Induction system hose clamp tightness

455 Bravo Uniform

455 Bravo Uniform

Final Approach
Joined
Aug 18, 2015
Messages
5,769
Location
KLAF
Display Name
Display name:
455 Bravo Uniform
How tight is tight enough? I found about half of mine loose enough where I could go a half or full turn more without worrying that I was gonna strip em. Would that looseness make any difference in performance?
 
I usually get them pretty snug because the next time you check them they will be loose again. Too loose and you'll have induction leaks but too tight and you can ruin the intake boots.
 
On a big Continental? Take a nut driver and cut a slot straight through the socket end with a die grinder to fit onto the thump clamps. Use all your wrist can develop to reef on those clamps. You can do the same slot in a socket. Hard to over torque with a 1/4” ratchet. Be careful with a longer tool.
 
455 Bravo Uniform said:
How tight is tight enough? I found about half of mine loose enough where I could go a half or full turn more without worrying that I was gonna strip em. Would that looseness make any difference in performance?
Click to expand...

Here are all of the Continental torque settings on the 470 series engine. Not sure what engine you have, but there is probably an engine manual for it.

https://csobeech.com/files/TCM-Torque-SB96-7D.pdf


Sent from my iPhone using Tapatalk
 
I’ve never seen or heard of anyone using a torque wrench on worm clamps. You guys are joking, right?
 
Stewartb said:
I’ve never seen or heard of anyone using a torque wrench on worm clamps. You guys are joking, right?
Click to expand...

I’ve never used one on a worm clamp but it’s possible to torque them. I was just answering the questions with the torque values on induction nuts which do have to be torqued.


Sent from my iPhone using Tapatalk
 
Stewartb said:
I’ve never seen or heard of anyone using a torque wrench on worm clamps.
Click to expand...
FYI: perhaps you need to get out more. In some circles every fastener, clamp, etc requires a torque wrench and the torque value listed in the mx log. But if you don't understand the difference between 40 inch pounds vs 40 foot pounds you might want to use a torque wrench until you calibrate your elbow. Most clamp failures I seen were a direct result of using a German method of torque: guten-tite.;)
 
I hang around with several big Continental owners and I’ll wager none has ever used a torque wrench on induction worm clamps. And it isn’t necessary. My slot-end nut driver rides in the airplane tool kit and my clamps get checked every time the cowl is off. The primary suspect is always the Y pipe and those clamps are difficult to reach on my plane. Have just one engine fire attributed to a lean backfire from a Y pipe leak? You take it seriously, or at least I do.
 
From that Continental link posted by Fracpilot:

upload_2021-5-1_9-2-16.png

Do you guys have any idea what 28-35 inch-pounds feels like? It ain't much. Too much torque on those clamps can weaken them, and it can crush the rubber hose so that it's more inclined to fail. An old saying among mechanics is "One of the most dangerous things around an airplane is a pilot with a screwdriver." Lots of things get way overtorqued. I have found a lot of broken anchor nuts and stripped screws on inspection panel openings from that. Plastic fairings get crushed and cracked. Sometimes seeping engine rocker covers get tightened so much that the gasket is crushed/pinched right through and the leak gets massive. I have found brake caliper bolts stretched to the breaking point, and one broken bolt (meaning no brakes on that side). You can easily overtorque wheel bolts, bringing them to the breaking point, or crushing the wheel casting and ruining it. Overtightened hydraulic fittings crush and distort the mating faces so that they never seal again. Overtightened SCAT hose clamps crimp can wrinkle the sheet-metal nipples and the hose will just slide off after that.

Here are Lycoming's torque specs for hose clamps:

upload_2021-5-1_9-12-27.png

https://www.expaircraft.com/PDF/Lycoming-OH-Manual.pdf Right near the end of the book.

You save the most money by doing things right, and aircraft hardware is not the same as car or tractor hardware. You don't use heavy tools and big forces on it. If rubber hoses leak when the clamp is properly torqued, the hoses need replacing.

You don't really need a torque wrench. You can limit it by using a screwdriver. A ratchet of any size can easily overdo it. If you have access to a low-range inch-pound torque wrench you can use it to tighten a few clamps, then use your screwdriver on them to see how much it takes to turn them a bit further. Gives you a good idea. As Bell206 says.
 
Last edited:
If this is for a continental, you had better make sure that you follow the torque specifications exactly.

Using more than the torque specified will very likely dent the thin aluminum tubes in the induction system, causing permanent induction leaks.

There are also service bulletins so generally you will need between 25-40 inch-pounds depending.

I'd guess every one of you posters above that answered "make it as tight as you can," if you're of average strength and have a 470 or 520, has a bunch of dents in your induction pipes and the accompanying leaks!
 
IO-470. Owner with a screwdriver (or at least without an A&P cert).
 
GRG55 said:
I hate to think what they call a "pilot with a torque wrench". :D
Click to expand...
I'd call him smart... unless he was using the TQ wrench to beat out his nose wheel axle bolt.:rolleyes:
 
Capt. Geoffrey Thorpe said:
I have three.
Click to expand...
So do I, but being retired I don't use them a lot anymore and they're out of calibration dates. In one shop I had bought a torque screwdriver similar to this one, 10 to 65 inch-pounds. Most 1/4" torque wrenches start at 20 inch-pounds, and the Slick mags have internal hardware with torque specs of 18 inch-pounds. When it was due for calibration I sent it in but the lab couldn't find any calibration instructions for it and wouldn't touch it.

41JxwfMFS%2BL._AC_SL1000_.jpg
 
Interestingly - my oil analysis came back high in silicon. Possibly was the loose induction hose clamps. Filter looked fine. I’ll have to look more closely at the cowl-to-throttle body hose and the alternate air door (or whatever it’s called) too.
 
Check the carb heat flapper too.
Depending on where you are based, I would guess an induction leak bad enough to significantly raise silicon oil levels would show up in a rough running or missing cylinder. Now, if your home drome is a dusty dirt/gravel strip ...
 
Don't make a big deal out of this.....hand tighten good and snug. I run a radial engine with dozens of clamps..they all will loosen a bit after a few hours after you tighten them..try not to cause damage to your hoses and fittings.
 
Most people don’t realize upwards of 80% of the clamping pressure is underneath the worm gear. The force is not equal distance around the circumference.

When I bought my plane there was a small induction leak. Removing a rubber induction coupling on the O-470R it had rupture blister on the inside of the coupling.

To fix this problem the previous owner just kept tightening it. It was way beyond torque limit on the fitting and a dent had formed on the intake tube just below the worm drive clamp screw. This was the other reason for the leak.
 
I wonder if smearing a bit of silicon grease would help the sleeve slide around the rubber and tighten more evenly? At least on the initial install before the perforations press-mold the rubber bumps.
 
Domenick said:
I wonder if smearing a bit of silicon grease would help the sleeve slide around the rubber and tighten more evenly? At least on the initial install before the perforations press-mold the rubber bumps.
Click to expand...
That will let the sleeve slide away from where it's supposed to be. I've sometimes had to degrease sleeves and tubes to stop slipping.
 
Last edited:
You must log in or register to reply here.
Back
Top