Preventive replacement of engine controls?

[DXB]

Question- From a wear standpoint, is there a good rationale for changing throttle, prop, mixture cables, even if they are working ok?   The reason I ask is that they are presently out from my plane (68 'C) to redo the panel and thus would require no added labor to install new ones.  The throttle control looks original.  I don't think the prop and mixture are, but they look old - I couldn't figure out from the logs exactly when they were replaced.

 

As a CB, I am not enthusiastic to swap them.  But of course it would cost much more to do later. Plus a broken throttle cable in flight sounds like a horrible day. Then again, my new carb heat cable decided to snap after 40 hours - mysterious event, not sure whether manufacture or installation was faulty. So there might be a case to stick with tried and true?

 

EDIT: Dang it, just became aware of a 1970's service bulletin that applies to my serial number sbm20-174 (http://www.mooney.com/service-support/service-bulletins/model/m20c/) - requires replacement of all 3 controls. I don't see an AD associated with it. I obviously need to dig a little more - I suspect the bulletin was complied with,  but I need to confirm.  Even then, the existing controls are old...

Edited August 30, 2015 by DXB

[MB65E]

I would try to change the throttle cable if I had cash on hand. It sounds like you are proactive enough to realize the situation. Ours was done at 3800hrs and came apart. Get ready, that big lawnmower cable is $500+.

-Matt

[KSMooniac]

Change them. Order from McFarlane and save a LOT versus the factory prices.

Sent from my VS985 4G using Tapatalk

[DXB]

Ok I think I've sorted this out. The throttle cable is original as far as I can tell, but the rod end connector was changed in ’75 from the slot style to the loop style.  The mixture cable was changed in ’69, and the prop cable is from ’75.   There was a service bulletin in ’71, without a related AD, that “mandated” replacement of all three: http://www.mooney.com/wp-content/uploads/2014/03/sbm20-174.pdf    Although this appears to have been complied with, the age of the controls seems to make it worthwhile anyway. I think I've sorted out the replacement part issues, in large part using prior threads on here, so I'll post the info all in one place:

 

The mixture control is the easy one, as it is available directly from Macfarlane as a PMA’d part for $162:

http://www.mcfarlaneaviation.com/Products/?ID=16393880&Make=Mooney&Model=M20C&Serial=680002&PartNumber=MC600-72&

 

The throttle and prop seem more complicated.  They are available from Mooney Service Centers like Maxwell, LASAR, or SW Texas for around $500 typically.  But they often need to get them made, with significant lead time, and what they will send you as a PMA’d part is simply manufactured by Macfarlane.  But you can get it directly from Macfarlane for less (around $375) and with a lead time of 2-3 days if you send them the old cables, but they must be installed and documented as “owner-produced parts.”   A link to a prior thread describing this, including confirmation email from a FSDO that this is ok, is here:

http://mooneyspace.com/topic/9818-wanted-propeller-control-cable/

[Hank]

While you're at it, check your carb heat cable. I replaced mine at annual, while completely redoing the swivel joints on both sides of the big butterfly valve in there. Picked up ~10 mph now that it shuts off completely!

[mike20papa]

FAA has a circular concerning engine controls for piston aircraft.  It's been a while since I read it..but it recommends replacing all cable controls at engine TBO.   Might be under the infamous "Instructions for continued airworthiness"

[DXB]

FAA has a circular concerning engine controls for piston aircraft.  It's been a while since I read it..but it recommends replacing all cable controls at engine TBO.   Might be under the infamous "Instructions for continued airworthiness"

Anyone familiar with this AC please let me know-  I could not find on a quick search of FAA website.

[DXB]

While you're at it, check your carb heat cable. I replaced mine at annual, while completely redoing the swivel joints on both sides of the big butterfly valve in there. Picked up ~10 mph now that it shuts off completely!

That's one heck of a speed mod! I had the same thing done after my prebuy - same stuff you allude to was in bad shape.

[RobertGary1]

What are the failure modes that are being seen?

