Prop bolts galled

I started my condition inspection / Phase 2 of my MLU today. I am *almost* certain that I will be installing a SDS CPI in place of the left mag. I decided that it would be easier to remove the prop to gain easier access to install the Hall sensor and magnets on the flywheel (plus I'll take the opportunity to replace the alternator belt at the same time - it feels less pliable than it should.) Anyway, it was *really* difficult to remove the prop bolts on the Sensenich 2 blade metal prop. Even when broken free, 4 out of six were not easy to turn, requiring significant force with a socket wrench until the bolts were just shy of falling free. Upon inspection, the stubborn bolts had evidence of galling along the shaft, from slight to significant. They will be replaced of course, but I'm unclear what caused the damage in the first place. Note that this is the first CI where I actually backed the bolts out, the previous two I had broken the bolts free, the re-torqued to spec. I'll attempt to include an image inline with this post, otherwise it will be a link to GooglePhotos.

https://photos.app.goo.gl/CawNSawBOuDq5e6V2

shows that only two or three bolts carry torque. the other bolts get a free ride. could be a manufacturing tolerance issue but all fits have this to some degree. give everything a good inspection.

Replace the lugs also, don?t try to run a tap thru them, they use a high preci$ion tap to make the threads. This per Saber, I assume it this applies to all lugs, not just the ones in his extensions.
Tim Andres

Take a Good Look at the Bolt Threads...

...if they all look the same and the threads themselves aren't misshapen, the problem is likely elsewhere. Also, dichromate (the gold color) missing from the threads is common. This is from friction between mating threads.
Check to see how the bolts fit thru the spinner plate. You may have to open the holes slightly- it doesn't have to be a size-on fit.
Terry, CFI
RV9A N323TP

The threads don't appear to be damaged at all. The galling on the stem of the two bolts seems to be what you are referring to. Honestly, I would not believe the bolts to be weakened, but polishing to remove the aluminum will leave them unprotected from corrosion, so replacement is in order. The spacer/prop is another thing.

You will have to track this down and may have to polish or replace the spacer or other components. I think polish is ok, but it must be free.

Possible causes:

Bushing thread axis is not parallel to the crank centerline, not squarely seated- thread in the bolts and measure centerlines at the heads.

Spacer holes not parallel or they have displacement error. Install spacer only (polish bores or lube them for test) with bolts threaded through the bushings and see if it binds or slides freely. Does it slide downwind sit square on the prop flange?

Same for the prop, but the axial length of the galling seems to be at the spacer.

You might scotch brite the offending bolt shanks and lube before assembly testing. Also clean the inside threads of the bushings with acetone and a bore brush.

Let us know what you find. I suspect an off axis bushing, the saber parts are such high quality.

I have not progressed to the spinner portion of my RV7a project so take these comments with a grain of salt. I had a similar experience on a different aircraft. The compression forces after torquing the bolts caused the steel metal backplate of the spinner to "squash" and tighten around the bolts. Common repair for this (after getting $300 new prop bolts) was to ream the steel spinner backplate for clearance. On reassembly, I used very slightly larger diameter washers (a different MS designation) under the prop bolt heads. Also put a little grease on the shaft (not threads) of the prop bolts (like antiseize). Whenever I remove the prop now, I remove all bolts equally...that is one turn on each bolt going around the prop. That way, the prop / backplate combination comes off together and does not allow scoring of the bolt shaft. I use an engine hoist to hold the prop secure while I am removing it. Once again, I'm unsure any of this applies to the RV...but it might so I am sharing.

Ellis
2017 paid

I talked to Sensenich today, and verified that the bolts are true and the threads are undamaged. One hole in particular is problematic: if you drop a bolt into the hole, it will stop partway down, and meets a lot of resistance. We think the spinner back plate holes may not be lined up properly. You can see edges of the back plate in the hole, which apparently you should not. Since I'm only two hours away, I decided to take the prop and the bolts to them for inspection, and pick up a mess of apples and cider from an orchard on the way home.

Went up to Sensenich today with the prop and bolts. We determined that the spinner backing plate had either slipped (unlikely because the spacer is tightly pressed to the prop) or had been improperly installed. Only one hole was impinging - a bolt would not slip through - so I guess there previous owners "helped" seat the bolt by either hammering it or started turning it earlier that the others. The solution was to either ream out the hole, or separate the prop from the spacer, and repress it. I elected to ream all the holes. Very little material was removed, more from the impinging hole. Then we sealed all the bolt holes, and poured Alodine in the holes for corrosion protection. Three bolts were damaged enough to recommend replacement, and they are NOT cheap. We surmised that that previous owners had removed the prop several times and didn't index the bolts to specific holes, hence damage to more than one bolt. So problem solved for now.

I did get a tour of the manufacturing facility, and saw props in production from the beginning (hammered 2025 forging from ALCOA) to the end, although the "factory" is in a shared flex building that does not hint on what's going on inside. Several CNC cabinets, a grandfathered steampunk lathe for making fixtures, and several hand finishing stages. Pretty sweet. Big thumbs up for the peeps at Sensenich. All the orchards were closed - what's up with that Pennsylvania?