Thread: Balancing and engine........needed???

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I posted this question in my build thread, but in case it gets missed I thought I'd post it separately. We need to make a decision this week.

Dan's motor is at the machine shop and almost done. The guy can balance it for $200 more. The money isn't the issue but we are only questioning the need to do it. The motor had no vibrations before, and it will never see more than probably 3500 rpms on the street. Is it worth it?


Don

oem engine with a stock over size piston change no . pistons and rods that are not stock then yes .mild build most all stuff gets balanced .race stuff Yes i done many oem engine this way and i will run threw the rods and get them all with in less then 1 gram .but like we talked about some shops like you to show every machine in the shop they have and you will see that on your Bill when done. many will say you need it and some may still be paying for there machines

Don, I know you stated he probably will never exceed 3500 rpms, but he might change what he wants to do with it in the future, or even move the engine into a new build. I'm guessing there is a lot of money already in the engine at this point. $200 may be good insurance toward future performance and reliability. But heck I'm just guessing, it sounds cool when you say it's been balanced! I know Dan is a perfectionist, by how detailed and exacting his standards were on this build, I think this just continues in that level of quality that comes out from you guys!

going past 3500 rpms with a bigger cam the bottom end is not going to bite you in the ass its the OLDS stock valvetrain ... rocker setup its P.O.S

It has forged pistons so I guess the balancing would not be a bad idea. What I like about this machine shop guy is that he hasn't tried to push stuff on us. He basically lets us make the decisions as to what we want done.

I guess we will have it balanced just because. BTW, are 455 Olds external or internal balanced? If external I need to take him our harmonic balancer and flexplate to have those included in the balance job.

Don

well it should be external on fly wheel .so he will need the fly wheel and damper

What all gets balanced?
I know on mine that they switched some of my rod numbers that I had stamped from place to place and ground on other rods. Weighed them with the pistons on. Line bored it also. I'm not sure what else got ground on. Probably the crank. I'm just curious what all gets balanced with an engine.

Essentially, everything that rotates. If an engine is internally balanced the flexplate (or flywheel) and damper are neutral, so they don't get balanced. If an engine is externally balanced those two parts must be done also. Some makes of engines come from the factory internal balance, and some are external balance, by design.

So, the crank, connecting rods, pistons, damper, and flexplate all get balanced. Pat , Jerry, and some others will know more, but my understanding is they find the lightest components and remove enough material from the others to make them all weigh the same, I think they also make the big ends of all the rods weigh the same, as well as the small ends all weighing the same. Then they do the pistons and pins. They will also remove material from the crank weights so that it spins with nothing out of balance.

The 350 Chevy engine I have in the shop was evidently balanced as I can see where material was removed from under each piston and also grind marks on the other parts. The idea is to make anything that rotates as close to perfect as possible to cut down on vibrations. I think the guy at the machine shop said something about him holding it to 1 gram, but I could be wrong on that.

If you can envision taking an electric fan and cutting a little off of one blade, how it would shake. By trimming all the blades exactly the same it would balance it, same thing they do iwth an engine. That is what little I know, or think I know, about engine balancing.

Don

yep it some what like don said the big and small end of the rods get match going from the lightest rod . same thing with pistons .if the crank can support the mass then it gets drilled or smooth sanded away counter weight or cut on a lathe this keeps deep holes out of the crank better oil control. when the mass is more then the crank counter weigths can support then heavy metal slugs get press in the crank counter weigth . there many ways to work the parts you have to get them the same weigth on each crank throw . your dealing with many parts some time if the rod on small end (pin end) is to light then the rest of the rods .then you find one or two new rods that match up to old rods if you do not have other rods on stock stuff you may have to get very creative as they can be waayyyyy off .or you can sand numbers off and move rods a round if pistons are stamp to each hole were the piston s may have a bit more weight and could go with lighter rods or they may just moved the weight of the lightest rod to a heavy rod on the same rod journal as the crank only see s mass weight not each part . internal cranks you can spin the damper and fly wheel even if neutral bal crank .with external bal engines you need the damper /hub and fly wheel is when crank was made it could not support the mass so part of weight hangs out side of the crank . and some OEM engines are 1/2and 1/2 were the front of crank is neutral and back is external this happens alot one pc rear main seal engines is with that crank hub you can not hang off the back of the crank is what i call a heel all that is a chunk of steel hanging off the back of the crank seen on many two pc cranks. on race cranks we move things around and try to keep all weight inside of the engine that were we will use heavy metal and slug up the crank or find a crank with more counter weight

I always thought it was a good idea to balance all rotating parts.

Me too, Don If I was gonna spend the $$$$ to have it balanced,the balancer and flywheel would go to the shop.

I agree. Last Monday I dropped off the flexplate and damper and told him to balance it all up. I'll be interested to find out how far off the stuff was. I asked him about how far off the pistons were sizewise from one another, and he said they were all actually very close. He said they will mark the pistons and rods so they all go back in the holes they honed them for originally.

Don

I find it amazing how much quicker that the crank and bob weights spin up to balance speed as the balance comes closer to the desired tolerance--IE-when I start a balance job it takes a certain amount od time to spin up to the 5-700 rpm balnce speed--as the job gets closer it spins up almost instantly--

hey jerry were have you been ? hope not working to hard ? your v blocks on your machine plastic Vs or steel rollers ?

well i been in Il, In, Mo,Ar,Miss,Lous,Ala,Fla,Ga,NC,Tenn<Ky,Ohio since July 1st---some of them 3 times---having a hard time finding a log cabin with a 10 car garage with 600 amps 3 phase power!!!!!

Steel rollers