We are convinced that anyone reading this has a good idea of what day two is all about, but if you don’t, here is our take. Many folks squirreled away speed equipment long before that brand-new muscle car rumbled up the driveway. And if you didn’t already have a stash, you probably had a speed equipment wish list as long as your arm. You started bolting on parts the day after you bought the muscle car. High on the list were things like “mag” wheels, bigger tires, headers, shifters, tachometers, and maybe aftermarket air cleaners. Not far behind were cast aluminum valve covers. Back then it was no secret that an engine wearing a set of Weiand, Edelbrock, or Mickey Thompson covers was special. It usually meant the muscle car engine was “worked on.” Those cast valve covers were truly badges of honor from a high-performance perspective. Any extra performance they added is debatable, but the fact remains that a set of polished, finned aluminum valve covers look great no matter what.
When it comes to hopped-up muscle car motors, the valve covers can certainly make or break the look, but in today’s world, if you are working on an era-correct car, you might find that many of the old (and correct) cast valve covers have, over the years, been discontinued. Time moved forward. Billet covers, painted steel covers, and tall chrome covers replaced the finned aluminum jobs. For some, finding a set of vintage valve covers means trawling eBay or swap meets for the privilege of paying way too much for a set of used (often abused) examples.
You don’t have to go that route, particularly for the more popular engine families. Several manufacturers with roots in the early days of hot rodding have dusted off their old valve cover tooling and are now manufacturing some cool era-correct pieces. One of those companies is Holley with its line of M/T (Mickey Thompson) valve covers, which are shown in the accompanying photos.
But bolting a set of valve covers on your engine isn’t quite as simple as it seems (and it never was in the muscle car era either). One thing you have to consider is that many of the really good-quality cast aluminum aftermarket valve covers were (and still are) equipped with large, built-in drippers. Those are pretty much mandatory with stock stamped-steel rockers. But if your engine is fitted with large-body roller rockers, the covers need to be clearanced or they won’t fit. You also have to knock out holes for the breathers, a positive crankcase ventilation (PCV) valve, and sometimes the oil filler cap; fit the baffles; install the grommets; and so on.
What follows is a look at how you prep a set of Holley’s new M/T valve covers today, which, coincidentally, was how it was done in the 1960s, too.
1 The rereleased M/T valve covers from Holley are exactly the same as the original Mickey Thompsons. It’s no secret that today’s polishing is quite a bit nicer, though.
2 If you run a big, widebody aluminum roller rocker such as this Crane example, you will quickly discover that clearance is an issue, particularly with the built-in drippers (there are eight of them per cover). More valve lift and/or a larger-than-stock rocker-arm ratio only aggravate the fit issues. You have to clear the drippers or remove them completely, something we will address later in the story.
3 Knocking out the plugs for breathers and the PCV (if you use one) is a necessity. Yes, it is possible to add breathers elsewhere on the valve covers, but Holley makes these knockouts easy to use.4 With the valve cover face-up on your workbench, simply use a small punch and hammer to tap out the knockout. The idea here is to use a small punch and an equally small hammer! Hit the knockout dead center, and it will eventually break away, though it might take more than one strike to break loose.5 After you have opened up the breather hole, trim the remaining flash with a half-round file.6 For our big-block application we used a set of reproduction grommets. The hole diameter in the valve cover is identical for breathers and the PCV. It is the grommet’s inside diameter that makes up the difference for the smaller PCV.7 A vertical mill would be the perfect piece of equipment to use for clearancing the drippers, but we don’t have one. Instead, we used a cutoff wheel on a small Makita angle grinder.8 You can see how we lightly clamped a cover in a shop vise to keep it steady. A couple of shop towels, along with small sections of 1×4-inch wood, isolate the valve cover sides from the vise jaws.9 This is how the drippers looked after they were sliced with the cutoff wheel. Due to overall valve lift in our combination, coupled with the heft of the widebody aluminum roller rockers, we elected to remove the drippers completely.10 To get the job done cleanly, we used a small air-powered die grinder along with ample cutting fluid. Rapid Tap keeps the cutters from becoming clogged by the aluminum.11 Here you can see that the drippers have been eliminated.12 Holley provides a set of baffles for each valve cover. The idea is to mount them under the breathers and/or the PCV so that they aren’t subject to a constant oil spray. It is best to use a bit of red thread-locking compound on the self-tapping screws. You don’t want the screws wandering around inside your engine. If you choose not to use the baffles, there is a really good chance you will end up with a healthy oil slick surrounding the topside of the breathers.13 This M/T valve cover has a reproduction OE-style 90-degree elbow and hose, which routes to the inside of an open-element Chevy air cleaner. With this arrangement you don’t need a separate breather.14 On the opposite-side valve cover we chose to use a PCV, although some might decide to simply use a second breather. (The PCV setup will actually prove far cleaner in terms of oil “rain.”)15 The chrome filler cap is a reproduction. When we set up the valve covers, we had not decided which side to use for the oil filler. We can change sides by simply swapping the PCV and breather hose locations in the respective valve covers.16 If you install the valve covers and still have rocker-arm clearance issues, it is easy enough to locate valve cover gaskets of varying thicknesses. For example, the big-block Chevy valve cover gaskets in this collection measured as thick as 0.175, 0.220, and 0.310 inch. You can use the extra gasket thickness to move the cover away from the rockers.17 Here is the completed valve cover project, ready to add that day-two look to our engine.
