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Intake hose

Blain

Well Known Member
These seem to be getting toasted. Is there an certified aircraft replacement in silicone out there? Not big on Summit Racing for aircraft parts.
 
I went full "experimental" and used blue silicone hoses from China. Where one of them passed close to the exhaust, I wrapped it with Thermo-Tec. I did notice that the band clamps needed to be tightened after the first 10 hrs. or so. I check the torque at every annual.
 
As someone who actually just bought some silicone hose from Summit for my intake tubes, I'm wondering if you have a specific objection to its use?

For the clamps, I'm discarding the old school school worm drive hose clamps in favor of modern constant tension band clamps. Easily sourced from the aviation isle of the nearest junkyard... Just look under the hood of the nearest 2002 Chevy Tahoe and snag the radiator hose clamps.

65a7fp.jpg


You might note that I'm using the same style spring clamps on my oil drain tubes.
 
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I used a marine grade rubber engine hose (very durable and resistant to everything). I am sure there are some that will expect me to fall out of the sky any day now due to the use of non-aviation parts.

My experience with silicone hose is that it is mostly silicone with a fiber core and therefore the quality is not that variable. However, I don't have that much experience with it. I do know that most large silicone hose is designed for pressure and not vacuum. However, in this application there is not enough un-supported area to allow deformation from the vacuum. Much of the rubber hose isn't either. That is why radiator hoses used to have internal coils to avoid deformation when the coolant system turns to a vacuum after shut down. The marine hose has a steel coil embedded in the rubber and is one of the reasons that I used it.

Larry
 
As someone who actually just bought some silicone hose from Summit for my intake tubes, I'm wondering if you have a specific objection to its use?

For the clamps, I'm discarding the old school school worm drive hose clamps in favor of modern constant tension band clamps. Easily sourced from the aviation isle of the nearest junkyard... Just look under the hood of the nearest 2002 Chevy Tahoe and snag the radiator hose clamps.

65a7fp.jpg


You might note that I'm using the same style spring clamps on my oil drain tubes.

Not outright objection. I just don't want to experiment when the wheel was already invented. I guess a good example is the silicone rocker cover gaskets. Not certified but plenty of service history. Thought I would find the same with these intake hoses. So were yours radiator hoses from Summit?
 
If you don't like the spring clamp idea and are still concerned about intake leaks resulting from loss of clamping pressure caused by rubber extruding through typical gear clamps, then there IS a product out there for you.

ABA clamps. Available from Wicks Aircraft. These clamps are serrated like a regular gear clamp, however the serrations don't go all the way through the band. They work just like a gear clamp but they don't come with the penalty of loss of clamping force over time, as suffered by gear clamps. An excellent upgrade.

While you're replacing the clamps on your intake runners, also replace the gear clamps on the oil drain lines (loss of clamping pressure on these lines is one of the most common and easily eliminated sources of leaks in Lycoming engines).
 
Do you homework first . . .

If you don't like the spring clamp idea and are still concerned about intake leaks resulting from loss of clamping pressure caused by rubber extruding through typical gear clamps, then there IS a product out there for you.

ABA clamps. Available from Wicks Aircraft. These clamps are serrated like a regular gear clamp, however the serrations don't go all the way through the band. They work just like a gear clamp but they don't come with the penalty of loss of clamping force over time, as suffered by gear clamps. An excellent upgrade.

While you're replacing the clamps on your intake runners, also replace the gear clamps on the oil drain lines (loss of clamping pressure on these lines is one of the most common and easily eliminated sources of leaks in Lycoming engines).

I bought an assortment of these with high expectations. The static friction torque is high, they are much more stiff and the lump under the screw is thicker. I was not impressed. YMMV

Silicone hoses with constant force clamps sure looks like a winner. Silicone WILL creep more than rubber and will need more different clamping designs, not constant circumference. There are alternatives to the spring clamp types but much more pricey. ~$7-15 each.
 
...So were yours radiator hoses from Summit?

This is just a straight section of 1.75 ID x 12 hose generally used for coupling custom induction systems together. I'll just cut it into 2 inch sections for my 6 tubes. There are plenty of similar silicone hoses from overseas without internal glass reinforcement, but this one has what looks to be 4 layers of glass imbedded. No way its going to collapse in this application. Silicone seems to have decent properties for "dry" fuel injected engines like I have, but time will tell if it holds up in service. If not, back to rubber. NBD.

Heres the link to the product Im using:

https://www.summitracing.com/parts/vpe-27051/overview/
 
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ABA clamps

I bought an assortment of these with high expectations. The static friction torque is high, they are much more stiff and the lump under the screw is thicker. I was not impressed. YMMV

Silicone hoses with constant force clamps sure looks like a winner. Silicone WILL creep more than rubber and will need more different clamping designs, not constant circumference. There are alternatives to the spring clamp types but much more pricey. ~$7-15 each.

Agree with you here Bill. I replaced old style clamps with ABA couple hundred hours ago. I did a lot of flying during cold winter months and I noticed oil leaks from return hoses. I tightened the heck out of those ABA clamps and the hoses still leak. Wasn't like this with old style. Yes the hoses were soaked with oil but old original Lycoming clamps were holding even with rubber extruded. I will try spring clamps at next condition inspection.

added: sorry for topic deviation we are discussing intake hoses.
 
Regarding clamps

I'm a fan of the constant tension clamps Michael is using, they work as advertised. Should you need them for applications other than intake tubes (and even for that) McMaster-Carr sells them in their Aviation section. Part numbers 7329K1x (where x = 1 - 8 depending on size) for clamps that fit everything from oil drain hoses to intake hoses. A bag of 10 ea 7329K18 clamps, the correct size for the intake tubes and enough to do all of them currently lists for $14.43 and they don't auto-loosen like all the stock clamps did on my engine.
 
Oil leak

I think I'll try that hose that Michael is using. I like the idea of the reinforcement.

I have an oil seepage somewhere on the aft side. Maybe it is those drain tubes migrating back from the airflow.
 
Hi Michael,

A friend and I are following in your footsteps and replacing the old rubber hose with silicon hose, did you need to remove your intake tubes or did you just cut the old rubber hose off and slide the silicon hose back into place?

Cheers
 
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I meant to comment on this when this thread was active a little while ago, but got sidetracked. Generally, silicone rubbers are not very resistant to gasoline, which likely includes avgas components. A comment earlier in this thread mentioned "dry" as in fuel injected. There is plenty of gas slobbering down those intakes during priming and after shutdown.

It might be a good idea to have a look at them after a few dozen hours - they would decompose from the inside out if they were going to. Heat increases reaction rates, so the shutdown is the worst case situation.
 
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