B18C7 Balancing and ITR Tech Guide download

[00dc2]

A while back on a thread talking about lightweight flywheels i bought up the question of whether the B18C in a DC2R is balanced with the flywheel on the crank or if they are balanced separately and then assembled. No one really answered my question and i am left unconvinced about whether a lightweight toda flywheel is for me.

A Highly balanced engine produces more power and lasts longer. I would hate to upset my engines balance.

this is the best page i have seen on engine balancing
http://www.aa1car.com/library/2003/eb10330.htm

After drilling, the crankshaft is again spun on the balancer to determine if additional corrections are required. If the crankshaft is for an externally balanced engine (such as a big block Chevy), the balancing will be done with the flywheel and damper installed. On internally balanced engines, the flywheel and damper can be balanced separately, or installed on the crank and balanced as an assembly once the crank itself has been balanced.

Even if the B18C7 is internally balanced it could still have been balanced with the flywheel and crank together, so replacing the fly could potentially throw out the balance?

Does anyone know anything conclusive about this?

Its quite conceivable that the B18C7 is internally balanced and the flywheel and internals are balanced separately (or not balanced separately but the flywheels are perfectly balanced already or something) and the flywheel can be replaced with no ill effect. Its just that i would like to know for sure.

[tinkerbell]

Even if the B18C7 is internally balanced it could still have been balanced with the flywheel and crank together, so replacing the fly could potentially throw out the balance?

Take something that is balanced, attach it to something else that is also balanced, and then balance that.

The first two are already balanced, so separating them will not make them less balanced as separate items.

However, to re-achieve the balancing that was achieved by balancing two already balanced items - you may need to get the assembly balanced once you change a part of the assembly...

but seriously - who cares!!!

Do you think Honda's flywheels are all perfectly balanced?

Do you think they re-balance the whole freaking engine if they change the flywheel? Or the crank pulley?

no way!

if Honda doesn’t worry, neither should you.


I’d swear we have already had this discussion too.

[BlackDC2]

Not so important for flywheel replacement, but i really think this is one thing people overlook when modifying their engines.

For those who are really concerned about engine harmonics (taken from http://www.fluidampr.com/HOWITWORKS.htm)

Why your engine needs a damper
Each time the air/fuel mixture inside a cylinder is ignited, the combustion that occurs creates a torque spike that is applied to the crankshaft through the piston and rod. This torque spike is so severe that it not only turns the crankshaft, it actually twists the crankshaft ahead of its normal rotation and then the crankshaft rebounds. This twisting action is known as torsional vibration. When these torque spikes and forces get into phase with the natural frequency, critical torsional harmonic vibrations occur and can be seriously destructive to the bearings and the crankshaft. Dampers are designed to control those destructive vibrations.

Rubber VS Silicone Fluid
Critical harmonic vibrations occur numerous times in a engine’s operating range. Stock rubber and elastomer-type dampers are frequency sensitive “tuned absorbers”, and work at only one critical frequency. In the case of a stock rubber damper, it is tuned for a factory engine’s critical harmonic vibrations. If you change the mass of pistons, rods, or the crankshaft, you change the natural frequency of the crankshaft assembly; therefore, the stock damper is no longer tuned to the new frequency of vibration, and you may be headed for early failure of expensive engine components. Dampers also create heat while they work, and rubber is a poor dissipator of heat. This heat and the exposure to the elements deteriorates rubber, causing it to crack and change durometer, which then leads to inertia ring slippage, damper failure, uncontrolled torsional vibration, and costly engine parts breakage.

[tinkerbell]

is a relationship between an engines balance and harmonics?

[BlackDC2]

what is your question tink?

[tinkerbell]

is there a relationship between an engines balance and harmonics?

sorry, left a word out!

[BlackDC2]

is there a relationship between an engines balance and harmonics?

sorry, left a word out!

well, flywheel aside, how i read it is, if you are changing the engines rotating mass, even though all the parts are balanced to one another, you are changing the overall harmonics of the engine.

therefore, the standard harmonic balancer is rendered useless as it has not been designed to work with the new harmonic vibrations caused by the differently (from standard) weighted components.

the reason for initially adding the information was due to the title of this thread being B18C& Balancing

[tinkerbell]

well, flywheel aside, how i read it is, if you are changing the engines rotating mass, even though all the parts are balanced to one another, you are changing the overall harmonics of the engine.

so what effect does increasing or decreasing the mass of a rotating component have on the harmonics of the engine? all else equal?

[BlackDC2]

so what effect does increasing or decreasing the mass of a rotating component have on the harmonics of the engine? all else equal?

..

