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Eberspaecher BA4 Overhaul
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anglodeutsch4
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PostPosted: Thu Dec 28, 2017 1:30 pm    Post subject: Eberspaecher BA4 Overhaul Reply with quote

This is the start of a thread detailing my overhaul of the Eberspaecher BA4 in my 1973 412 Variant. Note that said Variant (Nordhoff's Nomad) is INOP right now, I'm starting with the Eber because it's easy now that the engine and trans are out. Sad Idea Very Happy

First up, here are the part numbers on the Eber fuel pump, for future reference...

On suction end:
VW 411 261 467
Bosch 0 332 900 001

On discharge end:
Eberspaecher 201312 12V

I'm starting with the fuel metering pump because that seems to be a source of much fun and games getting the heater to light off and stay lit without smoking.

I am writing the below as a post directly, so the word gets out on confusing directions in the factory fuel pump set-up instructions. A monograph similar to Ray's recent works will be forthcoming at some point, with pictures and details on the whole process.

First up, the volume setting instructions on the BA4 you've probably seen are very misleading. I now remember chasing my tail long ago when I first got the 412 on the road, though that memory only came back to me after some recent frustration adjusting the pump.

For example...

http://oacdp.org/ebersp/023.png

Under "Testing fuel pump" on Pg 2-4, VW states "At a combustion air blower speed of 6000 rpm, the pump should deliver 24-5 cc/minute."

WRONG! The BA4 pump is incapable of producing that volume, and I chased my tail for an hour trying to make it do so.

On Pg 2-5, the same service document states that the pump should produce 23.7-25 cc at a combustion air blower speed of 6600 rpm, PER 2 MINUTES. In the explanation of the combustion air blower speed versus volume delivered chart on that same page, the vertical axis is described as "A - Delivery quantity cc/2 minutes". So, you should either have something like 12 cc/minute, or 24 cc per 2 minutes, NOT ~24 cc per minute.

The most reliable way to adjust the pump is what Eberspaecher specified in a more recent BN4 manual. The real quantity of interest is volume per stroke, not volume per interval of time. The combustion air blower triggers the pump in direct proportion to its rotational speed, and therefore changes pump delivery volume in relation to combustion air delivery. Measuring pump delivery volume per stroke insures we get as close to ideal air/fuel ratio in the combustion chamber as possible with a bench test.

Here's the Eberspaecher BN4 verbage. NOTE! THE QUANTITY IS NOT ACCURATE FOR THE BA4, I am using the quote for procedural reference ONLY!:

"Switch on the heater and check the quantity of fuel delivered in 200 strokes of the pump (each tick represents one stroke)...If the pump is set properly, 13 to 15 cc of fuel must be pumped every 200 strokes."

The math works out thusly. The fuel pump points close once every 33 revolutions of the combustion air blower shaft for both the BA4 and BN4 blowers. 6600 RPM on the blower are 6600/33 = 200 fuel pump point closures IN ONE MINUTE. So, at 6600 RPM, 200 "ticks" of the pump equals one one-minute measuring period.

From the BA4 volume delivery chart on Pg 2-5 of the above linked VW service document, 6600 RPM means 23.7 to 25 cc delivered per 2 minutes. For one minute, the expected delivery would be half that, 11.9 cc to 12.5 cc.

Let's cross-check the above statements for sanity. The newer BN4 service document states 13 cc to 15 cc per 200 pump strokes is expected. Since the BN4 is not of identical heat output or design, the figures are not exactly identical. The BN4 design is, however, close enough to confirm the hypothesis.

CONCLUSIONS:

1. The measuring period for all BA4 volume delivery adjustment instructions in VW documentation is 2 minutes.

2. The most efficient method of delivery adjustment is to count the pump "clicks". When 200 "clicks" are reached, the pump should have delivered 11.9 cc to 12.5 cc.

Now, I have a problem. My pump has started leaking through the connector seals on the discharge end. I recommend if you have your pump out for testing, make sure you do a running check with the test fuel tank at least 12" above the pump. I discovered the leak when I ran the pump with my fuel jar about 12" above the pump. Remember, the fuel tank level in the 411/412 when full is at least 12" above the Eber's fuel pump inlet fitting, and that the pump has an inlet lockout when de-energized. The pump will most likely NOT leak when not activated, if it has this condition.

More to come as I work through this.
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PostPosted: Thu Dec 28, 2017 4:23 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

This will be a good thread!

