Screw clamps or spring tensioned clamps. Which is best?

[Runtoeat]

I helped my friend track down and fix coolant leaks one month after his 5 year hose change. I dreaded looking at the back of his engine during the initial inspection for leaks. To my dismay, there was orange coolant on the engine cradle below the water pump on the back of the engine. Further inspection showed the hose connection at the pump inlet was driping. By sheer luck, the clamp screw was positioned in a manner that I was able to get my hand up into the gap between the firewall and air plenum and get a socket with universal extension on the screw head and tighten it. The alternative would have been to remove the air scat tube and air intake plenum to gain access to this area. A major PIA parts removal that would have required a visit with our A&P.

 

There are factory spring clamps up near the coolant expansion tank on the top of the engine. These clamps are very robust and seem to exert a high clamping force. There is a mixture of spring clamps and screw clamps on my engine and my friend's but I believe that the latest Rotax Heavy Maintenance manual shows spring clamps only being used for the coolant sytem? I do not believe that I've ever seen a leak coming from the spring clamps but sure have seen numerous leaks from screw clamps. The spring clamps appear to adjust to the gradual relaxing of the new rubber hose where the screw clamps are unable to do this. Question: would it be best to use a spring clamp in place of a screw clamp when hoses are replaced in inexcessible areas such as those on the rear of the engine? Or, are spring clamps now used totally and is my question moot?

[Anticept]

Hose clamps tend to pinch the hose on one side, whereas spring clamps are uniform. It depends on where the application is.

 

This is something you definitely want to ask the mfg about. I got permission from flight design to make a modification to N566FD, where we enlarged the fuselage fuel hose port near the wing root, and replaced the band-its with hose clamps, so we can easily take the wings off. I trailer 6FD around to schools and events, and I wanted to decrease the wear on the fuel lines channeled through the forward frame. Since trailering is a regular operation for us, we are often retightening the hose clamp, so leaking isn't an issue in our case.

 

What would be nice is a spring clamp with a screw, where you drive the screw in to relieve tension, instead of having to use special tooling for it. They have nice tools for spring clamps, but there are some really tight spots in areas that you just cannot fit those tools in.

[Roger Lee]

Hi Anticept,

 

I remove all those wing root Oetiker clamps and use good fuel injection clamps. FD doesn't have a say on which clamp so you can change it so long as it is an appropriate clamp for that application. I also widen the hole with a Dremel and sanding disk to allow the clamp to go into the hole properly and your right without doing these any wing inspection on the LS is a PITA compared to an SW.

[Runtoeat]

Anticept, thanks for the comments. Roger, the heavy manual shows only spring clamps for the cooling hoses - 75-00-00 pg. 16. Would you know if this Is how Rotax engines are now received by FD for their aircraft?

[Doug G.]

I need to call FD about these small parts. From you Roger I get it doesn't matter what part you use as long as it is appropriate. From others I get every part has to go through the SLSA manufacturer and unless they approve a different part you can't use it.

Tough to make sense of this.

[Jim Meade]

I need to call FD about these small parts. From you Roger I get it doesn't matter what part you use as long as it is appropriate. From others I get every part has to go through the SLSA manufacturer and unless they approve a different part you can't use it.

Tough to make sense of this.

Doug,

 

See if you can get something in writing or get a reference, if you don't mind.

[Jacques]

Would you know if this Is how Rotax engines are now received by FD for their aircraft?

Hi Dick,,yes,,,the engine are delivered from Rotax with spring clamps for the cooling system

[Runtoeat]

Hi Jacques! Did you get your hangar door yet? Thanks for the reply. Jim, not sure if the published Rotax Heavy Repair manual sufices as verification for you? The Heavy Repair manual, Edition 1, rev3, dated 10/1/10 is the most recent edition shown on Rotax' website. Referring to this, use of spring clamps for all cooling hoses is shown in section 75-00-00 pg. 16. There are also Rotax parts manuals but I have not verified that these manuals agree with the heavy manual. I also called and spoke with Mat @ FD USA today. He said Dave Armando would be back from attending the Rotax engine seminar and could discuss this if I call back tomorrow. Based on Jacques reply and the published information shown in the heavy repair manual, it seems logical to assume that the use of spring clamps is not only allowed but may probably be recommneded over use of screw clamps but will still follow up with a call to FD.

[Roger Lee]

The engine from Rotax uses the spring clamps, but not all hoses are supplied, but all the top ones are to the fill tank. The two on each side on the bottom of the engine are too. FD has to move and make changes to the stock system which has included rotating the tank, moving it forward of the carb balance tube, changing some stock hoses and some clamps. They make changes on the fuel pump hose too. The supplied Rotax coolant hose is different the FD coolant hose. Rotax does not supply all hose and some is left to the builder or MFG. You need to be careful with the spring clamps. They can be sprung and loose a slight bit of tension and then a hose can come off. Plus you should put them close to the bead the metal tubing and not way back by the hose end. If you have an oozing hose with a spring clamp try relocating it closer to the bead.

