Yoke position question

[howelldw]

New 170 owner question:

Can these yokes be inverted for more leg room? Are they even in the correct position now?

I don't know how they originally came. As it is right now, it sits pretty low on my legs and would like a better solution.

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[Bruce Fenstermacher]

They have been inverted for the reason you have. This I can tell you. This may be as simple as taking the bolt out of the shaft and chain sprocket and inverting the yoke and reinstalling the bolt. BUT It may not be that simple as many yoke shafts and sprocket are not drilled in the center, many on purpose.

At the yoke and shaft were rather large rivets from the factory. Removing them and replacing with the same rivets might (will likely) be a can of worms. Replacing the rivets with bolts has been done was well but then you are opening up the legality issue of substituting bolts for rivets. If you don't already have bolts rather than rivets at the yoke and shaft I wouldn't mess with it. I'd go through the trouble of of loosening the control chain and rotating the both sprockets and rerigging yoke control. Issue here maybe, I don't know, is the sprocket symmetrical, with a tooth straight up and straight down or not. And if not, is there enough adjustment to center each yoke to each other once the are inverted.

Perhaps someone who has done it can chime in as to what the job entails.

[howelldw]

Hi Bruce!

The yokes are bolted on. You can marginally see two bolts in the photo. I wonder if it just can be unbolted, flipped 180, then rebolted? I was wondering if owners do this. I don't think I'd go through the trouble of doing it if I got to do it at the sprocket level.

They have been inverted for the reason you have. This I can tell you. This may be as simple as taking the bolt out of the shaft and chain sprocket and inverting the yoke and reinstalling the bolt. BUT It may not be that simple as many yoke shafts and sprocket are not drilled in the center, many on purpose.

At the yoke and shaft were rather large rivets from the factory. Removing them and replacing with the same rivets might (will likely) be a can of worms. Replacing the rivets with bolts has been done was well but then you are opening up the legality issue of substituting bolts for rivets. If you don't already have bolts rather than rivets at the yoke and shaft I wouldn't mess with it. I'd go through the trouble of of loosening the control chain and rotating the both sprockets and rerigging yoke control. Issue here maybe, I don't know, is the sprocket symmetrical, with a tooth straight up and straight down or not. And if not, is there enough adjustment to center each yoke to each other once the are inverted.

Perhaps someone who has done it can chime in as to what the job entails.

[Bruce Fenstermacher]

I should have zoomed in on you photo. Then if the holes the bolts are in are drilled in the center, you should be able to rotate them there. As I've said, you wont be the first. But is is also not something you see everyday in a 170.

[GAHorn]

It’s my experience that the Best way to invert the yokes is at the universal-joint forward of the sprockets. They are Always “centered”…and have to be…because there is no “orientation” requirement of the universal joints when they are replaced.

On the other hand…if the yoke-to-shaft rivets have been replaced by bolts…. the correct method of doing so is to ream the holes to close-fitment when replacing rivets with properly-substituted bolts. (rivets fill the spaces but bolts will not if not close-tolerance bolts/holes. This matter comes up when replacing the wing-strut rivets with bolts…. if the holes are not reamed…then it’s possible than only one or two bolts carry the entire load instead of sharing the load. And also, btw, this is another example of how bolts can be perfectly legal substitutions for rivets if properly performed.)

[Bruce Fenstermacher]

It’s my experience that the Best way to invert the yokes is at the universal-joint forward of the sprockets. They are Always “centered”…and have to be…because there is no “orientation” requirement of the universal joints when they are replaced.

George I wouldn't count on the universal bolt hole or the yoke shaft being drilled in center. I recall it was not on my A model and it has not been on a few other planes I'm aware of in our shop in the last few years. I'm not sure you can even buy replacement predrilled universal.

I did forget about the universal-joint being there and it would be a more logical place that the sprocket to rotate the the shaft if the hole is indeed drilled on center at at least one end of the universal.

[brianm]

The McFarlane PMAd universal joints are definitely pre-drilled.

[GAHorn]

I’ve installed 4 sets of universals, acquiring them from McFarlane but also Spruce and they were all pre-drilled. (The difference may be if they are ordered as model-specific replacement parts (drilled) or unspecified, as “builder” or “experimental” parts (undrilled).

[Bruce Fenstermacher]

My first experience replaceing a universal was on my 170A, years ago now. I call the universal was not drilled in the center. This is why I recall this as it's just one of those things one notes they should remember. My other more recent experience was either a later Cessna 172 or 185 and Piper Cherokee/Warrior. At least one of those was not center drilled. In fact the new McFarlane universal, I' sure bought specifically for the application, was blank. Both the shaft and the sprocket were removed and sent to a machine shop to have the holes match drilled the the old parts.

I'm glad to hear from recent experience of others, these parts, in a Cessna 170, appear to be center drilled and universal also center drilled. This is how it should be. I still want to issue a warning, don't assume it is so. The set we sent to the machine shop cost us another new universal.

[DaveF]

Sorry, but I think the worry about rivets vs bolts in the yoke is amusing. I wish I were strong enough to shear two AN3 bolts!

[GAHorn]

Sorry, but I think the worry about rivets vs bolts in the yoke is amusing. I wish I were strong enough to shear two AN3 bolts!

Agreed…the substitution of bolts for rivets in the yoke-to-shaft is not likely to be a problem if they are not overtorqued…. but the issue of reaming/close-tolerance-bolts of substitution in most other applications is precautionary. If one researches the IPC it will be seen that AN bolts are allowed to replace the rivets in lift-struts. But if the holes are not properly reamed… it is possible that only one bolt carries the load, instead of all the bolts sharing the load. (My own B-model has bolts and according to Cleo Bickford who noticed my struts at the OCH mid-year, it was determined that during a period of model-changeover from Hi-shears to AN429 rivets, Cessna substituted AN bolts on a short run. Cleo’s research with Cessna resulted in a service-response that cautioned about reaming the holes.) I decided that, in any event, my hard-landings and TRW-penetrations have “set“ and proofed the bolts properly.

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