Prop Hub Clearance

[surfly]

Upon finishing the assembly of my case halves I have very smooth effortless crankcase rotation from 0* to 200*. In this arc the distance between the prop hub and the case halves is about thirty thousandths. In the last 160* of rotation the clearance between the hub and the case tightens up at the upper side of the case, opening more at the lower side, to where during the last 90* or so of rotation the hub actually comes into contact with the case causing the need for an increase in effort to turn the crank. This effort needed is not what I would consider to be a teardown issue feeling that during running this would settle itself.
My real concern is that if the hub is slightly crooked as it seems that it will cause a problem my prop arc alignment.

Opinions please
Surfly

[marsolgp]

Did you assemble the prop hub to the crank yourself? If so, did you have any issues and did the hub butt completely up against the slinger ring?

[gammaxy]

The prop hub seems closer to the case on one side of my engine. This doesn't change as I turn the propeller. What you describe sounds a little different. I'm not sure how perfectly smooth the prop hub is machined or if you can conclusively tell if it is crooked due to this interference.

I'd probably try to use a dial indicator (or at least some fixed reference point) to determine if there's any runout or indication of a crooked prop hub at the face of the prop hub.

Otherwise, it sounds like a question for Sonex.

[grevaly]

I have the same thing going on with my engine. The clearance between the hub and the crankcase halves is less on one side.
on the close side I can get a .002 feeler gauge in so it is not contacting the hub. I had no problems with my crankshaft assembly
and always had a nice rotating crank during assembly of the short block. The way I noticed the problem was just looking at the engine from the front and it just kinda stuck out. I wondered if somehow the front bearing alignment pin was not seated, however
the close clearance is on the case half that has those pins. So my conclusion is that the machine work to clearance the case for the
prob hub is not perfect. Is that possible? Are the cases set up for a line bore when this machine work is done to ensure a true center
with the crank? May not be a real problem. I sure do not want to tear down my engine to measure everything to find out
that this machine work for the prop hub is simply off a minor bit. Worst I can see is a area of slight oil egress?

I hope this helps. I do not post too much cause I do not type well.

Our Fuselage is about done..main wing spars done...engine hung and working on cowling...bought a turbo kit...
we will keep truckin along...

Mark Conner
# 1242

[MikePousson]

I'd do as grammaxy suggested. Set a dial indicator in a fixed position touching the hub on the side where there is less case clearance, give crank a rotation and see if there's a wobble. Nows the time to figure that out.

[surfly]

I will use a dial indicator as other builders and Sonex owners here at X-59 have also suggested to see exactly how much apparent wobble is occuring. My crankshaft and prop hub assembly were assembled by Sonex.
Surfly

[SNX1508]

Upon finishing the assembly of my case halves I have very smooth effortless crankcase rotation from 0* to 200*. In this arc the distance between the prop hub and the case halves is about thirty thousandths. In the last 160* of rotation the clearance between the hub and the case tightens up at the upper side of the case, opening more at the lower side, to where during the last 90* or so of rotation the hub actually comes into contact with the case causing the need for an increase in effort to turn the crank. This effort needed is not what I would consider to be a teardown issue feeling that during running this would settle itself.
My real concern is that if the hub is slightly crooked as it seems that it will cause a problem my prop arc alignment.

Opinions please
Surfly

I had similar issues when assembling my AeroVee. After torqueing the crankcase bolts I could not turn the crank 360 degrees. Factory assembled hub/crank. I could see that the hub was rubbing on the case, so I measured the hub run out with a dial indicator:
Hub shaft .014" out of round
Hub flange OD .020" out of round
Hub flange face .007" wobble
On the flange OD there was an area that was of insufficient diameter to even be machined, not too much of an issue (?), but that would seem to indicate there was a problem with the piece before machining began.
I asked Sonex tech support about the out of round hub, and requested specifications/tolerances on the part, was told there are no specifications or tolerances available. I was then told the out of round hub should not be an issue, and that I should remove material from the case to allow free rotation. Since this did not make sense to me and could possibly cause oil leakage, I asked if they would inspect my crank/hub, which they agreed to do, but not while I waited. Sonex is only 2 hours from my home, so not a big deal, but wanting to get my engine built, I purchased and picked up a 2nd crank/hub assembly when I dropped off the original for inspection. Checking the 2nd crank/hub assembly I made these measurements:

Hub shaft .005” runout
Hub flange face .004” wobble

Better than the original crank/hub, but upon installing the crank and bolting up the case halves, I still could not rotate the crank 360 degrees. When Sonex tech support got back to me on the inspection of the original crank, I was told there is nothing wrong with it. When I reported my findings on the 2nd crank I was told to take my case halves to them for inspection. Eventually I was told the case was not machined correctly. I received a replacement case, I kept the better of the 2 crank/hub assemblies (the 2nd one), returned the original crank/hub, and assembled the engine. I was able to rotate the crank 360 degrees at that time.

With a hub shaft run out of .014” and .005” it does not make sense that the issue was an improperly machine case. I suspect that the replacement case just had the front hole opened up. The engine is completed and mounted on the aircraft, but I have not mounted the prop yet nor started the engine. I am interested in seeing how much tracking error there is at the prop tips. Hoping for engine start in the next couple of months.

Pictures and more details can be found in my builder’s log:

http://www.mykitlog.com/users/display_l ... 227&row=44

Terry

[Onex107]

Be aware. It is possible for a rod bolt head to have an interference point inside the block during rotation. In my case the forward rod, foreward bolt head, was contacting the rear edge of the front camshaft bearing. This was before the shims and flywheel were installed. Sonex said this happens very rarely. My point is, inside clearances are very tight. Be sure the resistance to turning is external, not internal.
In addition, small unmachined areas on the flange O.D., if they are large enough, can cause an out of balance vibration. Vibration analysis to balance a prop is corrected by adding small washers to the spinner back plate.

[surfly]

Yesterday I held the flat side of a 2' piece of 2" aluminum angle firmly across my hub to where the outside corner end of the angle touched my workbench and marked that spot. I then rotated my crank 45 degrees at a time repeating this process. The angle corner fell exactly on my original pencil mark through the whole 360 degrees of rotation. I concluded that my prop hub was not on crooked and am proceeding with my build. I believe the slight case interference that I was concerned about will not be of any consequence once my engine is running.
Building On!
Surfly