[RESOLVED] Balancing Engine ... Brain Fart.

[interex]

I'm getting ready to have my aftermarket internals balanced. Having this stuff balanced would make it internally balanced right? So do I require a fluid damper/external balancer or not?

I am just curious about what all I need to take to the machine shop.

 

[LiquidX]

I'd say yes just to be safe. You wouldn't want a snapped crank after all that balancing that got done and have it wasted.

 

[interex]

Hmm, I need to know if I should use the stock harmonic balancer or an after market one then with having this rotating assembly balanced.

 

[NB4G63T]

Anytime you change your rotating Assembly from stock to aftermarket you should run a fluid damper to keep the engine lasting. The shop doing the balancing should be able to tell you what you need.

 

[spoonman]

Balancing is without a doubt the most misunderstood part of an engine rebuild.
At 7000 RPM's a piston weighed in just ounces can exert thousands of pounds of force when it changes direction at TDC.

In a well balanced engine the weight of one piston should be off set by the weight of another.

Rotating weight

The crankshaft, main bearings, and the lower part connecting rod spin (rotate) so they are part of the rotating weight.

Reciprocating Weight

The pistons, rings, the top part of the connecting rod move up/down.


Before a machinist can balance an engine they must find the bobweight (The mass on a single rod journal) of a single piston, rod, rings, rod bearings, and connecting pin (some machinists also include the weight of the oil that is coated on the internals). The formula is usually the weight of all the separate components listed above added together, but the reciprocating weight is usually by multiplied 2.

Example;

Piston 100
Rings 15
Con. Pin 35
Rec. Rod 45
Rot. Rod 100 X 2
Rod Bearings 25 X 2
*Oil 5

100 + 15 + 35 + 45 +200 + 50 + 5 = 450



External

Externally balanced engines are those that have a heavy reciprocating assembly or long stroke. It is used when the weight of the crankshaft's counter weights do not have enough mass to offset the bobweight for the engine's internal rotating assembly. Well why can't they just add more weight to the crankshaft? Because there are usually limitations like space in the block. These engines are balanced by adding more weight to the flywheel or the harmonic damper. In some cases with big old push rod V-8's they have little counter weights that are attached to crank bolt. The flywheel and balancer needs to be in the exact position every time or else the engine will become unbalanced.

Internal

Internally balanced engines are those that have enough weight in the crankshaft's counterweights to reach the determined bobweight. Internally balanced engines can have the flywheel or harmonic balancer swapped out regardless of weight or position as long as they themselves are balanced individually.






The machinist will take all if the pistons, including the connecting pins, and weigh each individually. They will then take the lightest piston and machine the rest of the pistons to match the lightest. The material is usually taken off of the pin bosses. The connecting rods are next, the machinist will actually have to weigh each end of the rod because they fall into two different areas of kinetic mass (rotating-reciprocating). The lightest small end and the lightest big end of the rods are the goal of the rest. The material is usually grinded off of the head of the small end and the big end the material is usually removed from the balancing pads on the sides.







I will finish the rest later, we all have to sleep sometime. Except for you Defiant.

 

[TunaTalon]

The 4G63 crank pulley, more properly called a harmonic dampener, is independent of static balancing the engine internals. The rotating assembly should be balanced to prevent vibrations at the frequency of the engine RPM.

The harmonic dampener should be installed to dampen the effect of natural engine vibrations at higher frequencies that are not caused by static imbalance. There are many threads on this site about dampeners and the usual conclusion is to use the OE crank pulley.

Balance shafts do not affect the static balance of the engine. They counteract the harmonic imbalance at two times the frequency of the engine RPM. Many tooners remove the balance shafts and accept the vibrations for lower risk of failure.

The term "external balanced" does not apply to the 4G63.

 

[interex]

Okay, also do I need to take the clutch, pressure plate, and flywheel too?

I'm not going to say the machine shop is going to tell me what to bring, I'm sure all machinists are different in their ways of operation even if there is a standard to machining.

 

[95blackGsTurbo]

I've balanced more than my fair share of motors. The stock harmonic balancer will be fine. I would recommend just getting a new OEM one to ensure it lasts. Take your pistons, rods, crank, harmonic balancer, flywheel and pressure plate. Those are the only items that will be needed to balance your rotating assembly.

 

[rbwtrans]

One more opinion doesn't hurt, I guess, so here's mine. My cranks are spin balanced with the flywheel, pressure plate, timing belt gears, OE damper, and all attaching hardware. I'm anal about this stuff, so I also mark my bolts so that they go back in the same holes on reassembly. I can't do this part myself, so I pay to have this done. The guy I use will balance the flywheel and pressure plate, first, then bolt it all back together and spin it as an assembly. He says my aftermarket flywheels are ALWAYS out of balance. Pistons, rods, wrist pins I do myself, pretty much exactly as Spoonman said. I've never done it weighing rings, bearings, or oil weights, but I wasn't taught to. I do remove the balance shafts from almost every engine I've built that was balanced. Usually the balanced engines without balance shafts run smoother than stock engines with the balance shafts! Good luck. I hope that some of this has helped.

 

[Defiant]

I'm getting ready to have my aftermarket internals balanced. Having this stuff balanced would make it internally balanced right? So do I require a fluid damper/external balancer or not?.

Yes. The harmonic balancer has nothing to do with the engine's internal balance. It's for crankshaft windup.
http://www.dsmtuners.com/forums/cylinder-head-short-block/268533-broken-crankshaft.html

 

[interex]

So they will need my OEM Harmonic Balancer when they do the balance on the internals?

 

[Splitpi]

So they will need my OEM Harmonic Balancer when they do the balance on the internals?

Spoonman explained it pretty well in Post #5.

Also, here is a decent explanation:
Engine balance - Wikipedia, the free encyclopedia
Balancing machine - Wikipedia, the free encyclopedia

 

[BogusSVO]

take the crank, the rods, the pistons, wrist pins, flywheel and clutch plate, balancer and crank gear and all the bolts for the parts your taking.

they most likely will not do a bob weight since you have a 4 cyl.

the shop will weight match the pistons, to the lightest one in the set. and the same for the wrist pins.

the small end of the rod will be ballanced, then the overall weight of the rod.

the crank will be spun up and balanced, then the balancer will be added and spun, then the flywheel, then the clutch plate

make sure you make the clutch plate to flywheel, and the flywheel to the crank.

the price should be about $150-200 to have it done.

 

[interex]

They should need my bearings too .

 

[rbwtrans]

They should need my bearings too .

Might be a good idea to weight match the rods with the bearings included, but your crank bearings don't spin. They're considered more of a part of the block because they don't actually move.

 

[JStrateger]

What does a good balancing usually cost? Can I just take my block with the rotating assembly, clutch/pressure plate and flywheel to the machine shop and ask them to balance it or do all the parts need to be removed?

I'm thinking about getting my engine block balanced because I removed my balance shafts.

 

[spoonman]

What does a good balancing usually cost? Can I just take my block with the rotating assembly, clutch/pressure plate and flywheel to the machine shop and ask them to balance it or do all the parts need to be removed?

I'm thinking about getting my engine block balanced because I removed my balance shafts.

The cost depends on the shop but around $200-$350 for the entire rotating assembly. Unless the machine shop will be rebuilding and machining the engine, the engine's rotating assembly (crankshaft, connecting rods, pistons) need to be disassembled.

Removing the balance shafts only effects second order vibration. The balance shafts have no effect on the rotating assembly's balance, the only down side to not having balance shafts is that the engine will have more of a vibrating feel for the driver. If you are completely rebuilding the engine the rotating assembly should be balanced.