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Luftmeister Auxiliary Fuel Tanks
http://bmwmotorcycletech.info/luftmstrtanks.htm
article #2

Copyright, 2012, R. Fleischer


Description:

Luftmeister auxiliary fuel tanks fit many of the long wheelbase Airhead models, but NOT the short wheelbase R65/R45...(or so I originally thought), and per my Luftmeister catalog ...but, in 2005 I was informed that SOME were made for the R65/45, with either the backside being a plate cover, or some sort of plate covering the fuse area ...I have never personally seen these, only heard of them from one person.

All the Luftmeister auxiliary fuel tanks I have seen are made of aluminum alloy, and the ones other than the R65/R45 hold approximately 1 gallon plus 8 ounces of gasoline, if filled to the brim (NOT recommended by me).  The R65/R45 MAY hold the same, I have NO information on them.....all information that follows refers to the larger engine Airhead tanks, as I am very familiar with them.  NOTE:  The R65 in the 1980's had the larger displacement size of rear subframe.  It is my guess that the Luftmeister tanks for all the models other than the early R45/R65 will probably fit those larger frame R65.

These tanks were originally produced with foil strips ...probably Explosafe, stuffed inside. http://www.explosafe.com/   The stuff is aluminum, I think, rather than magnesium or any other metal, IS electrically conductive ...and looks something like silvery metal as might come out of an office paper shredder if you fed aluminum foil into it.  Removing that material, or much of it, which does not seem to have any great safety features, allows only a tiny amount additional fuel.   I have seen one set of tanks in which the stuffing appeared to NOT be metal, but an aluminum plated plastic material. It is my belief that the original stuff WAS shredded strings of aluminum metal.

It is my belief, with no proof, that the 'Explosafe' material MAY have been installed originally in these Luftmeister tanks for anti-sloshing purposes due to the early type of venting (never used for sold tanks??)....and that any idea of it being used to prevent explosions/fire, was probably quite secondary; and, likely unnecessary.

The tank petcock valves were mostly of a type that was equipped with a knurled knob, and those valves incorporated a fuel screen that sticks up into the tank, just like the later BMW fuel tank petcock valves, but on a smaller scale.   More than one type of valve has been fitted. Some valves have peg handles too easily knocked off by passenger's feet, those handles can be easily shortened first.   The packing material on at least one type of the valves is replaceable, and the adjustment nut can be set for smooth knob operation.  

The upper tank port, as well as the bottom port containing the valve, was designed in its final version to be plumbed into the Airhead fuel system as a CLOSED system, thereby avoiding noxious vapors that would annoy the rider, due to the vacuum effect that motorcycles tend to create in the rider area.   The original design was played with quite a bit by the Luftmeister folks, who, I think, originally intended the upper port to be for an outside vent.  They also experimented with vented caps ...and all the caps I have seen to date have been drilled and threaded for some sort of venting screw or similar method ...and then PLUGGED before they were finally sold ...as Luftmeister apparently changed its mind.  I never got this clarified with Matt Capri.  The method of venting needs serious consideration when installing these tanks.  Read this article carefully!
 

Use (preliminary) and Venting Considerations:
It is quite possible to install only ONE of these Luftmeister tanks, if that is what you want to do.

It is possible to install a NON-closed venting system.  This can be tricky.  The upper port on the tanks can be run, either using a T between two tanks and one hose, or separate hoses and no T, to a VERY rearward point on the motorcycle...perhaps at the license plate area.   If this is done, there is no special fancy method needed for remembering to keep the main tank petcocks open, when parking the bike in the sun with a high level of fuel in the Luftmeisters.  I'd recommend that Explosafe material be installed, to prevent sloshing losses ...although that might be moot, with proper travel of the vent hoses.   A small hole in a metal plug in the vent line should also be helpful.   The plug's hole need not be very large for proper venting...and to allow fuel to flow. All this is theoretical.

The assumption, below, is that you are using a CLOSED system.  If you are using a vent, as mentioned above, or similar, make compensation when reading the rest of this article.

