Prop Hub Interference?

[NWade]

Hi All,

So my AeroVee is proceeding with two steps forward, one step back... :?

After tightening my case bolts I found the crankshaft had a portion of the rotation that was stiff. Nothing appeared to be knocking or hitting; but upon close inspection I found my prop hub rubbing against the engine case during a portion of each revolution. After disassembling the case I found metal filings between the forward bearing and the prop hub, confirming my suspicions.

I know some other folks have posted about clearance problems in this area - but for me the clearance between hub & case seems to follow the prop hub as it rotates: I can make a mark on the hub and follow it around the case. Wherever the prop hub mark is facing, that area tends to have the least clearance. And when the mark is in the ~10 o'clock to 1 o'clock positions it is physically rubbing on the case (and the gap on the underside of the hub is quite large). When the mark on the hub is facing 6 o'clock I have OK clearance all around.

This leads me to believe that the hub is out of round or is not on the crankshaft straight. Photos are here: https://flic.kr/s/aHskPzJwFG

I ordered the pre-assembled crankshaft from AeroConversions, so I've contacted support. But per some automated messages they've got limited availability this week.

Anyone here dealt with a similar issue?

Thanks,

--Noel

[Area 51%]

It looks like whoever machines those prop hubs, needs to sharpen their axe.

Have you checked the prop flange for run-out to determine if the whole shootin' match is out of wack?

[jjbardell]

Did you check and make sure the doll pin for the bearings (particularly the front) isn't pushing the bearing up a fractional amount, causing the issue? I had to grind one of my pins down just a .003 to get the bearing to settle properly. Just a thought.

[jeff0196]

Anyone here dealt with a similar issue?

YES!

I had the exact same problem. I found it out before I assembled my cases. My first crankshaft was factory assembled. When I removed the bolt in the front to add Loctite and re-torque I found the bolt to be completely stripped. Upon closer inspection I could fit my fingernail between the prop hub and the oil sling ring on one side. After contacting Sonex, they had me get it back to the factory for correction. They claimed to have fixed it and shipped it back to me. The shipping method Sonex chose made me question how straight it was (single layered cardboard box and virtually no packaging paper-the crankshaft busted through the box at both ends and was partly exposed when found at my door). Sonex claimed it was ok to assemble, but I wanted to know for sure. So I supported it from different bearings in the case and spun the crankshaft while measuring run out with a mounted dial indicator at several locations. While doing this my prop hub contacted the case in the same exact spot as yours making metal shavings. The dowel pins where not a factor on my set up as I tested.

Getting back to the run out. The crankshaft had significantly less then 0.001" (the scale on my measuring tool) no matter where I measured it on the journals, but the prop hub was not so straight. In the area that the hub contacts the case my hub has a radial run out of 0.012" The face of the hub that mates to the propeller also has significant run out. The run out at the face of the hub in the axial direction measured as far out on the face as possible (about 5 inches on diameter) is 0.007" These numbers were provided to Sonex. They asked me to measure my crankcase bore at the prop hub opening. Mine was 2.204" on diameter. After telling them 2.204" they asked for both my crankcase and my crankshaft back for closer inspection.

Sonex gave my parts to their machinist. The solution by their machinist to this problem was to enlarge the opening on the crankcase where the prop hub goes through. After the machinist took measurements they said the hole was slightly undersized and off-center. They claim that the hole is now enlarged to the correct size and re-centered. I have not been able to verify this yet.

As far as the run-out of the prop hub, according to Sonex, my run-out is not a problem, and is "within their tolerance". However the only tolerance I can get then to commit to is that the face of the hub, measured in the axial direction at the 5 inch diameter is 0.010" or less, making mine at 0.007" ok.

I would be curious as to what yours numbers or anyone's AeroVee for that matter are if you measure run out and the crankcase bore diameter at the prop hub.

For reference, my engine was purchased November of 2013.

[NWade]

Thanks, Gents.

As for my dowel pin: It looks fine and fits in the proper spot without an issue. If the dowel pin was the problem I would expect the prop to be "off-center" left and right, not up and down.

