RV-8 throttle cable… grrr.

Yep, the stock Vans CT Q-60 throttle strikes again.

I know the stock cable doesn’t have great longevity and is a standard replacement item; I’m creeping up on 2000 hours and have already replaced it several times, with the usual interval at 500+ hours. But, my newest one was just replaced last year and has a wee bit over 100 hours and it’s already feeling grabby, or “notchy” if that makes sense. Harrumph!

To replace the cables in a -8 is truly a pain in the butt, so I’m thinking it’s time to (finally!) upgrade to a McFarlane cable and hopefully extend the replacement interval. Problem is, it’ll be a custom cable with measurements and all that. Are there any -8 drivers out there with measurements from the stock Q-60 that I can use to order from McFarlane? Otherwise I gotta pull my cable and be downed while waiting for the new to be fabricated and shipped. I’ve searched older posts and see that the travel is 2 1/4” and total length is 60”, but there are a few more measurements on the order form that I don’t have.

Any help is appreciated, thanks!

I just checked all my papers and sorry to say I did not keep a copy of my McFarlane custom cable order form. (at least not where I can find it )

But I do have my old cables at the hangar, so if you can wait til this afternoon or tomorrow I should be able to get the dimensions for you. I can confirm that 2 1/4" travel is a good number. The green Vans cables are 2 1/8" and are just a bit marginal, requiring pretty precise set up to get full travel on the throttle body, at least with my quadrant.

jbDC9 said:

Yep, the stock Vans CT Q-60 throttle strikes again.

I know the stock cable doesn’t have great longevity and is a standard replacement item; I’m creeping up on 2000 hours and have already replaced it several times, with the usual interval at 500+ hours. But, my newest one was just replaced last year and has a wee bit over 100 hours and it’s already feeling grabby, or “notchy” if that makes sense. Harrumph!

To replace the cables in a -8 is truly a pain in the butt, so I’m thinking it’s time to (finally!) upgrade to a McFarlane cable and hopefully extend the replacement interval. Problem is, it’ll be a custom cable with measurements and all that. Are there any -8 drivers out there with measurements from the stock Q-60 that I can use to order from McFarlane? Otherwise I gotta pull my cable and be downed while waiting for the new to be fabricated and shipped. I’ve searched older posts and see that the travel is 2 1/4” and total length is 60”, but there are a few more measurements on the order form that I don’t have.

Any help is appreciated, thanks!

Click to expand...

Have you installed a heat shield?

After struggling with cable replacements, I think I have worked out the least painful process.

1) disconnect all three cables on the engine side. Take off any Adel clamps that are supporting the cables, or clamping other items to the cables. Throttle, Mixture, and Prop cables all completely free to the firewall.

2) take the cover plates off of the aluminum eyeballs and remove the eyeballs.

3) clip any zip ties that are holding other things, like wiring, to the cables that would prevent them from moving.

4) remove the throttle quadrant mounting plate. (at least on mine, during the initial build, I made a different shape of mounting plate that does not have those two screws inside that go into the front face of the F-804. Instead, mine mounts to the side of the F-804, making it much easier to remove screws and pull the assembly out.

5) with the quadrant mounting plate free, pull the whole assembly out a couple of feet so you can work on it more comfortably. Put the new cables on and reverse the removal steps.

This might seem pretty obvious, but the first time I did it, I stubbornly resisted disconnecting the other control cables that I was not going to replace, so I struggled to hook up the new cable to the quadrant with it held in location by the other cables. The second time I had to do it, I followed the steps above, and my swear-word use dropped 95%.

Thanks Steve! I read those measurements from one of your posts a year or two ago; you’ve provided lot of good info! I’ve replaced cables enough times now that I have a “system” like yours… but I still hate doing it!

And yep, I have a heat shield plus have the cable wrapped in reflective insulating tape, but the throttle cable still just wears out. Meanwhile the identical prop and mixture cables just keep on working… I dunno why the difference.

Dimensions for custom McFarlane cables

OK, here is how I order McFarlane cables.

The example dimensions here are for a 60" total length cable.

Download the form from the McFarlane website. https://www.mcfarlaneaviation.com/section/services/custom-engine-controls/
Click on the quadrant type cables text to download the .PDF
Fill out the section for the Swivel Type Engine Control

Dimensions
A: 6.5" Extended
B: 4.25" Retracted
C: n/a you don't need a firewall wear sleeve
D: 49.25"
E: 6.5"
F: 4.25"

Note that 6.5 + 4.25 + 49.25 = 60. So one end extended plus one end retracted, plus the length of the sheath equals the total length. Adjust dimension D for other length cables.

Mark 10-32 pushrod threads both ends and 7/16-20 terminal threads both ends.

And honestly, I think it wouldn't hurt to get a little more travel - it will make it easier to get everything adjusted for full travel. So you could do
A=6.5
B=4.125
D=49.375
E =6.5
F =4.125

Hope that helps lots of people to never have to change their cables again aftward.

Vans or McFarland, put a heat shield in there.

I'm still running the original throttle and mixture cables, and they're just above a 4-into-1. This is the second heat shield. First one covered just the cables. This one was extended with some "wings" to also shield the paint on the cable bracket, which is bolted to the bottom of the sump.

Stainless or aluminum backed with 970 fiberfrax felt and wrapped in aluminum tape.
.

DanH said:

Vans or McFarland, put a heat shield in there.

