Sunday, May 27, 2007

AV -- CRANKCASE BASICS





I was dismayed to learn that some folks having no Volkswagen engine experience have been buying components, mostly from ads in car magazines, expecting to simply bolt things together, hang a propeller on one end, an airframe on the other and go flying. In at least one case a fellow thought he could buy a bunch of parts, haul them up to my shop, wave a lot of money at me and drive off with an assembled engine.

It simply doesn’t work that way. Here’s why:

When you buy a new crankcase what you’re actually purchasing is a ‘universal REPLACEMENT crankcase.’ These were originally provided only to VW dealers, where they were used for the repair of an existing engine whose crankcase has cracked due to age-hardening or collision damage. As received, your new crankcase can’t be used to build an engine from scratch because it is not complete. What’s missing are the things that make the crankcase specific to the vehicle Type and the model year. There is no sump-plate or oil screen, no studs for the oil pump nor fuel pump, no head stays (ie, studs) and no nuts & washers for the studs that are there. You’re expected to remove all that stuff from the original engine, the one with a cracked crankcase.

You can buy all the missing bits either in kits or per-each but if you’re building a flying Volkswagen you’ll be pissing away a lot of money because the parts in the kits are specific to automobiles. For example, in the standard ‘case kit’ (about $20) you get the oil control pistons, springs and slotted cap-screws. But for a flying Volkswagen you need a cap-screw you can safety-wire and an oil pressure relief spring that pops-off at 45psi instead of 27. You’ll also get a mild steel cover-plate for the big hole in the lower right corner of the sump where the dip-stick attaches on the Type III vehicles. Which goes straight into the trash because it weighs three ounces and one made of aluminum weighs barely half an ounce. Ditto for most of the studs since you’ll be using drilled-head bolts which you’ll have to procure and drill yourself. Bottom line is that it generally costs less to ignore the kit and buy the parts onsey-twosey.

A head-stud kit consists of the sixteen stays (in three lengths) that secure the heads to the crankcase, along with the required washers & nuts. Unfortunately, oft times one of the studs or nuts won’t have any threads and you end up having to beat the bushes for a replacement, since any effort to have the retailer replace the kit is like pissing into the wind. Indeed, you’ll often receive a head-stay kit clearly marked as being for a single-port engine that turns out to have the four short stays for a dual-port.

Even when you receive the proper head-stud kit, the things are bare metal. Before you can use them on any properly built engine they need to be plated, painted or coated - - and done well enough to withstand twenty years of exposure. (I usta have all my head-stays cadmium plated but when the tree-huggers forced the local plating shop out of business I went to two-part epoxy paint. Most recently I’ve been using powder coating.)

Finally, you will need nuts and washers and bolts to fasten the case studs and parting-line. Here again, there are kits available but most are the shoddiest stuff imaginable and price is no guarantee of quality. The nuts and washers may have a wash of zinc plating, good for at least a week’s exposure to the weather. Or they may not. And you can toss the ‘exhaust nuts.’ They are copper plated steel. (The good stuff is bronze.) Before you can use any of this crap on an engine you must provide it with some form of corrosion protection. If you don’t, not only with the nuts rust to the studs, you’ll see galvanic corrosion between the washers and the crankcase that will eventually cause the fastener to loosen.

But the biggest problem is that your new crankcase is for a stock ‘1600' engine. Flying Volkswagens tend to be larger, which means the crankcase must be machined to accept bigger jugs and, in some cases, a crankshaft having a longer throw. Plus it needs a critical bit of welding .

In the stock crankcase the spigot bore for the #3 cylinder is sort of hanging out in space. Even on the stock engines this area is prone to cracking. Indeed, a ‘cracked #3' is one of the most common reasons for the existence of Universal Replacement Crankcases. Machine the case to accept bigger jugs and you’ve made the situation worse by an order of magnitude. It’s no longer a question of IF #3 will crack but simply ‘when.’ To deal with that you preheat the new crankcase case and weld in a reenforcing plate using TIG.


