How to Build a Cummins Engine the Right Way (Part 1)

Ring gap is the small clearance between the ends of a piston’s compression rings when installed in the cylinder. Getting the correct ring gap helps prevent the rings from butting under heat (which can cause damage) and ensures proper sealing for compression and oil control.

Bearing clearance is the designed gap between engine bearings and the crankshaft/journals. Correct clearance is critical for oil pressure and lubrication; too tight can overheat and seize, while too loose can reduce oil pressure and accelerate wear.

Loctite is a brand of thread-locking compounds used to help prevent fasteners from loosening due to vibration. In engine builds, it’s often applied to specific fasteners where the manufacturer or builder calls for it, improving reliability of the assembly.

Head studs are threaded fasteners used to clamp the cylinder head to the engine block, often replacing or supplementing head bolts on performance or high-stress builds. Proper lubrication and torque procedure on studs helps achieve correct clamping force and reduces the risk of gasket failure or warping.

A machine shop performs precision work on engine components—like boring/honing cylinders and machining the block—to restore correct dimensions and surface finish. The builder’s job is to verify the work was done correctly before assembly, because small errors can ruin clearances and reliability.

A cleaning fee typically covers removing machining debris and ensuring oil passages are clear before assembly. Even with a cleaning service, builders should still verify critical items like oil galleries are properly plugged and free of debris.

Oil galley plugs seal the ends of the oil passages (“galleys”) so pressurized oil can flow where it’s supposed to. If they’re omitted or not installed correctly, oil can leak and the engine may not get proper lubrication to critical components.

“Oil rail” is a common builder term for the oil distribution passage/line that feeds oil to the engine’s internal components. In this discussion, it’s used interchangeably with “oil galley,” emphasizing that the same oil-carrying system must be properly sealed and cleaned.

The segment emphasizes that proper engine assembly requires more than just “spraying something in.” Oil passages must be sealed correctly (oil galley plugs) and thoroughly cleaned so debris doesn’t block lubrication paths or contaminate bearings and other wear surfaces.

Brake cleaner is a fast-evaporating solvent often used to remove oil and residue during engine assembly. While it can help, the key point here is that proper cleaning and verification of oil passages is still required—especially in oil galleys where debris can cause lubrication problems.

Bore brushes are used to scrub inside cylinder bores to remove leftover debris, machining residue, and contaminants. In an engine build, cleaning the bores helps ensure proper ring seating and reduces the chance of abrasive particles circulating.

Moroso is an aftermarket performance parts company known for engine-building tools and kits. Here, they’re referenced for an engine brush kit intended to clean cylinder bores and related surfaces during assembly.

A main oil galley (oil passage) is a primary internal channel in the engine block that distributes pressurized oil. From this main route, oil is routed through smaller passages to reach bearings and other lubricated surfaces.

An oil cooler is a heat-exchanger that helps control engine oil temperature. In this context, the host is describing how an oil cooler feed intersects with the block’s oil passages, so proper routing and cleanliness matter during assembly.

The “30 inch brush” refers to using a long cleaning brush to scrub internal oil passages through the engine block. The goal is to remove machining debris so oil can flow freely to bearings and the camshaft bearings after assembly.

This segment emphasizes thorough cleaning of internal oil passages during an engine build. Even small leftover machining particles can circulate once the engine starts, potentially accelerating wear or clogging small oil feed routes.

Main bearings support the crankshaft inside the engine block and rely on a steady supply of pressurized oil. The host is describing how oil passages feed the main bearings, making proper oil routing and cleanliness critical during assembly.

Cam bearings are the bearing surfaces that support the camshaft and control its alignment and lubrication. The host notes that oil is routed from the main bearing area into passages that feed the cam bearings, so incorrect installation can starve the cam of oil.

Oil bearings rely on a thin film of pressurized oil between the bearing surface and the rotating shaft. During a build, people check oil-hole alignment and passage size because the oil film and flow depend on those channels feeding the bearings.

The main cap is the structural piece that holds the crankshaft bearings in place. In an engine build, its alignment and bearing fit matter because they control crankshaft support and oiling to the bearings.

A cam journal bearing supports the camshaft where it rides in the engine. If the oiling passages and bearing clearances are off, the cam can run too tight or not get enough oil, leading to accelerated wear.

A hex driver is being used as a quick go/no-go gauge to verify oil passage clearance through the bearing/oil hole area. The idea is that if the specified driver size fits, the oiling passage is likely within the intended tolerances for that build.

This segment explains a common misconception: bearing oil holes and block oil holes may not visually line up perfectly, yet still be correct due to designed offsets and different hole sizes. Pro builders rely on specs and clearance checks rather than assuming “perfect alignment” is required.

