Relocation Of Rotax Oil Pressure Sending Unit

The Rotax 912 ULS engine has an oil pressure sending unit located on the forward bottom right corner of the engine. Quite a few builders have experienced the oil pressure sending unit going bad prematurely from what many believe may be engine induced vibrations. Once again DOG Aviation is attempting to make a preemptive strike in the hopes of having trouble free operation from the oil pressure sending unit … this will be accomplished by relocating it to the firewall and using a rubber mounting grommet. The new home for the oil pressure sending unit will be adjacent to the fuel pressure sending unit on the modified dual mounting bracket fabricated a couple of months ago.

To accomplish moving the oil pressure sending unit, Aircraft Specialty came to the rescue. Aircraft Specialty has a kit developed for the RV-12 to move the oil pressure sending unit to the firewall. The kit includes an adapter fitting for the block of the Rotax engine, a restrictor fitting, Teflon hose and an adapter fitting for the oil pressure sending unit. Because I was striving for an aesthetically pleasing mounting for the oil pressure sending unit, decided on making a modified dual sending unit bracket so both the fuel and oil pressure sending units can be mounted together on the firewall. Because this mounting is at a different location, Steve at Aircraft Specialty sent me all the fittings and suggested I remove the sending unit from the engine, install the fittings and run vinyl tubing between the fittings to determine the exact length of hose necessary … then return the fittings back to Steve so a custom oil pressure hose can be fabricated.

Removing the oil pressure sending unit from the engine … a paper towel ready to catch oil but not a drop came out of the oil pressure port when the sending unit was removed.

The Aircraft Specialty supplied fittings that will be installed on the Rotax engine at the oil pressure port … the left fitting screws into the port on the engine where the oil pressure sending unit was removed, the 45 degree fitting on the right has a restrictor built in and screws onto the fitting to the left.

Following Steve’s suggestion, the fittings were installed on the engine and a piece of vinyl tubing was attached and routed to the new home for the oil pressure sending unit on the firewall and a measurement was made for the amount of hose necessary. Also of note, the Rotax Illustrated Parts Manual shows Loctite 243 used on the oil pressure sending unit’s threads, so the threads on the fitting installed in its place had Loctite 243 applied to them. Initial thoughts were to run the Teflon hose under the engine but after thinking it through, decided the safest route was to run the hose up and across the top of the engine where it can stay cooler and away from the heat of the muffler and exhaust pipes.

My finger is pointing to the adapter fitting and restrictor fitting installed in the oil pressure port on the engine ... the 45 degree flair fitting with vinyl tubing attached so a measurement could be made on the length of hose necessary to relocate the oil pressure sending unit to the firewall.

At the firewall, an adapter fitting will sit in the rubber grommet and serve as an interface between the oil pressure sending unit and the Teflon hose fitting. The fitting used for measurements in the photo below is a 45 degree fitting … however, the Teflon hose will be made with a 90 degree fitting for the firewall connection.

Measuring the amount of tubing necessary to reach the new mounting location for the oil pressure sending unit on the firewall. The Teflon oil pressure hose which will connect to the oil pressure sending unit at this end will have a 90 degree fitting and not the 45 degree fitting shown in this photo.

Decided for my application the actual length of the hose material not including the fittings needs to be 37".

Return from the future:

The changeover to Aircraft Specialty’s remote oil pressure sender kit has finally been completed (well almost). Covered on a posting February 5, 2016, felt it would also be best if I were to return from the future and edit this post as a follow-up on installing the remote oil sender hose from Aircraft Specialty ... especially since this entire post covers their remote oil sender kit for the RV-12. As mentioned earlier, measurements were taken using a vinyl hose so Aircraft Specialty could make a custom remote oil sender hose for the DOG Aviation RV-12 utilizing a different fitting and length than the one they would normally supply in their retrofit kit. The reason for this, as mentioned earlier, is because a special mounting bracket was fabricated so both the oil and fuel pressure sending units could be mounted together in a bracket on the RV-12’s firewall. After measurements were taken and passed on to Steve at Aircraft Specialty … three days later, DOG Aviation’s receiving department took delivery of a custom, quality built, conductive Teflon hose in fire sleeve. Have to say, the customer service from Steve and follow-up has been nothing less than outstanding for each of the five kits that have been purchased from Aircraft Specialty for the DOG Aviation RV-12 … Teflon brake line kit, Teflon fuel line kit, Teflon remote oil pressure sender kit and the totally slick canopy locking system.

