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Q&A Vlog: Jeep 232/258 and 4.0L Inline Six-Cylinder Valve Adjustment 

Jeep CJ, Wrangler, J-Truck, Cherokee and Grand Cherokee owners find that the 232, 258 and 4.0L inline six-cylinder engines have no provision for valve adjustment. In this in-depth HD video vlog, Moses Ludel describes the procedure for adjusting the hydraulic lifters and valves on a Jeep inline six. The how-to describes troubleshooting, repairs, rebuilding and restoring the valvetrain of these popular Jeep engines.
     Note: For additional details, see the article below, including the Crane Cams information on shimming valve rocker arm bridges to correct lifter pre-load settings. This method eliminates the need for sizing pushrods!

Predecessor 196 cubic inch AMC inline six Earlier rocker shaft assembly on 232/258 inline six

  The AMC/Nash engines evolved from the 196 four-main bearing engine at left into the 232-258 cubic inch, seven-main bearing pushrod OHV engine at right. The 232, 258/4.2L and 4.0L era saw the seven-main bearing engine's success in popular Jeep 4WD utility vehicles and SUVs. Between 1971 and 1973, the AMC/Jeep six's valvetrain transitioned from a rocker shaft (shown at right) to stamped rocker arms with bridged pedestals (below left). Like many modern pushrod engines, these hydraulic lifter engines do not have a provision for rocker arm or valve lifter adjustment.

 4.2L and 4.0L valvetrain and non-adjustable rocker arms AMC 2.5L four uses same valvetrain design as 4.2L/4.0L inline six

 At left is a 4.0L inline six valvetrain on a 4.6L hybrid stroker. This is a typical OEM 232, 258/4.2L or 4.0L Jeep inline six-cylinder head layout. This familiar setup persists from the early 1970s through the final 2006 Jeep TJ Wrangler 4.0L inline six-cylinder engine. At right is an AMC 2.5L four from a 1987 Jeep YJ Wrangler. The 2.5L fours use the same rocker arm design as the inline sixes. These rocker arms are also non-adjustable. Adjustment of lifter pre-load on any of these engines is accomplished with correct length pushrods or repositioning the rocker arm heights*.

     *Note: Crane Cams makes an inexpensive rocker arm bridge shim kit (part #99179-1) that can alleviate valve adjustment issues and help with lifter plunger height adjustment. See the Crane Cams download PDF catalogs or your Crane dealer:

  "Crane’s Rocker Arm Bridge Shim Kit will correct for excessive hydraulic lifter preload on late model American Motors V-8’s, and I-6’s...Two different thickness shims are included to decrease lifter preload by approximately .030”, .060” or .090” depending on the combination of shims being used between the bridge and the cylinder head. Excessive preload may be caused by a camshaft change, valve job, head resurfacing, etc. These shims can be a quick and easy alternative to resorting to different length pushrods."—Quote from Crane Cams catalog

     Rocker arm bridge shims, used in conjunction with the adjustable "pushrod" gauge from CompCams (#7704-1) or an equivalent length Crane Cams adjustable tool, can measure the valve lifter pre-load needs. These shims correct lifter pre-load settings by raising the rocker arm height to compensate for cylinder head work, camshaft profile changes or cylinder block decking.

     Crane Cams and others (like Trend Performance and CompCams) also offer custom pushrods in whatever length your engine requires. (You can match each valve precisely with the right length pushrod.) Although this sounds time consuming, setting the lifter plunger location—or "preload"—is critical.

     Also, as Moses Ludel, Crane and others note, new hydraulic lifters should not be filled or "pumped up" with oil before installation. Once the lifters have been installed, with the rocker arms properly set, prime the engine* oiling system. This will fill the lifters safely, without over extending the plungers, and help the lifters fill quicker when the engine first starts up.

     *Pressurized oil pre-priming tanks are available from Goodson Tool and others. If you build engines regularly, purchase a priming tank for fresh oil fill-and-prime on your engine builds. Otherwise, you can prime the engine before starting it by filling the crankcase with fresh oil, then spinning the oil pump drive with a drive tool and heavy-duty drill motor. Once all galleys and arteries are filled in this way, the engine can be started without risk of oil starvation to new bearings and other vital parts! Always use a quality assembly lube when fitting critical bearings and parts.


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