Oil holes are the passages that route oil from the block to components like main and cam bearings. The key point here is that the hole size in the block doesn’t necessarily match the hole size through the bearing shell—design tolerances and oiling strategy can differ.

Aftermarket bearing makers often copy the “common specs” used by experienced builders and OEM-like designs. Over time, pro builder feedback can lead to small changes, but the core oiling geometry is typically consistent if you buy the right parts.

Deburring means removing sharp edges and raised material left behind after cutting, grinding, or staking. In this context, deburring the stake marks helps prevent damage to the plug and improves sealing. It also reduces the chance of creating a leak path in the oil passage.

A thread chaser kit is used to clean and restore damaged threads without removing extra material like a tap would. Chasing the holes in the block helps ensure the new plugs thread in correctly and seal. It’s especially useful before final cleaning so you can address stripped threads or debris in the passages.

Filing piston rings refers to carefully trimming or end-gapping rings to achieve the correct clearance in the cylinder. This is done before final cleaning so the rings and cylinder surfaces are ready for proper fit and sealing.

Thread chasing is the process of running a correct tap or thread tool through fastener threads to remove burrs, old thread sealant, or damage. It helps ensure bolts and studs seat correctly and that torque readings are consistent when you reassemble an engine.

The cylinder wall is the machined surface the piston and rings run against. Proper cleaning and inspection of the cylinder wall are critical because debris or poor surface condition can prevent rings from sealing and can accelerate wear.

An oil pump passage is the internal channel that routes oil from the pump to the rest of the lubrication system. Porting or modifying it is a common performance/reliability step aimed at improving oil flow and reducing restrictions.

Porting cylinder heads means reshaping the intake and exhaust passages to improve airflow. The goal is to reduce restrictions so the engine can move more air/fuel mixture (or exhaust) efficiently, which can support higher power and better throttle response.

The oil system is the network of passages, pump, pickup, and components that deliver lubrication and manage oil pressure/flow. In performance builds, oil system design is critical because it affects both lubrication reliability and how well the engine can sustain power under load.

The suction side is the portion of the oil pickup/pump inlet where the pump draws oil in. If oil flow is restricted there, the pump can pull in vapor bubbles (cavitation) or allow oil to separate, which reduces effective lubrication and can cause pressure/flow problems.

Cavitation is when vapor bubbles form in a liquid due to local low pressure, then collapse as pressure rises. In an oil system, cavitation can aerate the oil and reduce lubrication effectiveness, potentially leading to accelerated wear or oil pressure instability.

Here, “port that” refers to modifying passages (likely oil passages/pickup-related flow paths) to improve oil movement. The emphasis is on doing the flow-path work early so the rest of the build benefits from better oil delivery.

An oil accumulator is a reservoir that helps maintain oil supply during extreme conditions like hard braking or rapid deceleration. Race applications use them to reduce the chance of oil starvation when oil shifts away from the pickup.

MPT typically means a tapered pipe thread size (often used for fittings and plugs). Specifying MPT sizes helps ensure the correct hardware is used so the fitting seals properly and doesn’t leak under oil pressure.

“Pre modifications” refers to the work you do to an engine block before the actual build steps begin. In practice, it often means cleaning, inspecting, and preparing surfaces so later machining and assembly go smoothly.

Cleaning and brushing are early block-prep steps used to remove machining debris, oil, and contaminants from critical surfaces. Doing this thoroughly helps prevent grit from getting into bearings, rings, and oil passages during assembly.

Total Seal is a brand of piston rings, commonly used in performance and rebuild builds. The “ring” refers to the sealing rings that control compression and oil control between the piston and cylinder wall. In a build, ring choice and installation details can affect sealing and wear.

The speaker describes a green, graphite-like product used during assembly. This sounds like a coating/lube applied to cylinder walls or related surfaces to manage friction and protect surfaces during initial assembly. The “dry product” comment suggests it’s not a traditional wet oil-based lubricant.

WD-40 is a widely known aerosol product often used as a light lubricant or penetrant. In engine assembly contexts, it may be used temporarily to help with cleaning or initial lubrication, but it’s not a substitute for proper assembly lube where required. The speaker implies it’s used sparingly alongside the graphite-type product.

Rod journals are the crankshaft bearing surfaces for the connecting rods. Like main journals, their dimensions and surface finish affect bearing clearance and lubrication. Measuring rod journals is part of setting up the bottom end so the engine has correct oiling and durability.

“Clearances” refers to the engineered gaps between moving engine parts, such as bearing clearances. These gaps control how the oil film behaves and whether parts will run smoothly without overheating or scuffing. The speaker is setting up a bottom-end discussion focused on measuring and achieving correct clearances.

Vertical oil clearance is the measured gap between a bearing and the corresponding journal surface in the vertical direction. In a performance rebuild, getting this clearance within spec helps ensure the bearing gets a stable oil film for lubrication and heat control.

