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

Four-cylinder engine mounts fit further back on the frame rails. Unlike AMC-era CJ models, these mounts are factory welded to the frame. On CJs, the four-, six-, and eight-cylinder frame brackets bolt to holes in the frame. One CJ frame accommodated all engine types. This is not so with the YJ or TJ Wrangler!

Careful removal of frame mounts requires scarf cutting with an acetylene torch. Slight portions of the original bracket material are intentionally left in place to avoid cutting near factory welds. Surface grinding is cosmetic. A horizontal weld bead reinforces the area where the factory engine bracket attached to the lower edge of the frame.

Universal engine swap brackets from Advance Adapters form the base for new front motor mounts. Two thick additional plates are the platform for factory motor mounts. The goal is to mimic the factory brackets and place the 4.0L inline six in its proper position.

Additional side support adds strength to the top plate. Increase in metal gauge over factory mount brackets assures stamina. Wire is ER-70S 0.035-inch MIG type. Cushions are stock six-cylinder YJ parts. New brackets are substantially stronger than factory.

The front of the 2.5L four is nearly identical to 4.2L and 4.0L sixes. If on a budget, you can keep the brackets, alternator, and power steering pump from the four. If using the Mopar Performance crankshaft pulley and sensor pickup from the EFI conversion kit, you must specify either a V-belt or serpentine belt crankshaft pulley.

Measurements for these brackets were made with the engine in the chassis. After fore-aft positioning and final squaring up of the engine-to-frame, the holes for the cushion support bolts are drilled. Brackets on the engine block serve as a template for properly locating the frame brackets and mount cushions. Mounts must be precisely in position before welding brackets to the frame. If in doubt, don't weld the brackets yet.

This bell housing is 4.0L era for the AX-15 transmission. Note the provision for an external hydraulic slave cylinder, a great improvement over the earlier YJ-style hydraulic throw-out bearing. This housing requires a cross release arm (shown). There is provision for the factory crankshaft sensor's pickup at the top of the bell housing (must be used with a '91-up 4.0L flywheel). A Mopar Performance EFI conversion kit eliminates the need for this sensor.

This rebuilt Mopar starter motor is the later reduction type design. The original four-cylinder starter motor is not suited for this bellhousing. Subtle differences between fours and sixes, early engines and later engines, must be considered. Ultimately, the swap is no less complicated than a V-8 or V-6 hybrid swap.

The engine is aligned carefully--side-to-side, height and angle--to assure proper location of weld-in mounts. The engine must fit as stock. '87-up inline sixes use similar engine block brackets and motor mounts. Here, the fabricated bracket has been welded into place at the frame. Hardware is temporary, to be replaced with high-grade type.