Balancing out the Bounce---

[hotater]

Cris---

The moderator took out some ignorant rants but the answers from the good guys remain.  It ain't you that's 'clueless'!!   

Brain pick mode, please----
   You say you have vibration and accelerometers??  What output do they have?  Is it something a guy could rig a timing light to?  Are aircraft engines balanced in parts then assembled, or, are there things that can be done to dynamic balance them in place?   I've always marveled at turbine aircraft props but have never figured out what balances them...must be inside. Does the ACES attach to a machine or is the machine part mounted on the ACES?

I read your post and started acting like my bird dog pups trying to go on point!.   

<mission impossible theme>  Your mission should you decide to accept it is to assemble a portable balancing machine comprized of a vibration sensor on a  magnetic mounting base with an output to a strobe light and alligator leads for 12VDC source supplied by the user.   I'm betting such a thing would earn the builder a tidy rental income.
   I'll buy the first one to test various dynamic balancing experiments with.   

[quinnf]

Cujet,

No, you're not the clueless one.  The moderator did some editing, but failed to remove my retort to a post that isn't there anymore.  My apologies to you, or to anyone else who might have taken offense.  I'm really a nice guy.   

Quinn

[cujet]

No offense taken. I missed the other posts. I have thick skin, not to worry.

I wanted those willing to try to balance a single to try the stick on weight idea. It should be safe enough, as they would be captured by the flywheel and the rotational speed is really quite low. Much lower in fact than a typical car tire/wheel assy at highway speeds.

BTW, it is quite easy to put a pound of weight on with stickum weights.

Chris

[SHIPCHIEF]

Cujet Chris;
I remembered your last post here while reading your post on generator frames, so I'm resurecting this one, because it's relevant.
I have my 25/2 apart for sand removal, but it was a rough runner, and shook like my Jack Russell terrier after my wife bathes him.(visualize that )
I plan to ballance this engine before I put it back together, because I tried those tape on wheel weights and even used my lead melter for bullets to cast a pretty generous weight into the inner ledge of the flywheel. I moved those weights all around without any real satisfaction. I fact, I built an electric starter so I wouldn't kill myself starting it for so many tests. This engine has bolt on counterweights, but they don't have any drillings or grind offs, so I think the rotating assembly was never ballanced.
I have tried to read internet resourses on ballancing engines, not much there...? You seem to have some balancing equipment and some knowledge of how to use it, SO; How do you ballance a 180 degree 2 cylinder 4 stroke Listeroid to run smooth at 1000 rpm, --and not shake too bad while starting and stopping?
Scott E

[hotater]

After trying a LOT of different ways of taming the Lister Leap, I've come to a simplified conclusion--- the Brits got it right, again.  Tie it down SOLID and there is no vibration.

I think there are two ways to keep what the engine is doing to itself....  Mount it Solid or Isolated?  That's the question.

Theoretically a chunk of cast iron bolted to a major portion of Mother Earth has only the movement allowed by the elongation of the material and slop in the bearings to make it vibrate.   It surely wouldn't be enough movement to disturb the silverware.  That's the *Solid* theory.

In total *Isolation*,  a Lister with poured concrete flywheels should be perfectly smooth, if given a large enough place to jump around without hitting anything solid, (But I'd like a video of it).  For isolation to work one surface has to have enough room to travel equal to it's energy minus decelleration....or some such important-sounding formula... the more out of balance the greater the travel has to be of the 'pads'.
  So, it seems an engine has to be in *better* balance than the average Listeroid to take advantage of isolation pads, bumpers, treads, and slings that are small enough and cheap enough to buy or copy.

I think the Brits got it right---  '....start with a yard of concrete....'
Try once the instruction book way.  It's amazing how quiet and smooth the engine becomes at two grunts tight to something REALLY solid.

It's REALLY hard to break the "portability" habit.   Nail that sucker down with your best glue!!  I guess we move around too much....

   I have a 3.5 Mini-Petter pump sitting on two 6x6s, but bolted directly to, a re-inforced block of  seven sacks of Sacrete.
 It's less than six feet from, but attached to, the same concrete that forms a paved walk around a big hot spring.  THere's no ripples on the water from vibration but the steam patterns from the exhaust are sure neat!