I'm still running the original throttle and mixture cables, and they're just above a 4-into-1. This is the second heat shield. First one covered just the cables. This one was extended with some "wings" to also shield the paint on the cable bracket, which is bolted to the bottom of the sump.

Stainless or aluminum backed with 970 fiberfrax felt and wrapped in aluminum tape.
.

Click to expand...

Dan posted this idea awhile back. When I changed out my throttle and idle cutoff cables (Vans) I used this idea with very favorable results. Thanks for posting.

DanH said:

Vans or McFarland, put a heat shield in there.

I'm still running the original throttle and mixture cables, and they're just above a 4-into-1. This is the second heat shield. First one covered just the cables. This one was extended with some "wings" to also shield the paint on the cable bracket, which is bolted to the bottom of the sump.

Stainless or aluminum backed with 970 fiberfrax felt and wrapped in aluminum tape.
.

Click to expand...

Interesting that you have gotten more life from yours. Mine have always had a heat shield on each exhaust pipe that goes close to the cable housings. Also the cables are fire-sleeved in the vicinity and wrapped with aluminum tape -- the idea being to slow the heat transfer in to hopefully be closer to the heat transfer out via axial conduction along the cable to cooler areas. Can't tell if either helped, since it didn't help "enough."

In your picture, it looks like the part of your cable that is close to the exhaust, and protected by the heat shield, is near the ends of the cables. I wonder if that portion of the cable is different enough internally that it wouldn't have the same issue as the middle portion of the cable? Maybe the offending plastic liner ends short of the swaged end fitting with threads and guide bushings for the pushrod? Or that the ends stay cooler because of the conduction through the anchor bracket into the sump? -- all just question marks here.....

Thank you Steve!!

Order form in progress...

Whoa. Got the quote back from McFarlane; $525, plus shipping! That seems a bit extreme… I was expecting $300-ish.

Maybe I’ll rethink using the Vans cable and beef up my heat shields…

jbDC9 said:

Whoa. Got the quote back from McFarlane; $525, plus shipping! That seems a bit extreme… I was expecting $300-ish.

Maybe I’ll rethink using the Vans cable and beef up my heat shields…

Click to expand...

Hey John - I think the brand is Cablecraft, and they have distributors in most major cities - or even small ones, like Reno. I had a prop cable made a couple of years ago - called them on the phone, gave them the measurements, and they had it ready when I got up there 45 minutes later. And….cheaper. I’d bet Houston has a few outlets!

My experience has been that once I got the heat exposure taken care of, the cables actually last a very long time.

jbDC9 said:

Whoa. Got the quote back from McFarlane; $525, plus shipping! That seems a bit extreme… I was expecting $300-ish.

Maybe I’ll rethink using the Vans cable and beef up my heat shields…

Click to expand...

Yes, they are expensive, but they are very smooth and will last til TBO, so you only have to go through changing them once.

Unlike Paul and Dan, my Van's cables failed despite extensive heat shielding, and I didn't even have them particularly close to the exhaust pipes. YMMV.

scsmith said:

Yes, they are expensive, but they are very smooth and will last til TBO, so you only have to go through changing them once.

Unlike Paul and Dan, my Van's cables failed despite extensive heat shielding, and I didn't even have them particularly close to the exhaust pipes. YMMV.

Click to expand...

I do recall the mixture cable getting a moderate ratchet feel very early on, but it went away. The difference between yours and mine may be that mine has little curvature near the exhaust. Or exit airflow tends to cool the cable, as the entrance to the exit bell is right there.

First heat shield below. Added wings to a new one a year ago to protect the paint on the bracket.
.

scsmith said:

OK, here is how I order McFarlane cables.

The example dimensions here are for a 60" total length cable.

Download the form from the McFarlane website. https://www.mcfarlaneaviation.com/section/services/custom-engine-controls/
Click on the quadrant type cables text to download the .PDF
Fill out the section for the Swivel Type Engine Control

Dimensions
A: 6.5" Extended
B: 4.25" Retracted
C: n/a you don't need a firewall wear sleeve
D: 49.25"
E: 6.5"
F: 4.25"

Note that 6.5 + 4.25 + 49.25 = 60. So one end extended plus one end retracted, plus the length of the sheath equals the total length. Adjust dimension D for other length cables.

Mark 10-32 pushrod threads both ends and 7/16-20 terminal threads both ends.

And honestly, I think it wouldn't hurt to get a little more travel - it will make it easier to get everything adjusted for full travel. So you could do
A=6.5
B=4.125
D=49.375
E =6.5
F =4.125

Hope that helps lots of people to never have to change their cables again aftward.

Click to expand...

Steve - Thank you for the measurements and your tips on how to change the cable. Just to make sure I understand it correctly. The measurements above are based on the CT Q-60 with the top measurement being the cable with the original travel and the measurements below that with the slightly extended 2 1/4" travel? Is there anything to be aware of with the slightly extended travel? Could it have any impact on anything else? O and I guess, I would have to go for the swivel type engine control? Better ask before I order.

I have got a fuel inject Mattituck IO-360 on my RV8.

On a different note, I contacted McFarlane to see if they had the measurements for the CT Q-60 already as I would imagine that they get more clients ordering replacements. I don't really want to remove my existing cable to get their required measurements. They said the couldn't help. I am surprised. I told them it might be worth for them to buy some Van's standard cables, so they can serve clients like myself a bit better. Maybe even keep some replacements in stock. They charge enough. Anyhow, that is by the side.

Thanks

Rogier