Distributor Hole Plug

What Is a Distributor Hole Plug?

When building or converting a performance engine to a crank trigger ignition system, one critical — and often overlooked — task is properly sealing the distributor bore in the engine block. Distributor hole plugs (also called distributor block-off plugs or oil plugs) fill and seal the opening left behind when a traditional distributor is removed, ensuring the engine's oiling system remains pressurized and free of contamination.

A distributor is an electric and mechanical device used in older spark-ignition engines whose main function is to route electricity from the ignition coil to each spark plug at the correct time. Almost every modern gasoline-powered vehicle has replaced the spinning ignition distributor with a distributorless system. As performance builders and racers make the switch from a traditional distributor to a crank trigger or other distributorless ignition setup, the vacated distributor bore must be addressed — and that's precisely where a distributor hole plug comes in.

Why Does the Distributor Bore Need to Be Plugged?

On many classic V8 engines, the distributor may also drive the oil pump in some engine designs, meaning the distributor shaft reaches deep into the block and interfaces directly with the oiling system. When the distributor is pulled out and replaced with a crank trigger setup, the open bore can cause significant oil pressure loss and allow dirt or debris into the engine. A proper distributor hole plug maintains oil pressure integrity while also continuing to drive the oil pump through its own internal shaft — keeping the lubrication system fully functional.

This makes the distributor hole plug an essential component for any engine conversion involving a front-drive distributor and a crank trigger ignition. Chevrolet front-drive distributors brought the specific need for a distributor plug, and quality units are made of billet aluminum and feature a slip collar to ensure correct installation depth, for use on engines with a wet sump oil system and a front-drive distributor.

What to Look for When Shopping Distributor Hole Plugs

• Material: Billet aluminum construction offers superior durability and corrosion resistance compared to cast or stamped alternatives.
• Slip Collar Design: An adjustable slip collar is critical for setting correct installation depth, especially on engines with modified deck heights.
• Oil System Compatibility: Look for plugs with a dedicated oil tract that maintains lubrication to the distributor/cam gear area, and O-ring seals for modified blocks that need additional oil pressure control.
• Bearing Quality: A shaft guided by a sealed ball bearing and an extra-long sintered bushing, combined with an oversized polished steel shaft with a QPQ coating and a CNC machined billet aluminum housing, are hallmarks of a premium plug built for high-RPM use.
• Crank Trigger Pairing: Most distributor hole plugs are designed to be used alongside a dedicated crank trigger system, so confirm compatibility before purchasing.

Top Brands for Distributor Hole Plugs

MSD was the first company to develop and offer the multiple sparking, capacitive discharge ignition for engines, and early on focused squarely on ignition systems with revolutionary products like the multiple sparking CD ignition, timing and rev controls, billet aluminum distributors, and the Pro-Mag. It's no surprise that MSD's front-drive distributor lineup created the very need for a dedicated distributor hole plug solution. Their MSD Distributor Hole Plugs are precision-engineered to pair directly with MSD crank trigger systems, featuring CNC-machined billet aluminum housings and a refined slip collar design for exacting installation on both stock and modified engine blocks.