Hi Guys,
just wonder is it a must to go for crankshaft balancing on a used crankshaft for every rebuilt?

Some of our local engineering shop said it is not necessary as most importantly is to check for distortion and the condition of the bearings journal areas.

Hope to get some advise.

Thanks

 

If you keep the stock rods/pistons it will be "close enough" for a sub 400 build.

If you go H beam/forged, I would have it all balanced from the balncer to pressure plate.

The engine will be smoother, and the main bearings will thank you.

 

Hi Bogus, thanks for yr kind advise but why do we need balancing when we r using forged rods and pistons?
I will be using back my used BC I beam rods and a new set of wiseco pistons.

Hope to get more info on the crankshaft balancing.

 

It is my rule of thumb.

I also balance the rods and the pistons, so they are within .2g from heavy to light

The closer the balance, the less out of balance weight you have trying to throw the crank off center when under load.

A couple grams out will translate to several hundred pounds of force.

With a H beam set up, most are looking to spin past the factory engineered design, so when this happens, the out of balance is exponential scale.

So when balanced the crank is not fighting to stay on center (not as bad on a 4 cyl as a V8)

If you have looked at a balanced engine at idle, you will notice it will not rock in the bay near as much as the unbalanced one.


Good choice on the BC rods, past couple of days I just balanced about 10 or sets of rods, Scat, Eagle, Manley for several engines, 4g63 6 and 7 bolt, EJ, KA, and SR20

3 sets were BC, and all 3 times, they were the closest out the box

I also like the taper that the BC have on the beam.

 

Thanks BogusSVO, so do i need to send along my BC I beam rods & Wiseco pistons for my Crankshaft balancing?
Sorry for the noob question as the machine shop here did not request for the rods & pistons.

 

It depends. If you balance each piece individually then the end result will be as code as the stack up of your margin of error. So if you balance each piece within 1g then you could be up to 8 grams off from lightest to heaviest if you did rod piston pin and crank. If you do a dynamic balance you can weigh each part and then there are calculators that figure out the weight of a Bob weight to put on each crankshaft journal then you balance the assembly. It is best to balance all parts first individually then do a dynamic balance.

 

Thanks Batty

 

waste of money to balance factory crank. they are balanced extremely well from factory.
adding after market pistons and rods does not change that. they are balanced better than factory tolerances for pistons and rods.

 

Batty, close. Bob weights are not used on a 4 cyl, since you have 2 up and 2 down, they cancel each other out, unlike on a "V" engine.

To me, 1g is too much out of range, I tend to balance to .2g high to low.

Coupe, Sorry, I will have to disagree with you. I do not think balancing is a waste of money.

On avarage I have see 3-5g to have to be removed to get a 4g in balance, that may be good enough for the factory, but not for one that is looking to double or triple the factory HP Rating.

Yes the aftermarket rods and pistons are closer than factory, but there is still room for improvement.

The deal with engine building is you can be as **** as you want to be.

 

I have experience running early 4g63 28grams out on 1 piston and rod.(on purpose test) early motors pistons and rods are usually at least 6 grams out from factory and they last 200k miles are butter smooth to 8k rpm.. if you want to waste money go ahead. balanced to within 2g is plenty good.

unequal power per cylinder is a FAR greater concern. if you want a good balanced running engine get the cylinder to cylinder power closer

 

Great sharing 94AWD, and how do do abt the "cylinder to cylinder power closer"?

How to test test/check it?

 

Bogus-- I'll let you build my motors. Factory is crap a couple of grams out is always ok to them. Running an ounce out as stated by 94awd , while it will run isnt a true test of anything except that it will run. Good motors are all balanced better then factory specs and I want my stuff as close as possible individually and together and in rotating mass. And you are right with this stuff you can be as **** as you want to be and everyone has their tolerance for good enough. As to the point that power balanced between cylinders is most important while this is correct as well, having one cylinder pushing an assembly that is far greater in weight over its corresponding counter assembly certainly is taking more of the power made to rotate the heavier assembly.

 

I do not know of a test for it.

For me it is in the build, make sure air flow thu the head is the same from cylinder to cylinder.

Have the combustion chambers CC'ed and they are equal

Check that the piston to deck is the same on all 4 holes

In theory if the math is the same on each cylinder, the power for each cylinder is the same.

 

I had everything on my 2.3 rotating assembly balanced and used a Fluidampr as well. Definitely would do it again on my next engine.