Remember last week – holy crap was that really last week? – I was complaining about some mysterious entropy ray that must have hit my Citroën 2CV, because I had two odd failures pretty much at once: some little bits from my shift linkage returned unexpectedly to their home planet, and then one of the bolts holding my alternator in place snapped in two. I fixed the shift linkage pretty quickly, but the bolt took me a bit longer to source and fix. And now I’m going to tell you about that! Because, I assume, you enjoy hearing about small, mundane auto repairs of funny French cars?
There’s a little bit of a bolt-related mystery here, and a little lesson I learned as well that perhaps you may benefit from, too, so perhaps I won’t be entirely wasting your time. We’ll find out, I suppose!
Okay, just to recap, the root of my problem was that a long bolt that holds my alternator in place – and, relatedly, helps keep tension on the belt that drives it – broke, after what is likely many decades of tireless service:
Now, the repair isn’t exactly complicated: I just need to replace that bolt, get the belt back on, adjust the alternator to get the proper belt tension, and there you go. But, as always, there are always some complications.
The first one I found was trying to find a good replacement for that bolt, which proved harder than I would have thought. When I finally found one of the right length, or close enough, I checked that its diameter would fit through the holes by seeing if the original nut would fit.
It did! The thread pitch looked more coarse, but it threaded on just fine, which I took to mean that the bolt itself was the correct diameter to slide through those (unthreaded) holes.
It wasn’t.
I was pretty baffled about this – if the nut fits, that has to mean the diameter of the bolt is correct, right? Why would it not fit if the nut fit? Eventually, I really looked at the bolt and saw why:
Ohhhhhhhhhhh. The bolt increases in diameter after the threaded portion! Why? Just to make me think I was going crazy and the laws of physics didn’t fully apply within the engine compartment of my 2CV? Until I saw where the bolt shank increases in diameter there, I had no clue what the hell was going on. They should put a warning sticker on bolts that do this!
After I figured this out, I went to a hardware store and just got a bolt and nut that would fit close enough; this isn’t exactly a precision thing, it just needs to hold that alternator mount in place.
To get the bolt in, I had to remove one of the heat exchangers, which provided two extra perks: first, the process made this fun sooty “brand” on my arm from the exhaust header:
…and second, it gives me a nice thin justification to talk about the 2Cv’s heating system, which is pretty much the same as the one in a VW Beetle, and, really, many air-cooled cars like early Porsche 911s. Here’s how it works:
Those black boxy things are heat exchangers, and they’re the core of everything. All they really are is an exhaust pipe enclosed by a secondary outer pipe. The inner pipe has hot exhaust gases in it, while the outer one has fresh air that’s been pulled into the car by the cooling fan. Ideally, these two gases in pipes – outside air and engine exhaust gases – will never mix, otherwise you’re going to get asphyxiated, which I’m told is “bad.”
So, the cooling fan pulls in air from the grille, it passes over the hot fins on the cylinders, taking away the heat, and then flows into the heat exchanger, where the hot central pipe of exhaust gases heats the fresh air even more. The heat is exchanged, you see, from the hot gases in the inner piper to the fresh air in the outer.
Then, if you have the heat turned on, flaps will guide that hot air into the cabin, via floor vents or windshield defroster vents, and if its off, those flaps send the hot air out of these outlets that exit behind the front wheels in the fenders. So, I guess a 2CV kind of has heated tires, too.
The central exhaust pipe in the heat exchangers is just a pipe; on the VW heat exchangers, this pipe has heat radiating fins, which seems more efficient, but then again the Beetle has to pump that hot air all the way to the front of the car, while the 2CV has a much shorter path, so I suspect the resulting heated air temperature is probably pretty similar in both cars.
Anyway, after removing the heat exchanger and getting the new bolt in and all nice and tensioned, everything buttoned up nicely. I started the car, and look! The alternator is alternating again!
All is right in the world one again. And the lesson here is, um, don’t trust just threading a nut to assume the diameter of a bolt? Sure, why not?
The post I Fixed My Citroën 2CV And Learned A Weird Lesson About Some Bolts And Did A Lot Of Growing Up appeared first on The Autopian.
