Crankshaft balance

[XoX1de]

For those who got built engine, did you balanced the crankshaft with new piston and rod? Im preparing to get my motor build and my local town shop charges me 300$ to balance the crank, they said it will be balanced to run up to 10000rpm without much problem.

I wonder if the balance is a must, because I rarely rev over 6000rpm with our motor, I know is a undersquare one so rpm may stress the motor. If isnt a must then Ill simply go without balancing internal.

 

[XoX1de]

no takers!?

 

[MSP2024]

10k not sure about that but mine is being built right now and its all balanced dont know if its a must but it seems like a good thing to do

 

[Metallic36]

Yeah, I'd say to do it. Seems like a bit much to balance it though.. but if you're gonna build it, you need to do it right the first time.

 

[MSP2024]

i agree^^ if your going to do it,do it right the first time

 

[nullbyte]

If you are getting the engine rebuilt get it balanced with the flywheel on. Just because it's balanced doesn't mean that 10K is a good idea. Also $300 is a lot for balancing!

 

[XoX1de]

Ok guys after a hell lotta reading, I figured out it doesnt worth s*** to balance the crankshaft. It comes factory balanced which is very accurate... unless you want to rev a undersquare engine up to 8000rpm...

The inline engines, either 4 6 or boxer, are bein balanced in a different way as V engine. Inline engine got a perfect primary harmonic balance if each of the pistons assembly (rods, rings, rod bearings, wristpins, clips) weights the same. inline 4 always have 2 piston goes up and 2 goes down so they cancel eachothers, thats why the weight is critical.

I just got my wiseco pistons and k1 rods. Put each one on the scale and check the weight. The pistons are within .5 gram which is very well scaled. The rods are within 1gram, which is near perfect balance. I put the rod and piston together and scaled them again, each of them are within +/- 1 gram.

So people dont get scammed by those engine rebuild shops that asks you to balance the crankshaft... They get your money and doesnt change s*** on the crank. They are just scaling the piston assembly and remove weight if they are not equal, and you can DIY if you have a good precision scale

 

[slo03.5msp]

they are not balancing the crankshaft they are balancing the whole rotating assembly. I have never built an engine without doing it.

 

[AusOrion]

Ok guys after a hell lotta reading, I figured out it doesnt worth s*** to balance the crankshaft. It comes factory balanced which is very accurate... unless you want to rev a undersquare engine up to 8000rpm...

The inline engines, either 4 6 or boxer, are bein balanced in a different way as V engine. Inline engine got a perfect primary harmonic balance if each of the pistons assembly (rods, rings, rod bearings, wristpins, clips) weights the same. inline 4 always have 2 piston goes up and 2 goes down so they cancel eachothers, thats why the weight is critical.

I just got my wiseco pistons and k1 rods. Put each one on the scale and check the weight. The pistons are within .5 gram which is very well scaled. The rods are within 1gram, which is near perfect balance. I put the rod and piston together and scaled them again, each of them are within +/- 1 gram.

So people dont get scammed by those engine rebuild shops that asks you to balance the crankshaft... They get your money and doesnt change s*** on the crank. They are just scaling the piston assembly and remove weight if they are not equal, and you can DIY if you have a good precision scale

All quite true. But there are also other elements attached to the crank as well - such as the crank pulley and the flywheel. While these elements are generally pretty well balanced themselves, when you throw everything together it is possible that things aren't perfect. I would say that crank balancing is not a "must do" requirement but a recommended optional extra if you have the time and money.

 

[XoX1de]

they are not balancing the crankshaft they are balancing the whole rotating assembly. I have never built an engine without doing it.

I know but thats a pure DIYable stuff, a grinder and a good scale and grinding the good place...

