Agreed. The probability that I would ever come across this while browsing elsewhere is trivially low, and yet it was interesting enough to read through and learn a bit about piston maintenance.
I was looking for something else (automotive, but not related to pistons) when I came across this. The style of illustration and prose isn't so common in modern technical writing either, so it caught my attention and made for a very enjoyable read. It's fun and lighthearted, but that doesn't get in the way of being educational.
Some further searching reveals that there is a whole series of these with accompanying slide films:
Imagine if Tesla made booklets and videos like these for the technology in their cars... I guess 70 years ago companies were far more open with sharing such things, and willing to spend a lot more on it too.
> I guess 70 years ago companies were far more open with sharing such things
Thanks for this post I upvoted a few of your comments. That said being a bit older and in business for many years (since college) I think it's the opposite actually. When I was 'growing up' in business you didn't share your secrets or give out any information whatever that would be helpful to your competition unless it was disinformation. So this didn't start with Steve Jobs and Apple it was pretty much status quo for all business. The internet changed that and I think at least one of the reasons was the involvement of academics who were more used to sharing what they knew.
There was a time when all electronics had detailed service manuals with discussion of theory of operation and troubleshooting checklists. Early PCs came with ROM listings. The techo-secrecy culture set in during the 90's.
Will Eisner's work in PS Magazine[1] detailing preventative maintenance procedures for the army was in a similar vein. It was presented in full comic book form though, and seems like it was heavier on the entertainment than the information.
now they attempt to void your warrenty by plugging in a cable, and they know because they are always remotely monitoring the car, and whats more lots of people agressively defend behaviour like that.
We are witnessing the end of ownership for anybody that isnt hyperich.
Modern pistons have much less contact with the cylinder wall. The part Chrysler has "cam ground" is no longer even part of the piston -- it's missing! The main job of the fit is the rings, not the piston. Right, for the "thrust" parts, they are still there and much thicker than what Chrysler was showing.
There's much more now, e.g., titanium connecting rods.
I think also the machining has become more accurate.
I am old enough to remember when it was ordinary (for 2 strokes single cylinder race engines - think of karts or motcross bikes) to mount the piston in the engine, do a few kms/laps then disassemble the piston and remove with a very fine ceramic file where the aluminium became shiny, rinse and repeat 5 to 10 times.
When I was a kid plain old automobile engine breakin was a complicated dance of not overheating the engine but not running it too cold for the first 3000 miles and multiple oil changes like one at 500 miles and another at 1500 before setting down to normal use. Of course cars only lasted 50K miles back then before rusting out or breaking down, so you spent some significant fraction of the life of the car babying it.
Modern car break in procedures are like "don't do anything ridiculous for the first 500 miles, then it'll last at least 200K miles"
That's the effect of computer controlled machining to a fraction of a ten thousandth of an inch on all parts vs merely to a thousandth or so in the old days.
>That's the effect of computer controlled machining to a fraction of a ten thousandth of an inch on all parts vs merely to a thousandth or so in the old days.
Not at scale they don't
People get paid very good money to figure out how to get near equivalent results using wide open tolerances that any random supplier with run of the mill facilities could meet.
Certain parts might be spec'd to less than a thou. Nobody who wants to keep their job is going to spec out a tolerance on something that both wears over the life of the system and cannot easily be replaced to less than a thou. Ball bearing balls, sure. Crank journals, nope.
>That's the effect of computer controlled machining to a fraction of a ten thousandth of an inch on all parts vs merely to a thousandth or so in the old days.
Not only, if I were to select one single reason for the increased reliability of modern engines I would select the enhancements in tribology/lubricating oils (and to a certain extent also to "better" fuel, particularly for Diesel engines).
Hate to disagree, but there are some things much better than oils, etc.
