Sunday, December 10, 2006

VW - Pulling the Plug


The oil galleries on the VW crankcase are sealed with aluminum plugs. They come in four sizes and two flavors. The smallest size (and Vanilla flavor) is a small piece of aluminum rod to seal the 5mm drillings. The other flavor is an aluminum Welch plug (i.e., ‘freeze' plug*) that comes in three sizes (counting both early & late model crankcases) used to seal the larger openings, although unlike the freeze plugs found on an iron casting the Welch plugs on the VW crankcase are installed with the convex side out.

When starting with a used crankcase of unknown provenance you must pull ALL of the plugs in order to clean the oil galleries. This rule also applies to a NEW or used crankcase on which any machine work is done. The reason is pretty simple: When opening up the case to accept larger jugs, or when doing an align bore, it's impossible to prevent swarf from getting into the oil galleries. Once you get swarf into the oil galleries the only way to get it out is to scrub it out using a bristle brush and copious amounts of solvent.

Many shops don't do this. Instead, they give the galleries a blast of compressed air and ASSUME it will blow out all of the swarf. Unfortunately, the oil galleries have several blind corners where one drilling intersects another. Opposite the blind corner the drill usually leaves a cone-shaped pit or even a short, dead-end passageway. Blowing air into one side of a gallery that has a dead end or blind corner simply packs the debris into the corner. Even when using solvent and brushes, working from only one side of the corner, no amount of scrubbing or flushing guarantees you will get the swarf out of those dead spaces because your brush can't go around the corner. But when you're working from only one side of the corner your brush can pack the debris more firmly into the void, where heat and vibration will cause it to come free once the engine is assembled. And end up in your bearings, since the debris is already downstream from any filter that may be installed.

Everyone who has overhauled more than a few engines knows what I'm talking about here. You split the case and the first thing you see are little smears of metal on the #2 bearing, with lesser amounts on #3 & #4. Pop the #2 cam bearing shell out of the right-hand side of the case and you're liable to find the large oil passageway behind it completely blocked with swarf. And while everyone with a bit of experience has seen this evidence, what happens next is kinda funny. Some attribute the contamination to ‘bad bearings,' others to ‘bad oil' or a ‘bad case' or even a bad crankshaft. I imagine there are even some mechanics who will blame the contamination on an act of God or a voodoo curse but the funny part is the fact not one in thousand will blame it on themselves.

Let me offer you a hint: If you find metal particles BEHIND a bearing shell the odds are the debris was there when the engine was assembled. You can't blame it on the customer for using ‘bad oil' or the supplier for sending you ‘bad bearings' or the regrind shop for delivering a ‘bad crankshaft,' you gotta look in the mirror and blame it on the monkey who failed to properly clean the crankcase prior to assembly.

Which raises an interesting point. A lot of VW ‘experts' say it's a bad idea to use an align-bored case, even though Volkswagen did exactly that with more than 7,000,000 factory-overhauled engines. Those same experts often say that using bigger jugs guarantees an unreliable engine, even though the 1600cc engine is nothing more than a big-bore 1500, which itself is a big-bore 1300. Craziest of all are those instant experts that tell you full-flow oil filtration ‘doesn't work.' Remember them? (And if you don't, just check the archives.)

Before you buy-in to the instant-expert version of reality it might be a good idea to take a look at an engine built by such experts. When you do any machining on the crankcase, one of the of the plugs you have to pull is just to the left of the base of the distributor, clearly visible even when the engine is fully assembled and mantled.

Is the stock plug still there? (All it takes is a quick look.)

If so, was any machining done on the crankcase? If it's ‘yes' again then walk on by; whoever built the thing doesn't know what they're doing.

(Yeah, I know... you've built a zillion align-bored, opened-up engines and have NEVER had this problem. Since you're already perfect, this article obviously isn't for you. This article is for me. And all the other engine builders imperfect enough to realize we still have a lot to learn.)


Preamble: If you want to do it right, do all the drilling & tapping with a drill press. But since most of you don't have a drill press, or don't have one that is large enough for this task... or don't have the fixture to support a VW crankcase standing on its nose... just do the best you can.

Start by center-punching the plug. Then drill through the plug with an 1/8" bit.

[Odds are, you don't have the right drill-motor for this, nor the right tools to position the crankcase. Aluminum is virtually transparent to a properly sharpened drill bit turning at the right speed. To drill a clean hole in aluminum an eighth-inch bit has to be turning about two thousand rpm. Unless you do a lot of aircraft sheet metal work you probably don't have portable drill motor that turns that fast. And unless you've got the jigs to position a VW crankcase on the drill table, you can't use your drill press. Just do the best you can. (If you've ever wondered why your holes come out sorta raggedy, perhaps you should look up ‘SFM' (surface-feet per minute) and do a bit of reading.)]