“Mains” refers to the main bearings and the main bearing journals that support the crankshaft in the engine block. Oil clearance at the mains is a key dimension for preventing metal-to-metal contact and ensuring consistent lubrication under load.

Crank journals are the machined bearing surfaces on the crankshaft where the engine’s main and rod bearings ride. Measuring them is critical because journal size and roundness directly affect oil clearance, which influences lubrication and bearing life.

Using a spreadsheet to record measured crank journal dimensions and resulting clearances helps reduce math errors and makes it easier to compare journals consistently. It also creates a clear build record for troubleshooting later if something doesn’t behave as expected.

A diagonal check is a verification step to catch misalignment or mixed-up bearing caps. Even if the vertical clearance looks correct, an offset cap can create different clearance at other points, which can lead to uneven bearing loading.

RPM (revolutions per minute) is how fast the engine is spinning. Higher RPM increases heat and load on bearings and can reduce the stability of the oil film. That’s why performance engines often adjust clearances and oil choice for high-RPM operation.

Idle oil pressure is the oil pressure the engine maintains when it’s running at idle speed. With larger bearing clearance, oil can leak past the bearings more easily, so pressure can drop—especially when the oil pump is turning slowly at idle. That’s a key downside for street or tow-truck use compared with race-only setups.

20W-50 is a common heavy-duty engine oil grade (a thicker oil) often used in high-load or race applications. In the context of this discussion, it’s mentioned as a thicker viscosity choice to compensate for reduced idle oil pressure caused by larger bearing clearance. The downside is typically worse cold flow and less ideal behavior for daily driving.

Straight 50 refers to a single-grade oil that stays at a relatively thick viscosity across operating temperatures. The speaker contrasts it with multi-grade oils and notes racers may use it to maintain oil film strength when clearances are larger. The implication is reduced cold flow, making it less suitable for daily driving.

This is a reminder that a “race engine” is typically built with different clearances, materials, and operating assumptions than an engine intended for street use. Race parts can be less tolerant of heat cycles, low-load driving, and long-duration towing.

The hosts are emphasizing that engine and drivetrain parts should be selected based on the vehicle’s actual job—street use, towing, or racing. A race-focused setup often has different durability and operating requirements than a street/tow setup, so matching the build to the duty cycle is key.

Main clearance is the gap between the crankshaft’s main journals and the engine’s main bearings. It affects oil pressure, lubrication stability, and how safely the engine tolerates heat and load.

The hosts reference “mega power builds” from builders who loosen clearances more aggressively. This highlights a common tradeoff in high-output builds: pushing clearances to manage oiling and thermal behavior under extreme conditions, but potentially increasing risk if the engine isn’t built and tuned for it.

Rod bearings sit between the connecting rods and the crankshaft, handling high loads as pistons move. Bearing clearances and bearing selection strongly influence oiling, wear rate, and how the engine survives high power or sustained stress.

“HX” is a bearing variant that provides extra clearance compared with the standard “H” bearing. The host describes it as having an additional thousandth of clearance, and using only part of an HX stack-up to fine-tune clearance in smaller increments.

“H bearings” refers to an upgraded performance bearing used in an engine build to control internal clearances. In practice, builders choose bearing thickness/clearance targets so the crankshaft and connecting components run smoothly without excessive play.

“Main galley” appears to refer to the main bearing journal area and/or the oiling passages associated with the main bearings. The host mentions measuring and recording main journal thicknesses so the builder can select bearing combinations to hit the desired clearances.

“Main journal thicknesses” are measurements of the crankshaft’s main bearing contact surfaces. Accurate journal measurements let the builder choose bearing thickness/clearance combinations (H/HX) so the final bearing clearance is correct and consistent across the engine.

The host uses an “800 horsepower build” as a reference point for how much bearing/clearance strategy they prefer at different power levels. The idea is that higher-output builds may need slightly different clearance targets to ensure there’s room for parts to move under load and heat.

A “non water cooled block” or “solid block” implies an engine block design without conventional liquid-cooling passages in the area being discussed. In extreme-duty builds, cooling strategy affects how the block and rotating assembly expand under heat, which in turn influences clearances like bearing gaps. The speaker suggests that more radical clearance changes may only be necessary when the cooling/heat behavior is significantly different from a typical water-cooled setup.

Sled pulling is a motorsport where a vehicle drags a heavy sled, demanding sustained high torque and traction. Engines built for sled pull typically see different stress patterns than a street truck, including long periods of high load at relatively low speeds. That’s why builders may talk about tighter clearances, stronger components, and more conservative limits depending on the class and cooling setup.

Cummins is a major manufacturer of diesel engines, widely used in trucks and performance builds. In the context of this episode, “Cummins range” refers to the variety of Cummins engine families and how builders tailor clearances and components based on the intended duty cycle (street, towing, or competition).