If you change the mass of pistons, rods, or the crankshaft, you change the natural frequency of the crankshaft assembly;

[tinkerbell]

i read that, but but which way does it "change"?

decrease reciprocating weight = rise in the harmonic frequencies?

increase reciprocating weight = fall in the harmonics frequencies?

in reality - can it even be measured?

[00dc2]

Take something that is balanced, attach it to something else that is also balanced, and then balance that.

The first two are already balanced, so separating them will not make them less balanced as separate items.

However, to re-achieve the balancing that was achieved by balancing two already balanced items - you may need to get the assembly balanced once you change a part of the assembly...

but seriously - who cares!!!

Do you think Honda's flywheels are all perfectly balanced?

Do you think they re-balance the whole freaking engine if they change the flywheel? Or the crank pulley?

no way!

if Honda doesn’t worry, neither should you.


I’d swear we have already had this discussion too.

I know we have already had this discussion but you left me unsatisfied Tinkerbell



I agree that the Honda flywheels are probably not individually balanced. So when they were balancing the engine (crank,pistons,rings etc) they may have just attached the flywheel and balanced the whole kit and caboodle (fly, crank, pistons, pins etc) together in one go. So if you replace any part (be it piston or ring or flywheel you will throw out the balance).

Whether this is an issue i have no idea. Its very possible that flywheels are so evenly made that changing them doesnt effect the balance much. Same goes for clutches,pressure plates...

But i would like to know definitely that i dont need to even think about this...

Honda obviously cant rebalance the engine when you need to replace the fly, its not an option. It could just be cos its prohibitively expensive to do and the cost is only slightly more engine wear and slightly less power in an already highly used car.

Harmonics: Every item in the world has natural harmonics due to its weigh/size. Like bridges. Remember that bridge that the wind destroyed because they didnt think about the harmonics when they built it. I think the item resonates at its harmonic frequencies so needs to be damped at those frequencies. It would be the same for an engine.. but how big is the potential problem? no idea...

[tinkerbell]

I agree that the Honda flywheels are probably not individually balanced.

but they are!

So when they were balancing the engine (crank,pistons,rings etc) they may have just attached the flywheel and balanced the whole kit and caboodle (fly, crank, pistons, pins etc) together in one go.

no, they balance each part!

So if you replace any part (be it piston or ring or flywheel you will throw out the balance).

Whether this is an issue i have no idea. Its very possible that flywheels are so evenly made that changing them doesnt effect the balance much. Same goes for clutches,pressure plates...

But i would like to know definitely that i dont need to even think about this...

Honda obviously cant rebalance the engine when you need to replace the fly, its not an option. It could just be cos its prohibitively expensive to do and the cost is only slightly more engine wear and slightly less power in an already highly used car.

you answered your own question. dont worry.

Harmonics: Every item in the world has natural harmonics due to its weigh/size. Like bridges. Remember that bridge that the wind destroyed because they didnt think about the harmonics when they built it. I think the item resonates at its harmonic frequencies so needs to be damped at those frequencies. It would be the same for an engine.. but how big is the potential problem? no idea...

i have been running a toda lightweighrt flywheel and a B18C crank pulley plus hand carved valve reliefs on a B20B vtec since 2006 and won the NSW supersprints 3B class with it (so i havent babied it)...

with all this weight confusion, if it doesnt throw a B20 off, surely it won't throw the venerable B18CR off?

or is this flawed logic?

[00dc2]

but they are!

If this is true then i dont think there is anything to worry about.. where did you get this info from?

no, they balance each part!

I think i see what your saying, Yes, when they balance a inline 4 they just make sure each of the components are within 0.Xgrams of each other. But they dont stop there, they spin all the parts together and then make more adjustments possibly due to uneven crank and flywheel weight distribution...

I think most likely this is not much of an issue, but i'd like to know for piece of mind and for curiosity sake... so that when i need my clutch replaced i can pull the trigger on a Toda flywheel without any reservations

[tinkerbell]

If this is true then i dont think there is anything to worry about.. where did you get this info from?

i usually look at flywheels when i remove them, and the holes of varying depth and placement around the circumfrence of the flywheel seem like an attempt by the producer to balance it.

i note that these holes are also evident on the crankshaft (big end) and the crank pulley.

But they dont stop there, they spin all the parts together and then make more adjustments possibly due to uneven crank and flywheel weight distribution...

"they" do? who is they?

[00dc2]

"they" do? who is they?

your saying that the B18C7 wasnt actually spun balanced. The crank came already balanced and the pistons and pins etc were all simply chosen with matching weights...

http://www.hondatech.com.au/forum/showthread.php?t=441

Ok that makes some sense... and that explains why Toda bother making a balanced flywheel/clutch/pressure plate kit