Completing Safety Directive SD-00001 Replacement Of Trim Servo Motor

A potential safety issue has been identified with RV-12’s that have the Ray Allen ES MSTS-T3-7A-2 trim servo motor installed. The issue involves the threaded portion of the trim servo motor shaft just forward of the AN315-3R lock nut that secures the AN665-21R clevis. The shaft is bending and, in some very rare cases, snapped altogether. The service directive requires mandatory replacement of the ES MSTS-T3-7A-2 trim servo motor with an upgraded Ray Allen ES MSTS-B6-7T-165 trim motor if the shaft is determined to be bent … or after 1000 hours of flight time.

Drawing from Safety Directive SD-00001 showing the location of the fatigue area.

The replacement Ray Allen trim servo motor has a part number of ES MSTS-B6-7T-165 and MUST to be installed with a bushing (Van’s part number BUSH-BS.188X.313X.222) that slips over the short threaded area of the shaft preventing the shaft from bending. Van’s also suggests when replacing the trim servo motor to also replace the F-1287A servo mounting tray with the newer F-1287A-1 mounting tray. The new F-1287A-1 mounting tray supports the DB9 connector Van’s has switched to … replacing the micro-Molex connector (problematic for some builders not having the proper crimping tool for the tiny pins) used on legacy RV-12’s.   When switching to the new F-1287A-1 mounting tray, you will also need to order an additional AN315-3R nut and Bag 2670 from Van’s which contains the male and female electrical pins, bodies for the new DB9 electrical connectors along with the necessary mounting hardware, plastic bushings and some rivets.

Drawing from Safety Directive SD-00001 showing the new ES MSTS-B6-7T-165 trim motor, bushing BUSH-BS.188X.313X.222 and AN665-21R clevis.

The decision was made that it would be better to take the approach of being proactive rather than reactive so decided to change out the trim motor …. Especially because, to Ray Allen’s credit, the company is offering RV-12 owners a substantial rebate if exchanging the old trim motor for a new one.

The DOG Aviation RV-12’s trim servo motor did not have a bent shaft. However, decided to make the exchange anyway and not need worry about the trim servo motor shaft bending issue anymore. Plus, I liked the idea of switching over to the new F-1287A-1 mounting tray which supports a DB9 connector to replace the micro-Molex connector.

New F-1287A-1 mounting tray which needs to have the doublers cut away and riveted onto the servo tray. Also, my finger is pointing to the new mounting flange for the DB9 connector.

After separating and smoothing the edges of the servo tray parts, they were primed with SEM primer and top coated with white paint for extra protection. Van’s calls for LP4-3 rivets to assemble the doublers onto the servo tray, but I used solid AN470AD4 rivets instead for the assembly. Next the plastic bushings are installed and filed down so they just clear the servo tray. (This is the same process as used on the original servo tray … in fact, I probably could have gotten by using the plastic bushings from the old servo tray).

Below is a photo of the new Ray Allen trim servo motor on the right and the old trim servo motor on the left. The three most notable differences on the new motor are … the round brass portion of the actuator that the new brass bushing will seat against, only four mounting holes as opposed to the six on the older unit and if one looks closely, the four corners of the case are scalloped a little.

Original Ray Allen ES MSTS-T3-7A-2 trim servo motor on the left and the replacement Ray Allen ES MSTS-B6-7T-165 trim servo motor on the right.

On the original trim motor instillation, Van’s covers the trim motor’s mounting flanges with doublers … but they are not called for on the new trim motor. I like the idea of the doublers because the trim motor’s mounting flanges appear to be just a tough plastic. Unfortunately, because of the scallops on the case of the new trim motor the old doublers can’t be used. I tried to file the correct profile in one of old doublers and was not happy with the results … because of the center hole in the old doublers, it leaves a very thin doubler in the area of the center hole.  Although not called for, I decided it would not hurt to just make a pair of doublers as can be seen in the photo bellow.

After trimming the old doubler (top of the photo) to fit the new trim servo motor, one can see how thin the metal is around the center hole (which is not on the new Ray Allen trim servo motor). So a new doubler (bottom of photo) was fabricated to mount the new trim servo motor in the F-1287A-1 mounting tray.

The new Ray Allen ES MSTS-B6-7T-165 servo trim motor installed in the F-1287A-1 mounting tray with my handmade doublers added for good measure.

