CP

I wanted to ask this over on the i-club board but I value the technical opinions here much more. The topic was about underdrive pulleys that were the same size as stock but lightened(?). This would in turn cause resonant frequencies to emit from the spinning crankshaft at higher rpms, causing main bearing damage over time. Lightened flywheels also appear to exibit this phenomena.

Any experience with this? Balancing an engine was also brought up. What does this process entail? Obviously engine specs are the basis here, but what has to be done to balance it? Does the machinist take material off of centain compontents so that its weight will correspond with its twin part?

In the dark here...<ul><li><a href="http://www.i-club.com/ubb-files/Forum24/HTML/002111.html">Underdrive pulleys - harmonics</a></li></ul>

CharlieGSanD

also i beleive they will remove some of the counter weight from the crankshaft

if youre engine has a few grams extra weight out of balance it will show up at higher revs as a slight vibration

basically it allows the engine to rev highter (slightly) and rev smoother,
causing less wear on the bearings

think of a balanced wheel, and what happens when its out of balance,

from what ive heard Audi has pretty well balanced engines as far as stock motors, some older chevy 350's can have as much as a few grams extra, thats why its so popular with the domestic crowd

as far as scoobies go, i have no clue about thier manufacturing process

ask lucas in the perf forum he had this done recently

xr4tic

The rods are made so the big ends all weigh the same, and the small ends all weigh the same. Pistons should all be the same weight as well.

If the crank, flywheel, and pulley, are balanced separately, then there shouldn't be a problem. If they are balanced as a unit, and the pulley is swapped for a lightened unit, then there may be a problem.

For blueprinting:
This is the hard part. Basically you make sure everything is the same between each of the cylinders and everything else is in spec. Ring gaps all the same, combustion chambers same size, etc.

StevenH

for blueprinting they also put it at whichever extreme of the tolerance is optimum, for example, if the pistons can be 4-6 ounces(random numbers) they will make sure they are all 4 ounces.
Steven H

Inie

Yes and few other things we used to do.
Making sure all surfaces are perfectly mated to one another. And the crank also get spin balanced too. There is also porting and polishing 3-7 angle valve jobs. Matching spring height(?) and pressure. Some of the new methods involve cryo-treatment of the internals. All these things contribute to longegvity and performance. Especially critical while racing.

$$$$$$$$$ yep!

CharlieGSanD

ooooooo, cryo treatment! want it