4140 crankshaft modifications - propeller hub build

[RobinHood]

the prop hub absolutely pisses oil, vw never used a seal, aerovee doesnt use a seal, great plains used a seal jb welded to the front of the case.

Is this a slinger ring which is part of a case labyrinth seal?

Could it be that the negative pressure (slipstream) created by the prop is “pulling” the oil past the seal when doing static runs?
This could go away once the plane has some forward velocity and the pressure around the hub changes to positive?

Maybe you have too much blow-by in your cylinders, pressurizing the crankcase?

 

[phaxtris]

Is this a slinger ring which is part of a case labyrinth seal?

View attachment 63970

Could it be that the negative pressure (slipstream) created by the prop is “pulling” the oil past the seal when doing static runs?
This could go away once the plane has some forward velocity and the pressure around the hub changes to positive?

Maybe you have too much blow-by in your cylinders, pressurizing the crankcase?

Yes the slinger is the oil seal, the only thing i do not have is a left hand thread on the exterior of the prop hub, and i knew that would create some level of oil loss, but it should not be as bad as im witnessing

this is a picture of the aerovee, they do not use a seal (i emailed them), you can see the very slight left thread cut into the od

i did not do a leak down, so i cannot say for sure the blowby is not significant, i do not believe it to be significant, compression test numbers were all very good, and it does have good compression pulling the prop through. I think i will run the breather into the airbox, that should provide some negative pressure and help with some crankcase pressure, its currently vented

This is another option, sealant blocking this return passage, i feel this is very unlikely, this appears to be silicone, i used Permatex aviation form-a-gasket, it is very thin, and drys very thin, that passage is relatively large, i dont think i could plug that passage with aviation form-a-gasket even if i tried



I did not consider the slipstream causing a negative pressure, i could see this being possible, the oil doesnt just seep out and leak down the front of the engine, it is thrown all the way out onto the right exhaust pipe, thats a pretty long ways so its possibly making its way into the slipstream

this is the oil seal that is/was used by great plains, National 6815, it has the right ID, is inexpensive, it is 6.35mm tall overall, thats the only issue. I think i could modify it by cutting down the height and installing it "backwards" to the conventional install (into a wheel shaft or whattever). I of course would need to cut it in half, but this has been done successfully by others. i think this might be worth a shot, that combined with routing the breather into the airbox and maybe ? i will need to get a seal and do some measurements to see if the rubber will end up where i want it

 

[Susquatch]

Anyone know where to get seal rope in the 21st century ?

Some of the older farm sprayers use a rope seal. You might be able to get some at a farm equipment supplier. I know that Lampton farm supply has it, but that's an hour drive for me and I know he won't ship. I'll have to see if I have any left from my old sprayer. If I do, it's yours. Pretty sure I could just mail it.

 

[jorogi]

i could probably get it off, but getting it back on is an issues, interference fit, have to heat it up to 450 deg to get it back on. So the re-install would probably cook to seal

some guys cut a something like a axle seal in half and jb weld it in place, i didnt leave enough straight shaft i think for something like that, either it needs to extend far to the straight section, or the seal would be running on the taper, not sure how well running on the taper would work with a standard rubber seal

i was thinking it might be possible to use something like this

https://www.amazon.ca/Sterling-Seal-Supply-SSS165LA-187x1-V-165LA-V-187/dp/B076MD7W2B/ref=sr_1_9?dib=eyJ2IjoiMSJ9.uO5ahUqhXx9kH6EM7yKw_-JvP7Tc_DIFTEAPgtJoDe2iDeMNFh7pawbe9WshHnS2DPK2p6KfwCV93euxd52e2lP7GCp51cqR5v_Vfjm_ZIz2xAcDfK6oNMa7I36TrBIgNRvZHEDt8iuaUSTFscKhX72f40JvKzPU322EBiO6QbclHMK_u4BV-EapFcM2iVY6GVcHYf_RlU8Ll_T5uxNmcT58awITljNyfSt-4tupzas4HwahmFUu77r5qKKbDlXm8heZ12WIHzO4doogOraL4Eg1H031KrVVuoKHGohvNhE.LpfPbDR-MLos5Ne4cz4OyLrTFzfBsQ7UdC-kkrLJTZ8&dib_tag=se&keywords=graphite+packing&qid=1746061585&sr=8-9

i could put that around the base of the flange where it meets the case, tighten it around with some form of clamp, and jb weld the whole shebang onto the case

