i had a sweet little aluminum crank pully made to only run my alternator i was told by a few people it will wear out my crank bearings is this ture? it makes sense that it would with no vibration dampener but how bad is it realy? it scared me enough to take mine off and put a stock on back on.

 

In a word, yes.

It's a long argued issue. The thing everyone confuses is that the crank pulley does three things, a pulley for accesseries, (may be) statically balance for internal engine balance, and has an embedded rubber ring to filter out high frequency flexing of the crank, which rings like a bell everytime a cylinder fires. it's that third feature that causes the bearing problems. No rubber ring, no filtering, so the crank vibrates more a high rpm. Worst case the crank breaks, but usually the bearings go before that happens. I had one and never installed it, after doing my own research.

As far as what the pulley vendors say about the pullies being harmless, keep in mind they want your money, so they're not a good source of "facts."