Friday, November 24, 2006

VW - How to Prevent Engine Fires in Air Cooled Volkswagens

A trite phrase sprang up in southern California in the late 1960's following the introduction of the fuel injected flat fours. "There's only two kinds of Volkswagens: Those that have had an engine fire and those that are about to." But the odd thing was, veedubs have always had engine fires, and in the case of the bugs and buses, the cause was almost always the same.

In over 90% of early VW engine fires (*) the steel fuel line breaks where it passes through the breast tin on the driver's side of the engine compartment. The broken line dumps fuel directly onto the neck of the #3 exhaust outlet. The rest is history. Once the fuel line breaks, gravity keeps the fuel flowing to the fire. When the magnesium tranny housing heats to the point of ignition, even water can't put it out.

Why does the fuel line break? Because of the failure of the rubber grommet where the steel fuel line passes through the forward breast tin. Located only inches away from the the #3 exhaust stack, which runs red hot, the grommet soon hardens. Vibration does the rest, first crumbling the grommet then providing the motion that allows the breast tin to cut through the steel tubing like a hacksaw. A dull and toothless hacksaw but one that cuts a lot faster than you would think. This scenario of component failure and wear is generally known as The Engine Fire Syndrome.

The fix? Make a bulkhead fitting.

You can make a bulkhead fitting that's good enough for the job using lamp repair parts, purchased at a hardware store. The light socket is attached to the lamp by a piece of threaded 3/8" steel or brass tubing. The threaded tubing is widely available, often sold bubble-packed in an assortment of lengths. You need a piece about an inch long. Matching nuts are sold the same way, they are usually hanging side-by-side among the other lamp repair parts. You will also need a pair of flat washers with a 3/8" center hole. Be sure the washers are large enough to cover the hole in the breast tin. Fender washers work best but you'll have to drill them out to pass the threaded tubing.

Assemble the parts so as to sandwich the breast tin between the two washers. To make sure it doesn't come apart, bed the washers and nuts in high-temperature RTV compound. It's messy but I've found this is the only assembly method that stands up over the years.

In proper terms, what you end up with isn't a bulkhead fitting but a pass-through. And what you pass through it is a piece of 5mm steel fuel line (that is, regular VW fuel pipe) about three inches long. Bed this in RTV as you insert it into the threaded sleeve with a twisting motion (but don't get any in the fuel line). NOW you have a bulkhead fitting. Use regular push-on fuel line (but with clamps, please) to connect to the bulkhead fitting and you're all done.

The Engine Fire Syndrome was first identified about 1958. Despite frequent fires, VW showed no interest in fixing the problem, insisting the lame rubber grommet they used was good enough so long as someone inspected/replaced it every 3,000 miles or so(!), which they did, back when there was a VW dealer in every town and service was cheap.

Making a bulkhead fitting from commonly available parts will prevent a lot of engine fires but the fuel system on early Volkswagens remains a compromise between safety and cost. Having invested considerable time and money keeping our bugs alive, it seems silly to put that investment at risk by using push-on fuel lines. Threaded aircraft-type fittings are a better solution; the carb and fuel pump can be modified to accept such fittings. Using a true bulkhead fitting through the forward breast tin, and braided stainless steel flex lines between there and the carb, will give you the safest possible installation.

If you're serious about safety and long-term durability, you may wish to carry the fuel line modifications all the way through to the gas tank, even to replacing the fuel pipe in the center hump with stainless steel tubing. This is best accomplished during a body-off resto. Once things are back together you'll know your fuel system will never fail.

A neat trick that gets around the difficulties of replacing tubing in the center hump is to run a new 3/8" diameter stainless steel fuel line externally. It is protected by a piece of 3/4" angle iron welded to the belly pan in the form of a 'V'. A bit of artful grinding and some careful bending allows the angle iron stock to follow the contours of the belly pan stampings. Tacked and then welded full-length, the modification is strong, attractive and durable.

I've been working on VWs since 1956 and have seen, personally or in photos, the results of several fires as described above. The cause of the fire was often overlooked because the steel fuel line appears to be intact. But on cleaning away the fire's residue you'll discover the tube is cut half through, which for a fuel pipe is as far as you need go to make the juice flow.

(*) That was then. Nowadays VW owners have come up with an even easier method of setting their cars on fire. How? By simply adding an after-market fuel-filter to the rubber hose between the fuel pump an the carb. Over time, the vibration due to the added mass of the fuel-filter causes the brass ferules in the fuel pump and carb to loosen. Once they come loose, the engine is bathed in gasoline and another bug or bus becomes history. Fortunately, it's easy to fix and the procedure is included in this collection. -rsh, 2006

1 comment: said...

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