Using these tanks requires some definite thought and care. If the main tank valves are improperly used, you can cause the Luftmeister tank seams to split when they are quite full, since liquid does not compress.  This can happen from the motorcycle sitting in the sun.  For garage storage, I recommend using only the center-stand, closing the main tank valves, and then loosening the Luftmeister side tank caps a bit, perhaps a couple of turns, and closing the Luftmeister valves.   This will almost totally eliminate any possibility of a dangerous leaking condition from the carburetors (from a bad float bowl needle), which can cause a fire, explosion, etc.  Many folks have gas fired water heaters in their garages, or electrical switches...etc.   You must remember to lightly tighten the auxiliary tank caps before riding off.  There is a fair amount of fuel left in the lines and filter above the carburetors, so any serious leak from the carburetor, usually a faulty bowl in some way, or a faulty float needle, should be addressed immediately....this is all on even a stock system on an Airhead.

When filling up at a gas station, CLOSE the main tank valves during actual filling of the main and side tanks.

The final design of these tanks were designed by Luftmeister to be used in a closed system, with no external venting. At one time they had other ideas.   Matt Capri said he designed these tanks for a sort-of similar closed system as I described, per a talk I had with him.  I have tried other venting methods.  I originally really did not want a closed system due to the careful watch you must make on all the above mentioned valve and cap operations. In particular I tried just running the Luftmeister valve outputs to a T at the carburetors, and ran the upper Luftmeister vent connections to a common T and thence to the existing BMW tank venting hose under the tank.   This resulted in BAD fumes, especially from a siphoning effect!   I then tried combinations of running a hose up high (to top of windshield!), but still could not eliminate the problems. I determined that almost 3 feet higher was necessary.  I suspect Luftmeister found the same problems.   I think they also experimented with vented caps, since all the ones I have seen had that vent sealed by a screw.      The closed system works fine, but you MUST remember the cautions on using the main tank petcocks, etc. (see prior comments on using an open system with hose to the license plate area).



Installation Details:

I will describe the left side, the right side is identical:
Fit the tanks in mockup form first.   Be sure they fit as the welded-to-the-tanks clamps may not be shaped just right, and you may very well want to line the two clamp areas with rubber, so the tanks fit better. It is important to keep the mounting of the tanks as high as possible.  If they are NOT mounted quite high enough, you will NOT be able to use all their contents.  After you fit them, and bolt them to the BMW rear subframe area, you are ready to install the plumbing. NOTE that the outlet valves must either have the internal screens sticking up into the tank, or, an external small fuel filter.  SOME folks use BOTH.  I do.   I also put rubber onto the tanks clamp areas.....you don't want to mar the BMW frame tubing, nor do you want the tanks moving about. 

For fuel filters, this is the ONE place I use the smallest of the plastic aftermarket folded-paper-containing filters.  Install them in a convenient position in the hose from the tank petcocks.  Remember that if you run that hose upwards, then you will NOT be able to fully use the Luftmeister tanks contents!   Use ONLY FUEL HOSE!!

From the main tank on/off/reserve petcock valve, connect a METAL BMW gas line "T", rather close to the main tank petcock valve, using an 'arm' of that T and hose as required. The BMW metal T fittings are #13-11-1-336-900.   The other 'arm' goes, via hose, to the 90 degree fitting of the TOP outlet/inlet area of the Luftmeister tank. You will need two more of the metal T fittings for this side, and some more hose. From the first T mentioned above, the NON-arm goes downward to another T, its arm. The other arm of that 2nd T goes downward to a final T arm and the final T arm goes to the lower valve outlet of the Luftmeister. 

This leaves you with two each NON-arms to finish:  the NON-arm of the middle T goes to the old crossover rubber hose that leads to the right side of the machine. The lowest T non-arm goes to the carburetor. It is important that the lowest of the three T fittings that goes to the carburetor (non-arm outlet) is as low as possible, so use a really short section of rubber fuel hose. If this is not low enough, you will not be able get all the gas from the side tanks.

Use of hose clamps are optional, and may not be needed with many types of fuel hose.  I found them mostly unnecessary, although I used them at the Luftmeister TANK fittings, due to the SHAPE of the particular fittings I used there.

