1987 Jeep Wrangler YJ - Wrangler Four-Banger To 4.0L Six Engine Swap

This is the passenger (right side) frame bracket. Pedestal mount fits atop the frame bracket. The factory block bracket (black and visible below the oil pan ledge) bolts to the side of the engine block. Note heft and strength of the fabricated bracket. Advance Adapters' bracket served as a valuable starting point for this conversion bracket.

In place with plug, stitch and lengthy, full-strength welds, the fabricated frame brackets accept six-cylinder Wrangler mount cushions. For this YJ application, the engine block requires left and right cast brackets. The pedestal mount cushions attach to the cast engine brackets with a through bolt and nut.

An added, thick brace ties the upper frame bracket to the top frame rail. With the bracket rising above the frame, this measure helps reduce torque twist and stress to the frame section. These brackets have been torture-tested in this YJ since 2005. Design features and safeguards have paid off.

From the topside, the 4.0L motor mount cushion looks stock, supporting the engine in its proper position. Factory appearance makes a difference. Common Wrangler mounts are readily available, and the engine fits as intended.

The AX-5 and AX-15 use different transmission mounts. This stock skid shield fit an AX-5 and NP207 transfer case. A six-cylinder skidpan would work here. The option is to use the four-cylinder AX-5 pan and fabricate a mount location for the AX-15 transmission support. Plasma cutter makes neat work of the cuts.

Mounts in place, through bolts and fresh hardware secured, the engine is well supported at the front. Note the "factory" appearance of this conversion. All parts other than the welded frame brackets are stock Jeep. These are the basic requirements for making the inline six fit a four-cylinder frame.

A box section made with rugged steel plate and ER70S MIG wire creates a strong mounting point. On YJs and TJs, this skid plate supports the transmission and transfer case. Once aligned carefully, with the engine/transmission centered, you can drill holes in the plate to match the mount cushion studs.

Boxed section is on rails of thick plate. This support platform is far stronger than the original. Using the factory skidpan permits easier side-to-side alignment plus reasonable transmission/transfer case protection. Goal when finished is to make this conversion appear "factory" and neat.

Rear mount fits at tail housing of AX-15 transmission. AX-15's 23-spline output will mate with a 23-spline NP/NV231 or Atlas transfer case. Mopar 4.0L remanufactured long block, a freshly built AX-15 transmission, Mopar Performance MPI conversion pieces (with the crankshaft sensor/trigger at the front pulley damper), and a factory header pipe create a new, six-cylinder powertrain.