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?
You originally bought a shoulder bolt, not a through bolt. On through bolts the overall dia matches the outer thread pitch. Buy a cheap set of calipers.
I think the entropy ray has been firing all over the place. Last week it hit our old trusty Expedition, causing it to become very lazy shifting from 1st to 2nd. So I decided to get off my butt and take my RX8 into the shop to get the AC fixed, as it had stopped blowing cold the last time I drove it. The shop said it needed a recharge, but isn’t sure where the leak is yet, so they recharged it with dye so that we can find out where the leak is. I pick up my RX8 and my wife calls me to tell me that the AC just went out in her car. So the next day we take her car in. Bad news is that it is the evaporator leaking, and the compressor doesn’t sound great either. $2500 for both repairs if we want to do it, but she’s been driving it for 15 years and 180k miles, so we might trade it in for something newer. While my wife’s car is in the shop, my in-laws ask if they can borrow our Expedition because they need to take their car into the shop. Bad news for them too, coolant leak that is a known issue on their car, and repairs are $4-5000. There is an extended warranty for the issue, but they are 4k miles outside the window. So entropy has hit 4 of our cars within a 2 week window.
Rolled vs cut threads. Cut threads remove material to make the threads, rolled threads are pressed into the bolt, similar to curling, so the average diameter is unchanged.
I thought this was common knowledge. Anyway, rolled are reputed to be stronger.
From time to time it’s a nice change of pace from engaging in small, mundane auto repairs of funny French cars.
Heh – The Battle of the Unexpected Bulge
or
NO ONE EXPECTS THE SHANK IS IMPRECISION!
Apparently there will be no Shank Redemption!!!
Sorry couldn’t resist!
The Flaw Shank Redemption? 🙂
Well done sir. He bought a shoulder bolt.
Even better. Are we having fun yet?
Every damn day
Sounds like you’ve got some more entries for your 2CV CV.
Oh just wait ’til you find out that you can actually adjust the suspension ride height on all four wheels on the 2CV! Whether your preference is standard, cool-low-rider or french-countryside-off-road.
Well, It’s probably rusted shut anyway… but in THEORY 😉
I’m all in on a lowrider 2CV
That’s what I’m here for. My level of interest in a bunch of wealthy-people car collections or yet another hypercar is as close to zero as modern instrumentation can measure.
Would this be akin to the battle of the bulge?
If the bolt don’t fit, you must acquit
This all reminds me of most of my experiences with plumbing components, which I’m convinced are designed to wear you down with incompatibility until you call a plumber, who then gives a kickback to the hardware or plumbing supply store.
It is somewhat maddening that no local auto parts stores carry those little cigarette lighter voltmeters. I really try not to order things from the jungle site, but I feel like my hand is being forced here. C’mon, NAPA, take my money! I’m willing to pay your 500% markup just to not give Bezos a couple of pennies.
If it makes you feel any better, the selling physical products is a very small part of Amazon’s profit.
AWS is their Golden Goose, half the internet runs on it.
You can probably find it from some independent vendor on ebay.
“Because, I assume, you enjoy hearing about small, mundane auto repairs of funny French cars?“
This would be an appropriate warning label for the entire site. Remember everyone, the first step to recovery is admitting you have a problem. The second step is coming here and indulging in that problem. Nobody knows what the third step is, and the fourth step, as usual, is PROFIT!
https://www.lowes.com/pd/Kobalt-0-35-mm-to-3-mm-Metric-Thread-Gauge/5013352665
Or better yet, get a tap and die set and it will almost certainly have one in there, and you can roll your own.
A die will cut the thread, but it most certainly will not roll it.
Ugh. I’m never going to sell all these metric threaded cigarettes, am I?
Smoke em if you got em!
There’s a part of me that would’ve done the dad thing – that being measuring the bolt, then choosing the closest drill size I have to it, then get out the cordless drill and “just open ‘er up a bit.” Because “I’m not driving all the way back out to Ace, damnit!”
I am glad you’re not like that, Torch.
Well – who has proper size metric through bolts in the States. I own a small drill press and indexed bits… Run a quick ream through it and Bob’s your uncle.
That is valid, but also you’d be surprised what obscure fasteners some of these locally-owned hardware stores will carry. Usually a bit better than a home center or farm store.
I’d have been tempted to grind that bolt down and send it. It doesn’t need to be terribly strong. Or drill the mounting holes to match the new bolt. Seems like more adjustment range is a good thing, no?
Hmm, I read this twice, but I missed the part where you did a lot of growing up. Hopefully you didn’t grow up too much; we enjoy you the way you are.
With the ability to heat your tires, you can now track this thing and avoid having to use external heaters, or swerving around the track as they do when following a pace car at slow speeds!