Vehicle Maintenance: How to Change an Aftermarket Valve Cover
I’ve been putting aftermarket valve covers on engines for years, and twice I have had immediate leakers during my vehicle maintenance projects. I thought I would take a few minutes to document an avoidable pitfall and hopefully save a few people the trouble of doing this auto maintenance job twice. When I am building a motor to go into one of my projects, I often choose a clean, shiny-looking aftermarket chrome valve cover. They look sharp, are fairly inexpensive, and half of the projects I work on come without valve covers, so they are a much easier option than finding stock covers, cleaning, prepping, and painting. Most of my own motors are roller cam/roller rocker engines and are non-adjustable. I try to avoid premade cut gaskets, as they can dry out, take compression set, and shrink, leading to weeping leaks. My weapon of choice is Loctite® 598™ Silicone Gasket Maker. It has excellent oil cutting and instant seal properties, as well as being resistant to hardening or shrinking with thermal cycling. The two leaks that I have had were both user-related. Both were when I was installing stamped chrome valve covers. One set was on a Pontiac 400 cid, and the other was on a 318 cid Mopar. So the problem is not specific to only one manufacturer’s engines. It is common to most. The issue was that the stamped covers had a recessed lip around the perimeter to allow for positioning of a cut gasket. The lip was 3/16” in some areas and interfered at the corners rubbing on the heads, preventing even pressure around the valve cover sealing area.
This is the area where you typically see the interference with the head. The socket is where the lip contacts the head. (This is a real nice aftermarket set of SBC covers and the lip is small, but I used this picture so I didn’t have to disassemble a running motor.)
Here you can see that I am putting down a large bead directly from a 10 oz. caulk-style tube with no nozzle. It makes a nice, clean, large bead, about 3/8” diameter. When you are not using a cut gasket, this allows for a perfect-sealing filling gasket. I then assemble (do not overtighten) and wipe off the excess, for the nice clean appearance. You can also trim excess cured material with a sharp-edged tool when you are done, if you prefer.
If I am installing valve covers on a motor that will require valve/rocker adjustment, I use a smaller bead of 598 on the valve cover side, then place in the cut gasket. This prevents leaking on the one side and adds additional elasticity to help aid in leak prevention on the head side contact area. I leave the head side clean and dry so that the valve cover can come off clean and be re-used after adjustment.
When you are installing valve covers (new aftermarket, or OE stock) always inspect and dry-fit the covers to see how they fit and to ensure that your sealing system is appropriate for the application. I’ll include some pictures to try to show the fit issues that I have run into in the past.
This is a picture of a large bead on what is actually a very good (low edge) stamped valve cover. If this were a cover with the 3/16” lip, the bead would be about 1/8” – 3/16” exposed above the lip.
This application was a 318 Mopar. You can see the large lip on the corner of the valve cover (just above the freeze plug on the head) hitting the head and preventing it from seating properly on the head.
Complete 318, Loctite® 598™ on the valve covers, no leaks.
BONUS: Here’s an infographic on a commonly misunderstand product.