The custom Teflon hose made for the DOG Aviation RV-12 by Aircraft Specialty is a different length and has a 90 degree fitting where a straight fitting would normally be on their standard kit hose.

There are two mounting options possible with the hose I ordered … depending on the final location for the voltage regulator. If the German built Silent Hektik (or Ducati) voltage regulator is mounted using the old mounting location on the firewall shelf reserved for the voltage regulator, the remote oil sender hose can be routed across the top of the Rotax engine, down under the engine mount and then sweep over to the oil pressure sending unit on the firewall. This arrangement still allows for a cooling cap to be installed over the regulator and room for the cool air blast tubing to supply cool air to the regulator.

The hose for the remote oil pressure sending unit is routed so it won't interfere with the cooling shroud or blast tube if a voltage regulator is mounted on the firewall shelf. Because the regulator sits directly under the oil pressure sending unit, with the hose paralleling the firewall, there is plenty of room for the shroud and blast cooling tube used to cool the regulator.

The other option available which is likely better (especially for those who have followed Van’s latest mounting instructions to move the voltage regulator under the instrument panel shelf) is to run the hose for the remote oil pressure sender following the same path as the hose for the fuel pressure sending unit. The hose length I chose will work for this route, but ideally could be an inch or two longer.

Hose for the remote oil pressure sending unit routed along the same path as the hose to the fuel pressure sending unit. This may be a preferred solution if the voltage regulator is not directly under the oil pressure sending unit.

At this point in time, the final decision has not yet been made on where the voltage regulator will be mounted, so only the engine end of the remote hose will be tightened ... the fitting on the sending unit will remain loose until a final decision is made regarding the location of the voltage regulator … which will dictate which way the firewall end of the remote oil pressure sender hose needs to be routed.

The Aircraft Specialty conductive Teflon hose for the remote oil pressure sending unit is connected at the lower right portion of the Rotax 912 ULS engine via the supplied adapter/restrictor fittings installed on the engine's block.

Installing Aircraft Specialty Teflon Fuel Lines Completed

The first task for the work session was to finish up installing the Aircraft Specialty Teflon fuel line kit on the DOG Aviation RV-12. The work session began by installing the fuel return line. There is a restrictor orifice in the original Van’s supplied VA-216 fuel return hose. I have read this is a Mikuni #35 idle jet but have not verified that … regardless, the hole in the restrictor is VERY tiny. The purpose of the restrictor is twofold, in that it allows the fuel pressure to remain at a normal level while allowing a metered amount of fuel to return to the fuel tank insuring a constant flow of cool fuel delivered from the fuel tank to the engine compartment to help prevent vapor lock. In addition, the orifice also helps dissipate any vapors that occur from heat buildup on the ground by allowing built up vapors to pass through the orifice and back to the fuel tank. Because there is an orifice is inside the VA-216 fuel line which is being replaced, a special restrictor fitting is supplied by Aircraft Specialty for the fuel return line.


The special restrictor fitting that Aircraft Specialty supplies attaches onto the existing fuel return fitting on the firewall shelf. The restrictor fitting has a VERY tiny orifice drilled into it which accomplishes the same task as the restrictor inside the Van’s VA-216 fuel return hose. So the order of assembly is to first install the restrictor fitting with the TINY hole onto the existing fuel return fitting on the firewall shelf, then attach the fuel return hose (#5 in the second photo of the previous post) that comes from the aft fitting on the fuel marshal. In order to photograph the hole in the restrictor so the viewer can see the hole more clearly, the restrictor was taped onto a flashlight with red tape so light could be photographed coming through the hole.

The Aircraft Specialty fuel return fitting with the TINY orifice that will be installed onto the fuel return fitting on the firewall shelf. This takes the place of the restrictor orifice inside the Van’s VA-216 fuel return hose. The fitting was taped onto a flashlight so the viewer can get an idea of just how tiny the hole in this fitting really is.