For interest....the 1971 to 1974 "Without Guesswork" book....it lists 11.8 to 12.5 ML per 200 strokes for the BA4 in the type 4.

The Clymer manual which at least notes a decent amount of info...for an aftermarket shop manual.....says 9-10cc's (same as a milliliter).....per minute.

I have also found the same inaccuracy issue a long time ago. Ray
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PostPosted: Thu Dec 28, 2017 4:36 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Happy New Year Ray!

Good to hear VW fixed the issue in the WOG. Forgot to check my copy.

Clymer is just wrong I think, I can't see any way you get the same BTUs from half the fuel...unless there's some "early/late Eber" thing going on.

Just slathered the (cleaned and roughened) pump terminal area with JB Weld Marine Epoxy. We'll see tomorrow if that stopped the seepage. Speak to the hand
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PostPosted: Sat Dec 30, 2017 11:00 am    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Good news! The marine-grade epoxy I slathered around the terminals appears to have stopped the leak. Pressing on with pump calibration and testing.

If this leak repair holds after extended testing, it may be a good preventative measure for anyone with the BA4-style pump to apply before it starts leaking. Will advise.
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PostPosted: Sun Dec 31, 2017 12:02 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

anglodeutsch4 wrote:
Good news! The marine-grade epoxy I slathered around the terminals appears to have stopped the leak. Pressing on with pump calibration and testing.

If this leak repair holds after extended testing, it may be a good preventative measure for anyone with the BA4-style pump to apply before it starts leaking. Will advise.


Its interesting....the pump is one of the most...irreplaceable parts of the system.

You can get a range of coils that work. Glow plugs can be had. In fact...I have a scheme I drew up that calls for a machined "thimble" or adapter that has a single wind or ni-chrome wire as a heater coil but uses a regular spark plug as the igniter...so I know that I could do that if glow plugs became unobtanium.

The thermo probe and thermostat...can even work when they are slightly off....but the pump is kind of unique.

Really...I have been wondering if...sicne it works on an single impulse...if something like a Facet fuel pump could be used and metering simply set with an orifice?
Ray
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PostPosted: Sun Dec 31, 2017 1:34 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Or better yet, an SU-style diaphragm pump, low pressure (1.5 PSI max). I have a Hitachi clone from a '79 Honda on my MG right now, it solved a strange intermittent fuel delivery problem. The PO had installed a ticks-all-the-time Carter E8016 pump, and it seemed that style of pump (similar to the Facet, but cylindrical) gave the SU carbs a case of the vapors. I suspect it was the rapid pressure pulsations that type of pump puts out, maybe. In any case, the more constant, lower discharge pressure would be good for this application.
Seems some of the early Eberspaecher heaters used a German diaphragm-type pump along with a pressure regulator, and a fixed orifice, too.

It would give a fixed feed rate, so along with a fixed feed pump, maybe pulse-width-modulated speed regulation for the combustion air blower, to keep its speed constant. Still need a positive fuel supply lockout, electrically triggered, like a fuel tank selector solenoid maybe.

Yeah, I've been thinking about Eber parts availability, too. The safety switch can be replaced with a 555-type timer circuit, the ignition coil with almost any small coil, maybe with a ballast resistor (I've got that on mine, the original coil died long ago). I've got two circuits to offload the points in the combustion air blower, transistor amplifiers effectively, simple little things. Oh yeah, glow-plug, why not use an ALH diesel plug with an adapter? The spark plug part can be a hole drilled in the adapter to pass a Teflon-insulated wire to act as the"center electrode"...
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PostPosted: Sun Dec 31, 2017 1:57 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

anglodeutsch4 wrote:
Or better yet, an SU-style diaphragm pump, low pressure (1.5 PSI max). I have a Hitachi clone from a '79 Honda on my MG right now, it solved a strange intermittent fuel delivery problem. The PO had installed a ticks-all-the-time Carter E8016 pump, and it seemed that style of pump (similar to the Facet, but cylindrical) gave the SU carbs a case of the vapors. I suspect it was the rapid pressure pulsations that type of pump puts out, maybe. In any case, the more constant, lower discharge pressure would be good for this application.
Seems some of the early Eberspaecher heaters used a German diaphragm-type pump along with a pressure regulator, and a fixed orifice, too.

