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What are those letters stamped on my engine and piston?
6K views
Jan 7, 2025
Solving a Mopar mystery with the help of a Trenton Engine man who worked on the Chrysler, Dodge, Jeep, and Plymouth V8s, sixes, and fours - and why you won't see them on a modern car!
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hey everybody this is Dave from motals
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here and I'm here to tell you a little
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story about little markings on your
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pistons and your engine
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blocks on your piston you might notice a
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tiny tiny little marking a tiny little
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letter or on your block you might notice
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a bunch of letters they might go a d c d
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or B CCA or something like that so
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here's the deal is that you know
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everything varies when you make it first
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thing that you learn in statistics class
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including my statistics ICS class is
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that you have a machine and it's making
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the same thing over and over and over
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there is going to be some
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variation and it might be very very
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small variation that you have to measure
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with a microscope or it might be
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relatively big that you can see with a
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hand wielded micrometer or ruler and
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that's the way it used to be with the
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automated Machinery at Trenton engine
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and other Chrysler plants the engine
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plants and everybody's engine plants you
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bore out your cylinder and it'll be
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slightly different depending on the
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state of tooling the weather the
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material you know there's variations in
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the metal there's variations in weather
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all these things they add up and just
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Randomness that we don't know why it's
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happening but it's happening so what
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they did was they said you know these
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variances are so large that if we just
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put any piston into any cylinder some of
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them will barely fit and they'll be
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tight and you know you'll have problems
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there because they'll drag and it'll be
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more resistance and it'll wear out maybe
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uh the engine faster other ones they'll
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be too loose and you'll be blowing oil
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out and you'll have low compression and
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the seals are only meant to have a
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certain range that they'll work in so
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what they did was they marked they
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measured each cylinder and they measured
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each piston and they marked them by
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taking a a die and a hammer and going
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Bam Bam Bam Bam until they had the
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letter now according to uh my source
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here who is a retired uh worker at
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Trenton engine Dave
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vanban that in the uh V8 and slant 6 era
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they ran from a through G's and then if
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they were overboard by 02 in there were
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a whole bunch more classifications so
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they wanted to get things pretty pretty
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close to what they were supposed to be
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and they would Mark both the cylinder
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again and they had Pistons very
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so they'd basically look in the bin you
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know they'd see the engine had a c on
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this cylinder so they'd look in the bin
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for a c-size piston and they'd put it in
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uh when they went on to the
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four-cylinder engines the 2.2 and the
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2.5 the tolerances were better and they
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ran just from a through e and uh he
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thinks that it was about
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0.3 or
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.004 inches that separated each one so
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we're not talking about stuff that you
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would see with your naked eye they had
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to measure it more carefully because
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these are very very small variations but
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they are still very important for your
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engine so Dave said that one of the
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first jobs he had on the V8 assembly
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line was running a teletype machine so
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when a block was loaded onto the
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assembly line he would put in the type
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of engine and the b sizes in order and
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then it would print out in the Piston
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area and they'd load up uh the right
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number of Pistons wrist pins and
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connecting rods assemble them together
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and send them to the line in the
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sequence now apparently uh some people
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would go around looking at the new
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engines and trying to find the ones that
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were overboard or at least had the
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largest variation the largest cylinders
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just again from random variation and
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they would want to use those for racing
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because every little bit helps now over
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time they were able to manufacture with
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much greater Precision you know
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everything got more precise the
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tolerances got smaller and it got to the
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point by the time that Trenton was
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making V6 engines they were able to
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trash the entire system and just have
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one size piston one size cylinder I know
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it was exactly right and move on from
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there so that's progress but if you open
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up your vintage engine or your you know
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your 2.2 engine which I guess today is
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vintage if you open that engine up and
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you see a bunch of letters now you know
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what they're all from and what they and
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why they're there dccd don't try to
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figure out the acronym it's not an
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acronym and don't see you soon at
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motels.com where I hang out
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