Balancing your engine

[GuyFawkes]

Here's how you do it.

#0

Pull BOTH flywheels and weigh them, they MUST be identical, if they are not, add the required amount of weight to the light one but be SURE you distribute it evenly radially, DO NOT just tie it around one spoke. then balance each flywheel as below on a dedicated dummy shaft and bearings, ensuring all the while that the weight of both remains IDENTICAL

#1

Do ___ALL___ the machining, eg borings, crank grinds, dressing up con rod, etc etc etc FIRST, and make sure your mains are clean and free and your oil is fresh


#2

Weigh accurate to less than an ounce the complete connecting rod + shells + piston + gudgeon / wrist pin + rings + one half of a piston volume of oil

#3

make up a weight = this amount to wrap EVENLY around the big end journal, if you "weight" is something like hammered lead pipe, remember to include the weight of the jubilee / hose clip you use to retain it tight on the big end

#4

spin the crank by hand, it will settle more or less with the excess weight at the bottom, I say more or less because the less out of balance it is, the less this will tend to happen, so you put a chalk mark at 6 o clock and do it ten times, then add an equal test weight to BOTH flywheels at 12 o clock, wipe the chalk marks off,  rinse and repeat until the chalk marks are as truly random as you can make them, then get someone else to spin them ten times to double check.

do not be tempted to correct weight problems by drilling mass out, that can work for steel if you know what you are doing, it doesn't work for cast iron

lead is a pretty good way to add weight, auto wheel balancers use it, a dab of epoxy and it will stay put forever provided you site it so the centripetal (spinning) force throws it against a part of the flywheel body

a 24 inch flywheel spinning at 650 rpm has a rim speed of 3.14 x 24 x 650 inches per minute, that's about 49000, that's about 4000 feet per minute, that's about 66 mph

you may well have a few pounds of lead on there, if it comes off you get a few pounds of lead going in a straight line at 66 mph, which is more foot pounds than a .44 magnum at the muzzle, so don't be casual about it

the following picture (the flywheel hub is 1" thick) should tell you all you need to know about how far the flywheels need to be out of balance to counterweight the crank assembly

[SHIPCHIEF]

Guy;
So we call that 100% ballance, when you add up all the weights of the rotating and recip parts.
You don't think 50% ballance is the way to go? 50% of the small end of the rod and 50% of the piston assembly + 100% of the rod big end and bearing shell (and also proportional for oil).
My 25/2 twin mostly rocked back and forth because of the reciprocation of the pistons. It actually runs smooth just a few RPM below 1000, and at about 1050 it gets noticably worse. The firing pulses are noticable as load increases too.
I'm considering a derate to 850, based on longer life, smoother running, and not needing more than 10 Kw. It's got a 12 Kw head. So I would be under rated but still powerful enough to run the whole house with very little load control, if any. (We don't have air conditioning)
I wonder what RPM your Startomatic would start hopping?
Scott E

[GuyFawkes]

I wonder what RPM your Startomatic would start hopping?

not about to test, but, my only experience is listers and this whole idea of hopping etc is quite strange...

[oldnslow]

Guy, I am very interested in doing this so I'm making sure to clearly understand your procedure. After equalizing the weight of the flywheels, I would install them back onto the crankshaft complete with jib keys etc. The crankshaft is already installed into the bare crankcase with lightly oiled mains. No piston and rod assembly installed.

Then I wrap a weight evenly distributed around the journal that's equal to the rod and piston assembly according to your instructions. I'm confused a little bit about determining the size of the weight. Could you not just weigh the entire piston and rod assembly together? Why does weighing the piston by using half "its volume of oil" when figuring the weight of the assembly need to be done?

Is there any significant difference in this "static" method versus a "dynamic" method? Thanks alot.

[solarguy]

Part of the reason is:

The piston goes up and down (purely linear).  The flywheels and the big end of the con rod go around and around (purely circular).  Those two things can't really cancel each other so it is impossible to perfectly balance a one cylinder engine. That's why opposed engines like the 6 cylinder boxer of the porsche and the 4 cylinder VW air cooler are inherently smoother than other arrangements because there are linear components that can mostly cancel each other out.

Since the big end of the con rod is "purely" circular, you can compensate for all of it's mass with a flywheel/crankshaft counterweight addition/subtraction (in theory.  Don't remove any material from YOUR flywheel).  Between the piston (purely linear) and big end of the con rod, the motion is a hybrid, partly linear and partly circular.  Thus there are various schemes for compensating for that mass mostly sort of.

Dynamic balancing is much different than static balancing.  For one thing, static balancing doesn't care at all what speed you operate your engine.  Ahhh, but vibrations are often highly sensitive to rpms.  Dynamic balancing can help with that at any specific speed, but it will never make an old one lunger truly smooth.

Good luck and have fun!

troy

[oldnslow]

Thanks Troy, you saved me a couple days research for that answer. I was reading a thread in another section of this forum http://listerengine.com/smf/index.php?topic=35.60 On page 5 Diesel Guy  mentions a balancer filled with weights suspended in a circular tube filled with dampening fluid called "CentraMatic". It might work excellent for the flywheels. Going to try contacting them if no one in the other thread does it first. The diameter is probably key to making it work for our application? Any of you guys ever seen one? Looks promising as they make a heavy duty one for military apps. Thanks.

[binnie]

Oldnslow, Let us know what you find out. I did check with something similar for wheel balancing of tyres with my tyre man, was the insert of beeds into the tube but he said they don't work for colder climes like ours as the humidity clumps them together & you have the first 50miles rough run to break them up before they work. Don't know if this would be the same or not for application in Cda, with the below zero freezing on top of humidity. This looks like a locked system & some lubricant to keep the beeds free. At $300.00usf a pop, (not sure if that is for a pair or just one.). A little tinkering might be inorder first, and this as a last resort. Let us know if it works for you and worth a try, or what you find out. binnie (sounds like an easy solution, if it works)

[oldnslow]

I called them and have some info:
You would want to balance a flywheel that is non-counterweighted because these balancers would try to cancel out the counterweight and not work for us.

They are a zinc plated unit with a tubular rim (the military ones may be different). The rim is filled with alloy beads and proprietary oil. It can run from -50F to much hotter (?) the guy didn't give me a temp but said they would survive emergency braking, etc.

They cannot be accelerated too fast. I guessed 3-5 seconds to get my flywheel up to 1000rpm, between cranking to running? That is OK. Also, the rep seemed to agree that the balancing part should be closer to the flywheel rim also. They make them in diameters up to 22.5"  So...they might work.
 
On the engines with "stover" type flywheels and counterweighted cranks it might work. The rep suggested that we match the weight of our flywheel as close to one of their applications (like the weight of the flywheel should be similar to the combined weight of the rim and tire the balancer is designed to work with). I think the 400 series might work on my 25/2. I have to measure the exact flywheel diameter. They have ones that are 19.5" in diameter (part 400-406) that might work. These run $190/pair. Make sure you are looking at the ones for REAR wheels because the driven (rear axle) ones are constructed differently than the steering ones.

That's it so far. Lots of "ifs" and "mights" here.  My engine runs pretty smooth so I can't justify spending $200 to try this. I will probably do the manual balance that Guy laid out in the beginning of this thread. Any thoughts?

 

[lister-deaf]

Do you think  The Centralmatic  will help our lister engine to smooth with their either suv or semi size put on Lister Flywheel?
let me know it would work??

http://www.centramatic.com/Demo/video2.mpg

Visit   http://www.centramatic.com/index.html