It would give a fixed feed rate, so along with a fixed feed pump, maybe pulse-width-modulated speed regulation for the combustion air blower, to keep its speed constant. Still need a positive fuel supply lockout, electrically triggered, like a fuel tank selector solenoid maybe.


Yeah, I've been thinking about Eber parts availability, too. The safety switch can be replaced with a 555-type timer circuit, the ignition coil with almost any small coil, maybe with a ballast resistor (I've got that on mine, the original coil died long ago). I've got two circuits to offload the points in the combustion air blower, transistor amplifiers effectively, simple little things. Oh yeah, glow-plug, why not use an ALH diesel plug with an adapter? The spark plug part can be a hole drilled in the adapter to pass a Teflon-insulated wire to act as the"center electrode"...


You do not want to keep the combustion blower speed constant.

I will have to find the discussion on this from a couple of years ago....but its one of the few controls the system has. Its not just to vary fuel pump speed.

The speed is modulated in response to a combination of chamber flame temp and air duct temperature...in response to keeping the heat even for the dash timer setting.
While yes....one could say that modulating the fuel pump adjusts that temp range....the fan speed also adjusts cooling air for the chamber. This is why they are linked together.
You also have to remember that the pump will provide enough fuel and the chamber produces enough heat...that the pump frequently is shut off ...even while the main blower is still running because the level of latent heat is high enough to keep the programmed temp constant.

The information was part of Classic campers thread.
Ray
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PostPosted: Sun Dec 31, 2017 2:29 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

I'm not following you on this one Ray. The combustion air blower speed only varies in response to changes in its terminal voltage, which depends on battery state-of-charge when the engine is not running, and various other factors (electrical loads, engine speed, alternator output "flatlining" from being full-fielded, etc.) all related to line voltage. I can see nothing in the Eberspaecher's electrical design which attempts to manipulate the combustion air blower speed intentionally.

The thermostatic control turns off the fuel pump +12V feed when the duct temp rises over its setpoint, and turns the feed back on when the duct temp falls below the setpoint plus hysteresis, so I don't see anything intentionally attempting blower speed control based on duct temperature. The only possible Eberspaecher internal effect is when the glow plug is "on" at start-up, I2R losses in the common ground from the ~8A of glow plug draw cause the blower to slow down. So, for ~90-120 seconds, the blower slows. The rest of the time, it's speed is determined completely by outside electrical supply voltage. And BTW, I am working on a relay to offload the glow plug, and better wiring to eliminate the blower speed sag on start-up. That's part of what I'm working on now. I can get to everything in the system, and test it all on the bench without hosing the car up, since it's off the road Sad

Blower speed varies unintentionally of course, due to external voltage changes. That's the effect the manufacturer is trying to counter with the "dosing pump" and fixed-ratio pump trigger points in the combustion air blower, I believe.

So, with a fixed blower speed, you get a fixed combustion air delivery, and need a fixed fuel feed quantity over time to maintain a fixed air/fuel ratio...or, you tie the pump delivery to blower speed, and (partially at least) compensate for blower speed changes by changing fuel delivery. About that compensation...

I have my doubts about the effectiveness of the 33:1 fixed-ratio pump triggering and A/F ratio maintenance over the entire speed range of the blower. I suspect blower rotational speed changes do not linearly translate into air volume or weight delivery changes, things are usually not that simple in aerodynamics! But, I also suspect the changes are close enough over a small motor speed change range that the A/F ratio is maintained reasonably closely to stoichiometric.

Hmmm, I need to figure out a way to test this theory! Idea Measure airflow versus input voltage, and convert to mass airflow for an A/F ratio comparison versus blower motor speed. It's a low airflow, so finding a way to accurately measure it will be interesting.
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PostPosted: Sun Dec 31, 2017 4:41 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Yep....you are right. I had to go back through the BA4 book and my notes.

For some reason I had it in my mind that the system had two distinct speed ranges. That idea got there....from experiences in the late 70s/early 80s.

What I was seeing was as you note...voltage sag. And.....there in my notes from the mid 80's.....was the note I wrote to myself....."get twin battery set up and seperate the heater from the main line" Rolling Eyes .....and I still have not gotten to it.

What I also have miles of in my notes.....is that the fuel ratio problem is not just a three point...or three variable problem. Its actually four.....main ones.

So yes.....as the fan speed varies (V-1).....so does fuel pump speed (V-2).....to keep fuel and air ratio "equal-ish"......but that can be screwed up by pump volume adjustment (V-3).

