Rotax engine modifications

Next, I removed the two carburetors. I disconnected spring between each carburetor and the cross-connect tube. These springs appear to be there merely to stabilize the carbs mechanically. The carbs are mounted to the intake manifolds by rubber sleeves, using what are essentially hose clamps. I loosened the clamps, removed the carbs and sealed them in plastic zip lock bags until it's time to reinstall them.

The plastic zip ties securing the spark plug wires must be cut to move the ignition assemblies aside

I disconnected the water hoses from the water pump at the aft bottom end of the engine, which allowed a few ounces of coolant to drain out. Two of the hoses could not be completely disconnected until the water pump was removed. Removing the pump was straightforward, accomplished by removing the bolts and pulling it off, being careful not to tear the paper gasket. In some places the gasket will stick to the pump and in others the gasket will stick to the engine case, so a little careful coaxing is required. By leaving a couple of the bolts backed off but still in place, the pump can be pulled out a couple of millimeters, then the gasket freed up carefully with a knife blade where it is sticking to the pump housing or the engine case.

The kit manual instructs to modify the water pump, but the specifics are not clear. I have written Tomaz at the factory for clarification on that and some other details that I can't quite figure out from the pictures in the kit manual. I also need to determine how to support the engine for further work. So far, I have left it mounted to the bottom of the shipping box, but I'll need to get it up in the air to complete the mods.

I received answers and photos from Tomaz in reply to my questions about the engine modifications. Tomaz confirmed that they support the engine while working on it by bolting the prop flange to a circular bracket. This allows the engine to be rotated around the crankshaft while working on the top and bottom and mounting the various accessories.

Tomaz also provided some more detail about the water pump modifications, including the one pipe that is replaced by the 80-degree pipe supplied in the kit. He also clarified that the water connection box described in the kit manual is not used anymore, and has been replaced by the welded tube manifold assembly supplied with the kit.

I added the photographs from Tomaz to the Supplemental Photos and Drawings page.

Meanwhile, I read through the Rotax engine installation manual, the line maintenance and heavy maintenance manuals, and the illustrated parts catalog. These were very informative and enlightened me quite a bit about how the engine is put together, plus things like bolt torques, types of Loctite to use in various places, assembly sequences, etc.

I ordered an assortment of gaskets, lock washers and various specified types of Loctite from Lockwood Aviation Supply. The Rotax maintenance manual specifies that the lock washers are not to be reused, nor does it make sense to try to salvage the old water pump gasket, since a replacement new gasket is not expensive.

I bought a 2-ton shop crane from Harbor Freight and used it to get the engine up in the air, remove the bottom of the shipping container that the engine was bolted onto, and put the engine on my workbench. Note that the engine is supported for the lift by heavy straps passed under the intake manifold. The Rotax maintenance manual says that this is an approved way to lift the engine, and it worked nicely.

I can do some of the modification work with the engine sitting on the shipping brackets, but plan to build a plywood support structure to which I will bolt the propeller flange in the same way that the factory does it. Note that when rotating the engine around the propeller flange, it is important to rotate the engine so that crankshaft rotation that the engine sees is the direction of normal propeller rotation. The Rotax manual explains why this is important, and is also the reason why the propeller on a Rotax engine should never be rotated backwards.

I removed the generator cover and rotated the engine two full turns counterclockwise (as viewed from the magneto end) as described in the Rotax manual for preservation after the engine has been stored for a full year. This was because the engine was packed for shipment in May, 2006, and is the method specified in the Rotax maintenance manual for engines that have been stored for more than one year prior to installation. The engine is turned by applying a wrench to the large nut on the magneto end of the crankshaft.

The engine turned over smoothly, with noticeable compression at the proper points. The engine seems to be in good shape -- smooth and tight. The anti-corrosion packing was intact until April of this year, and it has been in the dry workshop for several months, so this is not surprising.

I removed the bolts and fittings in preparation for installing the Pipistrel engine mount.

The mount itself is about 1 mm narrower than the distance between the mounting flats on the engine. I wrote Tomaz and asked him for a recommended fix.