Rod bolts must be torqued to a specified value (and often in a specific sequence) because they control the clamping force that sets bearing alignment and oil clearance. Many builders also use new bolts and follow the manufacturer’s torque procedure to ensure consistent stretch and strength. Incorrect torque can lead to bearing failure, oil starvation, or crankshaft scoring.

A rod vice is a clamping tool used to hold a connecting rod securely during inspection or assembly. “Soft jaws” are replaceable, non-marring jaw inserts that grip the rod without damaging the bearing surfaces or deforming the rod. This matters because connecting rods are precision-machined parts, and even small damage can affect bearing alignment and clearance.

Connecting rods (often shortened to “rods”) transmit force from the pistons to the crankshaft. In this segment, the hosts discuss tightening rods to a target torque and the practical steps that affect bearing clearance and fitment.

A torque wrench is a tool that tightens fasteners to a specific torque value. In engine building, it helps ensure rod bolts and related hardware are clamped correctly to prevent failures and maintain proper bearing clearances.

Rod clearance is the small gap between the rod bearing and the crankshaft journal. Builders measure it to ensure the oil film is thick enough for lubrication while avoiding excessive clearance that can reduce oil pressure and increase wear.

A dimple die is a marking tool used to create small, repeatable indentations on parts. Here it’s used to mark rod caps/ends so they can be reassembled in the correct orientation, especially when caps can be swapped.

Carrillo (often misspelled as “Carillo” in transcripts) is a well-known aftermarket connecting-rod manufacturer. The mention here is about rod design features (like dowel/pin alignment) that affect how the rods can be assembled and oriented.

Numbering connecting rods (and matching caps) is an assembly practice that preserves the original fitment and orientation. Since each rod/cap pair can have slightly different machining and wear patterns, labeling helps maintain consistent clearances across cylinders.

Piston rods (connecting rods) are matched pairs that are machined and assembled to work together. During factory assembly, rods and caps are torqued and honed to a specific size, so swapping caps between rods can change bearing fit and roundness.

The segment emphasizes that connecting rod caps must stay with their original rods because the assembly process (torque and honing) creates a specific bearing fit. Even if parts “bolt together,” mismatching can lead to incorrect bearing geometry and reduced durability.

When connecting rods are assembled, the bolts are torqued to a precise specification and the bearing surfaces are honed to the final dimensions. This creates the correct clearance and roundness for the crankshaft journals, which is why mixing parts can cause problems.

Factory Cummins connecting rods may include serial numbers that indicate the rod and its matching cap. That matching is important because the cap and rod are treated as a matched set for the final machining and assembly.

Pin clearance is the small designed gap between a piston’s wrist (gudgeon) pin and its connecting-rod bushing/bore. Too little clearance can cause binding when parts expand with heat; too much clearance can increase noise and wear. Builders measure it with precision tools and compare it to the spec for the rod/pin combination.

Rod knock noise is an audible knocking/tapping sound that can occur when there’s excessive clearance or worn components in the connecting-rod/piston-pin area. In this segment, the host notes that too much clearance when cold can create slop that sounds like a knock. It’s a clue that the fitment/clearance may be out of spec.

Piston-to-wall clearance is the small gap between the piston skirt and the cylinder wall when the engine is assembled. It matters because pistons expand with heat, and the right clearance prevents scuffing while still controlling piston movement and wear. Builders measure it during machining to ensure the engine will run reliably under load.

“Trust, but verify” is the idea that you can rely on a machine shop’s work, but you should still confirm critical measurements yourself. In engine building, small dimensional errors can cause major problems, so independent checking reduces the risk of expensive mistakes. It’s especially relevant when clearances and tolerances are tight.

The piston skirt is the lower portion of the piston that guides it in the cylinder. Measuring the skirt is a common way to determine the clearance to the cylinder wall because that’s where the fit and wear behavior are most critical. Skirt shape and taper affect how clearance changes from top to bottom.

“Oblong” describes a piston shape that isn’t perfectly round—its diameter differs in two directions. This helps control how the piston behaves as it heats and expands, and it affects clearance at different points in the cylinder. Engine builders account for this by measuring in the correct orientation and locations.

Piston taper refers to the piston being wider at one end and narrower at the other (often wider near the skirt bottom and tighter toward the top). Because the piston is tapered and also shaped to be slightly oblong, the clearance is not uniform at all heights. That’s why builders measure at specific locations to calculate the real running clearance.

A “Molly piston” typically refers to a piston with a molybdenum-based coating on the skirt (often used to reduce friction and scuffing). Coated skirts can be sensitive to measurement technique because you don’t want to damage the coating. Some coated pistons include a specific “window” area so you can measure without scratching through the coating.