Monday, August 6, 2012

The big bodge

I couldn't quit. Although I was pretty exhausted after Saturday's long bodge-a-thon in the heat, I had to have another go at it Sunday. And, long story short, after much use of the old thinking cap, it worked. Finally, we have a quiet land Rover.

Here's what I couldn't see when I gave up on Saturday afternoon. The new stud had cracked off, taking a sizable chunk of exhaust manifold with it.

Ordinarily, this wouldn't be repairable, but there was just enough of a hole there to hold the stud in place while I welded it, and the manifold was off, the welding rig right there, and off course, I had one-and-a-half sticks left of 50% nickel-alloy welding electrode.

Probably if the electrode had been 99% nickel, this wouldn't have worked, but there was enough mild steel in there to fuse with both the black iron stud and the gray cast iron head.

Metallurgy is an interesting area of study. I'd love to know just what those iron atoms think they're doing in their various crystal lattices.

Trying to fool us poor mechanics, is what. Clever little buggers, they are.

I was pleased with the results of my bodging though, not so much because I think I saved my part here -- the weld, or something else on this heavily compromised exhaust manifold will break, and we'll need to have that new one on the shelf.

Indeed, and although this is a violation of "if it ain't broke, don't fix it" rule, it would be better to switch out the manifold as soon as I can whether or not it breaks again.

But what I was most pleased by is the new capability we have now we know I can weld cast iron to cast iron, and cast iron to mild steel. I can think of lots of potential vehicle and farm equipment problems that might be solved with that new skill.

Once welded, I decided to take the extra step of test-fitting the downpipe to the manifold on the bench, to find out if there was anything else wrong I couldn't see when the unit was in the car. There was. This is when is where I realized I still needed to drill out the holes on the downpipe flange (from 3/8ths to 7/16ths). The new oversize studs fit through the downpipe flange holes all right, but they're not properly square to the manifold flange like the old ones, and so they put pressure on the manifold as they're tightened down. Hence the piece that cracked off. Reaming out the holes using the drill press relieved this pressure.

That simple test fit, and the reaming job, was what was needed to make it all go back together smoothly.

The next job (because I was done with the exhaust system by 10 am) was to have another look at that carburetor.

On the second reading, the two technical bulletins mentioned in yesterday's blog no longer seemed to contradict each other. The aluminum alloy components of the Zenith 36IV carb are prone to warping as a result of improper heat treatment of the castings at the factory. (More metallurgy!) The mating faces warp and no longer fit together, allowing gas to leak from the main circuit to the idle circuit and adding too much gas to the main circuit. Although a temporary cure for a rough idle can be obtained by plugging one internal orifice with a bit of o-ring, a better overall cure for both the idle and main circuit leaks is to gently grind down all the carb's internal mating surfaces on a proper flat grinding surface.

Although I knew I needed the proper gasket to finish the job, I realized that I might as well have a go at the grinding job since I had the time to do so, and since while I might not know for sure whether or not I succeeded until I had the proper gasket, I could very well determine whether or not the surfaces had been properly made flat using a engineer's steel ruler as a straight edge.

Ideally, and according to my very proper British engineering training, you'd use a flat lapping plate made of machined steel and some engineer's blue marking paste for this job.

But a piece of plate glass, some 150 and 220 grit emery paper, and a shot or two of "three-in-one" oil were adequate substitutes. I happened to have a small six-inch square piece of 1/4 inch plate glass that I keep as a spare for our woodstove's glass door, which is also prone to cracking, and a bunch of different kinds of sandpaper. I might as well give it a go.

I could clearly tell I was succeeding by the appearances of the surfaces. To begin, the mating surfaces were only scratched clean around the screw holes. After a little more very gentle elbow grease, the clean area extended slowly across the whole assembly. Although even once the whole surface was scratched clean there was still light visible between the steel ruler and the two mating surfaces I stopped grinding at this point, reasoning that the gap was only about a thousandth of an inch, and the gasket, when it finally came, had to be at least 3/1,000ths thick. It wouldn't hurt to leave a little metal there for future grinding, if the surfaces continued to warp.

I cut a new temporary paper gasket using the same technique as before, put the carb back together and back on the vehicle, tried the engine, and was rewarded by the proper purring, ticking sound of a quiet Rover engine, running much better than before, especially at anything above 1200 or so rpm.

It actually runs well enough at operating speeds that I took it on the road.

The engine still won't idle correctly, and so you wouldn't want to be in traffic with it. There's a lot of black smoke below 1200 rpm, so it's still running rich, a condition I expect will resolve itself once I get the proper, thicker gasket. I also saw a good deal of wear on the accelerator pump spindle, and so will be looking for something in the gasket kit to resolve that problem, as well as a new o-ring for the venturi.

Failing that, we'll buy a new carb as well as a new exhaust manifold when payday comes around again.

I was pretty content as I washed up and ate dinner and rested. I even had an extra glass of rhubarb wine. My car isn't properly fixed yet, but I know know it can be made to run very well indeed, and soon.

I've been thinking about it, and I've finally figured out what it is I like so much about this Land Rover work.

The Land Rover is an engineer's car, designed by British engineers and tradesmen for engineers and tradesmen to work on and drive. At every juncture of the design, whatever function they were thinking of, from windshield wipers to drive train, the designers asked themselves "what is the simplest, most straightforward way we can provide this functionality." As a result, the car is very repairable, almost completely so. It might be possible to total a Land Rover in a crash, but there isn't any condition of normal mechanical wear I can think of that is would be mechanically impossible, or even cost-ineffective, to fix.

You can, therefore, literally keep these things going forever.

A long time ago I worked on old Royal Air Force training airplanes, Jet Provosts, Bulldogs, and Chipmunks. The Mark 3 Jet Provosts and the Chipmunks in particular were antiques even then. I worked on them from 1978 to 1985, and the oldest ones I worked on had been flying since the 1950s. But they were safe to fly for the simple reason that they were eminently repairable. Any part could be exchanged if it wore out, and there were no fatal flaws in the design. The series Land Rover is the same way.

More than anything, it responds to reason.

With reason, logic and a little skill with tools and technique, you can fix anything that needs to be fixed.

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