Tomax replied that it's very difficult to achieve precise dimensions on welded assemblies, and that it's OK to bend the flanges on the engine mount enough to slip over the engine mounting points.

I assembled an engine stand from 3/4 inch plywood, allowing the engine to be supported from the propeller flange as Pipistrel does it at the factory. I used 1/2 inch bolts to mount the engine, which are within half a millimeter of the 13mm diameter holes in the outer rim of the propeller flange. The stand is fastened together with wood screws and glue.

I used my engine hoist to support the engine, then I bolted the plywood stand to the prop flange, then I lowered the assembly onto my workbench and clamped it to the bench with some heavy C-clamps. Now I can rotate the engine easily to work on both the top and bottom of the engine for the remainder of the modifications.

The email from Tomaz mentioned that the angles of the elbows coming off the water pump are intended to prevent interference with the engine mounts, so I unpacked the lower engine mounts and attached them to the engine temporarily. Then I held the unmodified pump in place to confirm where the interference occurs. It was apparent that in addition to replacing lower right elbow as instructed, the upper left elbow needed to be repositioned slightly. The pictures below show the unmodified water pump. You can see the interference with the engine mounts.

The water pump photos from Tomaz clarified that the lower right elbow is the one to be removed and replaced with the new elbow supplied with the kit. I clamped the water pump in my bench vise, protecting the surfaces of the pump with wood strips. I turned down the end of a wooden dowel to fit into the open end of the elbow, then heated the attach point with a high-temperature heat gun I purchased at Home Depot.

The Rotax maintenance manual specifies green Loctite 648 for these joints. The manual also says that to separate parts secured by Loctite 648, they must be heated above 250 degrees C (480 degrees F). After applying heat for a couple of minutes, the elbow was easily removed. I then tried fitting the new elbow and discovered that it interferes with the upper right elbow when screwing it into the water pump, so I removed that elbow, also.

The photo below shows the method of turning the HOT elbow to unscrew it from the housing.

The photo below shows the original elbow with a 45 degree bend and the new one with an 80 degree bend.

First, I inventoried the parts in kit package F0022 -- engine installation. This took quite awhile, checking the parts against the kit manual and the photographs to try to figure out where everything is used. There are a few discrepancies, but I concluded that this is because a few of the parts listed in the parts inventory were installed at the Pipistrel factory. These appear to be associated with the mounting of the electronic ignition assembly.

As Tomaz suggested in his last email, I bent the flanges of the upper engine mount slightly so that it would fit over the engine attach points. This turned out to be pretty easy.

Then I studied the various photos supplied with the engine to be reasonably sure which parts are used to attach the engine mount. I concluded that the right side of the mount is attached with the original 10 mm socket head cap screw that also goes through the engine case halves at that point. I used the original flat washer under this bolt, and replaced the lock washer with a new one that I had ordered from Lockwood Aviation. I attached the left side of the engine mount with an M10 x 25mm socket head cap screw from package 1031600 and a 10.5mm plain washer from package 1030020. For the top mounting hole I used the spacer bushing, 20 mm diameter, 8 mm hole, 10.2mm long, part number 1031400, between the engine mount and the engine block, secured with an M8 x 30mm socket head cap screw from package 1030020 and an 8.4mm flat washer, 25 mm diameter, also from package 1030020. I applied blue Loctite 243 to all of these screws.

The photos below show the three bolts that attach the engine mount to the engine block.

The next step is to fit the carbon fiber engine cooling scoop. After looking at how it fits onto the engine, it became apparent that I will have to remove the intake manifold assemblies to get the scoop into position. A close look at the engine assembly pictured in the kit manual confirms that at the Pipistrel factory they have the manifolds removed for this step.

I'm leaving in two days for a week-long business trip, so I will tackle this step when I return.

