258 Aluminum Valve Cover - JeepForum.com
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post #1 of 6 Old 04-30-2010, 12:26 PM Thread Starter
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1986 CJ7 
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Location: Everett, WA
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258 Aluminum Valve Cover

Ok I have searched the threads but nothing answered my question. I pick up this one of craigslist for $60. Valve Cover Black Aluminum Kit* "Jeep" Logo*DMC-6914 by the Jeep Specialists | Morris 4x4 Center I am curious to what size I need to flat tap the holes too? 1/4 x 20 or something else?


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post #2 of 6 Old 04-30-2010, 02:23 PM
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totally depends on what size bolts/studs you are going to use. did yours come with bolts? (I prefer studs)

if not, you can use whatever size you tap, as you'll be buying those, too.

it also depends on your head. some are tapped threaded already, others are drilled but need tapped, and some have a helicoil type insert in them from the factory.


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post #3 of 6 Old 04-30-2010, 03:12 PM
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1984 CJ7 
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Location: Doylestown, PA
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For your 1986 model year, you will reuse the front and rear 1/4-20 bolts that are already tapped into the head but then you must tap 5 additional 5/16-18 holes on either side of the cylinder head. Two on the drivers side and three on the passenger side of the cylinder head. Get yourself two taps of good quality, one starting tap and the other will be a bottoming tap. You will probably have to drill holes for the 5/16-18 tap holes as they are usually not pre-drilled from the factory but may have a small pilot hole for a tip on the old plastic valve cover. Do not drill any deeper than say 3/8 of an inch in depth into the cylinder head or you risk breaking through to the water jacket that circulates coolant through the head. Cylinder head removal is not necessary when drilling and tapping, just have rags around to mask off and isolate the area for drilling and tapping. I used a shop vac that was turned on while drilling and tapping to suck up all the cast iron chips being produced so they wouldn't fall into the engine oil galleries. Have done several heads this way without incident.

1984 CJ-7 Renegade
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post #4 of 6 Old 04-30-2010, 03:19 PM
1974 J-Series Truck 
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JUST did mine this week..it wasnt hard..but wasnt fun either..hardest part was the rear bolt..(i liked the idea somebody had of installing a stud instead! if u have time/patience..might help the job..i didnt do it..but i can see why it would be nice! my only other advice is to take ur time! i got a tap set from napa...cost me $6 did the job..oh..and also may have to check on ur clearance of ur bracket holding the pulleys on in the front?..i had to shave mine down a lil..it was holding up the cover a tad..other than that..its not too bad..and worth it!
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post #5 of 6 Old 05-03-2010, 08:10 AM Thread Starter
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Thanks guys, Yah I have to buy the H/W so I will also check to see what I have to drill and tap. Thanks again!

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post #6 of 6 Old 05-06-2010, 09:08 AM
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On mine, I'm not using the rear bolt since I ran out of patience trying to put it and used a decent amount of RTV on the gasket (all of it). So far it's not leaking (been about six mths). Also, pay close attention to what Keith460 mention about going too deep with the drilling. You'll be amazed how easy is to break into the coolant passages. It happened to me, but after realizing that it was not the end of the world, I just used thread sealant on the driver's side bolts and Voila!!! No leaks. It definitely worth the effort, changes the look of the engine from miles away. Remember to cut off the studs on the valve rockers bridges!!!!!


TropicalNusselt- 1986 CJ7 w/ 258, T5, D300, D30/D44(3.31:1), Weber 38DGES, DUI, 2.5" Lift, 33" X 12.5" X 16", DC1
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