For the final assembly, the forward threaded shaft temporarily receives two AN315-3R nuts which are tightened together or "double nutted", as they say. The nuts are temporarily used so a wrench can be used to hold the shaft from twisting and torqueing the internals of the trim motor when the AN665-21R clevis is tightened against the bushing. Prior to final assembly Van’s wants the clevis to be 15° from vertical when dry fitting the parts together using only fingertip pressure.

Two AN315-3R nuts are used to double nut the servo motor’s shaft so a wrench can keep the servo motor’s shaft from twisting and possibly damaging the servo when the bushing and AN665-21R clevis are tightened together.

The bushing in the above photo is slightly longer than necessary. To insure a proper fit, Van’s recommends using a drill press with some sandpaper to remove a little material at a time from the bushing so the bushing’s edges remain square. This is one place you don’t want to do any hand filing because Van’s wants the bushing to be a tightly mated fit between the trim motor and the clevis. Material is removed from the bushing until the slot in the AN665-21R clevis is approximately 15° degrees BEFORE vertical when the clevis is hand tight to the bushing. Note: Go slow! … only remove a few thousands at a time because it doesn’t take removing much material to make quite a difference in the positioning of the clevis ( I almost over did it on the second cycle to the drill press where I removed quite a bit more material than I did the during the first cycle). When a finger tight dry fit 15° shy of vertical is achieved, the bushing is ready for final assembly. Permanent red Loctite thread locker is applied to the aft threaded portion of the trim servo motor shaft and while holding a wrench on the double nuts to prevent the shaft from twisting, the clevis is threaded on further beyond the 15 degree point where it should become snug as the clevis reaches its proper vertical orientation.

Completed trim servo assembly ready for electrical connections and final instillation. Note, the two AN315-3R nuts are not yet removed from the forward threaded portion of the Ray Allen servo motor. The two nuts need to be removed at this point prior to installing the assembly back on the RV-12.

As previously mentioned, the new F-1287A-1 servo tray is designed for use with a DB9 connector. Female pins are attached to the wires coming from the trim servo motor and male pins are attached to the wires exiting the tail cone. There is a small change in the colors of the two power wires going to the new trim servo motor (the three trim position wires remain the same colors). The old trim servo motor power wires are both white … the new trim servo motor uses a white and a gray wire. Before permanently installing the wires into the DB9 connector bodies, I thought it best to use a 9v battery to make sure the new motor moves in the same direction as the old motor did … doing this insured the two white wires (servo trim motor power) exiting the tail cone will be connected to the new trim servo motor so motor movement is the same as the old trim motor. After the correct motor movement was established, the trim motor power wires exiting the tail cone were marked. Next, the pins were inserted into the DB9 housings. Van’s suggests sealing all the wires with silicone RTV so that was done prior to final assembly.

After the silicone RTV cured, the DB9 connectors were installed onto the F-1287A-1 trim servo tray. While trial fitting the connectors together, I noticed the DB9 connector was not fully seated. Upon a little investigating it was determined that because the male DB9 connector from the tail cone rests on top of the F-1287A-1 servo tray which has approximately a .060" or so of thickness, the standard sized threaded barrels are a tad too long … so I removed .060" from each threaded barrel and now have a fully seated DB9 connectors (If one chooses not to do this, it is not a big deal. However, I wanted my connectors fully seated and it was easy to accomplish just by removing a little material from both threaded barrels).

The DB9 connector #4 mounting hardware is NOT a piece of cake to install. Access is limited and the use of the tiny #4 MS21042 all metal hex stop nuts makes instillation a real hassle. The hex stop nuts are slightly egg shaped so they really grip the pan head screws … the problem is they grip just a little too tight when trying to install in such close quarters using a 5/32" wrench and only being able to tighten one flat at a time. I finally resorted to placing the head of the screw in a vice and running the metal stop nuts on and off a couple of times using CorrosionX as a lubricant to reduce the bite. The other issue I ran into was my long thin Philips screwdriver was 70 miles south at the southern outpost, so I needed to cobble together another way of accessing the #4 Philips screw heads from above the stabilator while using the 5/32" wrench from underneath the stabilator. Standard Philips screwdrivers are too short to accomplish this task when working by yourself. Below is a photo showing a drawing of how the DB9 connector is to be mounted onto the F-1287A-1 servo tray and the Rube Goldberg use of tools to fashion a way to get on the heads of the #4 Philips mounting screws from above.

Lacking immediate access to my very long thin Philips screwdriver, a Rube Goldberg assembly of various tools from the tool box was used to devise a way to hold the #4 Philips screws from above the stabilator. The photo also shows the drawing for mounting the DB9 connector.

