Jeep 225 V6 Cylinder Head Machining Issues

[Dick B]

Had my 1971 CJ5 225 V6 rebuilt. Machinist decked the block 0.065 and angle milled the heads 0.125. I am having problems with push rod lengths and intake manifold fit. The machinist did not mill the intake side of the heads to match the head rotation or machine the intake manifold for the change. I appear to have a vacuum leak under the manifold. Possibly not seating low enough. The push rods also appear to be too long not allowing the valves to seat correctly. I am looking at adjustable push rods from TA Performance for the push rod problem. but I am not sure how to address the manifold issue. How do I determine how much to machine off the manifold and at what angle?   I am using an Offenhauser Dual Port manifold. Should the intake side of the heads be machined to correct the angle to match manifold angle?

[Moses Ludel]

Hi, Dick...That's a wholesome amount of deck material removed, were you striving for maximum compression ratio?

You have this well in perspective:  Dropping the heads down that far, even if done at the correct deck angle, would create an intake manifold and head port misalignment.  The head intake ports and intake manifold ports now require "port matching".  This also involves correcting the intake manifold and/or cylinder head flange angles to make these parts seat parallel.

The objective is to have the intake manifold's port flanges set parallel to the head flange angles when the intake manifold is torqued into position.  At this same point, the port flow (i.e., the alignment of the ports) must match between the intake manifold and the cylinder heads.  

Note:  Consider that the intake manifold flanges must be wide enough to compress the gaskets while matching and aligning the ports.  The torqued manifold should achieve port alignment with flanges that are parallel at that same point.

The proper angles are simple geometry:  1) The manifold pulls downward when tightened, but the angle of the head flanges and angle of the manifold flanges remains the same and 2) the manifold needs milling at the reciprocal angle to the angle of the head flanges. The angle of the head flanges can be determined with the heads in place and torqued (as you indicate they are now).  Actual angle to consider is between the heads' intake flanges and the lifter valley's top decks (measured at the front and rear of the block).  

The unknown is whether the head surfaces were angled properly during milling/surfacing.  The intake manifold must have enough flange material (the overall manifold width) to gap the void between the heads; allow for the compressed intake gasket thicknesses under normal tightening/torque values with the manifold torque'd into place.  

Note: If he machined properly, the machinist had something practical in mind when selecting the angle of cut for a 0.125" shaving of the heads.  Ask the machinist about the strategy here.

As for pushrod lengths, decking apparently lowered the rocker shafts and non-adjustable rocker arms more than the lifters can compensate.  Also check whether the angle of the head decking kept the pushrods centered between the lifters and the rocker arms.  There cannot be interference between the pushrods, block and head openings.  The actual pushrod angles should be close to the original factory angles, too.

Your idea about aftermarket adjustable pushrods is one solution, and there are also custom pushrod builders that can make pushrods of the correct length.  Sometimes, and much less costly, a pushrod catalog will provide a similar diameter and ball-end size pushrod of the correct length.  If this is a 225 and not a later 231 transplant, the pushrods do not require a hollow tube with pushrod ball ends that have oil holes.  (Do your OEM pushrods have oil passageways?)

The 225 V-6 rocker shaft/rocker arm oiling circuit flows oil to the top ball ends of the pushrods; oil then drips down the pushrods to oil the solid cup disc at the upper end of each lifter. Unlike the later 231 Buick V-6, a small-block Chevy V-8 or a Jeep 4.0L inline six, the lifters on a Buick/Jeep 225 V-6 do not send oil up through the pushrods to oil the rocker arms and valve stems.

If you have further questions, please ask...If you need to post photos of your findings, feel free to do so...

Moses