Lycoming Narrow Deck Cylinder Base Wrench Set – 3/8" & 1/2" | Spline-Type

Make cylinder removal and installation easier with this professional-grade Lycoming Narrow Deck Cylinder Base Wrench Set. Specifically designed for the internal spline-style cylinder base nuts found on Lycoming Narrow Deck engines, this two-piece set includes the two sizes needed for servicing compatible cylinder installations.

The set includes both 3/8" and 1/2" spline-type wrenches, each with a 1/2" square drive for use with compatible ratchets, breaker bars, and torque wrenches.

Drop-forged from 4130 steel and hardened to approximately 48 Rockwell, these specialty wrenches are built to withstand the demanding torque requirements of engine maintenance and overhaul work.

Product Features

• 2-Piece Cylinder Base Wrench Set
• Includes 3/8" and 1/2" sizes
• Internal spline-type wrench design
• 1/2" square drive
• Designed for Lycoming Narrow Deck cylinder base nuts
• Fits compatible IO-390 and IO-580 applications
• Drop-forged from high-strength 4130 steel
• Hardened to approximately 48 Rockwell
• Designed to resist wear and deformation
• Suitable for cylinder removal and installation
• Professional engine maintenance and overhaul tool

Engine Compatibility

Designed for:

Lycoming Narrow Deck Engines

• All applicable Narrow Deck engine models
• IO-390 Series
• IO-580 Series

Narrow Deck or Wide Deck?

An easy way to determine which cylinder base wrench you need is to inspect the nuts securing the cylinder to the crankcase.

NARROW DECK:
Round cylinder base nuts with an internal spline → Use this wrench set

WIDE DECK:
Cylinder base nuts resembling conventional external hex nuts → Requires a Wide Deck-style cylinder base wrench

TIP: Many Lycoming engines manufactured before approximately 1960 are Narrow Deck configurations. However, engine components may have been changed during previous repairs or overhauls, so the cylinder base nut style should always be visually verified before ordering.

Ideal for Engine Maintenance

This wrench set is designed for:

• Cylinder removal
• Cylinder installation
• Cylinder replacement
• Top overhauls
• Complete engine overhauls
• Cylinder base nut removal
• Cylinder base nut installation and torquing

What's Included

(1) 3/8" Narrow Deck Cylinder Base Wrench
(1) 1/2" Narrow Deck Cylinder Base Wrench

Airboat Solutions

A must-have specialty tool when servicing Lycoming Narrow Deck engines. The spline-type design properly engages the unique internal cylinder base nuts, while the drop-forged 4130 steel construction provides the strength required for repeated engine maintenance and overhaul work.

Set: 2 Pieces
Sizes: 3/8" & 1/2"
Drive: 1/2" Square
Style: Internal Spline
Material: Drop-Forged 4130 Steel
Hardness: Approximately 48 Rockwell