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Posted by Veeduber on August 6, 2009, 12:40 am
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CC'ing Your Heads... seems to generate more messages than any of the
other head-related chores. Which is only fair since cc'ing your heads
is one of the most important tasks in building a reliable engine.
Some argue that cc'ing isn't necessary with stock heads since the spec
for stock chambers is good enough. This is called Good Enough
Engineering. The truth is, the stock spec can vary by as much as 4cc
across four chambers and that's really terrible. With nothing more
than a 50cc syringe you can adjust the chamber volume to within 1cc
across four chambers.
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The very first thing you want to do is to mark your heads and the
combustion chambers. Use a broad-tipped Magic Marker and keep it
simple, such as A and B for the heads and 1 and 2 for the chambers.
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What Solution Should I Use?
Water. About a gallon of it. Add two drops of liquid detergent to
defeat the waters surface tension. Then add food coloring... which
will help you read the fluid level.
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Drying the Chambers
After each measurement you must empty the fluid from the chamber.
Just pouring out the solution won't do... the chambers must be
PERFECTLY dry. That means blowing them out with compressed air,
either canned or pumped. But even that won't get all the fluid out of
the spark plug. So do this: After pouring out the fluid and wiping
the chamber with a cloth or paper towel, give it a shot of 70% alcohol
THEN blow them dry.
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The Syringe is Too Small...
...meaning your chambers are larger than 50cc. So put a couple of
marbles in it.
Seriously. Suck up a full syringe of solution then pull the plunger
out of the syringe while keeping your thumb over the outlet. Using
your thumb, allow about half of the fluid to escape back into the
bucket or whatever. Do this carefully, so that the fluid comes into
alignment with one of the marks. Then drop a marble into the syringe
and record its volume. That is, see how much the fluid rises. The
volume of the marble will be equal to the difference between your
first reading and the second. Now do it again for a SECOND marble.
Chamber volume can vary by quite a bit. Your first effort is to
determine their approximate volume so you'll know how many marbles
you're going to need.
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Using a burette and a jig to hold the head(s) level will make the work
a lot easier.
Your accuracy will improve if you cc each chamber a multiple number of
times for each step. For a stock head that means cc'ing each chamber
about a dozen times. If you must open up the chambers it will mean a
lot of grinding and measuring, but it's bench-work -- you can make
yourself a little work station and take all the time you need to get
it right.
The Compression Ratio equation will tell you how many cc's the
chambers should be to give the desired CR. The odds are, you'll have
to open them up by quite a bit to match the equation. And that means
you'll need to measure their cc's a multiple number of times.
Something to remember is that in many cases you only have to work on
THREE chambers, not four. That is, the largest chamber may not need
any work at all. All you have to do is open up the other three so
they match the volume of the largest chamber.
Some people worry about not having any experience cc'ing heads but if
you think about it, if you measure each chamber a multiple number of
times, by the time you get done you will have gained plenty of
experience.
-R.S.Hoover
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Posted by Stealth Pilot on August 6, 2009, 8:50 am
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On Wed, 5 Aug 2009 21:40:48 -0700 (PDT), Veeduber
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>CC'ing Your Heads...
>-R.S.Hoover
magic stuff bob
dont think we're not reading
Stealth Pilot
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Posted by RST Engineering - JIm on August 6, 2009, 1:17 pm
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> CC'ing Your Heads... seems to generate more messages than any of the
> other head-related chores. Which is only fair since cc'ing your heads
> is one of the most important tasks in building a reliable engine.
> Some argue that cc'ing isn't necessary with stock heads since the spec
> for stock chambers is good enough. This is called Good Enough
> Engineering. The truth is, the stock spec can vary by as much as 4cc
> across four chambers and that's really terrible. With nothing more
> than a 50cc syringe you can adjust the chamber volume to within 1cc
> across four chambers.
Couldn't you just drop BBs into the largest chambers to bring them down to
the smallest?
{;-)
Jim
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Posted by Bob on August 6, 2009, 3:21 pm
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> Couldn't you just drop BBs into the largest chambers to bring them down t=
o
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> the smallest?
>--------------------------------------------------------------------------=
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Dear Jim,
I don't understand.
The initial goal is to determine the volume of the LARGEST cylinder.
The marble trick allows us to measure a volume that is GREATER than
the 50cc volume of our syringe.
For example, let's assume our marbles are equal to 20cc. We dry the
marbles, place them in the chamber to be measured, install the cover
plate then fill the chamber with fluid. If it takes 37cc of fluid to
fill the chamber then its actual volume will be 57cc. I don't see any
benefit from using BB's. In fact, I can imagine several situations
where the BB's would be a real PTA to work with.
But I'm always willing to learn, especially from someone with your
credentials.
-R.S.Hoover
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Posted by RST Engineering - JIm on August 6, 2009, 6:23 pm
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> Couldn't you just drop BBs into the largest chambers to bring them down to
> the smallest?
>------------------------------------------------------------------------------------------------
Dear Jim,
I don't understand.
*********************************
Bob ...
Didn't you see the smiley face? Don'cha think those BBs would rattle around
a bit when you fired the engine up?
Jim
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>-R.S.Hoover