A 94mm barrel will hit the threaded steel inserts that are standard on all new crankcases. Not only must you open up the spigot-bores to accept the larger barrels, you must deck the case to provide a uniform sealing surface for the bigger barrels. Since decking the case moves the heads closer to the centerline of the engine, it upsets both your valve-train geometry and your compression ratio. Because of the normal variation in the size of after-market parts, resetting both the CR and geometry is best done by inspection, meaning you’ll need to devote a couple of pre-assemblies to each of those procedures.

Opening up the interior of the crankcase to accept a bigger crankshaft is called clearancing and while most shops use a humongous cutter to do the job at one go it leaves a lot of feather edges that are guaranteed to precipitate cracks, so you have to dress the edges smooth by hand, using a flapper wheel, files and #600 grit sand paper.

If you’re doing the HVX mods you need to pull the plug from the oil gallery on the right-hand side of the crankcase, extend the existing oil gallery and connect it to the #3 cam bearing saddle. This is when you also open up the oil channel behind the #2 & #3 cam bearings (which is how all of the oil gets to that side of the engine.) If you’re installing anything in the distributor hole other than a plug you must also do the grub screw mod.

If you’re going to install the oil temp sensor in the location used by Volkswagen you need to pull the 3/4" plug to the lower-right of the oil pump and thread it to accept a 1/2"-NPT x 1/8-NPT adapter. The oil temp sensor then threads into the adapter.

If you’re running a full-flow oil filtration system (and you should) you tap the main oil gallery to accept a 3/8-NPT to AN8 (flare) adapter. Some engine-builders also thread the oil gallery leading from the oil pump to accept a 1/4-NPT pipe-plug.

If you’re going to run an external oil cooler you thread the oil cooler ports to accept pipe plugs.

And having done all that, it’s time to clean the crankcase.

No, you can’t just blow it out with compressed air. There are a couple of blind corners in the oil galleries that act as swarf-traps. To clean them out you must pull all of the soft aluminum plugs (except the two small ones associated with the oil pressure valve... you can check for contamination by using a mirror down the bore of the valve) . After pulling the plugs you tap the oil galleries to accept socket-head aluminum pipe plugs of the appropriate size: 1/16, 1/8, 1/4 and 3/8. Now you can scrub the bores and visually inspect them.

As with the ‘case kit’ You can buy a ‘plug kit’ but they don’t include the four 1/16-NPT’s you’ll need for the 5mm plugs. Instead, they’ll sell you eight 1/8-NPT’s and shug; that’s what they use in dune buggies.

And finally, once all the machining is done and the case is cleaned and sealed up, if it’s a magnesium case you paint it. Because if you don’t, it’s going to corrode. Use regular flat-black Rustoleum. If you can’t get flat-black use gloss-black cut with a little naphtha. (If it’s an aluminum case you apply Tech-Line Coatings ‘TLTD’ thermal dispersant then bake the thing in an oven not used for food preparation.)

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So what’s all that going to cost you? Dollar wise, it depends on where you’re located and how much of the work you can do yourself but at a guess, expect to pay between $150 and $400 over and above the cost of the crankcase. Here in southern California there are several good shops that do nothing but high-performance VW engines. In other parts of the country I know of guys who have paid twice as much and gotten less for their money. If you’re tooled-up to do the drilling & tapping you can cut the cost by as much as $200.

And that’s just for the crankcase. The cylinder heads, crankshaft, camshaft, pistons & cylinders, push-rods and push-rod tubes also require a significant amount of preparation before they’re ready to be used.

So hold your horses. You are not building a dune-buggy engine. You’re building an aircraft powerplant meant to deliver at least twenty years of reliable service. In future posts I’ll show you how I do it - - and why. It’s up to you as the Mechanic in Charge of your engine to decide if you want to follow suit.

-R.S.Hoover
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