How to Reduce Oil Accumulation in the RB Cylinder Head – The RB series engines are notorious for oil accumulation in the cylinder head. This causes many issues such as oil passing through the valve guides, lack of oil at the crank journal, and the oil pump sucking up too much air instead of oil during excessive force. Using the Tomei oil gallery orifice, we're going to go ahead and take the new restrictors and pound them on top of the old stock ones. As you can see here, that's our stock, and we're going to replace it with the new one, and it's going to take us from 2mm to 1.5mm.