It says it is appropriate for marine propeller shaft and 4400 fpm. With some totally unreliable advanced mathematics (only half a cup in yet) a 2" shaft would be well within that limit. However a marine shaft is not under any significant pressure as possibly compared to your crankcase. Also in marine applications the rope is in a gland nut and is tightened from time to time so gooping on will probably not work and is non adjustable. If you could fit a cap over the rope to clamp it to the case it might work. If the cap has a shim stack under it you might be able remove shims to adjust the clamping pressure.

 

[jorogi]

Is there anyway to attach a pressure guage somewhere to get an idea of the pressure in the crankcase ?

 

[phaxtris]

It says it is appropriate for marine propeller shaft and 4400 fpm. With some totally unreliable advanced mathematics (only half a cup in yet) a 2" shaft would be well within that limit. However a marine shaft is not under any significant pressure as possibly compared to your crankcase. Also in marine applications the rope is in a gland nut and is tightened from time to time so gooping on will probably not work and is non adjustable. If you could fit a cap over the rope to clamp it to the case it might work. If the cap has a shim stack under it you might be able remove shims to adjust the clamping pressure.

they ran rope seals in quite a few engines in years past, even the original 2 piece rear main on a small block chevy was a rope seal, you can still buy it as that, but its little chunks, i would want a length obviously. That seems to be the issue, finding the right stuff on a spool, and i agree, without adjustment it would leak in time, im sure of that, even if i lost say 1/2qt in 6 hours i would be ok with that, check oil every fuel stop, and add every second. I fully expect some oil loss with this motor, valve cover gaskets, pushrod tubes and gaskets, all marginal leaky designs from the 30's. The front nose of the case is rounded, i have seen one guy machine that part flat and make a seal retainer, i didnt do that however, so it makes it tough to make a proper stuffing box

Is there anyway to attach a pressure guage somewhere to get an idea of the pressure in the crankcase ?

i could probably rig something up, what i will do is run the breather into the airbox, i could tee off that and run a pressure/vacuum gauge. Maybe it is just a case of high crank case pressure due to the venting, add that in with some likely negative pressure as @RobinHood suggested, and that may be the majority of the issue

Im going to run out today and pick up one of those 6815 seals, see if i think i can make that work, not much to loose there.

in any case i have time, i need to order some brake parts, mfg wont ship to Canada, and acs doesn't have stock. Part of my taxi testing i found the left brake does not grab well enough for differential braking. With the full castering non-steerable tail wheel and no differential braking slow speed taxing is dam near unsafe, a blast of throttle and full rudder barely gets it turning.

 

[Bandit]

I am not sure if a pump packing is the same. If so, or maybe for a try, a pump supplier/repair outfit may have something. In the past I had got rope style packing from them for some of the various pumps we had at work and on the farm.

 

[phaxtris]

I am not sure if a pump packing is the same. If so, or maybe for a try, a pump supplier/repair outfit may have something. In the past I had got rope style packing from them for some of the various pumps we had at work and on the farm.

I'm not sure either, it's such an uncommon thing now it's hard to be sure

I have a plan with the 6815 seal, me and my scruffy helper are on our way to try it out, I'll update in bit with how it went

 

[phaxtris]

here is what i ended up doing, the 6815 seal is ment for a slightly smaller shaft (.5 mm), and is about twice as thick as what will fit on the straight portion of the shaft so it wasnt as simple as just cutting the seal in half and gooping it on, i turned off a portion of the metal shell, and trimmed the inner part of the seal, now im sure it wont work as well as it could with half the seal missing, but it will be much better than nothing.