The secret is now out but long was not: Often the poor engine suffered that agonies of the damned. Why? Too much gas and water got into the oil, ruined the lubricating qualities of the oil, and made the engine wear out much faster. The worst situation was running the engine cold in cold weather. In particular there was that little device, the "choke": It's job was to flood in lots of excess gas hoping to get an explosive mixture from the cold air. Well, a lot of that gas didn't burn, got past the piston rings into the oil. Similarly for water from condensation.
The big step up was to have some exhaust flow under the intake manifold to heat the incoming fuel-air mixture to do better vaporizing the gas and need less extra gas from the choke.
What solved that was fuel injection, in various forms, throttle body, port, and cylinder. Then the pressure on the gas was high enough to get good vaporization.
Next biggie was spark timing: Usually it was far from where it should be again causing inefficient combustion and gas and water in the oil.
One of the most critical needs for lubrication was the rocker arms, e.g., where the rocker arm was pushed on by the push rod from the lifter on the camshaft. On a classic small block Chevy, I had a push rod go through rocker arm and the valve cover! We got a new, 'crate', engine via Chevy.
"Of course cars only lasted 50K miles back then before rusting out or breaking down, so you spent some significant fraction of the life of the car babying it."
Oh wow! Seriously!? This is so crazy to me. People always talk about how things were better made "back in the days" but I was always skeptical of that. I haven't lived long enough to know this first hand but being a technology oriented person, I've always assumed things generally get better engineered over time.
Your experience is genuinely shocking because my 2013 BMW has 55,000 miles now and still runs like it's new. I looked under the hood recently just to check on it and the engine bay is still perfectly clean, no oil leaks, etc.
It was partially by design, and partially limitations of technology. It was not quite as bad as 50k though, the EPA estimated the EOL for a vehicle at 100k miles in the 1960s.
Having (unfortunately) the age to remember how it was (and how it is now) the "shift" is for certain aspects non-existing.
In the sense that why it is entirely true that cars (not only the engines, but also the clutch, and brakes) needed a lot more maintenance and much earlier repairs/replacements, the cost of them was relatively low.
The big advantage is that you can run now a car for thousands of km/miles without doing anything to it and - usually - it never stops/breaks. (but when/if it does, your wallet will notice it)
Besides the "almost continuous" oil changes and filter replacement, once upon a time it was "normal" if you were planning to make a - say - 500 km trip, to go a few days before to the mechanics and having him check the car, and anyway you rarely had a clutch go beyond 60,000 km (40,000 miles) or (drum) brakes go beyond 40,000 km (and registered/checked every 20,000 or so), and the same goes for minor components (that someone that only had "new" cars probably don't know they even exist) such as the steering rack, rod ends, wheel bearings, all of these were routinely replaced or fixed at a relatively low mileage, besides needing to be "constantly" greased manually.
But for example the water pump, that rarely lasted more than 40/50,000 km, was fixed by disassembling it, replacing the bearings and seals, with a cost of a few dollars.
Nowadays you replace it only maybe once in the life of the car, say around 100/120,000 km, and it is easily a 300-500 US$ job.
The only thing that I find has gone "for the worse" (though there are reasons for the change) is the timing belt.
Old engines had a timing chain instead that never broke in 120,000 km or more (in some rare cases it may have "jumped over" a tooth of the sprocket, going slightly out of sync) and even when it broke, the engine was built in such a way that the valves had no interference with the pistons, if the timing assembly broke the engine would simply stop working, and in any case you could "hear" that the timing chain was worn out by the typical "ticking".
New engines timing belts need (in some cases) to be changed much earlier, like 40,000 km or so, and the issue being that they break more easily and when they do they do it "suddenly", and since new engines are more compact and differently designed (for efficiency/low consumption), when a timing belt breaks it will inevitably bend some of the valves (if you are lucky) or break the engine head (if you are unlucky) in both cases you have before you a mechanic's bill of several hundreds or a few thousands dollars.
