Balmar 48-YP-IDL Idler pulley for Yanmar JH engines

If your alternator belt is hitting against some engine accessory this can be used to deflect it.  This is typically used for Serpentine Kit installations with larger alternators.  What sometimes happens is that because the alternator is larger it has to be a bit further out from the engine and in that case the belt position moves on the engine.  If some non-standard piece of aftermarket equipment has been added to the engine and it gets in the way of the belt then the idler pulley can be used to deflect the belt away from the offending item.  This will invariably require a longer belt than the standard.