Engine Block Oil Gallery (Galley)

Oil Gallery DiagramThe oil gallery, or as is often called galley, is the primary passageway cast or machined into engine blocks to distribute oil to critical internal engine components. Oil is feed into the oil gallery by the oil pump and is filtered by the oil filter to protect internal engine components from small debris such as chips, flakes and particles. In the picture to the left, you can view the pan rail side of a bare 302 Ford block that highlights where the oil pump mounts, its proximity to the oil filter and the primary passageway.

As noted previously, the primary purpose of the oil gallery is to supply oil to critical engine components that require lubrication. Oil galleries are typically routed to supply oil to the crankshaft main housing bore and to the lifter bores. From these areas, oil is transferred to the connecting rods and up the pushrods to supply oil to the rocker arms. It is important that the oil galleries are clean and free from obstructions so that the proper flow of oil can be maintained.

Removing Oil Gallery Plugs for Cleaning

All vehicle manufacturers, including Ford, General Motors and Chrysler, have engineered provisions to clean the oil galleries in the engine blocks that they produce. In the picture to the right, you may view a diagram of a 302 Ford where the three front oil gallery plugs have been removed for cleaning. Plugs are also used on the rear side of the engine block to allow cleaning.

When an engine block is degreased, hot tanked in acid or shot blasted, the oil gallery plugs must be removed. In most cases the rear oil gallery plugs (bell housing side of block) are threaded and use NPT pipe plugs. These plugs can be removed using a properly matched four point (square) socket. Other manufacturers, or engine builders for that matter, may have installed rear pipe plugs that require an allen or torx bit socket for removal. Once these plugs are removed, a long drift may be used to knock out the front press fit oil gallery plugs. Once again, a previous engine builder may have used a tap to thread the front oil gallery plugs that need a socket for removal.

When an engine block is cleaned, it is wise to use a long specialized brush and solvent to clean out the primary oil galleries. Smaller stiff bristle brushes may also be purchased from an auto parts store to clean out the main housing bore oil holes. Though it may be difficult to clean out each lifter housing bore gallery orifice, angled brushes may be used with compressed air to achieve a suitable level of cleanliness.

Installing New Oil Gallery Plugs

Location of Oil Gallery PlugsAfter an engine block has been finish cleaned for assembly, one of the first things an engine builder will do are install the cam bearings, freeze plugs and oil gallery plugs. Since the front oil gallery plugs on most engines require a press fit, it is best to install them first in case there is an alignment problem that requires the plug be knocked out and replaced. Often press fit front oil gallery plugs are peened in their fixed position with a chisel that collapses the plug’s housing bore slightly. The rear oil gallery plugs are installed with the appropriate socket and high temperature silicone is used around the threads to prevent leaks. Should a press fit front oil gallery plug not seal entirely, any leak would be contained in the timing cover.

Now that you have learned more about the importance of an engine block’s oil galleries, please visit our engine block information page to learn more about other critical areas including the cylinder bores, the deck and much more.


Engine Block Tips

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Oil Galleries Information