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 once again. And the lesson here is, um, don’t trust just threading a nut to assume the diameter of a bolt? Sure, why not?
I’ve never met an air cooled exhaust heat exchange system I trusted. Simple, cheap, solutions make sense for extreme budget constraints, but over time, it seems doomed to fail. By the looks of that rusted exhaust tube, guessing replacement is past due. Don’t like the grey foam in the cardboard tubes either. Reminds me of the disintegrating chunks that would occasionally blow out of the vents of various water cooled VWs I’ve had. Other than that, Congrats!
those tubes are new, at least!
I wish you many happy years of ownership.
I’ve long ago, turned my back on admittedly fun, if you have the right mindset, “Needy”, “constant work in progress”, type vehicles.
I’m not looking to generate “content”! Just a couple of weeks ago, my otherwise near mint MB, sunroof drive motor cog decided it would rather split into 3 pieces than continue its service. Had to tarp it for a week while waiting for 2 shipped from China. No U.S. inventory! (We’re F’d)
I’m looking at “Aircraft Flexible Ducting”, SCAT or SCEET type, as a (hopefully) permanent replacement for the cardboard ducting in my 67 Beetle. Not cheap, but mostly under $20 a foot and I won’t need that much. (Aircraft Spruce & Specialty)
There was a time when we all knew
What was butcus and what was true. We exist, We must rejoice, time is fleeting, if it exists. We have but now, make the most, before we,re All just a bunch of toast. I sounter though knowing not, what best to do. We have only have but one of me and only one of you.
There was a time when when laughed, alas the time has passed. I fear not now, but what will be. There was a time, when we were young, our story sought, but not yet song. Our children must be tought, what we did wrong, lessons learned, but not abbided. This I fear, our legacy forbidden. Shall we have a future, or by our means smitten.
We only have our selfs to blame. Will we continue, or will it be shame.
Replacing the crumbling foam on the blend doors and in the vent tubing of my almost 40 year old pickup while replacing the heater core was one of the most satisfying things I’ve done on it. It felt better than the full engine rebuild, honestly.
I would think that with a die and tap set, you could cut the threads past the bulge
It’s not really a bulge but the entire unthreaded potion is larger in diameter.
yeah, i think you’re right. It looked like a little bump or something. You could thread the whole bolt with a die, if you had to.
This is the issue. Most common hardware store bolts have an unthreaded shank of a larger OD than the threaded section. It appears Citroen used a shank of the same OD as the top of the threads.
I ran into that many years ago while trying to make a cheap BMW Airhead clutch disassembly tool. Fortunately Metric and Multistandard had some 70mm long M8x1.0 cap screws so I didn’t have to get creative with bolts. (a cap screw is fully threaded, a bolt has a plin shank)
That would probably not work
I think what you’d really need is a lathe to cut it down. But then you lose any galvanization or other anti-corrosion coatings.
Only the threads need to be rust-resistant. The rest of the shaft, eh.
Fastener nerd here and longtime lurker, first time commenter; I can’t tell if the old bolt is cut or rolled thread but the issue is not that, it’s the blank shape they used before threading; consider head studs since they have rolled threads but necked bodies to clear the internal threads in the block. Prob just different standards between 1940s France and modern US ones…
The new bolt is most certainly an in-feed style rolled thread. The original is prob cut, but could also be rolled. Rolling can have the effect of increasing the diameter of the base material because you are displacing it versus removing it. But that newer bolt doesn’t, but it’s still definitely rolled.
With all the intricate-knowlegable people like you here in autopia, I feel eventually there will be a David Tracy project where he crowd-sources everything at every step. Will probably end up being the best built thing he ever owns.
that voltmeter also improves gas milage and your electric range!
It aligns the ions in the fuel
Which makes it tastier!
You learn something new everyday. I always thought heat exchangers were gay discos.
I took a tour around Paris is a 2CV this Summer. Apparently, those heat exchangers work well in the Winter, and even a bit in the Summer, too. So if you think it’s making the cabin too warm, apparently you can pull that cabin pipe and stuff a tennis ball in its place, just like on our touring car.
Love that solution.
Of course! I’m used to fasteners that disappear entirely, not ones that snap.
Funny French cars often have minor parts disintegrate into pixie dust and croissant crumbs.
60 years of cyclic fatigue.
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 was going to call you out but I guess they are called this. Shoulder screw or shoulder bolt to me is this: A screw with a shoulder to stop it entering the threaded hole and a shaft that acts as a pivot or retainer without applying clamping force..
You are correct, but most general hardware store bolts are shoulder bolts unless specified otherwise.
Shoulder bolts are different than this, for sure. But, I can see how you might suggest this one is one too.
