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Oil return lines

RV7A Flyer

RV7A Flyer

Well Known Member
Patron
So a question came up over beers this evening...

Seems a common source of small oil drips are the little rubber hoses joining the hard lines from the cylinders to the oil sump...the oil "scavenge" or return lines. Hard line from the cylinders to rubber hose to the engine.

Why don't they use flexible hoses all the way? IIRC, the engine connection is an NPT fitting with a nipple or barb...couldn't one put an AN fitting with flared tube on that end, and then run a flex line with flared ends at both ends between the cylinder and the engine?

I don't plan on doing this, of course, just wondering why it's such a jerry-rigged, cobbled-together-looking combination of fittings and aluminum tube and rubber hose and hose clamps, and not something more, well, elegant.
 
RV7A Flyer said:
I don't plan on doing this, of course, just wondering why it's such a jerry-rigged, cobbled-together-looking combination of fittings and aluminum tube and rubber hose and hose clamps, and not something more, well, elegant.
Click to expand...

I'm guessing full length rubber lines may not tolerate the heat very well, or at least didn't in the old days. Baffle exit air temp is about 240F on my 390, plus there is radiant heating from the exhaust header pipes.

In any case, the only real problem is the cheap hose clamps. Over time ordinary hose clamps extrude the rubber hose sheath out through the slots and lose clamp force. In addition, often they are not very round when tight.

As soon as you get your brand new engine, replace all the clamps with the correct size ABA clamp:

http://aircraftproducts.wicksaircra...20?&plpver=10&origin=keyword&by=prod&filter=0
 
I'd imagine cost and weight are also a consideration for the OEM. Hose assemblies are total overkill for this "zero pressure" application.

You can get that silicone rubber hose often seen in turbo plumbing in all kinds of sizes - I wonder how that would hold up over time?

HoseKits.htm&h=1590&w=2564&tbnid=7LU-3ckIfz1lXM:&zoom=1&docid=g0F5v8O54ArYTM&hl=en&ei=frdXU6e2OJCOyATcnYHYAg&tbm=isch&client=safari
 
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RV7A Flyer said:
Why don't they use flexible hoses all the way? IIRC, the engine connection is an NPT fitting with a nipple or barb...couldn't one put an AN fitting with flared tube on that end, and then run a flex line with flared ends at both ends between the cylinder and the engine?
Click to expand...

Simple: cost and weight. And that is IFF certification was not a hurtle too.

Silicone is terrible in creep, so keeping it tight on a small diameter exacerbates the clamping problem that DanH nicely summarized. See Dans article in Kitplanes on this topic. I just subscribed so I could see articles from DanH, Ironflight and other quality posters here.
 
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Thanks for the tip Dan. Had Googled around without luck for better clamps.

Here is another source and recommended torques:
http://www.ultimategarage.com/abaprice.html

Seems a little pricier but good selection and information.....

Ordered mine here for VERY low cost. Had to ask if they were real ABA and it looks like they are. Total cost for 12 small and 8 large clamps under $20...


------------- Begin message -------------

All of our products are genuine. Your clamps are ABA, clearly marked manufactured in Sweden and distributed by the Norma Group.

--- Original message ---

Order ID 105-9435788-8425008:
12 of #4 ABA Hose Clamp M11X17 Stainless Steel Band width 9mm Min Dia 11mm Max Dia 17mm [ASIN: B00HPZV9B2]
8 of #28 ABA Hose Clamp M44X56 Stainless Steel Band width 12mm Min Dia 44mm Max Dia 56mm [ASIN: B00HPZVPLG]
 
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Any idea of the correct size to order - my engine is sealed up for paint at the moment. Not sure if they vary, but in my case it is the YIO-540.
 
hose

The hose is 3/8 id x 3/4 od, so a 3/4 or slightly larger clamp. I have had good results using a hose that extends further outboard on the aluminum tube. Lycoming and Lyclone hoses tend to be minimum length which creates leaks.
 
change of luck..

We have had better luck using the "ABA" clamps or import auto style clamps. They pull an even pressure around the full "O.D." of the tube. Next time you wish to change the hoses you may wish to try them. I think Wicks has them in stock. Oh use good hose. Yours as always R.E.A. III #80888
 
Can you define "good" hose? I assume you mean something other than the original hose type (whatever that is).
 
I believe that the hoses can safely be replaced with 3/8" MIL6000 hose, available from Spruce or other outlets. Cheaper rubber hose will probably degrade much more quickly...
 
Yep.

RV7A Flyer said:
Can you define "good" hose? I assume you mean something other than the original hose type (whatever that is).
Click to expand...

Yes a good Mil. speck hose. The cheep fuel oil hose you get down at the aircraft section of your friendly auto store will not take the heat for as long and start getting hard quicker on you. We have used the hi-pressure fuel injection hose from the same store and it will last as good as the "O.E.M' ly-con hoses. Yours as always R.E.A. III #80888
 
Spring band clamp

In my opinion, a spring band clamp is the solution. They give a constant clamp force even when the hose material creeps. Look under the bonnet of your car. They are used in cooling systems under pressure so a non pressure application is easier to deal with. They don't produce a pinching effect like screw type clamps do.
When engineering the joint, the fit between the hose and fitting, hose OD and clamp are important.
I do agree with the reason for this thread. When transporting liquids, the less joints the better.
Good discussion.
 
