This post is taken from the Vanagon Archives, and seems to be an excellent
treatment of the BA6 heater. Thanks to Mark Shelfo for the reference.

Marshall Ruskin

>From:         Jack Reed <jackr@fortnet.org>
>Subject:      Eberspacher BA6 heater article (long)
>
>Here you go folks,
>Please send me any comments, questions, etc., that you have and I'll do
>my best to answer them.
>Jack
>
>
>INTRODUCTION
>
>
>This is being written for all those that want some heat in their
>air-cooled vans.  It's also written for those that just want some info
>on gasoline heaters before taking the plunge, either by doing it
>yourself or by having someone else install it for you.
>
>------------------------- OBLIGATORY DISCLAIMER -----------------------
>Before we proceed I'd like to offer a few words of advice concerning
>gasoline heaters.  THEY ARE VERY DANGEROUS AND CAN BURN YOUR VAN WITH
>YOU IN IT TO THE GROUND IN A MATTER OF MINUTES.  IF YOU DON'T KNOW WHAT
>YOU'RE DOING, SEEK OUT A MECHANIC OR DEALER THAT DOES.  Sorry I had to
>shout, I just wanted to make sure that everyone was paying attention.
>
>All kidding aside, these things can be very dangerous if they are
>misadjusted or if the safety interlocks are broken or defeated.  I have
>heard of older units that had no safety interlocks built into them
>whatsoever.  I would be very cautious about having one of these units
>installed in my vehicle for the simple reason that you, the driver, are
>then responsible for ensuring that everything is always in proper working
>order.  If someone else installs such a unit for you, you may not be
>capable of determining when a problem with your heater occurs, with
>possibly disastrous side effects.
>
>One other note before we proceed.  I installed an Eberspacher BA6 heater
>in my 1981 Westphalia from scratch, which means that there was no heater
>in the van when I started.  The rest of this article refers to
>the BA6 since it's the only heater I have any direct experience
>with.  You should be able to draw certain references about general heater
>operation from this article but be careful about making assumptions
>about your unit if you determine that it's decidedly different in
>operation from the BA6.
>
>All comments and observations in this article are from personal
>experience and recollections.  Refer to the appropriate manual for your
>heater for exact specifications, trouble shooting tips and maintenance
>guides.  This article is meant to be a general info guide only for the
>DIY heater mechanic/installer and for those interested in learning more
>about their operation.
>
>Before I talk about the installation phase, let's talk first about
>general heater operation.  A gasoline heater is really a very simple
>affair.  Basically they are nothing more than a carbureator, since they
>employ a simple metering system for fuel delivery, a spark or glow plug
>for ignition, a means of delivering intake air and exhaust of spent
>gases.  Surround the whole thing with safety interlocks and you've got
>a gasoline or deisel heater.
>
>Each manufacturer (Eberspacher, Stewart-Warner, Southwind to name a few)
>has a slightly different way of accomplishing these tasks.  This article
>is going to concern itself only with the Eberspacher (or Espar as it's
>known in Canada and the US) BA6 which was originally installed in early
>air-cooled Vanagons.
>
>COMPONENT DESCRIPTIONS
>The BA6 has several different "packages" associated with it.  By
>packages I mean blocks of components that are installed in certain
>specific parts of the van.  The most important part of the installation
>is, of course, the heater itself.  This is a long, flat pancake made of
>sheet metal that basically consists of two parts, the inner shell and
>the outer shell.  Think of it as two clams, one inside the other if
>you're having trouble visualizing it.  At one end is where the
>combustion motor fan, the spark/glow plug, the inlet for the fuel from
>the fuel pump and the temperature regulating sensor reside.  In the
>middle are the flame and overheat switch and at the other end is the
>exhaust pipe.
>
>The combustion motor fan does two things, supply air to the combustion
>chamber by means of a rotating, finned fan as well as supply the signal
>to the fuel pump and the ignition coil by means of a set of points that
>are tripped by a cam on the end of the motor shaft.  The Bentley manual
>gives directions for adjusting the fuel pump by the number of "ticks" of
>the points, but as we'll talk about later, this method is only good for
>sea level installations.  The fan pulls outside air through a 2'
>corrugated plastic pipe that plugs into or connects to a hole in the
>rear cross member.  Great care must be taken that this plastic pipe is
>secured at both ends, otherwise vacuum could be created at the
>combustion motor fan inlet by air rushing by.  This would cause the
>flame that normally is contained in the heater to be pulled outside of
>it, which could cause meltdown of your heater, your van and you.