 

[slo03.5msp]

no that's not exactly how it's done. they drill into the counter weights on the crankshaft. It's actually a long lengthy process. I would reccommend it. Here lets put it this way. If you don't do it and the first time you hit 6k rpm and the motor throws apart because of the internal vibration and you have to spend the money to do it again you would be pretty pissed. $300 bucks to save a lot of hassle sounds like a better alternative. Again I have built some pretty insane cars and never once did the rotating assembly not get balanced.

 

[slo03.5msp]

http://www.popularhotrodding.com/enginemasters/articles/hardcore/0412em_rotating_assembly/index.html


http://www.rpmmachine.com/engine-balancing.shtml


If you have machines in your house that are capable of this than i'm coming over for my next engine build.

 

[XoX1de]

no that's not exactly how it's done. they drill into the counter weights on the crankshaft. It's actually a long lengthy process. I would reccommend it. Here lets put it this way. If you don't do it and the first time you hit 6k rpm and the motor throws apart because of the internal vibration and you have to spend the money to do it again you would be pretty pissed. $300 bucks to save a lot of hassle sounds like a better alternative. Again I have built some pretty insane cars and never once did the rotating assembly not get balanced.

The crankshaft is balanced ALONE, and FACTORY balanced. There are holes on the counter weight already drilled.

Here's how to balance a inline 4:

1. Neutral balance the crankshaft (+ flywheel +cpulley), so the whole assembly spins perfectly with NO vibration,this is odne WITHOUT piston or rod or anything but flywheel and pulley.

2. Weight matching of all piston and rod assembly, they are matched to the lightest weight of the 4. in my case all 949gram. And theres a special thing about the big end of the rod, it must be within 1 gram because the rod acts reciproc weight and rotating weight.

3. You are good to go.

 

[AusOrion]

Just because everything weighs the same doesnt mean that everything is perfectly balanced. Its where the weight is on the rotating assembly that is important too as it will affect how forces are applied to the crank.

I wouldnt expect that there would be issues with how all these components act on the crankshaft. But personally, I would pay the $300 to KNOW rather than THINK that everything is going to be balanced. After the $$$ that have already been spent, whats a bit of additional insurance?

 

[JDM Sam]

Quit feeding people bad information if you just learned or read something online! You are not an expert if you just read something online!

Performance built engines REQUIRE precise balancing.

You don't balance it with the flywheel or crank pulley. They are balanced independently. If you replaced the parts or machined the flywheel you would throw off the balance, thus is why the engine is internally balanced and should stay that way.

The forged rods and pistons stock are heavier than stock. Scaling the pistons and rods are only part of the balancing process.

 

[AusOrion]

Quit feeding people bad information if you just learned or read something online! You are not an expert if you just read something online!

Performance built engines REQUIRE precise balancing.

You don't balance it with the flywheel or crank pulley.

I was encouraging balancing. Never read this on the internet, I was told this by a performance engine builder. But Im not an expert, so I will defer to those with more knowledge like Sam.

They are balanced independently. If you replaced the parts or machined the flywheel you would throw off the balance, thus is why the engine is internally balanced and should stay that way.

The forged rods and pistons stock are heavier than stock. Scaling the pistons and rods are only part of the balancing process.

These are the other points I was trying to make, maybe my wording wasnt effective.

 

[JDM Sam]

Sorry that post wasn't directed to you.
The poster that suggested balancing was not required is way off!

 

[foxracer]

Listen to sam on this one he knows his sh*t. Just because you read something online dose not mean its true. Everyone i know gets the motor blueprinted and balanced. In some motors it actualy makes it preform better, and plus everything on theses engines have such tight tolerances that being just a hair off balance could eventualy destroy a motor. Its up to you though $300 to get it balanced or around $1000-3000 to do it again. good luck.

 

[dstmsp03]

balancing is a must!!!! $300 is a bit high for it though.. when i had mine all balanced it only cost me roughly $75, and for that they completely weighed, assembled balanced trimmed as needed and rebalanced. look for a different shop!

 

[BOOSTR]

Let him cut corners if he wants. He won't be the first one develop a problem on his built motor that could have easily been avoided.