Using the scrap hub i have, i played around and figured if i cut 2/3rd of the diameter of 1 of the seals, i could cut the another seal for the remaining 1/3, i could field fit it by trimming the metal shell with snips and filing, that way i could gain that extra bit of circumference with the second seal so as not to have either an extremely tight seal, or one that didnt cover the entire circumfrence.

i used a hose clamp and some pieces of aluminum filler rod to compress the seal around the shaft (and hold it while the jb weld cures), the gap you can see without the clamp i can close up by pressing the seal down with my fingers, so i dont believe it to be to tight

gooped on the jb weld, the filler rods also help to make sure i have an 1/8 of jb weld on the seal, although i may go back in a few days, remove the clamp, trim the filler rods, and add another pass of jb

i also grabbed the airbox so that i can add a bung for the crank case breather, hopefully that will provide some scavenging of the positive case pressure




my helper wasnt to motivated, layed around for a bit, and then went and passed out in the truck, good help is hard to find

 

[jorogi]

good help is hard to findView attachment 64005

Mine is only any help when I have to "bark up".
She is very popular at work, everyone comes to see her and bring her treats, she always says please.
I was stuck at the scale house window once a few years back. The two girls inside were fussing over her as usual. I got a banana out of the lunch bucket, peeled it and took a bite. Turning to Moggy I asked her if she wanted a piece, woof, woof, woof. After another bite I asked her if she would like another piece, woof, woof, woof. You get the idea now, so with the last little bit I again turned to Moggy but this time I asked her " Does daddy have the biggest schwinky ever ?" The reaction in the scale house was hilarious , raucous laughter from the one girl and the other girl had eyes as big dinner plates and a face as a red as a five dollar hookers lipstick.

 

[Mike R]

Do you have a PCV (Positive Crankcase Ventilation) valve in the crankcase anywhere? That will help tremendously by creating the negative case pressure and ensuring the oil wants to travel into the case and not out. A simple pvc to a catch can would be something I'd try, or check if you do have one that its working as it should. If there's a vent hose without PCV valve in it an inline one should be readily available, though checking online the prices are criminal for them now - its just a simple plastic ball or reed check valve, cost pennies to make and they're asking $20 - $50 for one?

 

[Susquatch]

I was stuck at the scale house window once a few years back. The two girls inside were fussing over her as usual.

Somehow I knew where this was going right off the git go.... You didn't disappoint - at least not me anyway. Can't speak for the girls......

 

[phaxtris]

Do you have a PCV (Positive Crankcase Ventilation) valve in the crankcase anywhere? That will help tremendously by creating the negative case pressure and ensuring the oil wants to travel into the case and not out. A simple pvc to a catch can would be something I'd try, or check if you do have one that its working as it should. If there's a vent hose without PCV valve in it an inline one should be readily available, though checking online the prices are criminal for them now - its just a simple plastic ball or reed check valve, cost pennies to make and they're asking $20 - $50 for one?

yes and no, the aircooled bugs use what is called a road draft tube, its basically just a crank case vent that is exposed to the air, driving at 45mph+ would create a draw, it pre-dates the pcv system



i did not have the tube attached to that elbow, so that may have been some issue

what im thinking to try is making a proper vent tube with a 45deg cut into the airflow (tube 90deg to the airflow), even not moving the air blown past it by the prop should create significant draw, probably more than could be achieved by plumbing it in front of the carb, im thinking of increasing the size as well, to something like 3/4"

doing a proper pcv system could create some headaches, finding the proper valve for the engine, drilling the intake, possible issues with tuning

 

[jorogi]

The Continentals have a breather set up like that. AD's were issued as it was possible to suck the oil out of the breather. IIRC the elbow into the front of the crankcase was turned upwards and was lengthened inside the case so it nearly touched the top, thus reducing the flow. It was possible to have things working fine on the ground but higher speed, power and altitude and you would want to be proficient in your PFL skills. Course judging by your pictures you'd be hard pressed to hit anything where you are anyway. So be careful.
There are oil separators for breather tubes that feed back into the crankcase.
Also bear in mind, on the commercial side of things an oil leak is a grounding defect, loss of oil in flight or oil fires in flight are serious.