What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Servo level for cowl intereference

1bigdog

Well Known Member
Good Morning All.

In starting to final fit the lower cowl and FAB I found the bendix server mixture lever interferes with the lower cowl on the left (as others have found).
RV-9A
IO320-D1A

The problem is the offset in the bent lever is extreme. There is an old thread that discussed getting a straight lever through Precision Airmotive (which is where I got the servo). Does anyone have a part number so I can tell them exactly what I'm looking for.

By the way, the new FAB doc shows a bent mix arm. If there is bent lever available with a smaller offset that would probably be better.

Thanks.
 
New FAB plate

Michael

Vans have recently changed the plate that attaches the FAB to fuel servo for a new design that has an offset.
You can either order the plate from vans or use the revised drawings to cut one out of .063

The offset positions the FAB in the centre of the cowl.
If you use a straight mixture arm you might not have enough clearance on the FAB. I found this on my -10 which uses the same setup so need a slightly offset arm.
You probably have 1 inch offset and need a little less. My hanger mate resorted to cutting and rewelding his.

Regards

Peter
 
Last edited:
reduced offset

Michael

Vans have recently changed the plate that attaches the FAB to fuel servo for a new design that has an offset.
You can either order the plate from vans or use the revised drawings to cut one out of .063

The offset positions the FAB in the centre of the cowl.
If you use a straight mixture arm you might not have enough clearance on the FAB. I found this on my -10 which uses the same setup so need a slightly offset arm.
You probably have 1 inch offset and need a little less. My hanger mate resorted to cutting and rewelding his.

Regards

Peter


Hi Peter

I have been reviewing the new and old FAB docs and tend to agree. I was hoping to find something about 3/8 smaller offset. Precision Airmotive confirmed they have the straight lever available but I don't know of a reduced offset part.

Had not thought of cutting/welding. I was worried enough about just bending that material. Guess I'll have to give this more thought.

Thanks.
 
Michael:

I'm running into the same issue with my mixture arm on the servo. Have you determined what your 'fix' will be? Cut/weld or straight arm from Precision?

Just curious.

Thanks!

Greg
 
Maybe a dimple

Michael:

I'm running into the same issue with my mixture arm on the servo. Have you determined what your 'fix' will be? Cut/weld or straight arm from Precision?

Just curious.

Thanks!

Greg


Hi Greg

After playing with the fit for a couple weeks as we are getting the airbox aligned I may be able to get this done using the original offset arm and using heat to make a bulge where the arm interferes with the cowl. I'll be testing that within a week or 2. With the new offset of the FAB I think we gained a bit of room.

Will advise.
 
I have the Precision EXP servo on my IO-320 RV-9A and swapped the offset throttle lever with this mixture lever from Airflow Performance. https://airflowperformance.com/index.php/product/mixture-lever/
It provides about a 1/4” - 3/8” clearance between the control end attachment bolt head and the cowling when the bearing end is mounted on the inside of the control arm. I did have to drill and ream the control arm mount to servo hole from 1/4” to 5/16”. No modification of the cowl needed.
 
Last edited:
Thanks, Michael and David. I appreciate the help. My cowl is complete or very nearly so, so I think I'll try the 'non-offset' arm. That's only about 1/4 of an RV unit.

Love this forum.
 
OK, so is this a stupid question? I purchased the modified mixture arm for my fuel servo and I think it will work great (the arm won't rub on or hit the cowl, with clearance remaining for the engine to move within the cowl a little). But how did anyone tighten the 5/16" nut to hold the new arm onto the servo? As you can see in the pics (old cast arm with 1" offset vs. the new aluminum arm with 5/16" offset), the spot for the nut to rest with the new arm is recessed. I understand why it is recessed, but I sincerely doubt anyone makes a wrench or socket thin enough to tighten the nut.

What am I not thinking of in this scenario??

Thanks for looking ................
 

Attachments

  • Mixture lever arm-1.jpg
    Mixture lever arm-1.jpg
    340.9 KB · Views: 97
  • Mixture lever arm.jpg
    Mixture lever arm.jpg
    290.2 KB · Views: 96
  • Mixture lever arm-2.jpg
    Mixture lever arm-2.jpg
    350.7 KB · Views: 103
OK, so is this a stupid question? I purchased the modified mixture arm for my fuel servo and I think it will work great (the arm won't rub on or hit the cowl, with clearance remaining for the engine to move within the cowl a little). But how did anyone tighten the 5/16" nut to hold the new arm onto the servo? As you can see in the pics (old cast arm with 1" offset vs. the new aluminum arm with 5/16" offset), the spot for the nut to rest with the new arm is recessed. I understand why it is recessed, but I sincerely doubt anyone makes a wrench or socket thin enough to tighten the nut.

What am I not thinking of in this scenario??

Thanks for looking ................

Buy a MS21042-5 All-metal Hex Stop Nut from Spruce. A lot of builders and better "knowers" than myself prefer all metal nuts in the FWF area anyways. It's what I did and it works great.

https://www.aircraftspruce.com/catalog/hapages/ms21042.php

ms21042.jpg
 
Last edited:
I have an all-metal nut in that size. It didn't appear to offer any more clearance to get a wrench or socket on. But I'll certainly look at it more closely.

Thank you for weighing in.
 
good timing

Amazing timing since I just ordered the straight lever from Airflow as well.
So, 2 things. First and foremost, there is a version of the lever with the correct 5/16" hole. Order the throttle lever instead of the mix lever.
That said, I can confirm once I get it.
For those about to order:
https://airflowperformance.com/index.php/product/straight-throttle-lever/
Same offsets. No need to drill.

Second is that I don't know now if the throttle lever has the same recess. I'm checking if this is the case with Airflow.
But I will change to the all metal lock nut regardless.

Cheers.
 
OK, I figured out where I went sideways. I ordered an MS21045-5 nut. I need the MS21042-5 nut. Ugh.

I'll order the correct one and should be on my way. Nothing like getting wrapped around the axle.

Thanks for all the help.
 
Back
Top