Stopping for a moment...one would think that the proper air fuel ratio would be attained just by combined fan and pump speed....and output volume (which is an orifice adjustment)....should not matter right?

No.....not so.

The fourth variable...and the one that screws things up the most.....is the thermostatic setting/values of the dash switch.

There are no distinct exact settings of this switch. While you can measure the dial position with a volt meter and it is fairly linear.....it does not mean the output is.

I found long ago that if you have the fuel pump volume set just at the low edge of the spec.....the heater runs too cool.
This is not just in the output of heat to the passengers....but the system "short cycles".

Let me explain that.
It has to run too long to heat the ducting up and reach the preset of the dash switch....because regardless of pump and fan rpm.....if the pump outlet volume setting is too low.....it has to burn for longer periods to reach this specific heat.....and with less fuel its producing less heat. You can actually "hear" the difference in flame volume.

And while this reduced output does not put as much heat into the ducts.....it DOES heat up the thermoprobe and chamber enough that it cuts the fuel off and just runs the blower until it drops far enough to resume.

I have found running like this ....from my notes....is harder on the glow plug.

So.....what I am getting at is that when specific fuel volume adjustment is low.....useful and stable heating is not produced at anything less than the dash dial all the way on high. Anything in the middle ranges between about 1/4 and 3/4 cause this short cycle.

I was finding this issue when ai first started adjusting the system. I found notes in the hook in my 1st 411....that the mechanic they were taking it to....tuned fuel delivery back on the heater....to combat a fuel mileagd problem in cold weather..... Rolling Eyes ...like WTF!

So if you also add in fan speed variation.....it can get ugly.

I found that actually running the heater near or at the top of its fuel pump outlet spec.....allowed better actual heat control using the dash switch knob....and less short cycling.

But....careful adjustment needs to be done...because when you get too much fuel.....and you do a lot of city driving....the heavy unburnt fumes from the tail pipe get looped back into the engine intake louvers.....and sucked into the circulating fan. You will know it when it happens.
Ray
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PostPosted: Sun Dec 31, 2017 7:39 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Yeah, adjusting pump output to keep it from smoking (too rich) or overheating the blower swirl tabs (too lean) does also need to keep the fuelling rate low, but not too low so as to prevent short cycling, I can see that.

Oh yeah, some early results from pump investigations. It seems the later Eberspaecher factory pump installation diagrams have some solid experimental data backing them up. At least, my sample of one BA4 pump is much, much happier when installed per their charts, with the discharge end at least 20 degrees above horizontal. Output is more consistent, less bubbles, volume does not vary as much. Also, their recommended 1.5mm ID discharge tubing does appear to purge bubbles better from the discharge, and gives more stable flow. More investigation to come, but this initial result is at least pointing in a direction to follow for fuel flow issues I had noted in my 412 in the past.

You may have also been thinking of that two-stage hot air blower, the one VW installed standard in Canada-bound Transporters certain years. The schematic in the Type 2 tech area on this website shows a resistor in series with a "honking big blower motor" (technical term) to bring the blower's speed down to a lower flow for parked operations. The resistor is shorted out by a relay, whose coil is energized by the field diode pack. The relay closes once the alternator starts producing juice, so the fan gets kicked into high speed only when the engine is running. That idea is getting stirred into the pot of mods I've been stewing for my 412...sounds like you've got a stew pot going, too. I replaced the standard wimpy 412 Variant blower motor with one of those "honking big blower motors" I stumbled across in the junkyard years ago, and that was one mod I've been contemplating. I've also thought that having two "notches" for the blower on the flap control lever might be useful, too.
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PostPosted: Thu Jan 04, 2018 6:49 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Let me throw out one hypothesis for discussion. VW designed the Type 4 heater with a de-aerator (that clear nylon bulb-looking "tee" thingy) in the FI return line from the engine as the fuel source for the Eber "dosing pump". The presence of that part would seem to indicate a knowledge on VW's part of a susceptibility to bubbles in the Eber pump feed.
I've not seen an Illustrated Parts Breakdown on the fuel system for the carburetted version, so can't confirm where the Eber pump got its feed. But, for the D-Jet equipped Type 4's, it's the return line with a de-aerator. Fuel in the 1960's had zero alcohol, and in my experience, lower vapor pressures than the muck we get today in the US and Canada. I strongly suspect the changed characteristics of gasoline/petrol/benzin nowadays leads to vapor bubbles in the fuel stream downstream of the D-Jet regulator. The regulator is throttling ~30 PSIG down to ~0 PSIG...I know when warm liquid refrigerant is throttled, "flash gas" is formed in the lower-pressure stream on the discharge side of the expansion valve. So, I wonder if a combination of lower fuel vapor pressures than designed for, and throttling in the D-Jet reg is causing more bubbles than the Eber pump can clear easily. All the bubbles have to do is disrupt combustion in the heater for 5-10 seconds every minute to make a difference in the heater's performance. Discuss!
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PostPosted: Thu Jan 04, 2018 9:46 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

