that concentrating that much weight on the far side of the flywheel may cause catastrophic disassembly. The counter balance weight that is cast into the flywheel is also a structural member of the flywheel. If this was my engine I would be inclined to follow your initial idea and grind off the counter balance weights to match the contour of the rest of the flywheel and then add lead weights to balance from there.

Can you confirm that there is indeed additional counter balance weights bolted to the crankshaft on your engine? If so those will need to be removed and the holes filled, perhaps by bottoming a bolt in the hole and grinding the head off.

A picture of the crank would also be interesting to see too.

Why remove the crank balance weights if he's going to neutral-balance the flywheels? He's gonna need balance weights somewhere. It if were mine (which it isn't & talk is cheap) I'd neutral-balance the flywheels (either by removing the existing weight or adding; doesn't matter from a math point of view), keep the crank weights, and then add only enough flywheel weight to tweak as needed -- same as Horsepoor's approach.
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cujet

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Re: Flywheel balancing question
« Reply #8 on: October 19, 2013, 02:04:34 PM »
On Single Cylinder Engines, the weight location is ALWAYS 180 degrees opposed from the crankshaft rod journal. Whether on the flywheels or on the crankshaft.

If, for example, you have flywheels that have a heavy spot in some random location, a dynamic balance, done as a running assembly, the counterweight will simply be off center from the 180 degree location by a small percentage.

From an engineering ideal, I'd rather have the counterweights on the crankshaft. Placing them on the flywheel adds a small additional stress to the crank and flywheels. However, I'm not at all convinced that a 650 or 800 RPM engine with a large flywheel weight is a risk in any way. A 2 pound weight, for example, at 650RPM simply adds about 250 pounds load to the flywheel/crankshaft. Not much more than simply standing on the flywheel rim.

One thing to be very mindful of: A properly balanced engine is always less stressed. Unnecessary vibration creates very high stress levels, that will far exceed the small load that the balance weights add.

The link is a neat tool to calculate force of a counterweight.

http://www.calctool.org/CALC/phys/newtonian/centrifugal
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xyzer

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Re: Flywheel balancing question
« Reply #9 on: October 19, 2013, 04:44:28 PM »
Hard to say what you have without a well planned test run. A 12/2 without internal balance in theory would take double the balance weight on each flywheel to counterbalance the same as a 6/1. The internal balance weights may only compensating for half of the imbalance and the external the balance. I would have to start it and see how it behaves............
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cujet

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Re: Flywheel balancing question
« Reply #10 on: October 19, 2013, 07:27:42 PM »
 A 12/2 without internal balance in theory would take double the balance weight on each flywheel to counterbalance the same as a 6/1.  

xyzer, that is completely true when pistons rise and fall together, such as on a parallel twin with a "360" degree crankshaft, such as many motorcycles. In such a case, placing weights on the flywheels and not the crank would be crazy. However, a parallel twin, like the lister, with a 180 degree crankshaft has perfect primary balance (one piston goes up and the other down, perfectly offsetting each other) but adds rocking couple, as the cylinders are side by side. The end result of a 180 degree crankshaft is an engine that has an uneven firing order, something weights cannot compensate for. And, in the case of the Lister Diesels with the cylinders quite far apart, extreme rocking couple. Something best compensated for, by 2 counter-rotating balance shafts.  

For those interested, Rocking couple can be demonstrated easily:

1) Move your fists up-down like a lister twin, as quickly as you can (right in front of you)
2) Move your fists up-down in the same manner, but place your fists over each other (no rocking couple)
3) Now extend your arms to your sides and try again. When left is up, right is down. (extreme rocking couple)

Now, try to consider how to balance out this type of vibration...
« Last Edit: October 20, 2013, 09:51:25 PM by cujet »
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millman56

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Re: Flywheel balancing question
« Reply #11 on: October 20, 2013, 08:36:20 AM »
Errr , make a horizontally opposed twin??? ;D                                                                                                                                                                           

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BruceM

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Re: Flywheel balancing question
« Reply #12 on: October 20, 2013, 03:44:53 PM »
+1 XYZer's comment.  I'd also be concerned that the crank mounted counterweights were designed to do only part of the job, and thus the flywheels also having counterweights.  Only a cautious running will tell... 




listard-jp2

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Re: Flywheel balancing question
« Reply #13 on: October 20, 2013, 06:35:58 PM »
I have debated using an angle grinder to grind out the weight, but from all that I have been able to gather that is a messy, time consuming, fraught with potential failure kind of idea.

Why not use an engineering company to machine off the counter balance weights, using a Bullard Vertical Turret Lathe or similar, that way you could machine over most of the remaining as cast sufaces in the web area of the flywheel, hence further reducing any out of balance mass due to casting irregularities on the surface of the web area.

After this process then have your flywheels dynamically balanced.

mike90045

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Re: Flywheel balancing question
« Reply #14 on: October 20, 2013, 10:05:24 PM »
I have debated using an angle grinder to grind out the weight, but from all that I have been able to gather that is a messy, time consuming, fraught with potential failure kind of idea.

Why not use an engineering company to machine off the counter balance weights, using a Bullard Vertical Turret Lathe or similar, that way you could machine over most of the remaining as cast sufaces in the web area of the flywheel, hence further reducing any out of balance mass due to casting irregularities on the surface of the web area.

After this process then have your flywheels dynamically balanced.

At that point, just have a new flywheel machined, no worries about india pot steel.