COMETIC

Cometic Gaskets Cylinder Head Gasket Bore 0.040 (C5691-040) GM Buick V6

 COMETIC  
 Cometic Gaskets Cylinder Head Gasket 3.860 in Bore 0.040 in Compres (C5691-040)

The Cometic C5691‑040 is a .040-inch thick MLS head gasket with a 3.860″ (~98 mm) bore, and it’s designed for GM Buick “Stage I/II” V6 engines—specifically the 3.8 L 3800-series Buick V6 found in a wide range of Buick and Pontiac vehicles 

🚗 Vehicle Fitment
The C5691‑040 gasket fits:
Buick 3.8 L (3800) V6 “Stage I/II” engines with a 3.860″ bore

Found in late‑’90s to 2000s GM front-wheel-drive cars & A‑body/co‑body cars like:

Buick Regal, LaCrosse, Allure

Pontiac Grand Prix, Bonneville

Buick Century, Century Custom, etc.

Also used in some GM minivans and light trucks with the 3800 V6 

⚙️ Gasket Specs
Feature    Specification
Part Number    C5691‑040
Gasket Type    MLS (Multi‑Layer Steel), 3 layers
Thickness    .040″ (~1 mm)
Bore Size    3.860″ (~98 mm)
Engine Application    Buick 3800 Series II/III (Stage I/II) V6
OEM Diesels    Not applicable

Designed for high clamp loads with minimal distortion and Viton surface for reliable sealing 

✅ Summary
The Cometic C5691‑040 MLS head gasket is perfectly suited to Buick 3.8 L V6 "Stage I/II" engines (commonly called the 3800 V6). You’ll find it in:

Buick Regal, LaCrosse, Allure (calendar: late 1990s–2000s)

Pontiac Grand Prix, Bonneville

Other GM FWD platforms using the 3800 V6