Once you've drilled the pilot hole, put a #8 sheet metal screw in your slide hammer, screw the thing into the hole and do what comes naturally. In about three slaps of the hammer you'll have a greasy little plug in your hand.


The rule is easy to remember: When in doubt, take it out.

On a used crankcase, pull them ALL.

On a late model crankcase we're talking about TEN plugs; eleven if you plan to the install a temperature sensor**.

On the pulley-end of the crankcase pull the little (6.25mm) plug on the #4 main bearing gallery, the pair of 14mm plugs associated with the main oil gallery and the 12mm plug on the gallery going to the oil cooler. On the top of the crankcase pull the 12mm plug just beside the threaded boss for the oil pressure switch. On the left side of the crankcase pull the small plug between the spigot bores for #3 & #4 cylinders. On the flywheel end of the crankcase pull the pair of small plugs for the lifter oil galleries, the 14mm plug blocking the end of the main oil gallery and the small plug just below it that goes to the oil pressure control valve. You may ignore the small plug on the bell housing flange; you can reach it's void space with a pipe cleaner. The above is for a late model crankcase.

Early model cases have fewer plugs to pull and the location for the oil temperature sensor is sealed with a THREADED plug. (To install the oil temperature sensor, simply remove the plug and replace it with the VDO adapter. [see the footnotes])


Before pulling the plugs give the crankcase a cursory cleaning so as not to turn your shop into a grease pit but don't bother making a serious job of it until you've tapped all the holes. The drilling and tapping will generate a lot of swarf which can only be removed by cleaning the case all over again.

Some of the holes are the right size to accept a large set screw. Back in the Good Old Days, whenever that was, I used mostly set screws to plug the holes. Of course, being steel and having a straight thread, they tend to leak a bit but being an idiot kid I was more interested in going fast than in the trail I left while doing so.

The proper way to plug the hole is with a pipe plug. They're tapered and when properly installed, don't leak. Assuming they're aluminum. Steel pipe plugs, which are a lot cheaper and easier to find than aluminum pipe plugs, tend to loosen up after a few years because of the different coefficient of expansion between steel and magnesium alloy. Properly installed, aluminum pipe plugs don't leak. Ever. The coefficient of expansion for aluminum and magnesium alloys are very close together; the plug expands at the same rate as the case, insuring the plug will remain oil-tight.

Whatever pipe plug you use, steel or aluminum, you want the ones that are installed with an Allen wrench. Ask for the ‘internal wrenching' type. Earl's sells them. Cost the earth but it's a one-time thing.


Tapping the hole to accept the plug is where most mechanics come to grief. Not so much in the tapping but in starting out with the wrong diameter hole, or making it too deep. Being tapered, a pipe-thread tap is happiest working into a tapered hole, which is accomplished by drilling a starter hole that's too small then opening it up with a tapered reamer. Most mechanics, VW or otherwise, have never even seen a tapered pipe-thread reamer and their eyes pop open when they see what they cost. But there it is.

The depth of the threaded hole is fairly critical. Go too deep on some locations and you're liable to block the oil flow. Ideally, the plug should be fully seated either flush with the case or no more than one thread below. If you start with a properly tapered hole you can achieve this fit every time by putting a reference mark on your tap but if you've never done this before it would be best to keep trial-fitting the plug.


I probably spend about two hours total, pulling the plugs and tapping the holes. I could probably do it faster but a single mistake can take hours to repair. I've found I make fewer mistakes if I work at a steady - but fairly slow - pace.

Anodized aluminum pipe plugs are expensive. Figure a couple of bucks each for the small ones, more for the larger sizes. See the web site of any automotive supplier that sells Earl's Performance Products; they usually list the prices. There are commercial manufacturers of aluminum, internal-wrenching pipe plugs but I've never found one interested in selling small quantities.

As for the price of the tools, I honestly don't know. Most of my tools are older than you are; some are older than me. (I've got a half-inch pipe tap that belonged to my dad.) You need pipe taps for one-eighth, one-quarter and three-eighths, plus half-inch if you're doing the temperature sensor in a late model crankcase. Good taps, not that Chinese junk. And you need a reamer for each. And you may need TWO of the same size, since some of the holes you need to tap are shallow; you have to grind the tap to the right length.

Instead of a reamer you can ‘step-drill' the hole, assuming you have a drill press and the right drill bits.