>
>As just something else to go wrong (not really), the combustion motor
>fan has a little "propeller" on the end of the fan itself that creates a
>long flame path in the heater to ensure complete combustion.  If this
>propeller is not in place because it was burnt off by an incorrectly
>adjusted mixture, you'll have to find/buy another.  Otherwise it's
>impossible to get your heater adjusted properly and you'll find it's
>operation intermittent at best, inadequate at worst.  I've been told
>that these fans are "mated" to the motor and that replacing just the fan
>will cause premature wear of the bearings, resulting in a $200+
>replacement.  This is reason enough to ensure that your heater is
>properly adjusted at all times.
>
>The spark/glow plug is just that, a spark plug that sits in the stream
>of gas from the fuel pump.  It has it's own ignitor or ignition coil
>that also gets it's signal from the points in the combustion motor fan.
>The spark/glow plug consists of an inner electrode, exactly like a spark
>plug and an outer shield that looks like a small, drilled tube.  Even
>though I've never seen one in action, I assume that once the spark gets
>everything nice and red hot, the shield just serves as a secondary
>ignition source for the fuel.
>
>At the base of the spark/glow plug inlet is a short metal tube that
>receives the outflow from the fuel pump.  By having these two points
>essentially coincide, the designers ensured that all fuel would be burnt
>as completely as possible.  Even so, these units were not designed with
>emissions in mind, although I have heard of mechanics that used their CO
>machines to adjust the fuel pump, hingeing on the 14.7/1 ideal air/fuel
>mixture.  I haven't been able to convince my dealer to let me use his CO
>machine for this purpose yet due to the excessive heat generated at the
>exhaust pipe.
>
>Which brings us to the other end of the heater, the exhaust pipe.  This
>pipe is bent in a 90 degree angle so that the exhaust doesn't shoot
>directly at the end of the transmission.  About one inch past the end of
>the pipe itself is a metal cap, roughly the diameter of the pipe, which
>is held in place by two metal straps that connect to the end of the
>exhaust pipe.  This pipe is there to ensure that the exhaust does not
>ignite leaves, etc. that rest underneath the van.  There have been
>documented reports of this occuring so make sure that your exhaust pipe
>is in place and has the cap as well.  If the cap is missing or damaged
>by some fumble fingered parts yard mechanic like mine was, you can
>easily fashion another using pop rivets, iron strap, and a small circle
>of 1/16" to 1/8" iron.  Don't use sheet metal for the cap, the heater
>will burn right through it.  An additional benefit of the cap that I've
>only surmised and never really researched is it's action as a venturi.
>The flow of air between the cap and the end of the pipe creates a
>natural vacuum that creates an increased draw of exhaust through the
>heater.  I'm not sure if this is true or not, but it's likely, so make
>sure that your cap is in place.
>
>In the middle of the heater is a contraption called a flame switch.  The
>purpose of the flame switch is to provide a signal to the control unit
>that the heater is up to temperature.  This signal is provided by a
>micro switch that is tripped by an expanding metal shaft that resides in
>the heater's core.  The flame switch is tricky to get adjusted properly,
>as the micro switch is held in positon by two screws terminated by nuts.
>The only way I'v ever been able to get mine adjusted correctly is by
>using a propane torch and a DVM.  Once I've got the micro switch in what
>I think is the correct location, I lock down the screws as tight as I
>can get them.  Then I set the DVM on the OHMS position and place the
>metal rod in the flame from the torch after hooking the DVM to the
>common spade clip and the NO spade clip.  If the meter shows infinity
>when the rod is cool and ~0 when in the flame for a few seconds then
>you've got it right.  The rod can get red hot pretty quickly while in
>the flame from the torch so be careful where you place it when you're
>done checking the adjustment.
>
>The flame switch adjustment has been at the heart of 90% of the
>problems I've had with my heater, so make sure you get it right.  If
>you're unclear on what's happening there or how to follow my directions,
>write me at the address at the end of the article and I'll give you a
>hand with the procedure.  The other 10% of the problems have been due to
>an incorrect mixture, which resulted in the premature demise of my first
>combustion motor fan.  This resulted in incomplete combustion of the
>fuel and erratic operation of the heater.  Information is provided on
>adjusting the fuel/air mix for your unit later on in the article.
>
>There is also a metal "button" in a ceramic ring that fits beneath a
>clip on the top of the heater.  This is called the overheat switch and
>it's nothing more than a breaker that will kill power to the heater if
>the temperature of the heater's outer "skin" gets too hot.  This could
>happen if the fuel pump were to lock in an open state, allowing
>unrestricted fuel to create a "runaway" situation.  It's your final
>defense against meltdown so make sure that it's in good condition by
>running the checks recommended in the manual.
