I just finished assembling a rebuilt Gen. IV 5.3L LS engine. I’ve deleted the AFM on this engine and I’ve tapped and plugged the stands inside the engine lifter valley. I checked the bearing clearances on both the rods and mains at around 0.0027 inch. I was surprised when trying to pressure lube the engine that I could not generate any oil pressure. My buddy has a pressure luber he made from an old Chevy oil pump in a plastic bucket and we pumped plenty of oil into the engine but we couldn’t generate any pressure. So that means it can’t be a problem with the oil pump since we were not using the oil pump to generate pressure. Any ideas?

J.K.

We’ve actually experienced this same issue when we first started building LS engines. There is a small, roughly 0.625 inch steel plug that is located in the front of the block just underneath the front timing chain cover. If you had your block cleaned by a machine shop, likely they removed this plug to ensure proper cleaning of that main oil gallery.

If that plug is omitted, this will merely dump oil right back into the oil pan from inside the front cover and there is zero chance that oil will reach the location where you are reading oil pressure.

close up of plug in an engine block
The arrow points to the plug that should be located in this hole in the main oil gallery. If this plug is not in place, then engine will never make oil pressure even when lubed from the outside as this will be a massive internal leak. (Image/Jeff Smith)

The good news is that the repair is easy. We will assume that the harmonic balancer is in place. You will need to remove the harmonic balancer and also the water pump if it is installed. Then remove the front cover bolts along with the two bolts that come in from the bottom through the oil pan. Remove the front timing chain cover and you will find the oil galley on the lower left (driver) side of the block

We will assume that once you remove the cover, there will not be a plug in that oil galley hole. This will require a press-in steel plug. The easiest way to find this plug is a simple freeze plug kit from Summit Racing that includes all new screw-in plugs along with this small steel press-in plug. All you have to do is hammer the plug into the galley flush with the face of the block and then replace the timing cover, balancer, and water pump and you should then have oil pressure. Iron and aluminum blocks use the same plug size.

While we’re on the subject of plugs, there’s a small oil pan cover plate that bolts on the oil pan just above the oil filter that is often missing from a used oil pan. Junkyard raiders often poach these plates because the GM replacement part with a threaded oil tap hole is a pricey item. We’ve listed the part number just for reference along with a standard non-threaded unit that is less expensive. 

Going one step further, Summit Racing offer several versions of this block-off plate in billet aluminum. The variations include a solid plate as well as one with one or more fitting holes drilled and tapped and ready for an oil pressure gauge or perhaps an oil feed line for a centrifugal supercharger or turbocharger.

The other plug that we often find ourselves searching for is the coolant plug located on one end of each LS cylinder head. This is where the coolant sensor is located on LS engine with the other hole plugged. This plug is often missing. If you need one, it takes a 12mm x 1.5 thread pitch application that is smaller than the coolant plugs located in the block. Trick Flow offers an inexpensive plug for this application and we’ve listed it in the Parts List below.

LS Oil Pressure Fix Parts List

  • Summit Racing LS Engine Freeze Plug Kit – SUM-G1584
  • Chevy Performance Oil Cooler Delete Plate (w/Tapped Hole) – NAL-12551587
  • Chevy Performance Oil Cooler Delete Plate (No Hole) – NAL-12577903
  • Summit Racing Oil Cooler Delete Plate (No Hole) – SUM-121025
  • Summit Racing Oil Cooler Delete Plate (Dual 1/8” 90° Ports) – SUM-121027
  • Summit Racing Oil Cooler Delete Plate (Dual 1/8” Ports) – SUM-121029
  • Summit Racing Oil Cooler Delete Plate (Dual 16mm Ports) – SUM-121030
  • Trick Flow Cylinder Head Coolant Plug for GM LS, 12mm x 1.5 – TFS-30600615
engine plugs & LS oil galley barbell
The Summit plug kit for LS engines includes the large, brass coolant plug along with the three oil and coolant screw-in plugs and the famous barbell that locates in the rear of the engine oil galley. Summit Racing also offers a more robust aluminum barbell kit for improved reliability, if you plan to replace your barbell as well. (Image/Summit Racing)
Keywords
Ask Away!, LS engines, oil pressure
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Author: Jeff Smith

Jeff Smith has had a passion for cars since he began working at his grandfather's gas station at the age 10. After graduating from Iowa State University with a journalism degree in 1978, he combined his two passions: cars and writing. Smith began writing for Car Craft magazine in 1979 and became editor in 1984. In 1987, he assumed the role of editor for Hot Rod magazine before returning to his first love of writing technical stories. Since 2003, Jeff has held various positions at Car Craft (including editor), has written books on small block Chevy performance, and even cultivated an impressive collection of 1965 and 1966 Chevelles. Now he serves as a regular contributor to OnAllCylinders.