Regarding checking the hub run-out or symmetry: I don't have a dial indicator. What I did was put a 1x1" piece of angle on the top of the engine case (across the flat spot where the breather plate attaches), and clamped it in place. I rotated the crankshaft to the worst spot and measured the distance from the angle to the top of the prop flange, using a sliding micrometer. Then I rotated the crankshaft 180 degrees and measured again. I don't trust the measurements totally since this was a bit of a ghetto setup; but I repeated the measurements a few times and got about a 20-thousandths difference between the two crankshaft positions.

Any further ideas on how to check the prop hub with a limited number of tools would be greatly appreciated, thanks!

--Noel

[jeff0196]

Harbor Freight item#93051 does the trick. It's $32 minus 20% if you have a coupon. Clamp the vise grip to the case and the arm adjusts and locks into any position. Put the Dial wherever you need it.

[WaiexN143NM]

Hi all, noel,
I ask the same question again. Where is the quality control on these parts? No conspircy theories, fake news, or alternative facts here. Good luck.

WaiexN143NM
Michael

[SNX1508]

YES !! I encountered the same problem.

I have AeroVee S/N 0736, ordered/purchased at AirVenture in August of 2013. I purchased the Sonex assembled prop hub & crankshaft option. I had .014" of run out on the prop hub, and could not turn the crank 360 degrees after tightening the crankcase halve bolts. This was because the crank was hitting the crankcase at a certain point of rotation. I noted on the outside diameter of the prop hub flange that there was about a 1/2" arc that did not have any material removed during the machining process. This tells me either the part was undersize to begin with or it was machined off center. After contacting Sonex tech support they suggested that I was measuring the run out incorrectly, so I sent them pictures and videos of the run out measurements. Tech support also said they had no specifications on the crankshaft dimensions or run out tolerances, saying "there are hundreds of these crankshafts and prop hubs out there, they are all machined the same, and no one else has reported issues". After reviewing my pictures and videos, tech support asked me to take sandpaper or a file to the crankcase to enlarge the hole for the crank/prop hub, but I declined thinking this might lead to oil leakage. Then tech support asked for the crank so they could inspect it. It is only a 2 hour drive, so I took it up there. Since they would not inspect the crank while I waited, and I was sure I did not want to use that crank, I purchased a second crank with preassembled hub and returned home. After reassembling the engine, this crank also could not be rotated 360 degrees without it contacting the crankcase. I found it to have .005" of run out on the prop hub. I then contacted Sonex tech support again, they requested I return the crankcase halves for inspection. After inspection it was determined the prop hub hole in the crankcase halves was machined incorrectly. I was provided replacement crankcase halves, and given credit for the returned crankshaft. I reinstalled the second crankshaft and there was no interference between the crankshaft and crankcase halves. The prop hub still has .005" of run out, but I have decided to live with it. I have since ran the engine, but have not flown the aircraft yet.

First engine start.....

https://youtu.be/K9wP77IqoZ8

Terry L. Cooper
SNX #1508
Tail Wheel
AeroVee #0736
N296SX
Aircraft build took 2005 hours, and was completed in October 2016
http://www.mykitlog.com/SNX1508
FAA Inspected & Airworthiness Certificate issued 11/4/2016
Currently training in a Citabria for tail wheel experience, then onto a LSA for ASEL endorsement on my Sport Pilot cert.

[DCASonex]

Got one of Sonex new hollowed out lighter weight prop hubs a while back and it was also machined off center, could easily see portion of OD that was not machined. Only way I see that happening is if lathe chuck had extreme run-out. I returned it for credit but was out the shipping.

David A. Sonex TD, CAMit 3300

[WaiexN143NM]

Hi all,
I too had a prop hub that didnt match up to our jab 3300 prop. I feel for sonex, they are the middle man . Many wasted hours , tech support, emails, phone calls ,extra shipping fees, sonex, and the customer. Todays world, especially things being mfgr. outside the usa, many times the quality and metalurgy and quality control is just not there. Extra vigilence needed, sonex, and the customers. Be safe out there.

WaiexN143NM
Michael