[Runtoeat]

Thanks Roger. I finally figured out the part of your comment which states, "close to the beacon the metal tubing". Think you meant to say, "close to the bead on the metal tubing". It makes sense that snugging the clamp up to the radius of the bead would improve the sealing. It still isn't clear to me why FD runs long lengths of hose away from the sealing areaswhich go unclamped. Some of the hoses run an extra 3" to 4" down the metal tubes past the point where the clamps are. Is there any reason why this is done?

[Roger Lee]

Hi Dick,

 

Darn spell check. I went back and fixed it? It was supposed to be bead. The extra hose over the aluminum tubing is for protection against abrasion from other objects and to help from heat next to exhaust. The ones close to the exhaust should have some fire sleeve wrapped over it as an additional shield.

[Tom Baker]

Thanks Roger. I finally figured out the part of your comment which states, "close to the beacon the metal tubing". Think you meant to say, "close to the bead on the metal tubing". It makes sense that snugging the clamp up to the radius of the bead would improve the sealing. It still isn't clear to me why FD runs long lengths of hose away from the sealing areaswhich go unclamped. Some of the hoses run an extra 3" to 4" down the metal tubes past the point where the clamps are. Is there any reason why this is done?

 

I think it is to protect the piping from abrasion.

[Tom Baker]

I wasn't quick enough.

[Jim Meade]

Jim, not sure if the published Rotax Heavy Repair manual sufices as verification for you?

 

It does, thanks. I got confused by some of the member commentary and your comment reminds me to check the docs personally.

[Roger Lee]

Some part changes need FD approval and some don't as some have pointed out. FD made a few changes from the Rotax supplied engine. It could be hard for a user to know what has been changed unless you have pulled a Rotax out of the box and installed a new one.

 

Here is a simple example for us.

When you did a hose change and kept the fuel pump you had to cut off the ferrules that Rotax had on the fuel line. Then you should have used Oetiker clamps to secure the new hose.

Raise you hand if you got an LOA for this clamp change.

How about the clamp on the fuel hose in the wing root area?

 

Fuel pumps and fuel pump changes are different now.

 

FD does a good job compared with what I see from other LSA MFG's at times.

[Doug G.]

A simple example. (I have not called FD yet. I am in Lyons, WI for the Rotax line maintenance course. Wanted to make the four hour flight, but gusts were up to 31kts and I was concerned about making it to the runway. So...I drove 9 hours! )

Anyway...you change the battery in a CT, it takes 4 nylock nuts. FD manual and best practice says they have to be replaced. They have no markings and appear to be generic. Do they need to be ordered from FD? Why, or why not?

[Runtoeat]

Doug and other A&P's, what is done on non FD aircraft regarding nyloc or other torque prevailing fasteners? Are these applied by "mechanic's judgement" of condition or are they thrown out after each use?

[Tom Baker]

A simple example. (I have not called FD yet. I am in Lyons, WI for the Rotax line maintenance course. Wanted to make the four hour flight, but gusts were up to 31kts and I was concerned about making it to the runway. So...I drove 9 hours! )

Anyway...you change the battery in a CT, it takes 4 nylock nuts. FD manual and best practice says they have to be replaced. They have no markings and appear to be generic. Do they need to be ordered from FD? Why, or why not?

 

Doug, it is my understanding where they give a specification for the part like they do for that nut you don't have to buy from flight design.

[Tom Baker]

Doug and other A&P's, what is done on non FD aircraft regarding nyloc or other torque prevailing fasteners? Are these applied by "mechanic's judgement" of condition or are they thrown out after each use?

 

The Flight design manual says they should be replaced when removed.

[Jim Meade]

AC 43j-13-1B

 

http://www.faa.gov/documentLibrary/media/Advisory_Circular/43.13-1B.pdf

 

f. Fiber or nylon locknuts are constructed

with an unthreaded fiber or nylon

locking insert held securely in place. The fiber

or nylon insert provides the locking action because

it has a smaller diameter than the nut.

Fiber or nylon self-locking nuts are not installed

in areas where temperatures exceed

250 °F. After the nut has been tightened, make

sure the bolt or stud has at least one thread

showing past the nut. DO NOT reuse a fiber

or nylon locknut, if the nut cannot meet the

minimum prevailing torque values. (See table

7-2.)

 

TABLE 7-2. Minimum prevailing torque values for reused

self-locking nuts.

