VW - Lower Tin-ware

The function of the splash shields (i.e., lower tin-ware which forms the exhaust plenum for the cooling system) is exactly the opposite of cooling, although there’s a footnote to that as well.

Here’s the situation: You are running at speed. You encounter rain, or a puddle, or you ford a creek (common stuff in Baja; no bridges!). Want to imagine what happens to your cast iron cylinders when they get an eyeful of water?

Situation 2. You’re running at speed, the air under the vehicle is at higher than ambient pressure. Beneath the cylinders the cooling air encounters higher exit pressure at cylinders 1 & 3, reducing cooling air flow. The result is that the portion of the cylinder at the 1 o’clock to about the 3 o’clock position (for #1 cyl; 9 to 11 for #3, in each case relative to an observer looking into the cylinder from the valves) is running hotter than the portion of the cylinder from about 4 to 6 (i.e., 8 to 6), since that lower portion is being super-cooled by the blast of air provided by the vehicle’s forward motion.

Situation 3 is as described in my sermon on push-rod tubes; they are part of your cooling system. But they are also part of your temperature control system, in that they help the oil heat faster thus achieving a stable operating temperature more quickly.

When the engine temperature is stable the engine performs more efficiently and with less wear. The splash shields form a plenum chamber for the cooling air exhaust, allowing the cylinders to enjoy a uniform airflow regardless of vehicle speed. Plus their name sort of gives it away; liquid water can cause sudden contraction of the cast iron jugs, resulting in oil leaks around the lower spigot and compression leaks at the heads. Bad things happen to a hot air-cooled engine when it gets doused with water. The splash shields form a baffle, and so long as the blower is blowing, very little water spray ever contacts the cylinders... and no liquid water at all... unless you’re really trying to win.

We learned all this the hard way, stripping our baja’s to the bone. Less weight, more acceleration. We eventually saw that Volkswagen engineers had already been there, done that. In the end, we re-designed our skid pans to perform the baffling/shielding function and thus ended a host of problems that had plagued us since our attempts to ‘improve’ on the original design.

If you really want to improve your engine, look at the Porsche, Corvair or the late 2000cc Type IV’s. Then work backwards, retrofitting to your bug or bus features found on those engines such as better lower shrouding (i.e., Kool Tin), shaft seals (i.e., Sand Seals), hydraulic lifters, full-flow oil filtration, electronic ignition, an external oil cooler (Dog-house Cooler) and so on. It’s really pretty easy to be a VW guru when Volkswagen, General Motors and Porsche has already paid the engineering bill.

-Bob Hoover