[cujet]

I can only assume the 25/2 you have has bolt on counterweights. Because it is a 180 degree twin, the balance would naturally be good. However who knows what the Indian companies do. If you have the engine fully apart, weigh each part on an ACCURATE scale.

Make sure to inculde the rings, clips (or whatever) and pin with the piston. Pistons must be weight matched. Next, weigh the rods (include bearings, bolts and all parts), end for end while suspending the other end on a point inside the bearing area. Add the weight of the rod small end to the piston, this is your reciprocating weight. The rods must be matched end for end also.

The 180 deg twin can use all sorts of balance factors. However 50 percent is a good place to start to aviod excessive rocking couple. In other words, the counterweight should counteract all of the con rod big end and 50% of the reciprocating weight. The crankshaft should not have a heavy side with no con rods attached.

This is a good place to start with static balance. Now, rocking couple is a different story. Weights on the flywheel can be used to counteract this. This is best done by trial and error. Once again the weights added should be added to a balanced flywheel. Using the ACES would make quick work of the job. Remember the rocking coulpe weights will always be in line with the crankshaft throws. It is a good thing to start with balanced components first. Otherwise the weight could be counteracitng some flaw in the flywheel balance or who knows what?

There really is no way to balance all the shake out of a single. A 180 degree twin is much better, however rocking couple now plays a part. Also, the forces of combustion give the 4 stroke engine an uneven level of vibration. Not much can be done about this. Singles and 180 twins both suffer from this, sorry. It is likely this is the majority of what you experience.

The ACES 20-20 I have is really a fairly inexpensive balancing set for helicopters/prop aircraft. It uses an optical pickup or magnetic pickup (your choice) for RPM and position. It uses accelerometers of nearly any sort. There is a long list of them in the software. Just make sure to plug in the right data...... The really neat thing about the unit is the vibration spectrum survey. It shows a line with peaks at each RPM. For instance camshaft, generator and crankshaft RPM are all different. On a heli, the tail rotor drive shaft may be the prob. The only way to tell is to do a survey. Maybe it is a starter generator turning at 8000 RPM vs the TRDS at 6400. Our EC-135 helicopter is pre wired for the ACES. Plug in and go.

Chris

[n2toh]

I recall my ME buddy once saying there is a way to dampen vibration by using a lever and counter weight. To stop the back and forth rocking of the head you would attach a threaded rod so you could adjust the height of a weight, both the value of the weight and the rod height are calculated. But I don't remember how to figure it out.

[cujet]

Sure enough, our EC-135 heli has such a counterweight. Actually I believe it has 2. They are tuned with a device that looks like a woofer voice coil and a specific frequency. Quite simply, it is a single flat "leaf" spring with a bob weight at the end.

From my end, I tune the hammers (shop name for the harmonic balancers) by adjusting the main rotor RPM slightly to match the hammers. This is also done with the ACES.

Chris

[SHIPCHIEF]

Oh;
I thought 50% balance was for 90 degree V engines, like American V8 cars, Ducati and Moto Guzzi motorcycles and the engine in my riding lawn mower.  Is it the same for singles, 180 and 360 degree twins, Harleys etc? If the 50% is a place to start, where do I go next if it still shakes?
My engine tends to rock back and forth from one cylinder to the other, when at rated RPM whether it has a large load or light load, so is that the rocking couple? It shakes the other way (Parallel to the drive belt) when it comes up to speed or is being shut down...Passing thru some frequency that is below idle speed. That's not a problem. When it's working hard I can feel the power pulses, but that's part of the charm of these beastie.
When I rebuilt my last V8, (400 Pontiac) I profiled and balanced the rods (used a digital painters scale) I was able to remove about 27 grams of excess material off each rod.  When the crank, rods, pistons, etc came back from the balancer, I noticed the crank counterweights had been drilled quite a bit to compensate for the reduced weight of the rods. That engine runs smooth, and 'gets revs' quicker, with the reduced rotating mass. 
In the case of the Lister, I'm reluctant to take it to a machine shop that advertises balancing service, because they may be experienced with chevy V8s and not much more. On the other hand, The Lister crank (without the counterweights on) is almost 100% machined, so it probably balances well. The removable counterweights, rods, pistons etc. can all be weighed, and the data logged, then adjustments made. I would like to do it myself if I could figure out the Mr. Science part .The flywheels look like they were neutral ballanced and drilled. They do not have the cast in weight of a single. I was thinking they could be balanced on a tire spinning balancer? Just make sure they have mount cones to fit the 2 inch bore?
Scott E