I had emailed Leon Brecelj at Pipistrel to ask for clarification on the rubber strips that the kit manual says are installed on the carbon fiber air cooling duct. Leon has replaced Tomaz in providing factory customer support. The kit manual says to install rubber strips, and the small pictures in the manual did not provide enough detail to determine exactly what is supposed to be done. I was looking for some sort of edge protector, but after receiving email clarification with accompanying pictures from Leon, I realized that I was looking for the wrong material. The pictures from Leon clearly showed foam material approximately 1/4" thick. So, I concluded that part number 1036201 from kit package F0025 was what I was looking for. This is adhesive-backed foam 1 cm thick, 5 cm wide, and one meter long. Following the photographs from Leon and in the kit manual, I cut the foam to appropriate sizes and applied it to the intake duct.

There is a stepped three-layer strip of foam at the rear center of the duct, and a foam rectangle on three of the four tabs that wrap down around the cylinders. The tab next to the air scoop at cylinder number 1 remains bare, according to the instructions and pictures in the kit manual.

Note that the foam has protective covering on both the adhesive side and on the non-adhesive side. The blue covering on the adhesive side is obvious, but the clear covering on the black non-adhesive side is easily missed. If you leave it in place, the layers of foam will quickly delaminate.

I removed the two air intake manifolds and the four water connection elbows from the top of the engine. That allowed me to place the carbon fiber cooling air duct on top of the engine, with some gentle coaxing. It fits nicely between the engine mount and the prop speed reducer housing.

A closer look at the water connection elbows revealed that the elbow on number 4 cylinder head has to be rotated about 45 degrees counterclockwise for the water hose to clear the engine mount. So, as with the repositioned elbows on the water pump, I clamped it loosely in a vise, heated it for a couple of minutes with my heat gun to loosen the Loctite and unscrewed it with the same tapered wooden dowel that I used before. I then cleaned up the threads on the elbow, applied Loctite 243 (blue) and screwed it back into the flange, rotated so as to clear the engine mount.

The photograph below shows the elbow prior to modification. You can see that it points directly at the engine mount.

Note that the water elbow fitting protrudes a millimeter or so from the bottom of the flange after it is screwed into the flange. This protrusion seals against the orange plastic ring visible in the photos that show the elbows removed. I didn't want to back the elbow further out of the flange to get the proper angle, because I had talked to another Pipistrel owner who had a problem with water leakage at one of these flanges, which he fixed by taking the flange off and screwing the elbow further into the flange. So, instead of leaving the elbow 45 degrees counterclockwise from the original position when I screwed it back into the flange, I rotated it 135 degrees clockwise past the original position, and then, since the flange is symmetrical, I reinstalled it with the flange rotated 180 degrees to get the proper elbow orientation to clear the engine mount. I hope that makes sense.

I then re-installed the four water connection elbows, using new lock washers and torquing them to the value specified on Page 1 of Chapter 34 in the Rotax Illustrated Parts Catalog. Later, while working on the installation of the water hoses and water manifold, I concluded that it would have been easier to have connected the elbows to the hoses and manifold first, then bolted the elbow flanges to the engine.

As Tomaz had mentioned in an earlier email, the cooling water distribution manifold has changed since the kit manual was written, but the photos that he sent make it pretty clear how to position it and connect it to the water fittings.

I attached the carburetor cable bracket to the upper engine mount with two M5x10 bolts and nylon lock nuts with Loctite.

I then removed the water lines from the Rotax water reservoir that came with the engine and cut them to the appropriate lengths to install the Pipistrel water collection manifold. The air intake manifolds need to be removed for this step. I had lightly bolted them in place after installing the cooling air duct, to keep any foreign material out of the cylinders. While working on the water lines, I used a crumpled paper towel to temporarily plug the cylinder intake ports.

Because of the relatively short hose runs, it is probably a good idea not to bolt the water line elbows in place until they have been attached to the water lines, but I had already torqued the elbows down, so with a little fiddling I was able to work the water lines over the fittings and get the hose clamps in place.

These steps took a lot longer than it seems that they should need, but it required some time to reconcile the parts with the inventory, compare everything with the kit manual, study the pictures from Leon at Pipistrel and convince myself that I was doing it all correctly.