As well, a modern car very rarely leaves you in the middle of a trip (unlike old cars may have), but the difference is that in the old times in most cases any mechanic/pump station would have repaired it somehow with available pieces, whilst now - in the much more rare case of an issue - you typically need a replacement car because what has broken is a small piece (often electronics, like a sensor) that local spare parts warehouses (where they still exist) do not have in stock, and that needs to be ordered taking two working days to get delivered, and possibly the replacing needs to be carried on by an authorized dealer because a special software is needed to do the pairing with the new sensor.
Can't say I've ever heard of a cammed piston. That was a fun read. I wonder if it just isn't used anymore because most applications now use forged aluminum and very short skirts. I haven't heard of pistons heating up non-symmetrically that would warrant that shape.
I wrote my diploma thesis in an industry research group trying to figure out the optimal (non-cylindrical) shape of the cylinder bore.
We attempted to model static stresses from mounting the cylinder head, thermal stresses, and mechanical stresses from mass forces, combustion forces and the like.
Our goal was to achieve low combustion gas blow-by, low oil ingress into the combustion chamber, yet low friction between piston and cylinder wall.
We used simulations (about three months worth IIRC) and measurements to generate data points for a continuous ersatz model of the physical phenomena, then performed multi-criteria optimisation on that model. The resulting shape was interesting, but not exactly earth-shattering. Kinda randomly warped.
This work was tremendous fun, and I learned a lot.
Top image is the cylinder shape without optimisation, bottom is the optimised shape.
Obviously, the contour distortion is massively exaggerated (ISTR a factor of 1000), otherwise it wouldn't have been visible; we're talking micron scale here.
I think nothing in the article is actually obsolete. Possible though that using modern computer aided design allows for better control of how the piston expands.
Thermal mechanical stuff is a big pain. One of my professors mentioned as a young engineer measuring expansion on exhaust manifolds by drawing faint scratches and microscope to measure how far they stretched as the manifold got hot. Important because localized thermally induced stress causes fatigue cracking.
I'd be surprised if they don't take asymmetrical heating into account when designing pistons of today, the oil cool the piston from below, and combustion heat it from above. But I can imagine that the effect is less, because emission regulations have been driving down combustion temperatures.
Bulk material is the water jacket temperatures. Those were the old days of 160F coolant temps as per the somewhat amusing artwork. My modern car has pressurized coolant and the thermostat doesn't even start to open until 180F. You are correct about combustion temps, but bulk materials like the cylinder walls and pistons run much cooler than combustion temps, yet bulk material temps generally only increase over time.
Most applications use hypereutectic pistons. They run better cold than forged but can't take the punishment of detonation as well. Skirt dimensions have to do with rod stroke and bore specs, you don't want too much side load on the cylinder wall nor do you want too much weight.
I quite like how it explains basics physics mechanics of heat expansion and contraction - i.e. you expand the piston in hot water and you don't have to use a hammer to take out the pin...
Sometimes I wish I had an apprenticeship in a car garage so I could learn all this cool esoterica. Eventually, this type of information will be relegated to the back of the library as combustion-engines in cars get phased out and electric motors take over...
This type of information is already largely relegated to the back of the library. I don't know a mechanic that has re-built a modern engine at this level. Reliability is so high and failure modes are probably generally more catastrophic (someone didn't change the oil) and warrant an entire engine replacement.
Plus, I'm curious if the economics work out at all anymore. Mechanic billed at $100/hour. How many hours does it take to rebuild anything to the piston level, versus the cost of a new (or used) replacement engine just dropped in place. I suspect they favor a replacement engine.
Exactly, car engine rebuilds are for hobbyists and mechanics working on very expensive or rare engines. But you are more likely to find a diesel mechanic rebuilding a 18-wheeler's engine.
> I don't know a mechanic that has re-built a modern engine at this level.
I do. Worked for my father and grandfather in my teens and early 20s. Water-we’ll drilling, so lots of gas and Diesel engines, as well as pump work, including high voltage AC and DC motors.
At the time, I thought it was “normal”. Little did I know.
Interesting, I know the word from early aircraft where dope was used on the fabric skin to tighten and strengthen it. The dope used was a thick gloopy soup.
