I recently built a Gen VI 454 big block Chevy street engine that came out of a late model Chevy truck. I had the local machine shop do all the block work and I checked all the clearances to make sure the bearings would be okay. I installed a flat tappet camshaft in the engine rather than a hydraulic roller because I wasn’t interested in making big power with a hydraulic roller setup, so we saved some money on the cam and lifters.

With the engine in car, we pre-lubed the engine and here’s where the problem came up. We could only get about 10 to 12 psi out of spinning the oil pump. We figured the drill motor just wasn’t spinning the oil pump fast enough. So we finished the pre-lube and installed the distributor but again, all we had at idle was about 10 to 15 psi of oil pressure at idle. We revved the engine and the pressure really did not come up much. We have plenty of oil and no leaks so we’re not sure what we did wrong. Can you suggest what to check? We’re hoping we don’t have to pull the engine but we will if you can think of where we screwed up.


There are a couple of places where you might look for the possible loss of oil pressure. Of course, first we have to mention that we will assume you checked all the bearing clearances including rods and mains before assembling the engine. We’ve seen instances where the crank was machined 0.010-under on the rods and mains and then the engine assembler used standard bearings only to discover low oil pressure in the engine. So if your clearance check was to spin the crank over then you need to start with always checking clearances.

Assuming the bearing clearances are correct, we’ve actually made the mistake of leaving the oil galley plugs out from behind the cam timing set. You’d think that leaving these plugs out would result in no oil pressure at all, but even a standard output pump can produce sufficient volume to still make perhaps 10 psi with cold oil. Of course, the only way to know this is to remove the front accessory drive and timing cover in order to check.

But before you remove the entire front accessory drive on the engine and the timing chain cover and loosen the pan, try this first:

Start by removing the intake manifold, which is much easier than the front timing chain cover. You mentioned that the engine in question is a Gen VI 454. When GM redesigned the big block Chevy with the Gen V/VI configuration, along with the one-piece rear main seal they also placed the main oil galley down the center of the lifter valley. This galley has three small pipe plugs installed down the middle of the casting. Most machine shops remove these plugs to allow proper cleaning of the galley. If one (or all three) of these plugs were left open, this would create an internal oil leak that would create the situation that you now face.

If you happen to have access to a plumber buddy who has a borescope, it might be possible to remove the distributor and peer down inside the lifter valley before removing the intake manifold to see if one or more of the plugs are missing. You will need to confirm that all three plugs are in place using this method but it does save removing the intake manifold and destroying the intake gasket.

Summit Racing actually sells a bunch of different borescopes—including an interesting unit from Klein Tools that is affordable because, instead of a video screen, it transmits the video to an Android smartphone. So if you have access to an Android device, this might be a quick and affordable way to use a borescope.

Another point we’d like to make based on what you mentioned, is that you did pre-lube the engine but the pressure did not come up as expected. Our experience is that a half-inch drill motor is more than capable of creating sufficient speed—around 800 rpm or so to create sufficient oil pressure. Our half-inch DeWalt drill motor consistently creates 60 psi of oil pressure. Remember that an 800 rpm drill speed is equal 1,000 to 1,600 rpm engine speed, since the cam spins at half crankshaft rpm. The point here is that only having 10 to 12 psi while pre-lubing was a major clue that something was not right with the engine, and the issue should have been addressed at that point, before the engine was installed in the car.

This would have saved you some work if the engine needs to be removed for repair.

This photo shows the location of the missing pipe plugs in the center oil galley. With the engine running, these three unplugged holes would be spouting oil in a massive internal oil leak. (Image/Jeff Smith)
Though this example is a small block Chevy, it illustrates the location of the three main oil galley plugs that must be installed to prevent a similar internal oil leak. (Image/Jeff Smith)
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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.