Bottom line is that you need a fair amount of tooling. Which is one of the reasons I started out using set-screws :-)


If it's a used crankcase it's going to have some oil trapped in the galleries. If the case has been laying around for a while the oil is liable to be harder than a bride's biscuits. I'm fortunate in having a cleaning tank large enough to submerge a crankcase. After the thing is tapped, if it's a used crankcase I generally leave it to soak overnight before attempting to clean the oil galleries. Soaking in diesel or mineral spirits will soften the oxidized oil, allowing it to be scrubbed out without too much trouble.

Most the brushes I use for cleaning oil galleries are bore brushes designed for cleaning rifles, pistols or machine guns. (I'm ex-Navy and have access to used, surplus bore brushes all the way up to 20mm.) I chuck them into a Makita cordless drill-motor and run them slowly up & down the oil gallery while keeping the thing flooded with mineral spirits. In a pinch, you can use nylon bristle brushes but it takes longer than with a ‘soft' stainless steel or bronze brush. Suitable brushes are sold as coffee percolator pump brushes, baby bottle brushes and the like. Be prepared to cut them down to the right diameter when necessary.

All of the oil galleries on the VW engine are drillings, meaning they are perfect circles with a smooth finish. The main oil gallery runs straight through the case and you can inspect it the same way you'd check the barrel of a gun. But it's also possible to VISUALLY inspect the other galleries if you provide yourself with the right light source. Such inspection lights come in all sizes; I've got one that's only a sixteenth of an inch in diameter. Not very expensive but you'll have to shop around. (The little one is a fiber optic thingee on a pen light. I think I got it from American Science & Surplus.)

The passageways are clean when you can SEE they are clean.


I use a round Swiss file (i.e., a little file with a fine tooth) or a small carbide burr to make a SMALL round-bottomed notch in the top edge of the plug. Just a little one; mebbe an eighth of an inch across and maybe the same for depth, although it's shallower on small plugs, deeper on large ones.

Once the plug is installed I use a ROUND NOSED drift to swage the metal of the crankcase into the notch on the plug. Don't hit it hard; use a series of light taps to gently flow the metal into the notch. You'll probably have to make the round nosed drift. Just polish the point of a center punch.

Swaging the metal of the crankcase into the notch on the pipe plug keeps it from coming loose.


Mostly, I use #3 Permatex. I start by putting the plugs in a little cup with some lacquer thinner or MEK to make sure they are free of oil. I use a Q-tip to wipe down the threads in the crankcase with MEK. Put the plug you're about to install onto the Allen wrench, blow it dry then put a dab of Permatex onto the threads of the plug and smear it around the full circumference. Then thread it in an bring it up to a firm fit.

For high temperature applications I use high-temp Loc-Tite. To remove the plug you'll have to use heat and the trick here is to put the Allen wrench into the plug then use a small tipped high intensity torch, such as MAPP or O/A to heat the area locally while applying torque to the Allen wrench. As soon as you feel it turn, move the torch away.


As with all VW engine work, the answer to that question depends on you. But to give you a hint, when you order a rebuilt crankcase from a reputable shop it usually comes with the plugs pulled and the holes threaded. On the other hand, I know some big name builders who insist such care isn't needed because their engines are built on new crankcases.

So how do they remove the swarf that gets into the oil galleries?

"Oh, we blow them out, really good."

And how do they KNOW the galleries are free of swarf?

They don't. They ASSUME blowing them out ‘really good' is all it takes, in every single case, to leave the galleries perfectly clean.

‘Assume' is another term for ‘guess-work.' In my opinion, and that of many other engine builders, the wiser course is to leave nothing to chance. By pulling the plugs you don't have to assume anything, you can visually inspect the oil galleries. Good engines are not built on guess work.

-Bob Hoover -April 2002

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* - They aren't ‘freeze plugs' and never were. Those holes in the side of iron and steel monoblock castings are to facilitate removal of the fragmeable sand cores used in the casting process.
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** - Volkswagen provided oil temperature and oil pressure gauges on some of their industrial engines. The oil temperature sensor was placed at the inlet to the oil pump. Early model crankcases had a threaded hole (M16x1.5) at that location. To install the sensor the threaded plug was replaced by the matching VDO temperature sensor.

On later model cases the hole is no longer threaded and is sealed by a Welch plug about 19mm in diameter . To install the temperature sensor, pull the plug and thread the hole to accept a suitable adapter. Be sure the temperature sensor extends far enough to be constantly bathed by the oil being drawn from the sump but not so far as to obstruct the flow.

On most late model crankcases, a half-inch NPT hex-head plug, drilled and tapped to accept the temperature sensor, makes a suitable adapter.
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(Ed Note: Since writing this article a number of people have created web-sites showing how they've done the work.)

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