Underdrive Pullies

[Lelandjt]

It is true that you shouldn't change the crank pulley on many engines. My Subaru flat four is an exception. If you are worried about changing the crank pulley some companies make larger, underdrive accessory pulleys. You can get them for just the accessories you want underdriven, they are lighter than stock, and it won't affect the crank. Ideal setup may be one of these on the alternator and electric water and steering pumps.

[VetteOwner]

whole point of underdrive pullies is to make the crank smaller and lighter(hence why i went from large steel to small aluminum), less mass to keep spinning/spin up.(hence why race engines typically have lightweight flywheels too and idle at 2k rpm lol)

[therealtime]

Originally Posted by suspendedhatch

Not so. Hondas are internally balanced, but the harmonic balancing is in the crank pulley. W/out it, at a certain high RPM there is a damaging vibration to the engine.

Only the Civic CX and VX lack a weighted crank pulley. This is due to the fact that the redline is quite low so you never reach the RPM where the damaging harmonic resonance occurs.

AFAIK Honda did not start using harmonic balancers until the 1996 model year. My 1993 del sol D16z6 does not have the rubber in the crank pulley. Neither did my 86 crx EW4, 87 civic D15A3, 88 civic D15B2, 89 civic D16A6.

In any case, if you were building an engine you could have the rotating assembly balanced with combination of pulley and flywheel you want.

Sorry to bring this thread back from so long, but I am planning to install a crank pulley and a lightweight flywheel, and I didn't want others misinformed.

[GasSavers_Erik]

My 94 Honda Accord (2.2L) does have a harmonic balancer built into the crank pulley- as well as rotating internal balance shafts.

[therealtime]

Originally Posted by Erik

My 94 Honda Accord (2.2L) does have a harmonic balancer built into the crank pulley- as well as rotating internal balance shafts.

perhaps my statement only aplies to the d-series engines then.

[seeodywhy]

I put an aluminum flywheel and crank pulley on a 1990 Z I had and I noticed a big difference and the idle didn't seem any rougher.

[zero_gravity]

it has nothing to do with a rougher idle. it has to do with crankshaft flex chewing up the crank bearings.

[Philip1]

I would underdrive my water pupmp but the ecotec uses the timing chain for that so....

[zero_gravity]

yea the accessories are fine, but unless theres some sort of internal dampener the crank pulley is just asking for trouble. they use them on race engines because they're going to rebuild them every race anyhow so who cares?

[Snax]

Let's be careful not to confuse harmonic balancers with dampeners. The difference is that a harmonic balancer is actually keyed to counteract internal forces, whereas a dampener only reduces the shock to and from accessory loads. An undampened underdrive pulley however just by virtue of underdriving reduces the amount of shock and vibration to deal with however. I.e., a larger pulley can both transmit and receive larger shocks by the difference in mechanical advantage.