I HIGHLY recommend installing fuel filters and NOT depending on the in-tank screens.   A good setup is to install one fuel filter at each main tank outlet, and install one small one in -line with each Luftmeister tank outlet hose.   The common clear-plastic-cased paper element filters work very well, as do the sintered types.    The smallest ones work fine for the Luftmeister tank outlet hose, but I prefer a larger one for the main tank outlets.   These are all available from NAPA, and most other autoparts stores.  The plastic nipples on these are slightly fragile (cracking possible if under side pressure), so install them carefully.  I have nothing against your use of other types of these filters.  Extensive information on fuel filters, hoses, petcocks, is in the following article:
http://bmwmotorcycletech.info/fuelfltrs&petcocks.htm



In late June, 2009, I saw a modification to the Luftmeister tanks, on a sidecar rig.   On an Airhead sidecar rig, the rear upright sidecar strut typically precludes using a Luftmeister tank on that side.   Here are a couple of photos showing what someone did ...they reversed the sides the tanks are used on, allowing both tanks, and modified one for the strut.   The total capacity of the tank that was modified will be reduced some, of course.  Notice that on the left side tank, since it was originally designed for right side use, that the filler cap is at the rear; and, same for the modified right side tank.

 

 


Filling up...assuming closed, non-vented installation:

When filling up at a gas station, CLOSE the main tank valves during filling of the main and side tanks!! 

Fill the main tank. Remove caps of Luftmeister tanks, fill to about a half inch below the bottom of the top threads.  Do NOT fill to the brim unless you plan to have the main tank and the Luftmeister valves all ON, and riding off IMMEDIATELY.  Install the Luftmeister caps, which may be drilled by Luftmeister along the knurled edge, and SEEM to look vented... but the caps ARE NOT VENTED, and are sealed with a plate, screw, ETC ...as shipped. The caps have a rubber O ring to seal them to the tanks.  Replacements can be any common type....see NOTES 3, end of this article, for information.

After filling the tanks and replacing their knurled caps, IMMEDIATELY turn the main tank ON, one or both valves, in accordance with your normal riding habits ...(which you may want to change ...to both main tank valves being on).    At this point you can turn on the Luftmeister valves themselves on if you want to.

IF the bike is parked in the sun the heating of the side tanks will cause the gasoline in them to expand a bit, and thus the level will rise slightly, compressing the small air space you left, and no problems will occur. If the tanks heat enough and the level was high enough, the expanding gasoline would move UPWARDS INTO the main tank, since you turned the main tank valve(s) on after refueling>>>...still no problems.  Even if only one main tank valve is turned on, the crossover hose (you DID leave that?...moot on some Airheads with one petcock, idea is same) will allow the auxiliary tanks to vent properly to the main tank.

IF you turn off the main tank petcocks, the pressure can continue to rise in the Luftmeister tanks ...and either overpower the carburetor float needle (not usually), or split a Luftmeister tank seam, or?  Thus, the reason I say to either not turn off the main tanks during storage; or, better, turn them off and then unscrew the Luftmeister caps a bit (main tank valves OFF).   Think over carefully what I am saying here.....NOW do you see why I said NOT to totally fill the Luftmeister's? >>...liquid will not compress!  You do not want problems on the road, or when parked, or when stored in your garage, etc. MORE in the next paragraphs....

Parking/storing the bike in your garage....or wherever:
It is best to use the center stand during parking or storage, and NOT the sidestand; otherwise, the right side tank can transfer gasoline to the left side, causing overflow, if caps are loose.  This CAN happen even if the right side tank is not quite or nearly full ...and its valve is open.   Turn main tank valves OFF. Turn Luftmeister valves OFF.  LOOSEN Luftmeister filler caps a few turns.  This will NOT work if the Lufty's have a lot of gas in them and you are using the side stand ...the right Luftmeister will feed the left, and you'll have gasoline all over the place. 

****If you must use the side-stand, leave the main tank valves on, and the Luftmeister caps tight.   For side-stand use and safety purposes if in your garage for STORAGE or even overnight purposes, drain the Lufty's and leave the main tank valves turned off.   Remember that gasoline fumes in enough concentration can make for a large bomb ...and light switches in your garage, static electricity, water heaters, etc.....can ignite the fumes.  Be cautious!   THINK!! about what I am saying in these paragraphs!

On-the-road.....For automatic feeding, and keeping your original main tank reserves, but adding the approx. 2 gallons in the Luftmeisters for use:
Simply turn BOTH main tank valves ON (levers DOWN) AND turn on BOTH Luftmeister valves. Ride until you need reserves, then turn main tank valves to reserve, just like you always have, one at a time if you want to (or, both at once, my recommendation). Any combination of using mains, sidetanks, reserves, etc., is OK with me, so long as YOU understand all implications!

