Throttle Arm 912ULS and SB 00026

[Pilotjim77]

I am performing my first condition inspection on an RV-12 with 912-ULS engine. Notes in the service records of the previous owner and original builder state, "SB 00026 - Did not comply; will check condition at each conditional insp."

SB 00026 directs me to install a new part, VA-00276, a Throttle Spring Retainer, to both carbs. The SB also directs me to Kit Assembly Instruction 50-05 for installation instructions. The problem is that the drawing of the Throttle Arm in said KAI 50-05 is not what is currently on the carb. The current setup has the Throttle Spring attached to an additional leg/hole on the throttle arm rather than to the throttle arm shaft. (See attached photo)

Would I be correct to assume the SB does not apply since there would be no wear to the shaft as the spring is not attached there? The only logbook entries that potentially address this is an engine log entry from Dec 2024 indicating that the carbs were sent out to Rotax for a 200 hour service. Would Rotax have replaced the throttle arm with a different one?

 

[Jetguy]

The picture on page 50-05, Figure 1, is accurate. The spring is simply not connected and is being pushed around the back of the shaft. A bit of history: I believe the Spring 00002L/R was initially installed without the new plate to provide a more positive action for moving the throttle arm. Without the new plate, the spring would gradually wear down the shaft. As I recall, some of the original Rotax Throttle Springs failed over time. You must remember that these airplanes can fly thousands of hours over their lifetime. Vans try to address issues as they arise and send out Service Bulletins with corrective actions. Therefore, you should comply with the SB to ensure maximum safety.

 

[Piper J3]

I have both the original extension spring and the torsion spring located around the throttle shaft. I like addition tension on the throttle cables to mitigate slack and cable friction to achieve a good uniform carb synch.

 

[Piper J3]

It looks like you have original drip tray which will crack with vibration. You might want to be proactive and install new reinforced trays with flange doubler plate

 

[Pilotjim77]

The picture on page 50-05, Figure 1, is accurate. The spring is simply not connected and is being pushed around the back of the shaft. A bit of history: I believe the Spring 00002L/R was initially installed without the new plate to provide a more positive action for moving the throttle arm. Without the new plate, the spring would gradually wear down the shaft. As I recall, some of the original Rotax Throttle Springs failed over time. You must remember that these airplanes can fly thousands of hours over their lifetime. Vans try to address issues as they arise and send out Service Bulletins with corrective actions. Therefore, you should comply with the SB to ensure maximum safety.

I'm a bit confused. The picture in the Vans drawing clearly shows the spring attached to the shaft. My photo above shows the spring attached to the arm, not the shaft. How can the spring produce wear on the shaft in the above photo?

 

[rvbuilder2002]

The spring related to the service bulletin is a totally different spring than the one currently installed on your throttle arm.

If you had it installed per the original instructions, the spring, you currently have would not be installed any longer, so technically the service bulletin you referred to does not apply to your airplane Since the throttle return spring was never changed.

 

[Pilotjim77]

The spring related to the service bulletin is a totally different spring than the one currently installed on your throttle arm.

If you had it installed per the original instructions, the spring, you currently have would not be installed any longer, so technically the service bulletin you referred to does not apply to your airplane Since the throttle return spring was never changed.

So, my spring setup is an older style? The airplane was built 2009-2011. When I look at the current manual in the Engine Installation section (46), all of the depictions of the carb look like mine. There are several drawings and photos, and they all look like mine regarding the throttle spring. So, I'm guessing this was updated at some point to this new design where the spring attaches to the throttle shaft. And then, a service bulletin came out addressing shaft wear on the newer design. My question is, am I supposed to update the spring design? Is there an SB about that?

 

[Piper J3]

This is throttle arm on RV-12 with ~300TT. We caught this during condition inspection when checking carb synch. Stock setup with single spring as supplied by Rotax. The hole in the throttle arm was elongated and worn accessively from vibration. My guess is throttle arm missed heat treatment at the factory and/or not tightened properly. Prop was dynamically balanced after this was found.