Completed instillation of the new Ray Allen ES MSTS-B6-7T-165 trim servo motor, F-1287A-1 servo tray with the DB9 connector in place. Per Van’s instructions, silicone RTV is applied to the wires to seal the connector.

With the exception of dealing with the #4 mounting hardware for the DB9 electrical connectors, swapping out the RV-12’s trim servo motor went smooth and is not a daunting task. However, one does want to be careful when using the drill press to remove material from the bushing. Go slow and only remove a little material at a time to creep up on that 15° sweet spot.

Beefing Up The F-1254 Roll Bar Support Frames

Entering and exiting the RV-12 is not hard or extremely awkward for the pilot or passenger but there are places one naturally wants to place their hand for support such as on the F-1254 roll bar support frame. In some instances, applying body weight to the F-1254 support frame has caused deformation of the support frame or an outright kinking and bending of the metal.

The F-1254 roll bar support frame is the angled piece in the photo that also has a slot for capturing the canopy’s C-1206 guide plate. As can be seen in this photo, there is a large unsupported area adjacent to the seat which is right where there is a natural tendency to place a hand for support when entering or exiting the RV-12.

Builders have come up with various clever methods of stiffening the F-1254 support frame but when Van’s changed the RV-12’s fuselage design to support the Rotax 912iS engine, they also designed a stiffener that can also be used on a legacy RV-12 fuselage, which the DOG Aviation RV-12 has.

I’ve known about this weak spot ever since the initial flight and have instructed passengers not to place their hands on the weak area while entering or exiting the cockpit. I had already purchased a piece of angle aluminum that I was going to rivet onto the underside of the F-1254 roll bar support frame … but when I discovered there was a Van’s solution consisting of adding a stiffener of sorts, I ordered the new part. The Van’s part number is 12-01254A which comes as two stiffeners that when separated become a left and right part.

The F-1254A-L stiffener clamped in place on the pilot's side of the RV-12 and ready for drilling.

Instillation is not complicated. Van’s suggests breaking the edge on the upper portion of the F-1254A stiffener that will be riveted onto the F-1254 roll bar support which is what I did. The bottom edge that will be riveted onto the F-1234 canopy deck does not need to be broken, but it won’t hurt to do so. One needs to take a little care prior to drilling to align the stiffener then clamp and drill away.

Drilling the F-1254A-L stiffener onto the F-1254 roll bar support.

Completed instillation of the F-1254A-L stiffener riveted onto the F-1254 roll bar support and the F-1234 canopy deck.

The F-1254A L&R stiffeners were installed quite a long time ago on the DOG Aviation RV-12. While reviewing camera photos for an upcoming project, it was discovered the instillation process and photos were never posted on the Blog.

I would suggest all legacy RV-12 owners who have not taken it upon themselves to reinforce the F-1254 roll bar support frame with some sort of stiffener consider this easy to install solution from Van’s. It promotes piece of mind knowing one does not need to closely watch where passengers place their hands as they get in and out of the bird.

Installing FOBO Tire Pressure Monitors

RV-12 owners (and probably owners of most Van’s aircraft) know once wheel pants are installed, it becomes a real pain to check tire pressures. The wheel pants cover the majority of the tires, leaving absolutely no access to the air valves … thus requiring the removal of the wheel pants just to check tire pressures. Sure, some have drilled holes in the wheel pants for access … but then trying to perfectly align the air valve stem with the hole is a pain … plus, it makes it very difficult to use the protective valve stem caps ... so the caps are typically left off which allows crud to get into the valve stem. Hindsight being 20/20, I should have taken a little more time with the wheel pants and installed a hinged access door with a Camlock fastener or two.


One way to get around removing the wheel pants just to check tire pressures, is by installing remote tire pressure monitors … akin to the tire pressure monitors used in most modern cars. I have read positive things about remote tire pressure monitors on the forums so decided to give them a go. FOBO makes just such a product that transmits via Bluetooth to their free App … FOBO’s free App supports both Android and Apple products. FOBO manufactures tire pressor monitors for cars, bikes, motorcycles and trikes. I purchased a trike kit from a company in California called SlingMods which sells the latest sensor 2 version.

The FOBO trike tire pressure monitor kit with the latest version 2 sensors purchased from SlingMods.

The FOBO monitoring system for trikes includes three sensors which screw onto the tire’s valve stem. Included are three lock nuts that can (if desired) be screwed onto the valve stem and cinched up to the back of the sensors to lock them in place … a convenient special molded wrench is supplied for tightening the lock nut up against the backside of the sensors. Also included in the kit are three backup batteries (standard CR1632 coin/button batteries) and three short valve stems for use with tubeless tires.

