Throttle cable rubbing on prop governor

[Vance Harral]

Hoping for some mechanics' wisdom and maybe a photo or two from another airplane.

The routing of the throttle cable in our 1976 M20F passes by, and touches, the prop governor.  The first photo below is one I found from one of our annuals back in 2019.  You can see the cable touching the governor, but it is protected by PTFE spiral wrap, and it follows a relatively "soft" edge.  The second and third photos are what I found yesterday during an oil change.  At some point, for reasons unknown to me, the interference between the cable and the governor moved to a "hard" corner of the governor and has experienced significant wear.

The good news for us is that the sacrificial spiral wrap did its job.  The cable itself is not meaningfully damaged, it just has the slightest of witness marks on the sheath.  So we caught this in time.  The question is, what to do about it?  The classic solution would be an Adel clamp, perhaps on a standoff, but the only bolt it could attach to in that area is one that secures the prop governor.  I'm disinclined to do that.  The IPC doesn't provide any detail on cable routing in this area.  Would appreciate any comments/tips on how to address this.

[Ragsf15e]

2 hours ago, Vance Harral said:

Hoping for some mechanics' wisdom and maybe a photo or two from another airplane.

The routing of the throttle cable in our 1976 M20F passes by, and touches, the prop governor.  The first photo below is one I found from one of our annuals back in 2019.  You can see the cable touching the governor, but it is protected by PTFE spiral wrap, and it follows a relatively "soft" edge.  The second and third photos are what I found yesterday during an oil change.  At some point, for reasons unknown to me, the interference between the cable and the governor moved to a "hard" corner of the governor and has experienced significant wear.

The good news for us is that the sacrificial spiral wrap did its job.  The cable itself is not meaningfully damaged, it just has the slightest of witness marks on the sheath.  So we caught this in time.  The question is, what to do about it?  The classic solution would be an Adel clamp, perhaps on a standoff, but the only bolt it could attach to in that area is one that secures the prop governor.  I'm disinclined to do that.  The IPC doesn't provide any detail on cable routing in this area.  Would appreciate any comments/tips on how to address this.

Ill try to get a picture of mine as I’m on this way to the airport anyway.  I’m having a hard time getting the perspective of your picture though… is that an A1A with the prop gov above the right mag?  Mine is a 68F.

[Ragsf15e]

4 hours ago, Vance Harral said:

Hoping for some mechanics' wisdom and maybe a photo or two from another airplane.

The routing of the throttle cable in our 1976 M20F passes by, and touches, the prop governor.  The first photo below is one I found from one of our annuals back in 2019.  You can see the cable touching the governor, but it is protected by PTFE spiral wrap, and it follows a relatively "soft" edge.  The second and third photos are what I found yesterday during an oil change.  At some point, for reasons unknown to me, the interference between the cable and the governor moved to a "hard" corner of the governor and has experienced significant wear.

The good news for us is that the sacrificial spiral wrap did its job.  The cable itself is not meaningfully damaged, it just has the slightest of witness marks on the sheath.  So we caught this in time.  The question is, what to do about it?  The classic solution would be an Adel clamp, perhaps on a standoff, but the only bolt it could attach to in that area is one that secures the prop governor.  I'm disinclined to do that.  The IPC doesn't provide any detail on cable routing in this area.  Would appreciate any comments/tips on how to address this.

So I figured out your perspective, and I can see that the prop governor is below the mag, not above it. My throttle cable does not have a clamp between the firewall and the bottom of the engine sump where it changes from the plastic sheathing to the metal pushrod. It is not touching the governor, though, the way it bends coming out of the firewall, keeps it along side, the copilot foot, well, and about an inch away from the governor.

[Vance Harral]

Thanks for the pictures, sir.  I looked at it some more this afternoon, and I'm coming to the conclusion that whether the cable rests on the governor or not appears to simply be a function of it's exact length.  The cable is secured at the firewall, and of course right at the point where it transitions to a metal pushrod.  Everything between is "slack", but the cable is fairly rigid, so a longer cable bows a little more and tends to not touch the governor, and a shorter cable bows a little less and tends to touch.

I figured out today that a zip tie or large MS21919 clamp around the body of the prop governor would hold the cable against the governor the way it used to sit, where it doesn't rub against the hard corner of the governor flange.  I'm going to talk that option over with my mechanic.