From Kitplanes...

The most popular OEM choice sidesteps the entire loss-of-clamping issue. Spring clamps (Fig14) are ?constant clamping?, meaning even if the rubber extrudes or shrinks, the clamp will contract and maintain sealing pressure. They work well with all medium to soft rubber compounds (including silicone), are lightweight, and require little space. They can?t wear out, so this kind of clamp can also be very economical - OEM clamps salvaged from late model import cars will be as good as any you can buy.

aelc04.jpg
 
Kyle Boatright said:
Nope. Cylinders move relative to the crankcase. A solid line would fatigue and break in short order.
Click to expand...

I didn't say use a solid line :). Flex line with flared-tube fittings on both ends.

N.B. I'm not going to do this, just kind of amazed at what appears to be a pretty unsophisticated (and leaky) combination of parts (AN fittings, hard lines, rubber hoses, clamps). I just would have thought there'd be a better solution after umpteen decades of engine development.

Then again, we're talking about aircraft engines, aren't we? :)

(ETA: the lines from the "spider" to the cylinders are solid, no? Albeit, steel ones :) ).
 
I know an engine overhauler that did the soft line returns on all his engines. It was like his signature thing. Never had a problem, but it's 4 more hoses that have to be replaced every 7-10 years.
 
I replaced leaking oil return hoses a while ago. They were extremely hard, completely misfigured and soaked with oil. I wish I did it earlier I was just tightening and tightening those clamps. :eek:


















 
If you ran a flex line to the crankcase instead of the rigid tube and hose combination, the flex line will be very close to the exhaust pipe of the neighboring cylinder. Make sure it can handle that kind of heat without deterioration or you could be looking for trouble.
Good Luck,
Mahlon
 


An excellent example of why you should never use band clamps with slots. Much of the original clamp pressure bled away when the rubber extruded through the slots. Use solid band screw clamps or constant pressure spring clamps.
 
clamp size?

I need to order some of these ABA clamps for my oil return lines. What's the best size - #6 (1/2 -13/16) or #8 (5/8 - 1 1/16)? I'm wondering if the #6 size might be a bit snug to get on with the hose over the aluminum tube.
Man, am I tired of these things leaking ...

thanks,
 
Mine leak too

RobertD said:
I need to order some of these ABA clamps for my oil return lines. What's the best size - #6 (1/2 -13/16) or #8 (5/8 - 1 1/16)? I'm wondering if the #6 size might be a bit snug to get on with the hose over the aluminum tube.
Man, am I tired of these things leaking ...

thanks,
Click to expand...

I'm in the middle of my condition inspection and decided to replace these hoses as well. I pulled them out and they look just like the one pictured above and are as hard as a rock. The spec on MIL-6000 hose shows 3/4 OD, my old ones measure closer to 11/16 so probably the smaller size would be best. Have you located a good source for these ABA clamps?
 
Size 4 ABA Clamp

Go with Size 4 from Wicks. Just replaced mine and the #4 fit perfectly.
 
pauldan181 said:
I'm in the middle of my condition inspection and decided to replace these hoses as well. I pulled them out and they look just like the one pictured above and are as hard as a rock. The spec on MIL-6000 hose shows 3/4 OD, my old ones measure closer to 11/16 so probably the smaller size would be best. Have you located a good source for these ABA clamps?
Click to expand...

See post #5. Whole set under $20.
 
I just replaced my oil return hoses at my first annual. One hundred hours and they were already starting to leak. ACS has these for $2.30 each. I went to O'Reilly autoparts and bought a one foot section of Gates fuel/oil compatible hose for $1.67. The spring clamps were $0.66 each at a local hardware supplier.
IMG_6501-M.jpg


I'll let you know how these hold up in the next 100+ hours.
 
I marked this flag awhile ago so that at my next annual I would take a look. Sure enough, after only 120 hours almost all of my return lines have a good showing of oil drops and dripping that has made the firewall area messy. I removed one of the tubes and like Vlad, it is very scored by the default clamps. I have new MIL 6000 3/4" hose from ACS and just ordered some ABA04 worm clamps from Wicks as I can't find a source for spring clamps around me.

20151012_214038849_iOS_zpsdi3upjlj.jpg
 
Anybody have reports of the spring clamps failing to hold the rubber portion of the oil return lines? I'm replacing mine since they are old, oily, and a bit gnarled.
 
Mine are seeping so this was a great thread to come across.

I won’t be able to visit the plane in the next few days, what’s a safe number of feet to order on the hose?

Thanks!
 
Oh 50 feet should cover what you need. They are only about 2 1/2" long and there is only 4 of them.
Get the constant pressure clamps while you are at it.
They are great
Art
 
Excellent, I’ll order 3’ to be safe. And I’ve got a set of steel spring clamps on order already.

Thanks for the help!
 
Power steering return line hose is the right ID, and is designed for high temp, low pressure applications. In 30 years I've never had it degrade or leak after jettisoning the OE Lyc rubber tubes.
 
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