FINE THREAD SERIES

THREAD SIZE

MINIMUM PREVAILING

TORQUE

7/16 - 20 8 inch-pounds

1/2 - 20 10 inch-pounds

9/16 - 18 13 inch-pounds

5/8 -18 18 inch-pounds

3/4 - 16 27 inch-pounds

7/8 - 14 40 inch-pounds

1 - 14 55 inch-pounds

1-1/8 - 12 73 inch-pounds

1-1/4 - 12 94 inch-pounds

COARSE THREAD SERIES

THREAD SIZE MINIMUM PREVAILING

TORQUE

7/16 - 14 8 inch-pounds

1/2 - 13 10 inch-pounds

9/16 - 12 14 inch-pounds

5/8 - 11 20 inch-pounds

3/4 - 10 27 inch-pounds

7/8 - 9 40 inch-pounds

1 - 8 51 inch-pounds

1-1/8 - 8 68 inch-pounds

1-1/4 - 8 88 inch-pounds

 

The table doesn't address smaller or metric threads. Does that mean anything is permitted or nothing is permitted?

 

This advisory circular (AC) contains methods, techniques, and practices acceptable to the

Administrator for the inspection and repair of nonpressurized areas of civil aircraft, only when there are no

manufacturer repair or maintenance instructions.

 

This site has some intersting discussion of Nylok, but not necessarily any more definitive guidance.

http://www.nylok.com/nylok-basics

[Roger Lee]

Hi Doug,

 

. Almost all manuals will say replace Nyloc nuts after one use. It's CYA. No MFG will go out on a limb and say to re-use them because some idiot will re-use them forever until there is no more plastic insert. In reality it can be used more than once and so long as you can't turn it by hand the the Nyloc plastic insert is still active. I have had them teach this in Rotax and LSRM school. If you like to replace after every single use by all means do, but in this case you can get the identical nut from Ace Aviation as FD most likely does. FD and other MFG's do not always get their parts from the original MFG even if they have a part number assigned, if they can get them cheaper and faster locally. The nut we are talking about is also an non criticle part.

 

You will get both answers from mechanics and MFG's and it just depends on who you talk to. I re-use them IF they are still good and IF it is a non critical application. I do toss them out often when in doubt.

[Tom Baker]

AC 43j-13-1B

 

http://www.faa.gov/d...ar/43.13-1B.pdf

 

f. Fiber or nylon locknuts are constructed

with an unthreaded fiber or nylon

locking insert held securely in place. The fiber

or nylon insert provides the locking action because

it has a smaller diameter than the nut.

Fiber or nylon self-locking nuts are not installed

in areas where temperatures exceed

250 °F. After the nut has been tightened, make

sure the bolt or stud has at least one thread

showing past the nut. DO NOT reuse a fiber

or nylon locknut, if the nut cannot meet the

minimum prevailing torque values. (See table

7-2.)

 

TABLE 7-2. Minimum prevailing torque values for reused

self-locking nuts.

FINE THREAD SERIES

THREAD SIZE

MINIMUM PREVAILING

TORQUE

7/16 - 20 8 inch-pounds

1/2 - 20 10 inch-pounds

9/16 - 18 13 inch-pounds

5/8 -18 18 inch-pounds

3/4 - 16 27 inch-pounds

7/8 - 14 40 inch-pounds

1 - 14 55 inch-pounds

1-1/8 - 12 73 inch-pounds

1-1/4 - 12 94 inch-pounds

COARSE THREAD SERIES

THREAD SIZE MINIMUM PREVAILING

TORQUE

7/16 - 14 8 inch-pounds

1/2 - 13 10 inch-pounds

9/16 - 12 14 inch-pounds

5/8 - 11 20 inch-pounds

3/4 - 10 27 inch-pounds

7/8 - 9 40 inch-pounds

1 - 8 51 inch-pounds

1-1/8 - 8 68 inch-pounds

1-1/4 - 8 88 inch-pounds

 

The table doesn't address smaller or metric threads. Does that mean anything is permitted or nothing is permitted?

 

This advisory circular (AC) contains methods, techniques, and practices acceptable to the

Administrator for the inspection and repair of nonpressurized areas of civil aircraft, only when there are no

manufacturer repair or maintenance instructions.

 

This site has some intersting discussion of Nylok, but not necessarily any more definitive guidance.

http://www.nylok.com/nylok-basics

 

Jim, I agree with what this says, but we are guided by CFR 91.327 which leads us to the manufacturer. If you look at the current MM for the SW page 1-13, it says they must be replaced. I sure wish we could copy and paste from the manual.

[Roger Lee]

Hi Tom,

You can and I post and print from protected manuals all the time. Download FOXIT PDF printer.

When you want to save a page hit print, then select FOXIT printer instead of your normal printer. This does not actually print, but will ask you where you want to save it. Pick a place like desktop or where ever you want and hit the print tab. It will then save that file in a PDF format.

[Jim Meade]

Tom,

 

My post included the FAA statement that the manufacturer rules. It's down near the end.

 

I started an edit that would have bolded the FAA comment but got tied up. It's good that you reinforced the point.

 

It's also worth nothing that in the situations where it is legal to reuse lock nuts (let's say your own E-AB) that the FAA doesn't say "finger tight" it says to use the torque tables. If a nut won't run on finger tight that may be an indication it will meet the torque test, but nevertheless......

[Roger Lee]

If you can screw it on or off with your fingers the insert is toast and no longer functional.