Balancing the Crank with the Pulley?

[JonnyPlus2]

Hi,
I'm thinking that the crank pulley (yes I have the solid one from QED) should be attached to the crank when it is balanced. Any thoughts on this? Thanks.

[512BB]

As you obviously have the crank on the bench and presumably the engine in pieces, why would you not have all the rotating parts balanced, especially the flywheel. If done correctly, the individual components are balanced and then as an assembly. While you are at it, get the rods and pistons equalled up as well, makes a difference.

Leslie

[englishmaninwales]

+1 on getting the whole lot balanced; I included the cluch pressure plate too.

[nmauduit]

you sure can, but imho a decent condition pulley likely has a minimal impact on rotational imbalance (small diameter)

[Hawksfield]

Hi
That reminds me of an incident a lot of years ago on my original +2 of a stone getting into the pully area and chipping a small piece from the crank pully (cast iron),thereafter I had a vibration but cannot cannot remember the revolutions but it was significant,
My present twin cam has been fully balanced well worth the effort.

[StressCraxx]

The additional cost of balancing the pulley is truly minimal. It's simply another run on the balancer. That said, if your engine is road going only, it's probably not necessary.

[JonnyPlus2]

Hi All;
Thanks for your replies. My engine guy is not a Twink man although he knows his stuff in general. American V8 cranks are apparently not balanced with the pulley/vibration damper thingie attached for some inexplicable reason.

He wants to send the crank to get balanced without the crank pulley which he calls the vibration damper. I shall overrule him.

Thanks much.

[Donels]

Interesting he calls it a vibration damper.

Many years ago my best mate had the pressed steel fan belt pulley on his mini fail. He got a cast one from a breakers and the guy told him “This is what they fit to racing minis” , “Right!” We said. Amazingly after we fitted it the difference was night and day. The engine was much smoother with far less noise, so the extra mass did damp down the crank vibration.

[Andy8421]

Hi All;
Thanks for your replies. My engine guy is not a Twink man although he knows his stuff in general. American V8 cranks are apparently not balanced with the pulley/vibration damper thingie attached for some inexplicable reason.

He wants to send the crank to get balanced without the crank pulley which he calls the vibration damper. I shall overrule him.

Thanks much.

There is a lot going on with 'vibration damper thingies' - which are generally called harmonic dampers, and are used to prevent harmful resonances building up in the crankshaft leading to failure. A rotating mass, coupled to the crank via some form of elastomer which absorbs and damps vibration. Usually implemented as part of the front pulley on the crank, with a outer mass attached to the centre via a rubber strip. Wikipedia has a description:

https://en.wikipedia.org/wiki/Harmonic_damper

Its not clear to me why you wouldn't want to ensure this was balanced as part of balancing the engine. The rotating mass can be quite substantial.

Edit: I should have added that the front pulley on the twinc is just a front pulley, and doesn't have any vibration damping duties, so my explanation above only applies to engines with harmonic dampers.

[2cams70]

I used a QED pulley in my build and had all rotating / reciprocating parts balanced. When they came back there were no balancing holes drilled in the front pulley. That means either 1) They neglected to balance the pulley 2) The pulley didn’t need balancing. I’d suggest it’s more a case of 2) than 1). Those QED pulleys are machined steel compared to the cast original. The machined steel is very uniform in structure compared to something that is cast and as was said previously the pulley’s diameter is quite small so any effect it has on balance is also quite small and probably within the accuracy tolerance range of the balancing equipment used

[JonnyPlus2]

Thanks everyone for your interesting and informed replies.

I have taken my crank, flywheel, clutch and crankshaft pulley to a different "old school" shop. They do all their stuff in house and they are perfectly happy to balance everything separately and then all bolted together.