GM GENUINE PARTS LS Rear Block Cover 12639250 — OEM rear main seal housing, factory fit

GM Genuine Parts 12639250 LS rear block cover is a factory-engineered replacement that restores original fit, sealing and alignment for GM LS-series engines.

This rear block cover (also known as the rear main seal housing cover) is produced and validated by GM engineers to meet the specifications used during original vehicle assembly. It’s intended for owners, technicians and engine rebuilders who need an authentic GM part that matches factory geometry, material choices and mounting locations. The part helps maintain proper crankshaft sealing and accessory alignment when replacing the rear main seal or servicing the back of the engine block.

What does this rear block cover replace and why choose the GM part?

The 12639250 replaces the original rear main housing cover on compatible GM LS-family engines, ensuring the same bolt pattern, bore sizes and sealing surfaces as the vehicle’s factory component. Choosing GM Genuine Parts reduces fitment guesswork during installation and avoids modification that can cause leaks or misalignment.

• OEM dimensions and mounting points for direct replacement
• Manufactured and tested to GM engineering standards
• Backed by General Motors for compatibility with Chevrolet, Buick, GMC or Cadillac vehicles

How does this part help during an engine service or rebuild?

When you service the rear main seal or remove the crankshaft, replacing the rear block cover with an OE-equivalent housing ensures sealing surfaces are correct and any locating features match the block and seal. That reduces rework and helps achieve a reliable sealing surface for the new rear main seal.

• Provides proper seating for rear main seal installation
• Maintains crankshaft alignment and torque specifications
• Minimizes risk of oil leaks from mismatched or worn housings

Will this cover fit my engine and what should I check before ordering?

Compatibility depends on the specific LS-series engine variant and vehicle application. Confirm part number 12639250 against your vehicle’s VIN, parts catalog, or a trusted dealer fitment search before purchase to ensure correct match.

• Verify using the vehicle VIN or year/make/model with a GM parts database
• Compare bolt pattern and mating face to the removed cover if possible
• Check for any updated superseding part numbers from GM before installation

What materials and quality checks make this an OE-quality choice?

GM Genuine Parts are engineered and validated by GM to meet design tolerances of the original assemblies. Materials and machining are selected to withstand engine operating conditions and to interface correctly with seals and fasteners used by GM during production.

• Designed and validated by GM engineers for OE fit and function
• Manufactured to rigorous GM testing and production standards
• Part of GM’s continual updates to integrate improved materials and techniques

Who is this for: This part is aimed at professional technicians, independent shops, and vehicle owners performing maintenance or full engine rebuilds on GM LS-series engines who want an exact-fit, factory-backed rear block cover. It’s especially useful when replacing the rear main seal, correcting leaks, or ensuring correct alignment during crankshaft or transmission service. If you need guaranteed compatibility with GM assembly geometry and prefer parts engineered by the vehicle manufacturer, the GM Genuine Parts 12639250 is designed for that purpose.

Note: Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE). Always verify fitment prior to installation.

• Some GM Genuine Parts may have formerly appeared as ACDelco GM Original Equipment (OE)
• GM Genuine Parts are designed, engineered and tested to rigorous standards, and are backed by General Motors
• GM Engineers design and validate OE parts specifically for your Chevrolet, Buick, GMC, or Cadillac vehicle
• GM regularly updates production and service part designs to integrate new materials and technologies