A Poor Man's Dynamic Balancer

[vile_fly]

I finally found an article on how to make a dynamic balancer for crankshafts, driveshafts, shaft-shafts, etc.
The link is here. http://www.antiqueautoranch.com/montana ... page4.html
I am applying my automotive knowledge here, so bear with me.
This procedure was explained to me as a kid, and I forgot the details since. Now that we have a nice cheap setup, we can go from there.
When balancing a crankshaft, you must simulate the connecting rod and piston weight using fabricated bobweights attached to the crankshaft throws. The mass is measured with the journal end of the connecting rod supported and the rest of the assembly resting on the scale. Now, there are many cylinder configurations that lend some interesting balancing problems.....such as a my V-twin configuration stirling that is a modified compressor block. These alternate configurations have some special rules of thumb to go by.
Some of this is dated from 1980 or earlier and may be out of date:
Rotating weight is the rod bearing if used.and the large end of the rod and an estimate of the oil in the throw and on the bearing surface(usually 1 gram).
Reciprocating weight is the piston,wrist pin,locks(if used),rings,and small end of the rod.The rods are weighed with one end on the scale and the other supported on a ball bearing fixture.
So:
v-8:Rotating=100%,Recip=50%
v-6 with split crankpins:
3.8L Ford:Rotating100%,recip39.2%
3.8L G M:Rotating!00%,recip36%
Single cylinder engines are inherently imbalanced.They cannot be brought into perfect balance but:use 100% rotating and
55-58% for 7500-8000RPMs
60% for 8000-10,000 RPMs
65% for 10,000-12,000 RPMs
Now onto Motorcycles etc.
This says for single cylinder engines use 61% recip and 100% rotating
Verticle twins:60-70% recip and 100% Rotating
BSA use 72-80% recip and 100% Rotating
3 Cyl use 42% recip and 100% Rotating
V twins use 52% recip and 100%Rotating
Inline 4 and 6 cylinder engines are balanced without bobweights except rare circumstances where the rods can't be matched and different weight bobweights are used.
By the way "Flat" opposed engines don't use bob weights either including the Corvair 6 cyl.
If you use a piston rod, don't forget to weigh it in as reciprocating weight, too.

The cheap system described uses a timing light to trigger at the right time......what is missing in my opinion, is the degree wheel that you point it at. Another guy on youtube used one. Newer timing lights also can scroll the moment of flash up or down about 40 degrees to zero your moment of maximum dial indicator travel more accurately. Here's the video link. http://youtu.be/ZbmozBlYylw Degree wheels are sold as high performance camshaft tuning tools at all automotive parts stores. Use a large one if you can for more accuracy.

As the article mentions, the slower you spin it, the less false reading you will get from secondary harmonics. After slow balancing it, spin it faster and balance again. Repeat as many times as you feel you need to, but faster than 800rpm is probably not needed. I will be building a setup for balancing my V-twin stirling engine, but not today. Mostly, I am storing information on the subject here.
If balancing an automotive engine gives you more power (it does), then balancing your stirling engine is paramount to getting the most power out of it. Especially when it is big and clumsy like mine.

[Ian S C]

You will have read Andy Ross' book, and seen his counter rotating shaft ballance for the Ross Yoke motor.
In an earlier life I used to over haul Contenental aircraft engines, mainly O-470,IO-470, and IO-520, these motors are flat 6, and have loose counter weights on the crankshaft to damp out 6th order harmonics.
At the moment I'm looking around for a suitable set of digetal scales, saw one lot yesterday but the only went to 100gms, I want 500 gm to 1Kg, I'll be able to use them when meassuring torque with the brake that I built some years ago. The scales will be better than the weight hung on the beam.
The idea of a dynamic balancer sounds good, I'll have to keep an eye on this. Ian S C

[vile_fly]

Building a prony brake, Ian? The best place for digital scales for me was the local grocery store or cooking supply shop. Chefmate is what brand mine is. It goes to 2kg, and has tare weight button and a timer. I use it for everything, including cooking and mead making.

[vile_fly]

Oh, I forgot.....a digital fish scale would work if you need a strain gage unit. They have a better spread in terms of weight, and are cheap. The cheapest ones have a lower than 10lb (4.5 kg).

[Ian S C]

have not seen the fish scales yet, mind you I don't go shopping every week, thanks for that idea. Ian S C

[vile_fly]

A degree wheel can be printed up as polar graph paper from this site. It also has tons of other styles of graph, dot, polar, notetaking types of graph paper you can download. It has been very useful to me. I am posting this in the links area, too.
http://incompetech.com/graphpaper/

Now, you can transfer the printout to your metal if you have a piece of wax paper, a printer, an iron, and clearcoat paint or a gluestick.
1st - coat the intended metal target area with your gluestick or clearcoat paint and let it dry. (the gluestick is probably quicker)
2nd - reverse the image you intend to print
3rd - print the image out on wax paper. (a used label sheet for mailing labels works nicely with all the label stickies gone with everything else)
4th- center the wax paper image where you want it, and iron it on. Just don't fry it on. It is not a piece of bacon, you know. just warm it so the coating on the metal sticks to the ink on the waxpaper. You could also rub it on if you like with a spoon, but I like the iron.
5th - remove wax paper, and admire how sexy those reference lines look on your work.

here is an example with wood that I did not do. http://www.toolgirl.com/toolgirl/2010/0 ... inter.html
I could not find the machinist's magazine I read it in, so I posted that.

[dasf444]

I totally read out you link superb work done...Digital fish scale i think is the right choice for the balancing the piston because this scale have ability to weight the piston balancing to all the other scales..