Replace Valve Cover

Aluminum Cover.jpg (34548 bytes)

Does Your Valve Cover Leak?

Most stock 258 motors with the plastic valve covers have a common problem with warped valve covers that leak oil.  The oil leak problem is not because the plastic valve cover can't withstand the heat in the engine bay, it's usually because the plastic cover wasn't installed properly.  The plastic valve cover's efficiency is compromised if there is uneven torque on the bolts, or if some of the bolts were tightened before all the bolts were installed.  In either case, it will eventually result in a warped cover.  Eventually, a new gasket and/or tons of silicon will no longer work and a new cover will be necessary.

Oil leak, note the oil above the intake and exhaust ports.

Oil seemed to keep pooling on top of the cylinder head (above the intake and exhaust ports).

When it came time for me to replace my plastic valve cover, I decided I wanted to try an aluminum cover instead of another plastic cover (Jeep did supposedly improve upon the original design of the plastic valve cover and offers a replacement part number for the cover if you so choose to try another plastic cover).   Upon looking into this a little further (through various forums and Jeep news groups), I found there were mixed feelings about the aluminum valve covers.  Many complained that after installing the new aluminum cover, a lot of oil was discovered in the air filter tray!  It turned out that some of the after-market valve covers didn't include the baffles for the PCV system ports and so oil was free to flow up the breather hose.  So the first tip here is to check that your replacement cover does have baffles!

Bottom view of new valve cover showing the PCV baffels.

Bottom view of new valve cover showing the PCV baffles on both ends.


Bottom view of stock valve cover showing the forward baffle just behind the oil fill hole.

To make matters more confusing for some (me included), Jeep used two different methods of valve cover attachments for the same motor.  Some 258's have their valve covers held down with two studs that extend through the top of the valve cover.  These studs are attached to the rocker bridges.  Mine didn't have these so I didn't have to worry about this, but all the aluminum valve covers appear to require the removal of these studded rocker bridges.  This means you'll have to buy a relatively inexpensive adapter part along with your cover.

The next concern I had when looking into an aluminum valve cover was that many covers have a note that reads "may require some drilling and/or tapping holes" in the cylinder head!  The thought of that seemed a intimidating to me.  How many holes would I have to drill?  How hard will it be to access these holes?  The hard part is, you really won't know for sure until you remove your old valve cover.  What to do?  I debated all this for quite some time until I finally found myself faced with another project (removal of the intake manifold) that was going to expose the motor and provide a good opportunity to tackle the leaking valve cover dilemma! 

I found a good price on an aluminum valve cover through Turner 4WD and when I tore into my other project, I brought along the valve cover and my camera and took some photos of the install to share.

Remove air filter tray and vacuum harness bracket Obviously, the first step is to expose the valve cover by removing all the parts on top of it and next to it, like the air filter tray, vacuum harness and miles of vacuum lines.  It may be easier if you remove the fuel line.  The bracket holding the idle pulley wheel (if equipped) needs to be removed.  Once the valve cover is exposed, you can start to remove the hardware holding it to the top of the cylinder head.  There is one bolt in the very back (slightly more to the driver's side) that will be fun to fish out!
Motor without cover. Once the cover is removed, clean the surface of the cylinder head and remove all the old gasket material.  Also, here is where you need to check all the holes to see if they are threaded.  On mine, the ones on the front and back (smaller diameter holes) were threaded, as were the three along the passenger side of the motor.   But the two on the driver's side were not threaded.
Tapping the head.jpg (40784 bytes) As the new valve cover included all the necessary hardware for installation, the size of the necessary tap was listed in the instructions.  In this case, a "bottom tap" was required.  I was unfamiliar with the term "bottom tap" but after looking at my taps and their chamfered points, it seems the bottom tap would not require as much additional depth of the hole as it could cut threads deeper into the hole.  I went ahead and deepened the two holes slightly to allow enough thread to be cut.  BE CAREFUL HERE!  A hole drilled too deep will intercept the water jacket of the cylinder head and will require the threads to be sealed.   Click here for a photo of both a bottom tap (left) and a normal tap (right).
Installing the gasket Once you've checked all the holes on the cylinder head to see that they are all clean and will work with the hardware provided (it's good to check this BEFORE installing the cover) you can place the gasket on the cylinder head.  Here will be the first time to check that the alignment of the holes in the gasket match with the holes on the cylinder head.  By design, the gasket is very think.  Using a gasket sealer will help to hold it in place while you fuss with installing the valve cover...
Offset on new cover.jpg (46631 bytes) Before installing the new valve cover, first check that the four screws holding the two baffles are all tight.  After the new valve cover is placed on the motor, check to see if all the holes will properly align with the cylinder head and the gasket.  Do this by loosely installing all of the bolts.  On my cover, all the holes aligned perfectly except the one in the very front.  Perhaps if one wasn't going to fit, this would be the best one!  I measured the offset of the hole, and marked the valve cover accordingly.   Then I had to remove the cover again...
Filing the cover.jpg (31027 bytes) Don't bother trying to drill a hole.  A round file (like one used for sharpening a chain saw) works very quickly on the soft aluminum.  Once the adjustment was made, I could reinstall the new cover and tighten all the bolts down.  On this one where I enlarged the hole, I used a washer to help the small allen head bolt hold the cover down.
Reinstall all the vacuum fittings onto the cover. Check that all seven bolts are equally tight and that the gasket is evenly exposed.  My new hardware included allen-head bolts.  The four large cupped washers that held the stock valve cover's shoulder (on the driver's side) are not needed with the aluminum cover.  Once the cover is secured in place, install the parts removed from the old cover in the first step.  Also, you can install the grommets for the PCV system ports and the rubber plug type oil cap.
Where did it go? And when it is all said and done, you probably won't even be able to see much of it!

After one full year the cover has not leaked!  The area surrounding the valve cover remains free of oil deposits.  The rubber oil fill port cover is very firm and does require a bit of force to extract.  So far, I am very impressed with the quality and look of this product and strongly recommend this upgrade over the plastic cover.

Note:  I recently installed a second valve cover on a 1985 CJ and discovered that the three holes on the passenger side of the cylinder head were a smaller diameter than those on my 1984 CJ.  The 1985 cylinder head had three 1/4" x 20 thread tapped holes on this side and the 1984 cylinder head had three 5/16" x 18 thread tapped holes.  The hardware included with the two kits appears to contemplate the five 5/16" holes and two 1/4" holes, like the 1984 motor.   So you may have to make a trip to the hardware store and get a few more allen head bolts.  Both cylinder heads required very-slight drilling (deepening) and tapping of the two plastic-cover index holes on the driver's side of the cylinder.