anglodeutsch4 wrote:
Let me throw out one hypothesis for discussion. VW designed the Type 4 heater with a de-aerator (that clear nylon bulb-looking "tee" thingy) in the FI return line from the engine as the fuel source for the Eber "dosing pump". The presence of that part would seem to indicate a knowledge on VW's part of a susceptibility to bubbles in the Eber pump feed.
I've not seen an Illustrated Parts Breakdown on the fuel system for the carburetted version, so can't confirm where the Eber pump got its feed. But, for the D-Jet equipped Type 4's, it's the return line with a de-aerator. Fuel in the 1960's had zero alcohol, and in my experience, lower vapor pressures than the muck we get today in the US and Canada. I strongly suspect the changed characteristics of gasoline/petrol/benzin nowadays leads to vapor bubbles in the fuel stream downstream of the D-Jet regulator. The regulator is throttling ~30 PSIG down to ~0 PSIG...I know when warm liquid refrigerant is throttled, "flash gas" is formed in the lower-pressure stream on the discharge side of the expansion valve. So, I wonder if a combination of lower fuel vapor pressures than designed for, and throttling in the D-Jet reg is causing more bubbles than the Eber pump can clear easily. All the bubbles have to do is disrupt combustion in the heater for 5-10 seconds every minute to make a difference in the heater's performance. Discuss!


This IS possible. I can tell you....that without that small chamber......with just a "tee".....fuel feed is erratic. A "Y" works better....just like it does in the front end where the return connects to tank and pump.

This tells me that the near 0 pressure in the return line can cause turbulence. The meterong pump does not need "pressure"...but does need uninterrupted VOLUME.

I have been contemplating that in place of the small factory tee-bulb.....a Y with a larger reservoir like the size of a normal fuel filter could cover it. Ray
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PostPosted: Thu Jan 04, 2018 10:54 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

anglodeutsch4 wrote:
Or better yet, an SU-style diaphragm pump, low pressure (1.5 PSI max). I have a Hitachi clone from a '79 Honda on my MG right now, it solved a strange intermittent fuel delivery problem. The PO had installed a ticks-all-the-time Carter E8016 pump, and it seemed that style of pump (similar to the Facet, but cylindrical) gave the SU carbs a case of the vapors. I suspect it was the rapid pressure pulsations that type of pump puts out, maybe. In any case, the more constant, lower discharge pressure would be good for this application.
Seems some of the early Eberspaecher heaters used a German diaphragm-type pump along with a pressure regulator, and a fixed orifice, too.

It would give a fixed feed rate, so along with a fixed feed pump, maybe pulse-width-modulated speed regulation for the combustion air blower, to keep its speed constant. Still need a positive fuel supply lockout, electrically triggered, like a fuel tank selector solenoid maybe.

Yeah, I've been thinking about Eber parts availability, too. The safety switch can be replaced with a 555-type timer circuit, the ignition coil with almost any small coil, maybe with a ballast resistor (I've got that on mine, the original coil died long ago). I've got two circuits to offload the points in the combustion air blower, transistor amplifiers effectively, simple little things. Oh yeah, glow-plug, why not use an ALH diesel plug with an adapter? The spark plug part can be a hole drilled in the adapter to pass a Teflon-insulated wire to act as the"center electrode"...

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PostPosted: Thu Jan 04, 2018 10:57 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Now that I'm determined to get this car back on track, I need to diagnose the heater. If I run it on high for too long, the fuse blows by the breaker. Low temp... it runs pretty good.


