Correct my crankshaft balancing

[NHerron]

I'm trying to figure the way I think the crankshaft is balanced. I've tried to understand this off and on for weeks with searching and reading. To be honest the threads here and Google confuse me so please bear with me.

All inline and four cylinder crankshaft are internally balanced. EXCLUDING the engines that don't have enough room for sufficiently sized counterweights in the block. CORRECT?

The reason these 4 and 6 cylinder inline cranks aren't balanced with bob weights is because the pistons/rods do NOT counter(no pun) the crankshaft counter weights. The crankshaft counterweights actually balances out the opposite set of crankshaft counterweights instead, -because they are on perfect opposite sides. Same idea with the pistons/rods. While one set of pistons/rods are on their way down the other set is on it's way up.

Of course, this is why the pistons and rods are still needed to be balanced within a gram of each other and the piston/rod balancing procedure is still the same as you would do for the V-8's.

SO the way the crank is correctly balanced is spun absolutely by itself with no bob weights. Once that is checked and drilled if need be, the flywheel is added. If there is a new imbalance, the machine detects it and the FLYWHEEL will be drilled. And so on with the harmonic balancer.

These are some of the links I used that helped me:

* Engine Balancing Questions [Archive] - DSM Forums: Mitsubishi Eclipse, Plymouth Laser, and Eagle Talon Forum: DSMtalk.com (<--best one, towards bottom where he got email response)

* Balancing and Blue Printing information - RPM (<--first big paragraph)

* Engine Balancing and the Performance Rebuild (<--under applied physics)


The reason I'm doing this is because when I got my crank back from the shop, it had a bunch of material drilled out and I remember the shop saying something about bob weights. I was NOT expecting the crank to be drilled that much because the cranks are usually pretty good from the mitsu. As it is with this shop, I would not be surprised by the slightest they screwed that up too. I paid good money for these guys to do my blueprinting but so far I am not happy.

Someone confirm this so I can take my parts and go elsewhere. :disaster:

 

[JacksonAuto]

You're correct in your understanding.

Most 4 cylinders have a 2-up 2-down configuration. They will "balance" each other out as long as the counter weights are all identical weights as well as each rod/piston combo.

The flywheel and damper would be zero balanced.

 

[NHerron]

Thanks that feels great coming from a reputable shop ! I will call them today and see how they balanced this sucker and report back. Maybe they can do it free this time if they happened to just have a brain fart that day.

 

[TunaTalon]

The two pistons going up have the same weight as the two going down but they are not at the same speed during the full revolution. The difference in acceleration rates causes a difference in forces. That is the cause of second order harmonic vibrations and the reason for the balance shafts in the 4G63. This does not affect the crankshaft balance or the counterweights.

The two pistons going up do pretty much balance the two going down but to do so without counterweights has the forces transmitted through the crankshaft. Each counterweight "counters" the piston next to it and reduces the stress on crankshaft. A crankshaft with no counterweights is still balanced but the crank carries more internal stress.

 

[NHerron]

Thanks Maurice! I can visualize that easily. The counterweights sound like a form of "capacitor" that absorb the massive forces during operation.

*I like your avatar, there's not enough natural scenery pics here haha.

 

[stuckwithgsx]

I've never heard of drilling holes in a crank to balance it?

Pictures of said crank, and work from the shop?

 

[Colt4G63 also]

I've never heard of drilling holes in a crank to balance it?

Pictures of said crank, and work from the shop?

Hmm, I just typed the word "Crankshaft" into google and here's the very first image on the list.

You must be logged in to view this image or video.

I don't think I've ever seen one that wasn't balanced that way.
Notice the holes of various depths drilled into the counterweights?

 

[NHerron]

Well everybody, I just got off the phone with the shop that balanced my stuff. Turns out the guy I talked to when I originally brought in the assembly was NOT the one doing the balancing. The person who did, I JUST spoke with and he did not use bob weights. He basically explained everything the same way I learned from the internet and the confirmation from here on tuners.

Good news #2: Shortly after I got everything balanced the first time, that's when I realized I needed to notch the stroker pistons for the oil jets. So I was thinking that I would have to screw up the whole balance! That is not the case, all you have to do is just weigh each piston and make sure they each equally weigh the same and YOU ARE DONE! That's awesome. Saves me money and most importantly, TIME.

Good news #3: Assuming the crank is zeroed, and the flywheel is zeroed, a new pressure plate should not throw off the balance too much. I also just called ACT and they say their pressure plates are "tight tolerances, and are zeroed out from a dynamic balance before they leave the factory" My machinist also told me that since my pressure plate was used he put the pp on several ways to find the best balance and marked it. So when I get around to putting on a new 2600 pressure plate in the summer, I shouldn't have a balance issue since the crank is zeroed to itself and the pp is zeroed to itself.

*oh and for reference, you can use the evo 9 oil jets if you don't want to notch the wiseco strokers since they aren't made for the jets. Well the DSM jets, anyway. Or just bend them a little from what I've read.

Well shoot, looks like I will be back on the road again this YEAR afterall! Thanks for the help everyone!

 

[Zack Huffman]

Glad to hear Nathan.
I couldn't imagine a successful company like ACT not doing that, but I wasn't 100% sure.

 

[NHerron]

If anyone reads this over the years and finds ANYTHING wrong please pm me I will fix it. I want this to help anyone in my situation. I don't want to spread bad info. Ill update in a month or so to confirm the engine is smooth once I get it together.

 

[JacksonAuto]

I've never heard of drilling holes in a crank to balance it?

Pictures of said crank, and work from the shop?

The holes are drilled in the counterweights to make the all the same. The casting or forging process is not precise so when you end up with a counterweight that weighs more than the others you remove that extra weight by drilling small holes.

Just for clarification for those that search in the future, a 4 cylinder crank like a 4G63 should NEVER be balanced using bob weights. If you've got a shop saying that's how they do it, run away screaming. Balancing with bob weights is for "V" engines where the counterweight must be matched to the rod/piston combo. The bob weights actually simulate the rod and piston on the balance machine.