I re-installed the propeller adjustment control arm into the bracket. I had to remove the control arm previously in order to perform the other engine work, but I left the bracket in place, so it was simple to mount the control arm with one bolt and two thin washers that appear to be made from teflon. I applied blue Loctite 243 to the nylon lock nut to ensure that it does not loosen.

I removed the cap screws holding the upper engine mount in place, then reinstalled the screws using my new electronic torque wrench to apply proper torque as specified in the Rotax Illustrated Parts Catalog, using blue Loctite 243.

Note that some individual bolts have a torque specified in the parts catalog where the individual bolt sizes and part numbers are listed, accompanying the assembly drawings. Where no torque is specified with the part number, the common torque for the bolt size applies. These common torques are found in Chapter 34 of the Illustrated Parts Catalog, at the top of page 1. Chapter 34 also repeats the proper torque values for all bolts found in previous chapters.

I then completed the installation of the intake manifolds with new lock washers and torqued them to specs.

I scraped a few remaining bits of gasket material from the water pump housing and reinstalled it on the engine block using a new gasket and new lock washers. Note that the bolt with a copper washer goes in the bottom mounting hole of the pump housing. I replaced this copper washer with a new one. All bolts were torqued to specs from the Illustrated Parts Catalog.

I then installed the water inlet elbow, oriented as shown in the photos provided with the kit. I used a new o-ring and new lock washers for this installation.

I installed the lower engine mounts using M10 bolts and Loctite 243, torquing them to the value specified for M10 bolts.

I then connected the water lines to the two upper elbows on the water pump. Then I slid the water line heat protection sleeve over the two lower water lines and connected those lines to the two lower water pump elbows.

The heat protection sleeve has an outer covering that is quite flexible and it can be pushed back onto the lines far enough to permit installation of the hose clamps. Then it can be stretched and worked over the hose clamps at the ends of the water lines, thus covering the full length of the water hose.

As instructed in the kit manual, I chamfered the two threaded holes on the left side of the gear box. I used a metal counter sink purchased from Home Depot to do this. The reason for the chamfer is to provide a slight relief that permits the threaded studs on the aluminum spacers to screw completely into the gear box, allowing the body of the spacer to fit flush against the machined surface of the gear box.

I mounted the two aluminum spacers using blue Loctite 243, then screwed two rubber shock mounts into the spacers. The threaded studs on the shock mounts were about 7 mm too long, so I cut them shorter so that they would seat flush with the ends of the spacers. I secured the shock mounts to the spacers with Loctite 243.

I then mounted the oil cooler to the shock mounts using two M6x10 hex-head bolts and lock washers, and one M10x16 hex bolt and lock washer, screwed into a matching hole in the gear box housing. In addition to the lock washers, I applied Loctite 243 to all three of these bolts.

The installation of the coils and electronic ignition assemblies has changed since the kit manual was written, but using the pictures provided with the kit and the pictures I took before I disassembled the engine, I reinstalled the shock mounts, spacer arms and the ignition assemblies.

Note that the two coil ground wires are secured under the forward mounting screw for the right-hand intake manifold.

I then slid the four female connectors onto the mounting arms until they clicked in place, and inserted the matching male connectors using the numbers that I marked on them during disassembly.

I attached the bracket that holds the throttle and choke cables to the mounting angle on the upper engine mount. I used two M5x10 cap screws (the mounting angle has matching nutserts installed) and blue Loctite 243.

I then removed the oil inlet line fitting from the oil pump and replaced it with a different fitting provided with the kit. This fitting has a nipple for attaching the flexible oil line using a hose clamp. I used blue Loctite 243 as specified in the illustrated parts catalog and screwed it in, applying the specified torque. I then attached the oil line to the nipple using a hose clamp. This oil line came already attached to the upper oil fitting on the oil cooler.

This picture shows the original fitting on the oil pump. This fitting is removed and replaced with a brass nipple fitting.