As can be seen in this photo, the FOBO sensors are actually quite small, about the size of a penny.

The FOBO sensors themselves are quite small (as can be seen in the above photo) and only weigh 7.6 grams … probably not  enough weight to worry about rebalancing the wheel, but I'll be sure to be on the lookout for take off or landing vibrations. The life span of the replaceable CR1632 battery is 1 year. Battery replacement is easy … the top screws off the sensor and the old battery is slid out of a holder and new battery slid in, piece of cake. The sensors support both Bluetooth versions 4 & 5, which is how they report to the free FOBO App. The free FOBO App supports Apple’s iOS 9.3 operating system and Android version 5.0 or later. I installed the FOBO App on my smart phone (which is running Android version 10) without running into any issues. The FOBO App is full featured allowing the user to select wheel configurations, set pressure high and low alarm points, altitude compensation, etc. and share the settings with another device or user. As a deterrent for theft, the FOBO App registers the sensors with FOBO … so if the sensors are stolen, they will not work on another vehicle.


First time setup is easy, after the desired wheel configuration is selected, the App will tell you when to install each sensor so it can be paired with the FOBO App and registered online with FOBO. This part of the process takes a few moments as the App scans, pairs, then registers the sensor. After the sensors are paired, they immediately begin updating the FOBO App with each tire’s pressure reading,  current temperature and sensor battery status. As previously mentioned above, entering the settings page will allow editing the settings for optimum tire pressure and to set high and low pressure alarm points.

Photo of a FOBO tire pressure monitoring sensor installed on one of the main gear’s wheels.

There is plenty of clearance to install the sensors on the main landing gear’s wheel … however, I did discover a clearance issue when installing the FOBO sensor on the nose wheel. The DOG Aviation RV-12 has the new thicker and much stronger WD-01230-1 nose wheel fork installed. The new nose wheel fork also requires a new mounting bracket for the nose wheel pant. The new mounting method involves riveting a mounting bracket directly onto the nose wheel fork. The clearance issue I discovered involved the shop heads of the two aftmost rivets used to attach the U-00006E-L-1 mounting bracket onto the wheel fork. The FOBO sensor cleared the nose wheel fork just fine, but made contact with the two aforementioned rivets. ( This should not be an issue for RV-12 owners who have not installed the new style nose wheel fork because the rivets that caused me grief are not present on the old style nose wheel fork). I used a file to remove a little material from the shop heads of the offending rivets so a little clearance could be obtained.

After filing down the shop heads of the two rivets a little, the sensor cleared the rivets as can be seen here if looking closely …  but just barely. Clicking on this photo should bring it up to full size making it easier to see.


Not feeling comfortable with so little clearance, I decided to add a 1/16" shim (washer) between the nose wheel fork and the U-01210B-1 axle spacer, essentially moving the wheel 1/16" to the right … so fabricated a 1" washer from .062" aluminum scrap. I remembered when first installing the nose wheel on the new WD-01230-1 fork, the fork pulled in a little as the axle bolt was tightened. So I felt pretty confident there would be room for the 1/16" washer to slip in between the U-01210B-1 spacer and the WD-01230-1 wheel fork without much of a fight. Sure enough, as the axle bolt was loosened, a gap appeared between the U-01210B-1 spacer and the WD-01230-1 wheel fork … so I inserted my newly minted washer in the gap and reinstalled the axle bolt. After tightening the axle bolt, there is now acceptable clearance between the FOBO sensor and the rivets. I can now flex the valve stem and clear the rivets …whereas before, any flexing of the valve stem would create interference between the FOBO sensor and the rivets.

Looking very closely, one can see loosening the axle bolt created about a 1/16" gap between the U-01210B-1 spacer and the WD-01230-1 wheel fork … just what I needed, the spacing washer was inserted into that gap.

1"x 1/16" washer fabricated to offset the nose wheel 1/16" to the right.

Photo of the nose wheel assembly with the washer in place. Now the wheel assembly is offset 1/16" to the right creating clearance between the FOBO sensor and the rivets that secure the U-00006E-L-1 mounting bracket.


