Balancing the rotating assembly?

[70spider]

I finally found a machine shop that will do the work on the block for me. I was wondering on how important it is to balance the rotating assembly? I understand the theory behind it but lack the knowledge on what they do to balance it. Also should I get a lightened flywheel?

[joelittel]

All I can say is that I've never read a post on the forum where someone is complaining about their lightened flywheel.

[vandor]

Balancing usually costs little and makes the engine run smoother. Most stock Fiat parts are fairly well balanced, so it is not essential.

Most people on the forum who have lightened flywheels also have 2-liter engines which have a lot more low-end torque. I am not sure if I would lighten the flywheel on a 1608 by much. Would be nice if someone could report who has done it on a 1608 engine.

[70spider]

Most stock Fiat parts are fairly well balanced, so it is not essential.

When I dis-assembled the motor last year I made sure I labeled everything and noticed that the connecting rods were numbered so I figured there must be a good reason they correlated with the cylinder I pulled them from. The only part being changed in the rotating assembly are the pistons, I'll ask the machinist to see how close they are to each. Thanks.

[carl]

I agree with Csaba, I don't think balancing is necessary for a street motor. I installed new HC pistons in my 2L motor without any balancing involved and the motor runs fine with no vibration.

My only experience with lightened flywheels was an X1/9 I bought that had a flywheel with a lot of weight taken off. The car was impossible to drive even around the neighborhood as it kept stalling while pulling away from a stop, even with healthy use of the gas pedal. My opinion is that for normal street driving the stock flywheel is just fine.

carl

[baltobernie]

If you look at the reverse side of your crankshaft pulley, you'll see a line of drill marks of varying depth. This is how Fiat externally balanced their engines after assembly. If you are rebuilding your engine, you have two options. 1.) Hope that the machine shop puts everything back together the way Fiat did, and presuming that all the replaced items are identical in weight and moment of inertia. 2.) Spend $100 and get it done right. I don't know if it is necessary to go further and include the flywheel, clutch assembly, etc. in this process; I did not.

How many times do you expect to rebuild this engine?

[70spider]

Hope that the machine shop puts everything back together the way Fiat did

I'll be putting it back together and will be assembling it exactly as I found it. I was very meticulous (for a change) when I tore it down and labeled everything in separate zip-lock bags and photographed every part removal. As for the parts the only items being replaced will be the pistons and bearings.

How many times do you expect to rebuild this engine?

If they don't outlaw petrol engines maybe one more before I'm worm food, so I can pass it on to the kids in good nick.
Thanks for the help. I'll probably get it balanced for the peace of mind if they are up to it.

[vandor]

> This is how Fiat externally balanced their engines after assembly.

I do not think this is correct. If it was then the engine would be horribly out of balance when people fit aluminum crank pullies, yet there are no complaints of vibrations with alu pullies.
As far as I know each component is balanced separately - crank pulley, crankshaft, flywheel. That way each item can be replaced with another balanced item.

[baltobernie]

I checked with the machine shop that balanced my engine, and you are right. The depressions drilled on my crank pulley are the result of balancing the pulley, not the entire assembly. I stand corrected.

[grrrdot]

I have a DOHC 1608 with a lightened 1438 flywheel.
Its great. Ticks over at 950RPM smoother than any Fiat I've owned.

I had to call around and eventually talk a machine shop into balancing just the flywheel. All the shops wanted to balance the whole assembly. Its a good thing I had it balanced too, they ended up drilling a few holes to bring it to neutral.

-G

[70spider]

I have a DOHC 1608 with a lightened 1438 flywheel.

Nice, what other mods have you done to the 1608 that worked for you? Like what is your carb? And do you have a stock cam or a performance one?

[grrrdot]

I got the short block with the cylinder head for free. It was built up by someone else so I couldn't get the specs. I used a syringe to fill a cylinder and it looked like stock compression, cams are stock as well. In terms of ancillaries:
- 1800 intake
- 32/36 DFEV carb with a 1" individual barrel spacer ( didn't want too add much plenum volume )
- Stock filter box with K&N filter
- 2L FI exhaust manifold
- Alum adj cam wheels
- Lancia beta electronic ignition ( block mount with vac adv)
- 1438cc lightened flywheel and bell housing

The engine reminds me of my old Honda motorcycles not much going on under 3K then it just wakes up and pulls like crazy, I usually don't go over 6K but feels like it could. I've thought about going the IDF route but the DFEV carb is so trouble-free and there is already enough to work on.

-G

[timinator]

>
As far as I know each component is balanced separately - crank pulley, crankshaft, flywheel. That way each item can be replaced with another balanced item.

Engines are balanced as an assembly. The balance shop needs the weight of the piston+pin, ring set, pin locks, and rod bearing. They will also want the front pulley, flywheel, and clutch cover(pressure plate). So no the individual items cannot be replaced with another balanced item that is an exact match. However, most cranks tend to be close in balance for a particular engine family. You just don't know how close. Factory balance is usually o.k., but not perfect. Change parts and the situation gets worse.

Just got an balanced assembly back from the balancer and the clutch cover had about 30 lightening drill dimples in it. The cover and flywheel are also indexed to each other so don't ruin the balance when you replace the disc.

[baltobernie]

It's probably more beneficial to have a Fiat TC engine properly balanced than other motors. First, these old engines don't have a harmonic balancer like modern cars, and second - these engines are revving higher than your DD at similar highway speeds.

The shop I used gave me two options and two prices: one for balancing just the internal parts he machined and assembled, the other for the entire rotating assembly as you've described. I chose the former, and although I don't have anything to compare it to, it feels awfully smooth.

[70spider]

I am convinced, balancing is the way to go. Midwest charges $250 for the service, they did my cylinder head so I might use him for the balancing. Thanks for the input.