The restrictor fitting was placed on the fuel return fitting on the firewall shelf and torqued to specs then the Teflon fuel return line was installed onto the restrictor fitting and connected to the aft port on the fuel marshal.

The Fuel the return hose (#5 in the second photo of the previous post) is attached onto the Aircraft Specialty provided fuel return restrictor fitting which is attached onto the fuel return fitting on the firewall shelf.

Connecting the fuel return line (#5 in the second photo of the previous post) onto the aft port on the fuel marshal. The other end of this hose runs to the fuel return fitting on the firewall shelf as seen in the previous photo.


The last remaining hose in the Aircraft Specialty fuel line kit connects to the last remaining port on the fuel marshal … this hose goes to the Kavlico fuel pressure sending unit on the firewall. The fuel pressure sending unit was prepared by installing a 90 degree fitting on the sending unit and mounting it onto a rubber grommet after the hole in the grommet was made larger per the plans.

The fuel pressure sender hose (#4 in the second photo of the previous post) connects between the remaining port on the fuel marshal and the Kavlico fuel pressure sending unit mounted on the firewall.


The remainder of the work session involved torqueing the fuel fittings, reviewing the wiring changes being made and making preparations to move the oil pressure sending unit from the engine to the firewall alongside the fuel pressure sending unit. Fittings needed to be installed and measurements taken for a custom oil line that Aircraft Specialty will be making for the DOG Aviation RV-12. Will post photos later once the hose is installed.

Instillation Of Aircraft Specialty Teflon Fuel Lines Begins

The Rotax 912 ULS engine has a couple of fuel related items that are not to my liking. First, there is a mandatory maintenance directive to replace ALL the rubber fuel lines at 5 years. Second, I’m not fond of banjo fittings in general because once the crush washers used to make up the fittings have been tightened, they crush a little to form a tight seal. However, they often leak when the fitting is taken apart and tightened again using the same washers … meaning, if one does not want any leaks, the washers should be replaced whenever the fitting is disturbed. So an assortment of crush washers need a part of the maintenance kit.


As a preemptive strike, DOG Aviation has decided to install the Aircraft Specialty conductive Teflon fuel line kit developed for the RV-12. The kit contains conductive Teflon fuel lines covered in fire sleeve which have been pressure tested to 2,000 PSI and have a 10 year replacement guarantee on them. Basically, they are lifetime fuel lines and only need to be replaced based on condition. Also included in the Aircraft Specialty fuel line kit for the RV-12 is all the necessary fittings to convert all the banjo fittings in the fuel system on the Rotax 912 ULS engine to standard aircraft 37 degree flare fittings, plus a few Adel clamps to secure the lines. So it is a win - win … getting rid of all the banjo fittings in the fuel system and installing fuel lines that have no mandatory replacement time limit.


Below are a few photos and some descriptions taken from Dave’s Schmetterling Aviation Blog. He received one of the first prototype kits a little over two years ago and did a great job of documenting the process … in fact, Dave’s documentation and photos are now used in the Aircraft Specialty instillation manual.


The fittings:
A: fuel 'out' from the fuel pump
B: fuel in to carburetor (B & C are identical)
C: fuel in to carburetor
D fuel 'in' to fuel pump
E: fuel return line at firewall fitting
F: fuel marshal - replaces funky block on top of engine

The seven fittings included in the Aircraft Specialty fuel line replacement kit for the RV-12.

The fuel lines:
1: Gascolator to fuel 'in' on fuel pump
2: input to left carburetor (this is the lengthier of 2 and 3)
3: input to right carburetor
4: input to fuel pressure sensor
5: fuel return line (uses fitting E)
6: fuel 'out' from fuel pump

The six conductive fuel lines included in the Aircraft Specialty fuel line kit for the RV-12 are all covered in fire sleeve.

The layout of the lines will be as in this photo.

The new fuel marshal will replace the funky fuel transfer block assembly attached to the balance tube that my finger is pointing towards.

The new replacement fuel marshal used to connect all the new Aircraft Specialty Teflon fuel lines.

