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  #11  
Old 07-10-2016, 02:27 PM
rvbuilder2002 rvbuilder2002 is offline
 
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I often see posts about people having leaks and changing to such and such sealant and thinking it fixed their leak problem.

It is very likely that a lot of the leaks on pipe thread fittings are caused by installation error rather than the choice of sealant that was used.

NPT threads on fittings are designed for a nearly net fit once properly tightened.
The thread sealant will take care of the last little bit of gap that exists at the bottom of each thread valley, but it does a poor job of sealing the rest of the thread area in instances where the fitting wasn't tightened fully. Particularly on high pressure hyd. systems such as the brakes.

This is not all that surprising since new builders that are "learning" have no way to know how tight is tight enough or too tight. It is also something hard to describe with verbal instruction. It needs to be good and tight, but not so tight it damages the threads. This is further complicated with a 45 or 90 deg fitting that has to be positioned at a specific clocking angle. It can be difficult to know when to stop or when to try for one more turn. Stopping one turn short of where you should can be a prime candidate for a leaking fitting in a high pressure system (brakes). In lower pressure systems (fuel) the sealant will do a better job of compensating for the fitting not being tightened as much as it should have been.

I believe a lot of the leaks get fixed by using a different sealant, because during re-installation they are tightened further than the first time, to help assure it doesn't leak again.

Loctite 567 is a great sealant and we use it for some applications in our shop, and it may help newbee builders because its lubrication properties may help them turn tighter than their limited experience makes them willing too, but many sealants will perform just as well, as long as proper installation technique is used.

BTW, a lot of the hate for the plastic lines and compression fittings is caused by people tending to under torque these also. The torquing process is deforming the internal compression barrel so that it seals around the line. They are not fully tightened until there is a significant increase in turning torque on the nut which indicates that the barrel has fully compressed.
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  #12  
Old 07-10-2016, 03:21 PM
sblack sblack is offline
 
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Scott in your opinion are plastic brake lines acceptably robust and leak free? A lot of builders go with steel braided lines because it seems like it would be better. I know there are a million opinions but what is yours?
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  #13  
Old 07-10-2016, 04:15 PM
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Mel Mel is offline
 
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Quote:
Originally Posted by sblack View Post
Scott in your opinion are plastic brake lines acceptably robust and leak free? A lot of builders go with steel braided lines because it seems like it would be better. I know there are a million opinions but what is yours?
I finished my RV-6 in the Spring of 1993. Plastic lines still leak free today.

Just one example.
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  #14  
Old 07-10-2016, 04:55 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by sblack View Post
Scott in your opinion are plastic brake lines acceptably robust and leak free? A lot of builders go with steel braided lines because it seems like it would be better. I know there are a million opinions but what is yours?
Every one of the company prototypes and demonstrators are built with the exact same parts shown in the plans and supplied in the kits.
Many of these have multiple thousands of hours (The original RV-6A has over 5000 Hrs) on them with no problems.

My personal RV-6A has the plastic lines.

So my opinion is that I think the plastic lines give excellent service if they are installed properly.

I hope that adequately answers your question.
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  #15  
Old 07-11-2016, 02:18 AM
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kinger kinger is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
This is not all that surprising since new builders that are "learning" have no way to know how tight is tight enough or too tight. It is also something hard to describe with verbal instruction. It needs to be good and tight, but not so tight it damages the threads. This is further complicated with a 45 or 90 deg fitting that has to be positioned at a specific clocking angle. It can be difficult to know when to stop or when to try for one more turn. Stopping one turn short of where you should can be a prime candidate for a leaking fitting in a high pressure system (brakes). In lower pressure systems (fuel) the sealant will do a better job of compensating for the fitting not being tightened as much as it should have been.

This was my issue on one of my eight fittings. I must have removed, cleaned and reapplied torque seal 7-8 times as well as trying 4 other fittings. All with no luck, then I finally said I will go one more revolution and get a good seal or crack the master cylinder. Lucy for me the extra revolution worked great an no leak.
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  #16  
Old 07-11-2016, 06:36 AM
David-aviator David-aviator is offline
 
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This is a good thread re plastic brake lines, I'v got a very minor leak that probably just needs a bit more torque.

FWiW Loctite 567 is also good in the engine compartment for fuel fittings if needed, it has quite a high temp rating.
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  #17  
Old 07-11-2016, 06:44 AM
sblack sblack is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Every one of the company prototypes and demonstrators are built with the exact same parts shown in the plans and supplied in the kits.
Many of these have multiple thousands of hours (The original RV-6A has over 5000 Hrs) on them with no problems.

My personal RV-6A has the plastic lines.

So my opinion is that I think the plastic lines give excellent service if they are installed properly.

I hope that adequately answers your question.
Sure does. Thank you.
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  #18  
Old 07-11-2016, 09:02 AM
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JonJay JonJay is offline
 
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As Scott has mentioned, Pipe Fittings are an interference fit. Some of the parent material in the threads will slightly migrate to make a mechanical connection between the threads in the fitting and body.
If you have a fitting that you just can not get clocked properly, there are a few things you can do. First, work the fitting like you would a tap - turn back 1/4 turn, then forward, back then forward, until it is in the correct position. However, the final turn needs to be forward only. They slightest backward turn will break the mechanical seal.
I have found that not all fittings are manufactured identically. If you have one that is just not working out, try a different fitting. It might fit better.

As a last resort, you can clean up the threads in the body of the brake cylinder with an appropriate tap. You must disassemble the master cylinder so any of the small chips can be cleaned completely. Again, this is a last resort and should not be necessary. I recently did this because my cylinders where already apart and I had a fitting that simply would not clock correctly. It was an easy fix but not something I would recommend unless you know what you are doing. It would be quite easy to ruin a perfectly good master cylinder.

PS - Factory Plastic lines, 9 years, 700 hours, no leaks, ever....
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  #19  
Old 07-11-2016, 01:10 PM
Stoo Stoo is offline
 
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It is better to use a pipe die on the fitting rather a tap on the female thread for clocking. It doesn't take much, the anodizing is barely scratched off in a few spots. Way easier to wipe off the male thread than to have to disassemble the master cylinder for cleaning.

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  #20  
Old 07-11-2016, 01:34 PM
rightrudder rightrudder is offline
 
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Another Loctite 567 advocate here. On the NPT fittings, I clocked them correctly until they were snug, then wrench-tightened them another entire turn, to the clocked position. As a previous poster said, it's a real "feel" thing...if you've got a trusted builder a couple hangars over, it might be good to have him/her check your work. Felt a little Medieval, but no leaks whatsoever. I used the plastic lines for feed, and stainless-sheathed numbers for the high pressure side.

It's worth repeating that a very small smear of sealant is needed, with none on the first couple of threads.
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