[SHIPCHIEF]

About balnace factor: I borrowed this from the virtual Indian:

The "balance factor" is the percentage of the reciprocating masses being balanced by flywheel counterweight.

A motor with low balance factor thus vibrates up and down a lot and vibrates fore and aft a little. The extreme case would be a vertically mounted single cylinder motor with ZERO balance factor (only rotating masses balanced). This motor vibrates only up and down. The same motor 100% balanced would only vibrate fore and aft. The basics apply to V-Twins as well, with other things equal the wider the cylinder angle the more the motor vibrates fore and aft. Thus: An identical flywheel assembly put in different cylinder angle motors would have a different balance factor.
Kinematics (the angle of the rod on the downstroke) play the role here.
Practical example: Late Indian Sport Scouts have a balance factor of 82%. If you put Sport Scout flywheels rods and pistons in 45 degree cases the balance factor rises to a little over 84%. This small difference would be only noticable in racing motors if at all.
Scott E

[hotater]

I *still* say-- Forget portability and ANCHOR it to concrete.  You'll be amazed.

All the hootchy cootchy of vibrations and twisting on shut down or (scary) over-rev is what I've seen an half a dozen flywheel engines that have room to move around.  Once BOLTED directly to Mother Earth they are so smooth running and quiet you'll be amazed.
  I drilled oversize holes in 6x6 timbers to slip over all-thread I set in the concrete....I set pressure treated timber (with all the extras copper sulphate and mineral spirits it would hold), directly on the wet concrete and leveled the timbers.  After curing I  then covered the timbers with a slab of 1 1/2" microlam,  then a sheet metal oil and rain cover, then the engine with  Nyloc nuts.

This Mini-Petter engine is mounted twenty feet from my concrete soaking tub.  I can FEEL when the engine needs tightning down again due to settling in the wood.  I feel no vibrations (and believe me I would) when the engine is tight on the mount.

By comparison, the Lister is mounted on a chunk  of concrete floor that it broke off for itself in  the first couple of days.  When the ground is wet, as it is now, I can feel the Lister run at a hundred feet away.  The concrete pad is still only moving .008 TIR, but it sure telegraphs it  a long way.

[SHIPCHIEF]

I agree. It looks like we have a choice of hopping up and down or wobbling back and forth for singles, twins get to add rocking side to side. I will go ahead and try some balancing, but the heavy massive foundation is required as you say. I guess we can forget about 'portable'
Scott E

[quinnf]

Y'know, something else to consider is efficiency.  Say your engine likes to bounce around.  You mount it on something resilient.  As the engine thumps along, it's twisting this way and that, bouncing up and down, side to side, sort of like a fat lady wearing a thong jogging down the boardwalk. 

Every time the engine moves up and down or sideways, or whatever, energy is required to move that mass.  F=MA and KE=1/2 MV^2 and all that stuff.  That energy has to come from somewhere and that has to be the rotational energy of the flywheels.  So let the engine float on rubber thingamabobs and you may have a quieter installation, and less ground pounding, but I bet the loss in power is noticeable.

If the engine is securely mounted to something heavier than it is, say a yard or so of concrete, there is nothing to give.  The bearings are sized to handle that load, and they're easily replaceable if you have an afternoon to turn some nuts and bolts.

Quinn

[hotater]

I could'a  done without the fat lady..... 

[quinnf]

Jack, you'd be surprised what washes up on the beaches around here!   

q.