Then after studying the kit manual and the supplemental pictures supplied with the kit, I determined the path for the oil line from the lower nipple fitting on the oil cooler. I worked the line over the nipple and secured it with a hose clamp. I then routed the line as indicated in the kit manual and secured the two lines together with a cable tie as shown in the pictures. The upper end of one oil line is tied to the right intake manifold using cable ties and a short length of oil line as a stand-off spacer. This was also copied from the pictures that came with the kit.

The right-side angle fitting for the carburetor compensation tube connection had to be rotated to avoid interference with the water collection manifold tube. I unscrewed the fitting from the intake manifold, cleaned the threads and applied Loctite 574 as specified in the Rotax Illustrated Parts Catalog. I reinstalled the fitting, reoriented to route the compensation tube behind the water manifold.

The left-side angle fitting was OK as originally installed.

I then installed the compensation tube and tightened the hose clamps that secure it to the two angle fittings on the left and right intake manifolds.

This picture shows the right-side fitting rotated so that the compensation tube passes behind the water manifold.

I loosened the carburetor mounting clamps, inserted the carburetors into the rubber mounting flanges and tightened the clamps against the spacer sleeves that control the clamping force on the rubber flanges.

I then studied the carburetor modification instructions in the kit manual and the supplemental photos that came with the kit to determine how the carburetors are modified for the Sinus installation.

I removed the throttle control lever from the throttle shaft and removed the support bracket from the top of the carburetor. The brass bowden cable mounting fitting for the throttle cable is removed from the support bracket and screwed into the carburetor, pointing down toward the throttle lever. The curved bowden cable tube that routes the choke cable to the choke lever needs to be loosened and rotated to point forward, angled to pass to the side of the throttle bowden fitting.

The large hole in the end of the throttle stop lever is opened up to 7 mm, and then the allen screw, brass sleeve, brass washer and nut on the end of the original throttle control lever are removed from that lever and remounted in the 7 mm hole on the throttle stop lever. For the Sinus installation, the throttle cable is connected to this screw/sleeve/washer assembly and moves the throttle shaft via the throttle stop lever, rather than the original throttle control lever.

The throttle return spring that was disconnected from the throttle control lever is now connected to the throttle stop lever as shown in the kit manual. Note that this revised return spring connection causes the spring pressure to hold the throttle at the fully closed position, rather than the fully open position that is standard for the Rotax. Thus the Sinus throttle cable pulls the throttle open against the return spring tension. In the standard Rotax throttle operation. the throttle cable pulls the throttle closed against the return spring tension.

The Sinus kit manual also appears to say that the bowden cable connection point on the choke control lever is drilled out to 7 mm; however, I checked the fit of the cable connect fittings from the Sinus kit and determined that they fit into the choke lever as delivered, so I did not drill the choke lever, but left it alone.

These parts remain after the carburetor modifications, and are not used in the Sinus installation.

I also noted in the supplemental photos from Pipistrel that the factory installed two rubber spacers between the water manifold that the upper engine mount. These spacers appeared to be short sections of water hose so I cut a piece of hose from some excess material, sliced it down the middle lengthwise, and worked the two pieces between the water manifold and each end of the upper engine mount.

I installed the magneto cover, using Loctite 222 (violet) on the three screws and torquing them to 70 in-lb as specified in the illustrated parts catalog. The catalog specifies Loctite 221, but it appears that Loctite 221 and 222 are equivalent products.

After careful study of the kit manual and the photos from Pipistrel, I began installing the fuel lines.

The kit includes a four-way splitter with three 6 mm fuel lines (with fire sleeve covering) attached to three of the legs and a restrictor installed in the fourth leg. The kit manual notes that this restrictor is where the fuel return line is connected. I routed the line opposite the splitter to the fuel pump and connected it to the output port of the pump using a 12 mm hose clamp.

I then installed a length of 8 mm fuel hose and fire sleeve to the input port of the fuel pump using a 13 mm hose clamp.

At this point I needed some more information regarding the location of the fuel flow sensor. The kit manual indicates that the sensor is installed just above the gascolator in the supply line leading to the intake port of the fuel pump. The photos that came with the kit appear to show the flow sensor in a line leading to one of the carburetors. The photos also show a fuel filter installed above the gascolator,