Attached photos show worn throttle arm mounted on carb and new replacements. I searched, and don’t have photo of worn arm as removed from carb.

 

[funflying]

Jim,
Here are a couple photos showing the retaining piece and different spring addressed in SB00026.

 

[rvbuilder2002]

So, my spring setup is an older style? The airplane was built 2009-2011. When I look at the current manual in the Engine Installation section (46), all of the depictions of the carb look like mine. There are several drawings and photos, and they all look like mine regarding the throttle spring. So, I'm guessing this was updated at some point to this new design where the spring attaches to the throttle shaft. And then, a service bulletin came out addressing shaft wear on the newer design. My question is, am I supposed to update the spring design? Is there an SB about that?

Your spring appears to be the spring installed on the engine from the factory.
When use of the McFarland vernier throttle was introduced, lighter tension springs were included to solve the throttle creep problem that was common. These new springs had a fatigue failure issue so Vans designed a torsional spring ( shown in post #9) which worked well but was causing wear on some carburetors. That caused the SB to be issued, and as far as I am aware there has been no further problems.

 

[rvbuilder2002]

This is throttle arm on RV-12 with ~300TT. We caught this during condition inspection when checking carb synch. Stock setup with single spring as supplied by Rotax. The hole in the throttle arm was elongated and worn accessively from vibration. My guess is throttle arm missed heat treatment at the factory and/or not tightened properly. Prop was dynamically balanced after this was found.

Attached photos show worn throttle arm mounted on carb and new replacements. I searched, and don’t have photo of worn arm as removed from carb.

Somewhere in the Rotax documentation, but I don’t remember where specifically, it recommends that the oil dipstick be used to apply a drop of oil to the clamp bolt during each oil change to help assure good throttle operation and prevent excessive wear on the throttle arm.

 

[Pilotjim77]

Your spring appears to be the spring installed on the engine from the factory.
When use of the McFarland vernier throttle was introduced, lighter tension springs were included to solve the throttle creep problem that was common. These new springs had a fatigue failure issue so Vans designed a torsional spring ( shown in post #9) which worked well but was causing wear on some carburetors. That caused the SB to be issued, and as far as I am aware there has been no further problems.

That answers some of my questions. Thank you so much, Scott. I flew this airplane about 10 hours and didn't notice a throttle creep problem that I thought needed addressing, but it's good to know this information just in case it does become an issue in the future.

Thanks to all for the photos and the input....very educational.

 

[DHeal]

Jim -- Perhaps I missed it but is your RV-12 equipped with the original-equipment non-vernier throttle or the later vernier-type throttle? The "throttle creep" issue is primarily associated with the original-equipment non-vernier throttle and not the later vernier-type throttle. Just a thought....

As a point of reference, a couple of years ago I removed the original Rotax (and later McFarland replacement springs) and installed the Van's SB torsional springs/retainers. I have been pleased with the torsional springs' performance.

 

[Pilotjim77]

Jim -- Perhaps I missed it but is your RV-12 equipped with the original-equipment non-vernier throttle or the later vernier-type throttle? The "throttle creep" issue is primarily associated with the original-equipment non-vernier throttle and not the later vernier-type throttle. Just a thought....

As a point of reference, a couple of years ago I removed the original Rotax (and later McFarland replacement springs) and installed the Van's SB torsional springs/retainers. I have been pleased with the torsional springs' performance.

I'm not really sure. Here is a pic of the throttle:

 

[DHeal]

Hard to tell exactly from your picture but I'm guessing that you have an original-equipment non-vernier throttle. Here's why: It looks like you have the older style panel/avionics and it looks like the non-vernier throttle knob. The non-vernier throttle works by simply pushing-and-pulling. The vernier throttle works by pushing-and-pulling PLUS you can fine-tune the throttle setting by twisting the knob clockwise-to-increase-power or counter-clockwise-to-decrease-power. See McFarlane website below.

Vernier-Assist Controls - McFarlane Aviation

Shop for the best Vernier-Assist Controls for your aircraft and place your order online. Free shipping on orders over $500 at McFarlane Aviation.

www.mcfarlaneaviation.com