>
>The two halves of the heater are held together by the use of rivets.  If
>any of yours are missing, pop rivets can be used to resecure the unit.
>The heater itself works like any home furnace you're familiar with
>where the actual combustion occurs in the inner jacket (or clam, if
>you're still using that image as a guide) which then heats the air in
>the cavity made by the second jacket (or clam).  The exhaust pipe runs
>through this outer cavity to get to the outside of the heater.
>
>Warm air is pushed through this outer cavity by means of two fans, the
>squirrel cage on the end of the alternator and the auxiliary fan that
>draws air through a hole cut in sheet metal underneath the rear seat.
>The auxiliary fan pulls the air from the heater boxes that surround the
>exhaust manifold and the squirrel cage fan pushes air through them.
>Another plus (besides the added boost of warm air) provided by the
>auxiliary fan is that by drawing air from underneath the rear seat it's
>recirculating warm air that's already in the passenger compartment.
>This means that the heater doesn't have to continually supply heat, it
>only has to replace the heat lost to air leaks and convection losses
>through the body, roof and floor.  I live in Colorado and these losses
>amount to a lot when it's 20 below outside and you're scooting down the
>road at 65.
>
>The fuel pump is a small, 4" affair that connects to the fuel line after
>the fuel filter.  Make sure that you get the "tee" for the main fuel
>line and the clamps that hold it in place, you'll need them to splice
>into the main line.  I've heard the fuel pump described as nothing more
>than a hypodermic in it's operation because of the way that it squirts
>gas down the hose the heater.  It attaches to the cross member by means
>of a rubber bushing and a nut and bolt.
>
>At the front of the heater is a temperature sensor.  It's a criss-cross
>arrangement with a resistor in the center of it.  It's used in
>conjunction with the thermostat to regulate the heater's output
>temperature.  The sensor sits in the output stream to the passenger
>compartment at the front of the heater.
>
>The final part to the heater section is the belly pan, a long, wide
>section of pressed sheet metal that runs from the gas tank to the
>transmission and between the frame rails.  The belly pan serves two
>functions, it protects the heater and it's components from rocks, salt
>corrosion, etc. and it traps "some" of the heat produced by the heater.
>There's a small door in the center of the belly pan to give you access
>to the flame switch.  There's also a cutout in the sheet metal to allow
>you to adjust the fuel pump without having to remove the belly pan.
>I've often thought about insulating the belly pan to reduce heat losses,
>but haven't only because I can't figure out why VW didn't insulate it in
>the first place.  I suspect there's a good reason for this and until I
>find out what it is I'll live with the heater in it's present state.  If
>someone has an insulated belly pan in use for several years I'd
>appreciate hearing about it.
>
>Last (didn't I say "final" in the last paragraph?) but not least are the
>two short sections of duct that connect the heater to ductwork at the
>front and rear of the engine.  These pieces of duct are needed to splice
>the heater into the old, single pipe that used to carry heat direct from
>the heater boxes to your frozen tootsies.  The ducts should be in good
>shape, with no cracks or breaks in them.  Suitable replacements could
>probably be gotten from a heating/ventilating shop if the dealer's
>prices are too dear.
>
>If after you've got the heater installed and running, it sounds like a
>locomotive has taken up residence there in the van with you, the inner
>jacket is cracked.  You need to get another one since I'm not sure if
>such a crack can be repaired.  I'm not saying it's impossible, just that
>I've never had to have it done so I can't say whether it's possible or
>not.  In any event, the heater is unusable until you get it replaced or
>repaired since carbon monoxide will be venting directly into the heated
>air flow to the passenger compartment.  Just in case no one's told you
>by now, carbon monoxide will kill you, either by depriving you of oxygen
>or by causing you to fall asleep at the wheel.
>
>The person that told me about this sound being produced by a crack said
>there's no mistaking it from the normal sound of the heater in
>operation.  If you're not sure if yours is cracked or not, but suspect
>it may be then have a heater/ventilator guy or gal probe the output from
>the heater in the passenger compartment with a CO sniffer for excessive
>fumes.  I can't caution you enough about this.  It's better to freeze
>then to die from carbon monoxide poisoning and possibly kill other
>innocents in the process.  In fact, after all is said and done, it's
>probably not a bad idea to have someone probe the heated air for CO as a
>final check of your work.
