Metal Valve Cover

[simple man]

I am in the process of an aluminum valve cover on 84 CJ7 with a AMC 258 i6 / 4.2l cu in engine and I have a question regarding the drilling and tapping of the mounting holes on the driver’s side of the head.

My concern is the risk of drilling into any water jacket in the head. I have done several searches and cannot find a diagram showing the layout of water passages in the head. I have read a message thread that implied that there was no water jacket located beneath the holes for locating the original valve cover the driver’s side of the head.

Can anybody confirm whether or not where the water jacket is in the head?

Also, can somebody recommend a safe depth for the new mounting holes?

Thanks

Rick

 

[shum8]

I am in the process of an aluminum valve cover on 84 CJ7 with a AMC 258 i6 / 4.2l cu in engine and I have a question regarding the drilling and tapping of the mounting holes on the driver’s side of the head.

My concern is the risk of drilling into any water jacket in the head. I have done several searches and cannot find a diagram showing the layout of water passages in the head. I have read a message thread that implied that there was no water jacket located beneath the holes for locating the original valve cover the driver’s side of the head.

Can anybody confirm whether or not where the water jacket is in the head?

Also, can somebody recommend a safe depth for the new mounting holes?

Thanks

Rick

Having never does this I can't speak from experience, but over the years everything I have read says most of the time the holes are there just shallow. If you drill too deep, it supposedly will hit a water jacket, so many folks just tap the holes already there and tap with a bottoming tap, then use shorter bolts. This thread is a good one...

https://www.cj-8.com/threads/aluminum-valve-cover.37372/

Let us know how it goes...

 

[Nelson130J]

I installed a metal valve cover on my 84 CJ7 with AMC 258 i6 / 4.2l about a year and half ago. I had the same concern about going too deep. If you use a bottoming tap as opposed to a taper tap you do not really have to worry about going too deep because it will stop at the bottom of the existing hole. You do not have to go too deep once you install the gasket and the valve cover there is probably less than 1/2" of thread engagement into the block. I used a hand tap and just worked slowly to make sure I did not go to far. It all worked out well and no more valve cover leaks since I installed it. Hope this helps a little.

 

[simple man]

Nelson,

I am curious as to what size hole you tapped? The existing guide hole in my head is approx. .281 inches in diameter which is a bit larger than the drill bit needed to tap the recommended the 5/16ths hole. My research seems to show that a 5/16ths tap calls for a .257 (F) drill bit.

Rick

 

[Nelson130J]

Rick, I used a 5/16"X 18 bottoming tap for mine. Just went out to the garage to confirm...hope this helps..good luck

 

[simple man]

Nelson130J

Hopefully, one last question. First, I assume that the guide holes on the drivers side of the head are uniform for all 1984 heads. The guide holes in my head are approx. .281 inches in diameter. My 5/16 tap calls for a .257 inch hole. My concern is whether tapping a slightly over-sized hole will leave sufficient threads for the 5/16 bolt

Thanks

Rick

 

[Nelson130J]

Rick,
I did mine about a year and a half ago and cannot remember what the diameter of the guide holes was. I also cannot remember if those holes had a slight taper towards the bottom or not. I do know that when I ran the tap into them it felt like it was biting adequately and cut clean threads. The bolts went in without issue. I checked them frequently the first few weeks to see if they were backing off. I got a few turns on them the first week or so and I attribute that to the gasket settling in. After that I check them every oil change and have not had anything back out. I am sorry I do not have a clear answer to your question. Good luck with the project.