
1947 Imperial and Chrysler Service Book – Cam Ground Piston - userbinator
http://www.imperialclub.com/Repair/Lit/Master/003/cover.htm
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donatj
This is super neat. Interesting read, my favorite kind of random thing to find
on HN

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larkeith
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.

~~~
userbinator
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:

[http://www.imperialclub.com/Repair/Lit/Films/index47.htm#194...](http://www.imperialclub.com/Repair/Lit/Films/index47.htm#1947)

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.

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gist
> 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.

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kevin_thibedeau
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.

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graycat
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.

~~~
jaclaz
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.

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VLM
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.

~~~
jaclaz
>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).

~~~
graycat
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.

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burger_moon
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.

~~~
InternetOfStuff
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_.

If anyone is interested (and can read German), it resulted in this
dissertation:
[https://books.google.de/books/about/Tribo_System_Kolbengrupp...](https://books.google.de/books/about/Tribo_System_Kolbengruppe_Zylinderlaufba.html?id=p3H0XwAACAAJ&redir_esc=y)

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csours
I see a picture of a book in that link, but no way to open it.

Do you have a couple pictures of the piston handy?

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InternetOfStuff
Turns out I lost all digital data of my thesis :-(

I scanned a picture from the dead-tree version:
[https://imgur.com/vQLIQ1F](https://imgur.com/vQLIQ1F)

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.

~~~
csours
Sorry to hear you lost your digital version =(

Thanks very much for the follow up!

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xchaotic
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...

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sp332
It took me a while to catch on that "mike" probably means to measure with a
micrometer.

~~~
olyjohn
I've never actually seen it spelled out before. I've heard people use the
term, and I assumed you'd say that you were going to "mic" it out.

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anonu
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...

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thewopr
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.

~~~
moftz
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.

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radiorental
Immediately reminded me of the Google Chrome comic

[http://www.scottmccloud.com/googlechrome/](http://www.scottmccloud.com/googlechrome/)

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zymhan
OpenDNS blocks this domain as a security threat, FYI

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bluejekyll
“... pick up some dope on the design of pistons”

I had to look that usage up:

‘Dope’

“information about a subject, especially if not generally known.”

I’ve personally never heard that phrase in that context. I also learned that
it’s original meaning was thick soup. Fun book...

~~~
mikestew
Meaning you’ve never been to
[http://www.straightdope.com](http://www.straightdope.com)? Or just always
wondered about the domain name?

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bluejekyll
I’ve never heard of that site. Good name, though.

~~~
mikestew
Good site, too; you should pay them a visit.