>
>That covers the components directly associated with the heater
>itself.  Let's move to the back of the van now, in the cavity between
>the bottom back of the rear seat and the engine.  A hole needs to be cut
>in this sheet metal to allow the auxiliary fan a place to pull air from.
>Make sure when you get your heater that you get the plastic cover and
>foam gasket that the fan mates to.  You can use the cover as a template
>when it comes time to cut a hole in the sheet metal.  There are two
>"dimples" in the sheet metal that you can drill out to receive the
>screws the hold the cover in place.  Once you've got the hole cut find
>a logical place to hang the auxiliary fan from so that it will mate to
>the port that juts out from the cover.
>
>Next you need to replace the ductwork that routes hot air from the
>control flaps to the original duct to the front of the cab.  These
>two units are almost identical, the only difference being a port to hook
>the auxiliary fan onto.  This is pretty straight forward, just check
>that the one-way air flaps in the ductwork are in place and functional,
>otherwise part of the pressure from the fan will just wind up fighting
>against the pressure from the squirrel cage fan and you'll wind up with
>zip for heat.  While you're back there it's a good idea to R&R the
>control flaps so as to get maximum heat out of the heater boxes.
>
>The last package of components are those that fit under the dash.
>Although these components can be installed without pulling the dash, it
>makes for a much cleaner, easier time of it if you do pull it prior to
>installing them.  There are five main parts to this phase, and we'll hit
>them one at a time.
>
>First there is the extension to the fuseblock that holds the two
>additional fuses for the heater's operation.  Didn't get it when you
>pulled the heater?  You can use the appropriate sizes in in-line holders
>instead.
>
>Next is the timer/thermostat, it goes in a hole in the dash just below
>the instrument cluster and to the right of the steering column.  If
>there isn't a dummy hole already in place try and pick a spot where
>you'll have room behind the hole to mount the thermostat.  The timer
>section of the thermostat allows you to preheat the heater on a cold
>Winter's morning.  Don't run the heater off the timer more than once
>when it's real cold or you take the chance of running the battery too
>low to start the engine.  Press in on the knob with the "+" on it and
>turn it to the right, you should hear the watch mechanism ticking
>merrily away.  If not then something's jammed the works and you'll need
>to take it apart to get it working again.  It's not absolutely critical
>that this section of the part works, so don't sweat it too much if it's
>broken.  Normal means of heater actuation is to turn the knob to the
>right without pressing it in first.
>
>Then there's the safety switch, which mounts there by your right knee
>when you're sitting in the driver's seat.  It has a bimetal relay that
>will "blow" if the heater doesn't come up to temperature fast enough or
>if it doesn't keep putting out heat after the flame switch rolls over to
>it's "closed" position.
>
>After that there is the heater relay which makes an audible "snap" when
>the heater kicks on or cycles.  That goes over in the area behind the
>glove box.  Last but not least, you need to replace the heater levers
>there in the dash.  The replacement lever assembly has a contact on the
>right or "HOT" side of the lever that supplies a ground signal to the
>electronics package.  I suppose that someone could bypass this step and
>just install a toggle switch in it's place but care would have to be
>taken to ensure that the temperature control lever was in the "HOT"
>region before the heater was actuated.  Otherwise heat from the heater
>boxes would be cut off.
>
>I'm not going to go into all the checks associated with these
>components by duplicating the work the Bentley technical writers put
>into the manual.  Suffice to say that you should pick one up and run the
>checks that they recommend.  If you can't afford the manual (and at $90+
>a pop who can?) there are several outfits that will sell you a copy of
>the heater section of the manual for around $10.  Or find someone who
>has a copy that is willing to make you one.  I don't have one.  Nope,
>not me, uh uh, don't ask.  Well, I don't know, maybe if you ask real
>nice.
>
>INSTALLATION
>
>Installation is pretty straight forward if you take your time and start
>sometime in June.  If you wait until September when the first flakes
>start flying you'll probably make a mistake and fry something that you
>can't afford to replace.  Try and start early if at all possible.
>
>I performed the installation in three phases: underdash components,
>engine area components and under van components.  Check your work as you
>go and replace anything that looks borderline like rubber boots or fuel
>lines.  If you have the room and the tools, check each component for
>proper operation by hooking them up to 12VDC or by performing whatever
>resistance checks you can before installing them.  I laid everything out
>on my garage floor and made sure that I knew where all the wiring and
>connectors went before I started the install.  Then I visualized how
>everything hooked up, where it was located in/on the van and how best to
>route the wiring.  Once that step was done, the rest just fell into place.
