Balancing crankshaft?

[jerry598]

I'm still in the middle of a rebuild on my 95 6.5TD and am wondering about the need to balance the crankshaft and how/where to get it done.

The shop is reboring the block and therefore replacing the pistons too. I was planning to just slap on a new Fluidamper and go, but after reading the Fluidamper article, I'm led to believe that the crank and or rotating assembly needs to be balanced first with the original damper before installing the new fluid damper.

Can anybody tell me how that's done?

[Robyn]

The pistons are all weighed and any adjustments to make them all equal are done.
The rods are weighed both on the large end and small end using a fixture and made equal.
The total rod weight is done and the set made all the same.

Now a set of special weights are made the simulate the weight of the rod/piston assembly and these are clamped to the crank throws.

The ballancer, crank pulley and flex plate/flywheel are installed and the thing is spun in the ballancing machine. (special set of rollers with sensors that measure vibration/out of ballance.

The counter wieghts on the crank, the ballancer and or the flywheel are then weight adjusted by drilling holes and or adding weight depending to achieve a perfect ballance.

From the factory these engines are fairly close but having them closer wont hurt anything.

For an engine that only runs at 3500 RPM the ballance is not nearly as critical as the engines that run at high RPM.

The benefit is that the internal harmonics of the engine will be lessened resulting in a much smoother running engine along with enhancing durability.

The fluid damper is a great investment for the 6.2/6.5.

Hope this helps

Robyn

[SmithvilleD]

Not certain if this will cut/paste to look right in a post, but here's what the components for my 6.5 build weighed before mix/matching the pistons/pins & the rest of the procedure to balance things.

Piston & Pin (my weights & #'s): 1271.5 1269.5 1271.0 1272.0 1266.5 1268.0 1269.0 1268.5 max variation = 5.5 g,18:1 marine pistons

Rod & bearing 1121.0 1121.0 1121.0 1123.0 1123.0 1118.0 1117.5 1118.0 max variation = 5.5 g, stock rods

Total Weight (g) 2392.5 2390.5 2392.0 2395.0 2389.5 2386.0 2386.5 2386.5 max variation = 6.5 g

There was a fair bit of variability (5-6 grams) but as Robyn said, these things don't spin ultra fast.

If you do have it balanced, make certain it's a shop that has adequate weight bob-weights to balance these heavier (than common domestic V8 gassers) diesel rotating/reciprocating components. Some shops will only be set up to balance the lighter gasser components.

And you're right that the Fluidampr isn't used when balancing the rotating components. It's supposed to be balanced correctly as new. I gather the internal viscous fluid might also present issues that could confound things if it's attached to the crank when balancing the crank.

[Robyn]

Personally I would not sweat the ballance job unless you have the extra $200-300 to spend. Make sure your flex plate is in good order and that the dampener pulley assembly is fresh. Install the fluid damper and rock and roll.

The bulk of the time these engine run around 1800-2300 RPM

The Fluid damper will knock out the harmonics as its supposed to do and things should be sweet.

Missy

[jerry598]

Thanks everyone for the replies. I will share them with the shop.

Since I really don't plan to run my rig at high speeds or rpm's, I may very well skip on balancing the crank, based on your replies. The shop did not suggest to me that it should/could balance the crank anyway, and they may not have the capability. I'll find out tomorrow.

Hopefully, this thread will be informative for others who might be trying to make the same decision.

Jerry