I totally love this heater, it really keeps the car comfortable. Just very tempermental.
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PostPosted: Fri Jan 05, 2018 4:06 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Which fuse, the 16A main or the 8A fuel pump fuse?
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raygreenwood
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PostPosted: Fri Jan 05, 2018 8:20 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

This is tbe fuse we were speaking of last year....right?.....inline fuse...olive green wire.

That is the high limit switch fuse. There are a couple of issues that can happen with this switch as we discussed...ranging from a direct short due to heat expansion and the crimped wires touching the heater body.

There is also the issue that with heat cyling and age....it just kicks in at too low of a,temp. Its job.....is to literally short to dead ground and blow that fuse.

I the have come to the conclusion over the years that the bi-metal high limit switch has issues with age. About 50% of the heaters i have worked on in otherwize perfect shape....all require a 25 amp blue fuse in that holder to run.

And....its not because anytuing in the system is pulling excessive amps. It because the high limit switch...seems to be kicking in.....partially....and at too low of a temp. Ray
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anglodeutsch4
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PostPosted: Tue Jan 09, 2018 4:18 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Well, my "field expedient" pump check valve O-ring has started leaking a bit. I did not have a 4mm ID x 1mm cross section O-ring in stock, so I forced a slightly larger one down over the pump cylinder end, skiving off a small remnant O-ring. That remnant worked OK until I adjusted the stroke a couple times. So, I've got a supply of Buna-N and Viton O-Rings of various hardnesses coming. Will advise when I get the pump back working and restart my overhaul.
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anglodeutsch4 (Samba)
73 VW 412 (the Nomad, dropped valve seat land now, argh!)
67 MGB (Built-In Rust from Abingdon)
76 Plymouth Duster /6 (looking for a new home...)
2002 NB TDI (40 MPG)
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raygreenwood
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PostPosted: Wed Jan 10, 2018 6:34 am    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

anglodeutsch4 wrote:
Well, my "field expedient" pump check valve O-ring has started leaking a bit. I did not have a 4mm ID x 1mm cross section O-ring in stock, so I forced a slightly larger one down over the pump cylinder end, skiving off a small remnant O-ring. That remnant worked OK until I adjusted the stroke a couple times. So, I've got a supply of Buna-N and Viton O-Rings of various hardnesses coming. Will advise when I get the pump back working and restart my overhaul.


Be sure you use viton if you can. The life with Buna-N was much shorter back in the day before ethanol. I had the same problem with the same o-ring for about 1.5 years long ago.

Buna-N was all I could get local and quick and it worked fine but started leaking at ahout 4 months. You may make it through the cold season with one. Very Happy
Ray
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anglodeutsch4
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PostPosted: Sat Jan 13, 2018 1:26 pm    Post subject: Re: Eberspaecher BA4 Overhaul Reply with quote

Yeah, that's why I got some Buna-N and some Viton,try a science experiment with prolonged immersion in old stale gasahol gas and fresh but still gasahol gas. Smile

Since my fuel pump is waiting for O-rings, I decided to pull the duct air temp sensor to get a calibration curve on it. Well, that's not going to work either. The little bar-type thermistor inside the little cage on the end has gone open-circuit. When I first started messing with it, it looked OK, but after measuring the fixed series resistance in the base (220 Ohms, BTW), I noticed the resistance reading was bouncing around. Turns out one end of the thermistor, under the epoxy coating, had come loose. So, I go to Plan B, replace the thermistor with a variable resistor, turn on the controller to full cold, set the test variable resistor so the controller turns off/on, and measure the resistance. Repeat to get a resistance versus controller knob angle curve. At least that gives me an idea what range the thermistor should have, with the VW troubleshooting "hot" value as a check. At 140 deg F (60 deg C), the temp sensor should read 3.5-5 K Ohm per VW.

I guess I get to figure out a good replacement thermistor, don't I?

BTW, from the design, it appears to me that all of these little beauties will eventually go open-circuit, maybe after being intermittently open for a while. Open-circuit in this application means the controller turns the fuel pump "on", so if you've had trouble with too much Eber output that you've not been able to pin down, the thermistor going intermittently open may be it.
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Lane
MGVWFAN (STF)
anglodeutsch4 (Samba)
73 VW 412 (the Nomad, dropped valve seat land now, argh!)
67 MGB (Built-In Rust from Abingdon)
76 Plymouth Duster /6 (looking for a new home...)
2002 NB TDI (40 MPG)
2009 JSW 2.5 (love it, love it, love it!)
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