How do machine shops balance engines?

[bull]

Do they simply try getting the weight of the rotating assembly parts (crank, pistons and rods) close to the same or do they do some sort of harmonic/kinetic computer balance?

[OttawaCharger]

 

[Challenger340]

BOY ! This could be a LONG thread ! I don't wanna too get carried away.

I'll attempt to keep this simple for explanatory purposes.

All Pistons & Pins are weighed, and adjusted, (milled), to weigh the same.
All rods are "hung" by their big ends, and the small ends are weighed, then adjusted(ground), so all small ends of the rods weigh the same.
Then, all rods are "hung" by their small ends, and the big ends are adjusted(ground), to weigh the same.
Note; more commonly, shops will skip hanging the rods by their small ends, preferring to simply adjust "total" rod weight (after the small ends are done), by grinding the big ends.
Rings are weighed
Rod bearings are weighed.
Pin locks(if appl) are weighed.

As we all know, some of the above parts go "round & round" in the engine, ROTATING.
and, some of the above parts go up & down, RECIPROCATING.

From the above weight data, a "bobweight" factor can be calculated. The Bobweight factor consists of 2X the rotating factor(Rod big ends with bearings, and an oil wt. calc), plus 1X the reciprocating factor(Piston/Pin/Rings).

This "Bobweight", is then bolted to each Rod journal on the Crank, an "apparatus" for doing this is attached to each journal.

The Crank, complete with attached Apparatus, balancer and flywheel, is then "spun" at various rpm's, on a machine that measures "imbalance" (for simplicity). Actually opposing forces, albeit, including non-linear running mates.
We'll refer to this imbalance as being LEFT, or RIGHT "plane", if you were looking at the crank laying horizontally on the machine in front of you. Really, it's front or rear, of the crank.

This is getting far too "long winded" here, but, the counterweights on the crank, flywheel/balancer, are then adjusted(drilled), to provide the optimum, or least, stresses @ rpm, as measured on the balancing machine.

To answer your question, YES, the parts are weight matched, the weights are then applied to the crank, and spun @ various rpm on a machine, and adjusted, to correct harmonics.

Hope this helps out.

Special note; Chrysler engines are sometimes "internal", or "external" balance.
Generally, this is because they are either "Cast Iron" Crank, or a Forged "Steel" Crank. STEEL is far more dense and heavier, than CAST, therefore, STEEL crank counterweights, while spinning, are able to counteract forces internally in engine operation, while CAST crank counterweights, being less dense and lighter, are not. Hence, additional weight External of the engine on the balancer and flexplate are required to "help out" on the CAST cranks.

[bull]

Wow, thanks for the explanation, it was very well-written. So it seems you're saying that engines are both spin balanced and weight-adjusted, not one or the other. That's good to know because IMO just weighing and adjusting the weight of the rotating parts wouldn't be enough -- it wouldn't take all the factors into consideration.

[Steve P.]

This is an old video. Todays machines are much better and there is no removing the crank from the machine to drill it. Everything is digital..

Click on the links and then scroll down to the video clip on the right..


http://www.diynetwork.com/diy/ar_replica_car_kits/article/0,2021,DIY_13707_2272192,00.html



http://www.diynetwork.com/diy/ar_replica_car_kits/article/0,2021,DIY_13707_2272193,00.html


I hope this works for ya.  I was trying to find the video from the machine shop that did mine. I will call them to get the linky....

[Challenger340]

What a great old video ! Thanks.

Those Stewart Warner strobe machines, worked just as good as anything out there today.

Feel sorry for those guys in the video though, working on a 429/460 Ferd JUNK !

[Steve P.]

I don't know all that much about the old machines, but, I would have to say today's machine would HAVE to kick the crap out of the old ones. The crank NEVER leaves the machine until it is completely balanced. It also tells you exactly the point to drill. What size bit to use and how deep to drill.  Did I mention that the drill press is part of the new machine?? Very little human error possible here. 

Also is recommended to bolt on your balancer and flex plate. Some of the old machines made it pretty hard to do that.  The digital scales are also much better as they plug right into the machines computer. Again, takes the human out of it..


The video I have been looking for was made by Branten,(Brenton)sp* communications. It was the older guy from TWO GUYS GARAGE and the video was made at Engine Lab of Tampa, Fl.

I have had no luck in finding it in my puter. Maybe someone else has it...

[Steve P.]

Here is a link to the most up to date balancing system out there.

Open the link. 

look on right side for Balancer 5000.

move your cursor over the sentence below to video. CLICK IT..

Then select your download speed in next window.


http://www.cwtindustries.com/MultiBalMovies.htm

This is well worth watching.  This is also the shop that just finished my motor. Notice how CLEAN everything is. It is alllllways like that..

[Challenger340]

The Balancing job, is only ever as good as the guy doing it, on ANY Machine !

[Steve P.]

The Balancing job, is only ever as good as the guy doing it, on ANY Machine !

This is true, but, a trained monkey could do it with this machine drunk.... Hahaha.........

[bull]

Thanks, Steve. Lots of great information there, and a nice shop too. I'll have to ask the shop I'm considering what type of machine they use.

[Challenger340]

Don't get hung up on the type of balancing machine, go for the reputation of the Guy/shop.

All I'm saying is;

I've seen shops with the best equipment, couldn't balance a "wheel barrow", and, conversely, I've seen shops with old strobe machines do SS/A HEMI super stock stuff, and win hold both ends of the world record for mph & E.T, look at Alan Lee, (Lee Bros).

Personally, I use a 2 yr old Computerized Sunnen machine. The same one the "drunk monkey" could do it on.

While I'm sure there's lotsa "shiny shit" in many shops out there, for guys to oogle at, like a bunch of old crows, go for the Guy/shops reputation.

It's the guy doing it, PERIOD !

[Steve P.]

So are you saying you are very good, or a drunk monkey??   

[Challenger340]

LMAO !

Depends,

if it's 2 am. and the room is VERY dark, the wife might think so !  LOL !

[Brock Samson]

good info!

thanks