NOTES, CAUTIONS, ETC:
The Luftmeisters are normally AND BEST INSTALLED in a CLOSED system.  In any main tank valve position (except OFF), the main tank then becomes the VENT for the Luftmeisters, allowing the Luftmeisters to vent and operate "automatically".  The main tank, with its petcocks ON, provide a venting of excess pressure and even gasoline from the Luftmeister side tanks, into the main tank, keeping you from finding your side tanks splitting, or having other ills befall you.  If you are using a vented system, then many things in this article do NOT apply; and I highly recommend AGAINST such a vented system, due to fumes and some dangerous possible problems.   I suggest not removing all of the 'Explosafe' material in the Luftmeisters.   While it is PROBABLY safe not to have ANY, it takes up very little actual liquid equivalent volume. I generally take about 3/4 of it out. Removing ALL of it adds only about a cup's worth of gasoline at the most.

NEVER park your bike in the sun with the main tank valves turned off!  ...the side tanks will pressurize and may burst a seam or leak at a fitting. The leaving of a small air space in the top of the Luftmeister tanks may help some, but do NOT depend on that!   I had one of my carburetors develop the usual 'tad of dirt in the float needle area' at a campout some years ago (Bad to the Beach campout). I had left the Luftmeister valves closed, main tank valves ON ...like I always do when out someplace on a bike with the Luftmeister side-tanks. Someone caused my extensive prep and painting work on my Luftmeisters on my 1983 R100RT to be ruined when he 'kindly' turned off my main valves to stop my tiny dripping leak.  So, you have been warned about how you use the valves, caps, etc.


Final thoughts added here, in edited form, due to E-mail exchanges on the Airheads Mailing LIST:

There are SIX, some say SEVEN, types of petcocks in BMW Airheads use, you may have to make modest changes to accommodate those petcocks, such as a minor rearrangement of the T connection at them, or perhaps your main tank petcocks are vertical downwards outlets type. 

The last of the Airheads had gas and fumes solenoids mounted to the underside of the starter motor area cover ...and BMW installed TWO right hand style petcocks to accommodate the plumbing.  Better, if you have removed all the solenoids, ETC., to install a proper LEFT hand petcock for the left side.

There are single outlet tanks on some smaller engine'd Airheads, and you can simplify the installation and they will work OK.

The Luftmeister tanks were not normally vented to the atmosphere directly.  I believe that originally they were to be, but my guess is that the fumes were very annoying, and most of the Luftmeister fuel caps are found drilled for venting, but sealed over, sometimes with a screw ...or the machining in-completed.  They should not be vented.   RE-SAID:  The CAPS are NOT vented, although they might look that way ...I think the caps were made with venting in mind, then that was not actually done.   My experiments showed that Luftmeister probably had venting problems during the design, and that is why they went to a closed system.  

I have had a number of sets of Lufty's here, and the caps are not all done the same way, but none are actually vented.  I have seen some that needed work to make sure they were sealed.     I tried an open system once, with a fume line up as high as the top of the windshield.  NO GOOD, fumes were nasty. I got the same annoying results if looped downwards or up and downwards.   I also tried using the main fuel tank venting on a 1983 RT and a 1984 RT ...that is ...the tank fill area overflow pipe or other vent pipe, that comes out, stock, under the main tank; ...still not good about fumes.  I then decided Peter Adams (Luftmeister owner) and Matt Capri (responsible party....), had it right as shipped.

An empty, cap sealed Luftmeister tank, will POSSIBLY fill SOME, from the main tank, but the situation is NOT dependable.  Main reason for the mention is that if you think you have used up all the fuel in these side-tanks, you might not have.

The original cap rubber O-ring can be replaced with a somewhat thinner version, such as the Napa R-26, which is 34.5 mm ID and 3.5 mm thick.


Revisions:
10/03/2008:  All prior updates incorporated, AND, major revisions to the text, etc.
06/30/2009:  Add photos and text about reversed and modified tanks.
10/09/2012:  Add QR code, add language button, update Google Ad-Sense code
03/06/2016:  Update meta-codes, justify things more to left, layout changes.
08/29/2016:   Update meta-codes, H.L., scripts, fonts, layout, slight clarifications.

Copyright, 2012, R. Fleischer

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Last check/edit: Monday, August 29, 2016