VW Heads -- Part 2

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.
--------------------------------------------------------------

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.

------------------------------------------------------------

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.

--------------------------------------------------------------

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.

-------------------------------------------------------------

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.

----------------------------------------------------------------

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

On Wed, 5 Aug 2009 21:40:48 -0700 (PDT), Veeduber
wrote:

CC'ing Your Heads...

-R.S.Hoover

magic stuff bob
dont think we're not reading
Stealth Pilot

"Veeduber" wrote in message
...
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

On Aug 6, 10:17*am, "RST Engineering - JIm" wrote:

Couldn't you just drop BBs into the largest chambers to bring them down to
the smallest?

------------------------------------------------------------------------------------------------

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

On Aug 6, 3:23*pm, "RST Engineering - JIm" wrote:

Didn't you see the smiley face? *Don'cha think those BBs would rattle around
a bit when you fired the engine up?

----------------------------------------------------------------------------------------------

Ah! I missed it, being a couple of lines down and not the usual :-)

I took it as a valid question/procedure since it doesn't HAVE to be
marbles, ball-bearings and so forth. If caught without any marbles
( I am frequently accused of having lost mine ) you may use virtually
anything else so long as it will not absorb the fluid, and will 'wet-
out' properly. For example, if using nuts, bolts or other hardware
that will fit under the sealing plate, you have to scrub them good in
lacquer thinner, MEK, etc., to get rid of any trace of oil.

Since I've built more than a few engines, I've provided myself with a
100cc burette that reads to a fraction of a cc, so I don't have to use
the marble procedure. But there have been times when I had to build an
engine using only the tools I had with me. Having to determine the
chamber volume -- as for setting the compression ratio -- is
always a bit of a chore in that it must be measured, whereas the other
factors -- swept volume and deck volume -- can be calculated. If
you're careful you can do this with a turkey baster, which is usually
marked for cubic centimeters or cubic inches. You can also use a
small syringe, such as used for hypodermic injections. This is where
you fill the syringe, bring it to the mark -- hopefully 10cc or larger
-- and empty it into the chamber, repeating this procedure as many
times as necessary until the chamber is full. And yes, this method
works perfectly well with a 50cc syringe and no marbles.

-R.S.Hoover

PS -- I'll have to keep an eye out for the smilies :-)

"Bob" wrote in message
...
On Aug 6, 3:23 pm, "RST Engineering - JIm" wrote:

Didn't you see the smiley face? Don'cha think those BBs would rattle
around
a bit when you fired the engine up?

-----------------------------------------------------------------------
-----------------------

Ah! I missed it, being a couple of lines down and not the usual :-)

I took it as a valid question/procedure since it doesn't HAVE to be
marbles, ball-bearings and so forth. If caught without any marbles
( I am frequently accused of having lost mine ) you may use virtually
anything else so long as it will not absorb the fluid, and will 'wet-
out' properly. For example, if using nuts, bolts or other hardware
that will fit under the sealing plate, you have to scrub them good in
lacquer thinner, MEK, etc., to get rid of any trace of oil.

Since I've built more than a few engines, I've provided myself with a
100cc burette that reads to a fraction of a cc, so I don't have to use
the marble procedure. But there have been times when I had to build an
engine using only the tools I had with me. Having to determine the
chamber volume -- as for setting the compression ratio -- is
always a bit of a chore in that it must be measured, whereas the other
factors -- swept volume and deck volume -- can be calculated. If
you're careful you can do this with a turkey baster, which is usually
marked for cubic centimeters or cubic inches. You can also use a
small syringe, such as used for hypodermic injections. This is where
you fill the syringe, bring it to the mark -- hopefully 10cc or larger
-- and empty it into the chamber, repeating this procedure as many
times as necessary until the chamber is full. And yes, this method
works perfectly well with a 50cc syringe and no marbles.

-R.S.Hoover

PS -- I'll have to keep an eye out for the smilies :-)

Serious question- Why do you have to see how much the marbles displace?
If you use the same marbles every time it shouldn't matter. I.E., the
two marbles + 35cc is two marbles +35cc in all cylinder heads.

--
"We have no government armed with power capable of contending with human
passions unbridled by morality and religion. Avarice, ambition, revenge,
or gallantry, would break the strongest cords of our Constitution as a
whale goes through a net. Our Constitution was made only for a moral and
religious people. It is wholly inadequate to the government of any
other." --John Adams, October 11, 1798

Anyolmouse

On Aug 6, 4:59*pm, "Anyolmouse" wrote:

Serious question- Why do you have to see how much the marbles displace?
If you use the same marbles every time it shouldn't matter. I.E., the
two marbles + 35cc is two marbles +35cc in all cylinder heads.
-------------------------------------------------------------------------------------------------

Dear Anyolmouse,

To determine our compression ratio we need to know the NUMERIC volume
of the combustion chamber. Using marbles (or whatever) to take up
some of the volume, reduces the procedure to one vey careful discharge
of the syringe. I've a hunch this question would have answered itself
if you had cc'd a head, when you find yourself wishing for an extra
hand or two :-)

Compression Ratio is normally defined as V1+V2+V3 (divided by) V1+V2
(where V1=the swept volume of the cylinder, V2=the volume of the deck-
space, and V3=the volume of the combustion chamber). I think I've
included this procedure in my blog.

-R.S.Hoover

Veeduber wrote:
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.
--------------------------------------------------------------

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.

------------------------------------------------------------

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.

--------------------------------------------------------------

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.

-------------------------------------------------------------

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.

----------------------------------------------------------------

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

At the risk of repeating myself--A veterinary supply has all sizes of
hypodeemic nurdles, syringes, etc. Atwoods farm stores here in the
Southwest--most feed & seed stores catering to large animals. Jerry

On Aug 6, 9:26*pm, Jerry Wass wrote:

At the risk of repeating myself-.....

--------------------------------------------------------------------------------

Dear Jerry,

Good. KEEP repeating yourself. The internet is not static, the
audience changes from minute to minute.

The message for VW engines is fairly simple but it NEEDS to be
repeated. Guys who already have the information may complain but the
guys who don't won't.

When you're talking about VW engines you're really talking about their
heads. Everything else is fairly sturdy; the kind of stuff that
breaks LAST. But it's the valves that break first. If you're flying
behind a VW you quickly learn what's sturdy and what's not. The
heads... the exhaust valves... are the weak link, be it Volkswagen or
Pratt-Whitney.

A VW engine attached to a fuselage with a couple of wings-worth of
lift and some scooter wheels on the bottom will allow you to get in
those ten hours a month that makes the difference between a pilot and
someone who drives an airplane. Doesn't matter if the thing is a
Teenie Two or a VP1, it's still a flying machine, more than able to
keep your skills well honed.

A leak-down test will tell you WHEN. Having built your own engine
tells you HOW. Pull the heads, toss the exhaust valves, re-lap the
intakes, button it back up, you're looking at a couple of evenings
work. Leak-down not only tells you when, it allows you to SCHEDULE
the when.

Better still, buy yourself a pair of NEW heads and machine them so
they are IDENTICAL to the set that's flying the bird now. When the
leak-down test tells you when, all you gotta do is pull the old heads,
replace them with the new heads, and keep on flying. You've got at
least five or six months in which to tear down the old heads and
return them to service.

-R.S.Hoover

Jerry Wass wrote:



-R.S.Hoover

At the risk of repeating myself--A veterinary supply has all sizes of
hypodeemic nurdles, syringes, etc. Atwoods farm stores here in the
Southwest--most feed & seed stores catering to large animals. Jerry

Mine come from the local Tractor Supply.