Since the carburetors were off the engine, decided the time was right to remove the banjo fuel fittings from the carburetors and install the new flare fittings from Aircraft Specialty. The washer shown in the photo below needs to be removed because the Aircraft Specialty fitting has its own washer and O ring assembly.

The washer shown in this photo needs to be removed before installing the Aircraft Specialty AN-4 flare fitting onto the carburetor.


Most builders (myself included) have had trouble getting a wrench onto the fitting that screws into the carburetor as the body of the carburetor prevents a wrench from sliding fully onto the fitting. The solution is to use the AN-4 cap that is included in the kit … the cap tightens on the fitting then when tightened more will tighten down the fitting into the carburetor. The friction created by the washer and rubber O ring is greater so when carefully removing the cap the fitting stays in place on the carburetor … this worked quite well. Looking closely at the photo by clicking on it to make it larger, one can see the washer and O ring on the fitting that is sitting  on the bench in front of the carburetor.

Using the AN-4 cap included in the kit to tighten the flare fitting into the carburetor.

After the carburetors were reinstalled on the rubber flange assembly, the fuel line to each carburetor was cleaned with compressed air and installed. The Aircraft Specialty fuel lines for the left and right carburetors look identical having a 90 degree fitting on one end … however, the Teflon fuel line for the left carburetor is just a little longer than the one for right carburetor.

The longer of the two carburetor fuel lines in my hand is installed onto the left carburetor.

 The Rotax fuel line on the left has been replaced by the Teflon fuel line for the left carburetor (# 2 in the second photo of this posting).

The new Teflon fuel line is attached to the flare fitting on the right carburetor (# 3 in the second photo of this posting).


The Aircraft Specialty instructions would have the builder remove all the fuel lines from the funky fuel transfer block but keep the block attached to the balance tube and use it as a tie down point for wire ties to hold the fuel lines in place. The decision was made to just remove the block  altogether since it no longer serves a truly useful purpose … so the rubber hose was removed from the balance tube so the fuel transfer block could be slid off the balance tube. An Adel clamp can always be used if necessary to secure the new fuel marshal down onto the balance tube.

The rubber tube that would normally be between my fingers was removed so the fuel transfer block can be slid off the balance tube along with all the fuel lines attached to it. They are all being replaced by Aircraft Specialty Teflon fuel lines.


The new “fuel marshal” was assembled and the two fuel lines going to the left and right carburetors were attached onto the assembly.

Attaching the fuel line for the right carburetor onto the fuel marshal … the fuel line going to the left carburetor (foreground) has already been attached.


The longest fuel line (# 1 in the second photo of this posting) goes between the Gascolator and the IN port on the fuel pump. The Aircraft specialty kit includes two flare fittings for the fuel pump. Older models of the fuel pump had the fuel lines screwed directly into the ports on the fuel pump and require both fittings to be installed. Newer versions of the fuel pump already come with AN-6 flare fittings on the inlet and outlet ports. Because the fuel line from the Gascolator to the fuel pump uses AN-6 fittings, the hose can be connected directly onto the existing flare fitting on the fuel pump’s IN port.

The longest fuel line (# 1 in the second photo of this posting) is screwed onto the Gascolator’s AN-6 fitting and was tightened with a torque wrench outfitted with a crows foot wrench, as can be seen in this photo.


A fitting change is necessary to install the shortest hose (# 6 in the second photo of this posting) because it uses AN-4 fittings. To install the hose, it is necessary to replace the AN-6 fitting on the fuel pump's OUT port with the AN-4 fitting included in the Aircraft Specialty kit. The old fitting had thread sealant on it, so the new fitting was installed using thread sealant as well.

One can see the lower fitting on the OUT port on the fuel pump has been changed to the AN-4 flare fitting.

Attaching the shortest hose in the Aircraft Specialty kit to the OUT port on the fuel pump (# 6 in the second photo of this posting).

The shortest hose (# 6 in the second photo of this posting) connects the OUT port on the fuel pump to the fuel marshal … this is the hose that supplies fuel to the fuel marshal for distribution.


I ran out of time so will continue connecting the remaining two hoses onto the fuel marshal during the next work session. One hose will be for the fuel return and the other goes to the fuel pressure sending unit on the firewall.