>
>Uh huh.  Believe that and I've got a bridge to sell you.  This is a
>painstaking labor of love that will easily consume at least three
>weekends over several months before it's right.  But your
>wife/kids/friends/frozen nose will thank you for the time spent doing it
>right.  I'm sure that someone could install a BA6 faster than that, but
>that's how long it took me and I've spent 24 years crawling around all
>sorts of vehicles.  If your level of expertise is less than that you may
>want to start in April (just kidding).  I don't feel that this is too
>much of a job for anyone with a fair degree of mechanical/electrical
>understanding.  But you will use all of that knowledge and then go
>looking for more, so don't rush the job if you don't have to.
>
>When it comes time to mount a component to the body, such as the heater
>or the safety switch, look for little "dimples" in the sheet metal.
>This is where you need to drill a hole to accept the screw for that
>component.  Be careful of punching through whatever is behind the dimple
>so that you don't, for example, punch a hole in the van's floor.  The
>bushings that the heater hang from will probably get trashed by whoever
>pulls the heater, mine were.  They run around $1.50 each from the dealer
>and I'd suggest that you install them as they will isolate the heater
>from road shocks and bumps.
>
>Items to check when inspecting a used heater are:
>- no worn through rust patches, in fact no holes at all
>- no big dents, the inner shell could be collapsed
>- good bearings on the combustion fan, with little or no play to them
>- points in combustion motor fan are in good shape (pull the end cap to
>  check them)
>- apply 12V to combustion motor fan to check operation, keep your
>  fingers, hair clear of the fins when performing this step as it runs
>  at ~7000 rpm
>- that combustion motor fan does not show signs of excessive heating and
>  that the little propeller on the end is intact
>- correct resistance on the ignition coil (check Bentley for specs)
>- spark/glow plug electrode and shield are in good shape and aren't
>  burnt or melted away by excessively high temperatures
>- apply 12V to the fuel pump, if it doesn't "click" it's probably NG
>- apply 12V to the aux. fan to check operation, check it's bearings also
>- rubber hoses to/from the fuel pump, replace if cracked
>- high tension wire to spark/glow plug, replace if not perfect
>- plastic pipe to combustion fan has no cracks and seals well to cross
>  member receptacle and combustion motor fan inlet pipe
>- that flame switch rod is straight, micro switch adjustment correct
>- inspect ductwork for cracks, repair with hi-temp silicon, epoxy, etc.
>- that all electronic components pass recommended electrical checks
>
>ADJUSTING THE FUEL/AIR MIXTURE
>
>Here's the part you've all been waiting for, adjusting the fuel/air mix
>(which is why I put it at the end of the article, naturally).  The
>manual states that 18.4 to 21.7 cm. of fuel should be dispensed every
>200 ticks of the fuel pump.  I did this and the heater smoked liked a
>runaway freight train.  Due to the nature of the beast, that being that
>these heaters are nothing more than big carbureators, they have to be
>setup for altitude.  Since there's no timing adjustment you can only
>throttle back on the fuel to accomodate the lower oxygen density at
>higher altitudes.  If you're in the mountains (I'm at 5,280') then you
>want to keep throttling back on the fuel pump until the heater stops
>smoking.  Leave the heater at this setting for a week or so then check
>the tabs and propeller on the end of the combustion motor fan.  If the
>tabs, etc. show signs of being burnt you need to richen the mixture a
>little so as to cool off the charge.  If you get things too lean you'll
>fry the fan and the heater won't work very well if at all, so keep
>checking the state of the fan until you're happy that it's not getting
>toasted.
>
>The only other way to adjust the heater properly is by use of a CO
>meter.  I'd suggest using a length of muffler pipe on the end of the
>exhaust pipe so as to cool off the effluent as much as possible.
>Otherwise you take a chance of frying the probe on the dealer's $15,000
>emissions machine.  And he won't be very happy about that.  If you can
>get someone to let you use their machine, set the heater at 1.5% CO,
>which is the ideal stochiometric ratio of fuel to air.  I'd still check
>the fan a couple of weeks afterwards just to be on the safe side.  But
>I've already roasted one fan so I'm a little more cautious than most.
>Those things are hard to find and you'll pay dearly for one when you do.
>
>
>That's it.  Pick a nice shady spot to do the installation and take your
>time learning how the whole thing works and goes together and you
>shouldn't have any problems.  I can be reached by email at
>jackr@fortnet.org if you have any questions about the installation, etc.
>Good luck and enjoy your old rolling icebox turned four season Van!
>
>
>
>