The FOBO sensors appear to be working nicely and sensitive enough to track pressure differences caused by temperature changes …. in that, reported tire pressures are slightly higher during a hot afternoon compared to the cooler mornings. The FOBO App works great and if selected in the setup menu, can also sound an alarm on the device you are using should any tire pressure go beyond the user assigned normal operating range. Below is a photo showing what the FOBO App display looks like after a front wheel trike configuration was selected, sensors installed and pressure limits configured. If a tire’s pressure is out of range, the FOBO App will display a red background for the offending tire.

Photo of the FOBO App on my smart phone after installing the sensors and configuring desired parameters in the setup menu.


Thus far, I’m very pleased with the FOBO sensors … they appear to be accurate and the FOBO App is easy to install and configure. Time will tell if the sensor battery lasts to the one year point … hopefully it will so it can be routinely changed during the yearly condition inspection. At this point the FOBO sensor system appears to be a good option for those pilots who don’t want to remove the wheel pants just to make a tire pressure check. Moving forward, I’ll be sure to update this post if any issues develop with the FOBO sensors. Oh, at the time of this writing, the FOBO sensors cost around $49 per wheel.

Return from the future: 

The clearance that was created between the FOBO tire pressure sensor and the nose wheel fork proved to be not enough. As previously mentioned above, I had to press quite hard on the sensor to deflect the tire’s valve stem enough to contact the nose wheel fork assembly. After completing some high speed taxi testing and checking it appeared all was well.

Not so! Apparently, the centrifugal force created by the 5” nose wheel instantly ramping up from 0 to 25 or 30 MPH must be very significant. After shooting a couple of touch and go landings, I returned to the hangar and inspected the sensor and found, much to my amazement, there was evidence of contact with the nose wheel fork assembly … so the nose wheel sensor  was removed from the nose wheel.

Guess I will have to check the nose wheel pressure the old way from now on. At least the sensors are working well on the main gear and the main gear wheel fairings are much more time consuming to remove.

Service Bulletin 18-03-06 Carburetor Throttle Return Spring Replacement

While reviewing some DOG Aviation photos for a fellow builder, I ran across some photos regarding replacement of the Rotax 912ULS throttle springs that I forgot to add to the Blog last fall.

Van’s Aircraft issued a service bulletin about two years ago switching to a newly designed throttle return spring for the Rotax 912ULS which will hopefully solve the throttle return spring issues that have been a nuisance for the RV-12 fleet.

Before diving into the latest throttle spring service bulletin (I think there have been at least two prior) … first a little back story regarding the throttle return springs. Rotax has designed the 912ULS engine’s carburetors go to full power in the event of a throttle cable failure. On older RV-12 aircraft the throttle return springs supplied by Rotax for the 912ULS engine were VERY strong … so strong, in fact, the throttle would constantly need to be adjusted and readjusted during flight because the strong springs would cause the throttle lever inside the cockpit to constantly creep towards full power. Another issue plaguing the Rotax 912ULS throttle lever return springs is, over time the throttle return springs were also prone to breaking.

In an effort to eliminate the throttle creep, new weaker springs were developed … but they did not totally solve the issue with throttle creep plus spring breakage remained an issue. While the DOG Aviation RV-12 was under construction, Van’s began supplying a vernier-assist throttle lever manufactured by McFarlane (a nice throttle unit), which became the standard offering. The McFarlane vernier-assist throttle is accompanied by weaker throttle springs supplied by McFarlane …. a step in the right direction, however, throttle return spring breakage remained an issue.

Van’s has now totally redesigned the throttle return spring and made it a helical torsion spring as opposed to the typical stretch spring. From a design aspect, I think this is a much better approach and should totally eliminate throttle lever return spring breakage.

Van’s Aircraft issued service bulletin 18-03-06 which covers removing of the old style throttle return stretch spring from the Rotax 912ULS engine’s carburetors and replacing the springs with the newly designed helical torsion springs. The service bulletin refers the installer of the springs to follow the procedure laid out in Section 50 of the plans. The Van’s part number for the new throttle return spring kit is SPRING-00002-1 2 PACK. That part number will provide two springs, one for the left carburetor and one for the right carburetor. Note: The spring for the left carburetor has an ink marking to denote it from the right spring.  Below is a photo of the old style throttle spring compared to the new style helical torsion spring.

The spring on the left is the old style throttle return spring … the spring on the right is the newly designed helical torsion throttle return spring.


As one can see in the following photo, the standard Rotax 912ULS throttle lever return spring is stretched between a hole in the throttle lever and a bracket attached to the body of the carburetor. I suspect, being stretched between two points and under constant engine vibrations, the throttle return springs are more susceptible to fatigue cracking.

