Tuesday, November 28, 2006

AV -- The Valve Cover IQ Test

Back in the Good Ol' Days, whenever that wuz, one of the most common of the lo-buck tricks me and the other fools applied to Volkswagens was to install a set of rocker arms that had a ratio higher than the stock one-to-one. That should give you the clue that I'm talking the 1950's here. (The rockers on later engines were one-point-one to one and the VW industrial engine that ran on alcohol was one and a quarter to one... but I'll get around to that in another message).

There were lots of tricks in making up a set of 'ratio'd' rockers. You'd usually have to bush the bore, since the VW uses a rocker shaft having a rather small diameter. Once you'd bushed your donor rockers you'd hone them to match the VW shaft. Or not bush them and make a new shaft and modify the heads to accept it. Lotsa ways to skin that particular cat.

American custom is to put the adjusting screw on the push-rod side of the rocker-arm. (Stock VW rockers have the adjuster on valve-side.) Unfortunately, the adjuster would often hit the valve cover, which could be kinda interesting if you hadn't figured that out ahead of time. If you had, you'd heat up the valve cover in the area where the rocker was making contact and forge a little blister to make room for the adjusting screw. Which worked fine, so long as you stuck with the stock cam, which like most chuggers doesn't have a lot of lift.

In the early 1960's following the introduction of the 1300cc engine things got a lot more interesting, with folks offering high lift cams and higher ratio'd rockers specifically for the VW. Now the rockers weren't just hitting the valve cover, they were knocking the thing clean off the engine.

What was needed was a deeper valve cover. And as you've probably guessed, they soon appeared on the scene. Cast aluminum. Leaked like a bitch.

Turns out, those pretty cast aluminum valve covers not only leaked, they ran hotter than the steel covers. That's because folks liked to polish them up, get them shiny as a silver tea pot. And that shiny surface did exactly what all shiny surfaces do and reflected the heat of the oil back into the valve gallery. And of course, they leaked like a bitch.

The leaking is an artifact of the casting, which is just a thin shell. A thin cast shell. Not real strong. Clamp or bolt the thing to the head of a Volkswagen engine, as soon as it heated up it would distort and as soon as it distorted, it would leak.

The solution to the leaking problem was two-fold. First, you had to cast some ribs inside the valve cover; you had to make it stronger. The ribs stiffened it up so that it didn't distort so badly once it heated up. You also had to make the casting thicker. It weighed more of course but nobody cared about that. Second, you had to abandon the stock valve cover gasket and go to a specially molded O-ring type jobbie that socketed to the sealing surface of the cast cover. Expensive as hell but if you wanted to run ratio rockers and wanted to keep enough oil in the engine to finish the course, you didn't have much choice.

They still ran hotter than the steel covers but the cure for that was pretty simple. You blasted those mothers to within an inch of their lives then had them anodized black. The blasting gave them an `infinite' surface and the black dye improved the thermal transfer properties of the anodized layer.

Of course, they ended up costing one hell of a lot more than the stock valve covers and weighed nearly twice as much but that's what was on the engines crossing the finish line first so naturally all the kiddies had to have them. Until they saw what they cost. So the after-market retailers whipped up these cheapie cast covers and sold millions of the things to naive youngsters.

And naive airplane builders, too :-)

Seeing cast aluminum valve covers on a flying Volkswagen is one of those reverse IQ tests that tells you quite a bit about the fellow who built the engine.

Don't take my word for any of this. Go weigh the things. You are the Mechanic-in-Charge of your flying Volkswagen, even if someone else did the work.

Be sure to include the bails with the steel covers. And the studs, barrels, O-rings and what-not with the aluminum covers. Their thermal emissivity is equally easy to check, especially if you have one of those IR thermometers. Most impressive of all is an IR photo. Just put an aluminum cover on one head and a steel cover on the other. Saves you a thousand words.

No one believes it of course. Conventional Wisdom sez cast aluminum covers are a necessity for any flying Volkswagen. Indeed, almost everybody uses them, especially those folks trying to sell you dune buggy engines with a fan on the nose :-)

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So what about the real engine builders running high-ratio rockers with blueprinted valve train geometry that requires a deeper valve cover? You section the original steel covers and make up new bails. Not nearly as pretty but if you're more interested in the steak than the sizzle, sectioned valve covers were the way to go.

Herez how:

Have you got a stock valve cover handy? Weigh it. 345 grams, right? About three-quarters of a pound. That's a VW valve cover. [Look for the VW logo just to the right of the center rib.] There are some after-market covers made from thinner gauge metal that weigh as little as 250 grams [just over half a pound]. Okay, now look at the area of the valve cover just above the flange for the sealing gasket. Notice that the side wall of the valve cover has only a slight amount of draft; it's almost perpendicular to the flange of the sealing rail. (You know it can't be perfectly perpendicular because it's a one-shot stamping; all such stampings require some amount of draft.)

You can section a VW valve cover by nearly an inch, although that would be unusual. The typical high-lift rocker needs less than half an inch of additional clearance. Most guys section the cover at about three-quarter inch above the gasket rail then allow the donor valve cover to overlap. Do a few tack welds to keep things lined up then dress the edge for a gap-free fit. TIG is best here; the valve cover holds the gas and you can really roar along. But gas or even MIG works too. I've heard of them being brazed but I've never seen one done that way.

After it's welded you can clean things up with the grinder. Some guys leave the donor gasket rail hanging right there. They say it stiffens the thing up. When using a stock valve cover for the base I've never found any need for additional stiffness and usually cut away the donor's gasket flange before doing any welding. If you use a stock valve cover as the base and a lighter, after-market cover as the top, it should end up weighing about the same as a stock cover yet it will be about five-eighths deeper.

To section the bails, cut them on the side. Don't cut them to length, allow them to overlap at least 1". Set up a head and a sectioned valve cover as a welding jig but do not install a gasket. Position the parts of the bail so that they overlap uniformly on both sides (I put one wire down below the other, relative to the engine running position). You want the bail tight to the valve cover, and you want a heat-sink on the little end, where it hooks into the head. Do a couple of tack-welds with MIG or TIG then do the finish weld on the bench. I generally use MIG because it's faster; way back when, I used gas. Be sure to keep the heat away from the little end; the bail is music wire - - high carbon steel - - you don't want it to lose its temper. Clean and paint the bail. Use an enamel if you got it and give it a good heat cure. Add the weld to your pre-flight inspection (just look for any cracks in the paint).

Keep in mind, the only reason to section a valve cover is when you need additional clearance. Most engines do perfectly well with stock covers and bails.

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"Ha!" the prize-winning VW-flying fat man barked. "Shows how much you know. You gotta use bolt-on aluminum valve covers because that bail thing will break on you. An' besides, there's no way to safety that bail."

In more than fifty years of almost-daily hands-on VW experience I have never seen a broken valve cover bail that wasn't due to a collision. Nor have I ever even heard of one breaking, except from the fat man in the funny jump suit at the Ramona fly-in twenty years ago.

As for securing the bail, you safety-wire it. Just like we've always done. Go dig up a picture of those little Jodel's from the 1950's, lookit the way the safety wire runs down from the top of the head, around the bail, and is secured to the bottom of the head.

Cast aluminum valve covers are standard equipment for the Dune Buggy set although they are rarely seen at the finish line of off-road events. That's because the stock valve covers cost less, cool better, weigh less and seal better than the typical after-market cast aluminum valve covers. Plus, they tell you a lot about the guy who built the engine :-)


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