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please explain about flywheel balance

15K views 20 replies 10 participants last post by  Forcedinduction 
#1 ·
hi all, i understand that the crankshaft has to be balanced to counter harmonic vibrations - at least in straight 4s and 5s - thus the use of a non-neutral harmonic balancer. a flywheel is for storing rotational energy and is at least by default neutrally balanced. right so far?

WHY would an engine swap require a custom or rare balanced flywheel, then? shouldn't the harmonic balancer which is already mounted to the donor engine do the trick to counter the crank torque, whichever flywheel is used? i have heard a lot about balancing flywheels, and this sounds to me like replacing the role of the harmonic balancer. wouldn't it be much simpler to just use the already balanced crank + HB?

thanks for your thoughts.
 
#2 ·
my question was a little abstract, so here is what i am looking into accomplishing: turbo 5 into my 240. i am aware i could swap the whole drivetrain in without rebalancing, but i intend to keep the manual transmission. how does that affect crankshaft balance?
 
#3 ·
I believe Flywheel for the Automatic Transmission is different than the Flywheel for a manual Transmission.

Therefore you need to replace the Automatic Transmission Flywheel with a Manual Transmission Flywheel that has not been balanced for your 5 cylinde Engine.
 
#4 ·
hi all, i understand that the crankshaft has to be balanced to counter harmonic vibrations - at least in straight 4s and 5s - thus the use of a non-neutral harmonic balancer. a flywheel is for storing rotational energy and is at least by default neutrally balanced. right so far?
The flywheel on the diesels doesn't necessarely have a neutral balance. On the four-cylinder engines the crankshaft is balanced in its entirety in the factory, so if you change a component (balancer, crankshaft or flywheel) you'll need to transfer the balance of the old component to the new one. On the five-cylinder engines MB balanced the entire engine in the factory and the same applies.
 
#14 ·
That's interesting. I thought that flywheels were just acumulators of momentum and thus uniformely balanced. I also thought that primary and secondary balance issues were solely counter-worked throughout balance shafts and crankshaft's added masses.

I am considering swapping an oldish MB engine + manual gearbox into my Lada Niva, so I am glad I've come across this bit of info. I was not suspecting the flywheel might be playing such an important role, let alone non-neutrally balanced flywheels existing... :eek
 
#5 ·
you guys have both said totally reasonable things, which i need to reconcile. does keeping the manual transmission require keeping the smaller old flywheel? if not, can't i install the balancer, crankshaft, and flywheel all together from an automatic, turbocharged 300D?
 
#6 ·
govert, i found your earlier post saying "The flywheel needs to be changed if you are going from automatic to manual and the balance of the old flywheel needs to be transfered to the new flywheel."

by this you don't mean that the flywheel matches more closely the transmission than the crankshaft and balancer...?
 
#7 ·
A MB diesel which was made for an automatic transmission has a light flywheel, which drives the torque converter. If you want to convert to manual, that flywheel has to come off and a manual (much heavier) flywheel has to be installed. The balance of the old flywheel has to be "transferred" to the new manual flywheel, that is done by drilling holes in the manual flywheel at strategic places. This is normally left to a machine shop, they are specialised and have machines to do this.

You can change the crankshaft together with the balancer and the flywheel, but it requires a lot of work: the engine has to come out, driveshafts have to be disconnected and on five-cylinders engines it might lead to unbalance, because the engine is balanced in its entirety in the factory. It is much much easier to change just the flywheel if you want to go from automatic to manual or vice versa.
 
#8 ·
a lot of people seem to think the automatic flywheel is heavier than the manual one (frequently citing 38 versus 28 pounds per). i understand that they are different. so for swapping a turbo in alongside my manual transmission, my options are:

1) keep flywheel from 240D - correct weight, balanced for wrong engine
2) keep flywheel from 300D - wrong weight, balanced for correct engine
3) balance flywheel from 240D to match automatic flywheel - correct weight, correct engine

if (3) is practical and correct then i don't see why people are paying hundreds of dollars for the euro manual 300D flywheel. thanks govert and 300Dman for your responses. i nearly understand it now :)
 
#9 ·
The best choice is to get a 300D Euro Manual Flywheel.

But, if you do it still needs to be balanced to match the Flywheel that you remove.

I do not know what the Various Flywheels weigh. But, the Torque Converter is also acting as a Flywheel (or at least part of it is).
 
#10 ·
Bricktron, the flywheel from the auto is very light, I believe much less than 28lbs. While it can be used there is not much inertia available to easily engage the clutch so it will require very careful gear changes to smoothly operate the car. At the very minimum it is best to use a 28lb 240D manual flywheel with the OM617. Even then it is highly recommended to balance the flywheel with the crankshaft as a whole unit. If you can't then it's a guessing game. How adversely will it affect the engine is difficult to assess.

I personally waited several years to have a proper 300D flywheel balanced with the crankshaft. Is it worth it? It's probably too early to tell since that is something only time will dictate however the engagement and smoothness is exactly the way I hoped it would be.
 
#11 ·
diametricalbenz, you balanced a flywheel against a crankshaft though the FSM (as i read it) says it's not practical, nice going. for the rest of us it must be OK to assume that the donor flywheel is indeed balanced to its engine, and rebalance the manual flywheel to match. it should be less than half the cost of the euro flywheel...?
 
#17 ·
Is this what you're talking about?

Well, another joyous, anticlimactic day.

I spent all of last night mentally preparing myself for a repetitive routine (check static balance, mark heavy spot, drill tiny hole, repeat). I had the tools, the guts, the FSM chapter.

Then I installed the two balancer plates diametrically opposite, as per the FSM, and gently turned it clockwise, then counter-clockwise. Twenty times I turned it, and twenty times the pair came to rest in a different position. How often do I buy something that is this perfectly matched to my vision of the outcome?

So I took off the new balancer, pressed out the bearing and shin, and installed it onto my engine.

Here is the original balancer, still with its bearing and shim, still installed on the purpose-built balancing frame and shaft.
I know, I know, this is only the front balancer. But the principle is the same. The round tubes, bearings and the stands may need to be bigger for two flywheels.
 
#15 ·
You must remember that the crankshaft twists and unwinds under the torque from the pistons. The pistons and conrods also have manufacturing tolerances, so no engine is made of perfect parts. All the components are made to spec, but once the engine is assembled, it has to be balanced to remove its own unique harmonic motion distortions.
 
#18 · (Edited)
1. You mark up how the old flywheel sits on the engine,
2. Take it to the engineshop/balancingshop along the new flywheel,
3. have them test the old flywheel and see how it is "unbalanced".
4. If they are any good, they can replicate that same "unbalance" to the new flywheel for the manual transmission, and mark up in the same way your old was marked.
4.5 if your old flywheel was balanced at "zero" have them make the new flywheel at "zero" unbalance.
5. Put new flywheel on engine, in same rotation to crank as the old one was (hence the markup)
and you ought to be good to go.



not al flywheels seem to be unbaöanced, some earlier was, and newer perhaps wasnt, not shure about that thou,.
 
#20 ·
ive been getting ready to do the 4 speed swap on my 83 300dt. ive got the euro 300d flywheel. i was just thinking about balancing today. i am going to go the a machine shop and have them check it out for me. do i take them the pressure plate and clutch disc as well? i mark my flexplate torque convertor and the crank?
 
#21 ·
Only the flywheels need balanced. The torque converter is naturally balanced by the fluid inside and clutches are always balanced neutral.

Use a chisel/punch and mark the crank and original flywheel together. Do not use paint/ink pen alone, if it gets washed off of either surface you will have no way to know where it was aligned.
 
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