is the cranks dynamic balancer needed?

Ralphh85 · Post by **Ralphh85** » Thu May 13, 2010 5:55 pm

i have a feeling everyone will say of course it is but thought i would ask anyway.

ealyer crank pulleys bolt on tot he middle bit which behind has a dymanic balancer (steel bit running with rubber on inside).

on serpentine engines the flat pulley runs outside the dynamic balancer, to me this defies the point of it in the first place, as hole point is the heavy balancer flouts on the rubber drive and will counter any force pushing it. if it has a flat belt over it which run pretty tight, its going to be always pulling that way anyway so wont be balancing anything.

so is it really needed?

can you get light weight "go faster" pulleys for the V8 like you can other engines? do they have dynamic balancers?

Ralph

stevieturbo · Post by **stevieturbo** » Thu May 13, 2010 6:52 pm

IIRC, RV8 is externally balanced.

So the crank damper/pulley is absolutely vital.

ChrisJC · Post by **ChrisJC** » Thu May 13, 2010 7:18 pm

It is not a balancer, it is a harmonic damper. It is to stop the crankshaft getting torsional vibration building up and breaking it.

External balance can be applied to the same assembly, but the rubber part is a damper.

Chris.

CastleMGBV8 · Post by **CastleMGBV8** » Thu May 13, 2010 7:27 pm

Ralph,

It's called a harmonic damper for good reason and is there to protect the crankshaft when harmonics set in at certain RPM.

If you had a crank out of the engine and tapped it with a hammer it would produce a ring like a bell which in itself is a form of self or imposed vibration, remove the crank damper and it is likely that the crank will destroy itself even if the engine is balanced.

The mass of the damper which seperated by the flexible joint serves to soak up the vibrations.

Kevin.

Ralphh85 · Post by **Ralphh85** » Thu May 13, 2010 7:46 pm

so does it still work even with the belt pulling on it?

have to agree about the harmonic thing, dont want them building up!

Ralph

mgbv8 · Post by **mgbv8** » Thu May 13, 2010 8:45 pm

Ralphh85 wrote:so does it still work even with the belt pulling on it?

have to agree about the harmonic thing, dont want them building up!

Ralph

Yes!!
The rubber may be under tension. But it will still smooth out the knobbly bits of the cycle

92rrrandall · Post by **92rrrandall** » Thu May 13, 2010 8:49 pm

http://www.rover-v8.com/jeales/web.nsf/ ... endocument

Ralphh85 · Post by **Ralphh85** » Thu May 13, 2010 8:50 pm

i will just leave it be then!

i wanted to make my own pulley for various reasons, could have tucked it in a bit better and made it alot lighter, also would like it to need 20mm less crank, but will leave it be.

Ralph

Ralphh85 · Post by **Ralphh85** » Thu May 13, 2010 9:04 pm

92rrrandall wrote:http://www.rover-v8.com/jeales/web.nsf/ ... endocument

thanks for the link, anyone know any more about that damper? it looks like it needs a pulley bolting on, yet says serpentine, my serp one has the belt running outside the damper? do they not all have this?

Ralph

spend · Post by **spend** » Thu May 13, 2010 10:02 pm

Ralphh85 wrote: anyone know any more about that damper? it looks like it needs a pulley bolting on, yet says serpentine, my serp one has the belt running outside the damper? do they not all have this?

Ralph

The JE Competition damper is for the inter serp front end, which has a bolt on pulley, sounds like you have the P38 which is quite different.

SuperV8 · Post by **SuperV8** » Fri May 14, 2010 12:21 pm

Having the belt acting on the outer rim of the crank damper effectivly makes the damper act as a heavier unit.

So the belt also helps with the damper at absorbing torsional frequencies.

Tom.

ppyvabw · Post by **ppyvabw** » Fri May 14, 2010 1:14 pm

Ralphh85 wrote:i will just leave it be then!

i wanted to make my own pulley for various reasons, could have tucked it in a bit better and made it alot lighter, also would like it to need 20mm less crank, but will leave it be.

Ralph

Not sure about other pulleys but if you need a custom pulley, get a rangie pulley which comes apart. Keep the damper/balancer thingy and there is nothing to stop you having a custom pulley made that will simply bolt on.