-Robert

[MB65E]

Robert, with the throttle cable, the last crimp on the cable just after it attaches to the sump usually wares out, then the outer housing separates or slides forward allowing the thin 1/8" wire cable to snake out of the housing. As for the old style ball and socket type hardware fitting, the housing and ball will eventually wear to the point where the can come loose even with a tight set screw and split pin. I'd recommend a newer style rod end on all engine controls.

That's what I have seen,

-Matt

[Bob_Belville]

This thread is timely for me. My '66E apparently needs a new prop cable. It is worn enough that's there's play in the cable itself causing or contributing to fluctuations in RPM great than 25 RPM. What is on the plane now is an ACS Products A-750. The cable was built in 1997 and I assume it was installed that year when a PO did a huge number of mods. 

 

Aircraft Spruce sells ACS and their 750 series vernier cables are listed at about $80. They are not FAA approved for certified aircraft but Spruce's site says "Are these A-750 vernier controls FAA Approved? No, to install these on a certified aircraft you will need to file a 337 Field Approval.

 

Does anyone here have experience with the ACS cables vs. McFarland/Mooney OE? My default attitude is to assume that there is a reason someone is able to get $350 for something others are selling for $80. Until I understand what that reason(s) is(are)... 

[Andy95W]

Bob-

Look through your logbooks to try to find the entry for this cable to see what the installation justification was at the time. If the original installer actually got the Field Approval on the 337, you can replace your cable with the same ACS part.

If that is not the case, then you will need to see if your mechanic is comfortable signing off the installation of the ACS (or McFarlane) control cable as an owner produced/provided part that is comparable in quality and function to the OEM.

[N601RX]

It may have been part of the SWTA panel STC that you have. If so its ok.

[Bob_Belville]

Bob-

Look through your logbooks to try to find the entry for this cable to see what the installation justification was at the time. If the original installer actually got the Field Approval on the 337, you can replace your cable with the same ACS part.

If that is not the case, then you will need to see if your mechanic is comfortable signing off the installation of the ACS (or McFarlane) control cable as an owner produced/provided part that is comparable in quality and function to the OEM.

Thanks Andy, yeah, I went through the log entry and all the 337s and did not find any detailed documentation. This is the airframe log entry dated 12/15/1997, it is possible they neglected a few details:

 

Aircraft modified by the following STCs:1)  Oil cooler relocated by Lake Aero Style STC SA2513NM 2)  Fiberglass nose cowl by AeroResources Inc  STC SA7589SW 3) Mooney 201 M20J Spinner & spinner bulkhead assys from Aero Resources Inc STC SA7589SW 4) Speed brakes by Precise Flight Inc STC SA5708NM 5)  Standby Vacuum System III by Precise Flight Inc, STC SA2168NM 6)  Mooney Bladder Tank 6 bay system by O&N Aircraft Modifications Inc STC SA2350CE 7)  Dorsal Fin Fairing by Lake Aero Styling, STC SA4443NM 8)  Tail Root Fairing Horizontal by Lake Aero Styling, STC SA4443NM 9)  Wheel well liner covers by Lake Aero Styling, STC SA4443NM 10)  Wing Root Leading Edge Fairing by Lake Aero Styling, STC SA4443NM 11)  Relocated Cleveland wheel brake assys by Lake Aero Styling, STC SA4443NM 12  Hinge cover on Aileron, Elevator, & Rudder assy by Lake Aero Styling , STC SA4443NM 13)  Aileron lower gap seals by Lake Aero Styling, STC SA4443NM 14)  Flap gap seals by Lake Aero Styling, STC SA4443NM 15) One piece fiberglass belly pan fairing with skid runners by Aero Mod Inc, STC SA4080NM 16)  Instrument panel by SW Texas Aviation, STC SA7828SW. 

 

Per N601RX good suggestion I'll check out the SWTA panel STC. 

 

(The mixture control cable is also ACS, I did not check throttle.)