When I hear shoulder bolt, I am thinking of a socket head shoulder screw, which is entirely different from this.
I have some concern that given the vibration of the engine, the finer pitch of the original screw may be necessary in order to not work loose, as compared to coarser pitck of the first replacement shown.
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.
Oof, that sucks.
The entropy ray hit me last week, too. I decided to flush the pondwater coolant in my 1980 Fiat. While I was running it to temperature, the car died. Bad alternator. So, I decided that, if I have to wait for the alternator to get here, I’ll order the timing belt and water pump and do it too. So I’ll repeat what I said last week, “If all goes well, I’ll have it running and driving this weekend.”
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.
Diameter can be whatever you design the fastener with. But rolled threads are definitely stronger without any post processing.
Well, yes, but that take extra steps in machining. I have lots of fasteners with multiple thread pitches, diameters. And more than a few with right and left hand threads on the same thing.
Sometimes do you ever get the urge to buy one of these?
https://a.aliexpress.com/_mKvCmmP
I wonder how many sctews it would make, it’s so cute!
Fully Automatic Screw Machine 110V-220V Arrangement Machine M1-M5 Screws Feeder Tools Track Screw Supply Machine
This description is horrible. What does it do now?!? Sort? Align and supply? It’s just so vague. Does it roll screws?? What does my $270 buy????
Yeah, I can’t quite figure it out.
Nor can I tell if it’s worth $270 to find out.
Perhaps I should start one of those buy stupid stuff and do stupid things YouTube shows? Channels? Aggregations of streamable files?
I think they call them channels, but that seems totally wrong.
There is a guy I run into at make and break engine meets (I’m worse than a nerd, I’m an anachronistic nerd) that has a 19th century screw making machine. You feed a long steel rod into one end and it spits out screws. I think it spits out a lot of swarf too, but it goes somewhere else. Slotting the head is done by another machine, but his can knurl thumbscrews.
Apparently it’s a device to arrange screws to be easier to grab with a screwdriver on a production line.
I would have been quite disappointed.
Unrelated to anything here, but FYI. AliExpress is very aggressive about tracking users, even accessing your computer’s audio system.
I personally wouldn’t go to their site.
https://cybernews.com/security/aliexpress-alibaba-audio-systems-tracking/
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.
But hopefully he doesn’t need new CV joints for a while
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
I hear the faint strains of War – Lowrider being played in a jaunty Parisian fashion.
So now I’ve located several jaunty accordion versions of Lowrider … Thanks. (I think.)
Gotta wear your best beret to *feel* those accordion jams.
Yvette Horner!
Well maybe Zeena Parkins?
Is that in the pre mid 70s moving mass suspension? So sophisticated it was banned from F1?
I’d like to get an early one from when they didn’t have shocks, and do a bmw swap.
Adjustment on the longutudinal tubes, no matter if it’s got the old or newer type shock absorbers, couldn’t find a good picture online, there’s probably a better one in the Haynes manual 🙂
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.
Just PC plumber it until it fits, nothing could possibly go wrong.
In all honesty shark bite has made fittings so easy these days.
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.
Don’t forget all that Slate money!!!
How do we not support Amazon’s AWS? Is there a competitor?
You use it in some capacity whether you know it or not. There are competitors, but frankly they’re not one I would support either if I had a choice.
You can probably find it from some independent vendor on ebay.
Yeah, but several times I’ve ordered from EBay, but had the order fulfilled by that company featured in the film Nomadland. This is permitted by EBay under certain circumstances, see https://www.ebay.com/help/selling/posting-items/setting-postage-options/drop-shipping?id=4176
Try one of the chain drug stores. They sell lots of cheap crap like that.
“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?
you’re screwed
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 know – my local Do It Best has a FAR better hardware selection than the big boxes. I also have a Fastenall nearby.
My Local Do It Best affiliate has “a mile” of fasteners. They seem to stock every Midwest assortment for all the little fiddly bits, but also have so many bulk bins and boxes of the bigger and more common sizes. They also have a number of Avue Co. bins of automotive specific christmas trees, scrivets, ect.
Then by work there is a Fastenall though I normally drive by it to Tacoma Screw.
Good point, that aluminum bracket probably has some heavy oxidation on the ID making the fit much tighter.
…I was trying to portray the character as a spendthrift and maybe a bit reckless…but yes, maybe carefully opening it up slightly would work as well. The fact Torch found a bolt that fit kinda tipped me off that the Citroën bolt was “correct” and maybe drilling it out was the wrong move.
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.
Yeah, I thought maybe there’d be a missive about how from now on he’s going to fix things properly with the right parts and whatnot.
In his opening Torch alludes to being one week older
One week is very important at certain points in life
Ah, but getting older is not the same as growing up.
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!