My finger is pointing to the old design throttle return spring. The upper portion of the spring is connected to a hole in the throttle lever and the lower portion of the spring is connected to a hole in a bracket attached to the body of the carburetor.


Instillation of the new throttle return helical torsion springs is quite easy. First the old style throttle return spring is removed from the throttle lever. Then the hex nut and spring washer that secures the throttle lever and throttle stop onto the throttle shaft is removed. Probably unnecessary, but I used a red sharpie pen to mark the position of the throttle lever prior to removing the throttle shaft hex nut. Use caution when removing the throttle lever … I placed a wrench on the throttle shaft and another on the nut then twisted the throttle shaft to make sure the throttle shaft was in the center of its normal range of movement … then proceeded to remove the hex nut. Making sure the throttle shaft is in the center if its range of motion assures that the force applied to remove the nut will not be applied to the stops … possibly bending metal.

This photo shows the red sharpie marks placed on the throttle lever (actually not necessary). At this point, the throttle shaft hex nut and spring washer have been removed from throttle shaft. As a note, the stop lever can be seen quite well in this photo, it sits on the throttle shaft directly behind the throttle lever … it will also be removed from the throttle shaft.


After removing the throttle shaft hex nut, the throttle lever is carefully slid off the throttle shaft. There is no need to loosen or remove the throttle cable to get the throttle lever off the throttle shaft. Behind the throttle lever resides the throttle stop, it also needs to be slid off the throttle shaft as can be seen in the next photo.

Here one can see the throttle lever and throttle stop have been slid off the throttle shaft. Once the throttle stop is removed one can see two Philips screws … my finger is pointing to the upper Philips screw that will capture one end of the throttle return helical torsion spring.


Instillation of the new throttle return spring is quick, simple and easy to accomplish procedure. The new spring slides over the carburetor’s throttle shaft … the inboard end of the spring will sit under the head of the upper Philips screw (the screw I’m pointing to in the above photo) and the outboard end of the spring will rest on the throttle stop. Instillation of the new spring, task wise, is not difficult. That said, however, finding the right tool for the job proved difficult. I tried a couple of varieties of spring tools I had in the shop, but they all seemed to have clearance issues. I did not want to use a small screwdriver to push on the spring (as most probably do) for fear of creating small scratches that, over time and vibrations, may possibly create stress fractures in the spring. After lots of pondering and playing around with various tools an idea occurred to me …. perhaps a piece of waxed string will work to tension the spring. That idea worked like a charm!!! I slid the throttle return spring partway onto the throttle shaft and slid the throttle stop onto the throttle shaft positioning the outboard end of the spring so it is captured by the throttle stop. Next I looped a piece of waxed cord over the inboard end of the spring and slid the assembly further onto the throttle shaft. As the assembly got close to the Philips head screw, I pulled on the waxed cord to tension the spring enough so the inboard portion of the spring could be positioned under the head of the Philips head screw. Worked slick … as documented in the following three photos.

In this photo, one can see how the inboard end of the new throttle return spring will be captured under the head of the upper Philips head screw when the new spring is in its final inboard position.

As one can easily see here, a piece of waxed cord was used to capture the inboard end of the spring so it can be tensioned by pulling on the string. Looking closely one can see how the outboard end of the throttle return spring is captured by the throttle stop. All that is left to do is pull down on the waxed cord so the inboard end of the spring clears the Philips head screw and push the assembly in the remaining 1/8” so the inboard end of the spring sits under the head of the Philips head screw.

This photo shows the final position of the new throttle return spring … the inboard portion of the spring is captured under the head of the upper Philips head screw and the outboard portion of the spring is captured by the throttle stop. Using a waxed cord to tension the spring makes this task truly a piece of cake.


Once the throttle return spring and throttle stop are fully seated on the throttle shaft, the throttle lever is positioned back onto the throttle shaft and the assembly is secured on the throttle shaft by the spring washer and hex nut …the hex nut is tightened to 44 inch pounds. I accomplished that by using a crows foot wrench attached to my torque wrench and holding onto the throttle shaft with another wrench … here again, making sure the throttle shaft was positioned in its center of motion so no force would be applied to the throttle stops.

Completed reassembly of the throttle lever on the throttle shaft. Unfortunately, once in position, the new throttle return springs are hidden from view by the throttle lever.


Service bulletin 18-03-06 is a very easy service bulletin to complete (especially if one uses my trick of using waxed cord to tension the spring) and having helical torsion throttle return springs should put an end to the broken throttle return spring issue.