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Fiber washers, fuel lines, and torque....


RJD2
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Hi folks, I am hoping some of you will chime in with your experiences that may illuminate an issue I'm having. The car in question is a 1976 Espada, so 6x Weber 40 DCOE carbs that are newly rebuilt, 4-6PSI fuel pressure, and a modern fuel pressure regulator with gauge. As of the fall of 2020, I had a fuel system that did not leak. I went to crank the engine yesterday, and after inspecting, 2-3 of the fiber washers were leaking fuel where the fuel supply line meets the carb inlet. Now I know the obvious answer to "what should I do?" is to torque the fittings/bolts down until they don't leak, which I plan on doing, but I wanted to get an idea of how much torque is too much torque, when it comes to brass fittings, fiber washers, fuel lines and carburetors. I pulled a head stud last year, and now I'm all paranoid about overtorque-ing things, but I also don't want a leaky fuel system, engine fires, and all that jazz. So do any of you have any "parameters" here? Is ____ft/lbs too much torque? Thanks for any advice.

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First check how tight these fittings currently are. If they pass that test I would replace the whole set of washers and keep a spare set handy.

 

Any possibility nylon washers are available for this application? They seem to work better on GM QuadraJet applications which are notorious for stripping inlet fitting threads.

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3 minutes ago, rocketraider said:

First check how tight these fittings currently are. If they pass that test I would replace the whole set of washers and keep a spare set handy.

 

Any possibility nylon washers are available for this application? They seem to work better on GM QuadraJet applications which are notorious for stripping inlet fitting threads.

thanks. when you say "pass that test", which test do you mean? i don't have a baseline torque here-the WSM is in italian, and also doesnt provide torque for all the upper engine bolts. as best i can tell, the ones that weren't leaking seemed to be somewhere in the 8-15 ft/lb range, but i was doing them all by feel, so i'm not entirely sure.

 

nylon washers may be available, but i do know the fiber washers are what are supplied from Weber with the full rebuild kit; these washers are effectively brand new, but i have had to take the carbs out a few times, so i could always go in with a new clean set.

 

on a quadrajet, do you have any idea of how much torque is too much? i know this is non-scientific, but i feel like if i could get a baseline idea of "that's waaaay too much torque" in several different applications, that'd be great, so i can make sure i'm staying out the danger zone, so to speak.

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Apply a thin, even coat of “anaerobic”* sealant on each side of each fiber washer, assemble and tighten to “reasonable” torque. Done.


99% of the time, this should provide fuel proof/leak free connections/fittings. If not, rinse & repeat, but only connections/washers that still leak or seep.

 

*Doesn’t dissolve in gasoline.

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TTR-Thanks! I have considered both going to copper washers, as well as loctite 518. when you say "reasonable", give me a ballpark. that's really what i need; a top and a bottom. 5 ft lbs on the low end, 20 on the high end? i'm using 1/4" driver for socket, and a ratcheted box wrench, so i'm not cranking away at it with all my might, but i would love an idea of what's "geez no you'll strip it" on a 14mm brass banjo bolt for a carb, in terms of an actual ft.lb number....

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How much torque is too much torque depends on the diameter and pitch of the threads, plus the material with the female thread.

 

For Webers, I don't know; but would suggest you contact the factory.

 

I am going to offer a different opinion to some of those already expressed in this thread:

 

(1) For fuel use, fiber washers are superior to nylon washers (they crack).

(2) Unless told to do so by the manufacturer, NEVER use a sealant around fuel (or learn how to rebuild the carburetor(s) )

 

Personal and professional opinion - anytime the carbs are removed, the sealing washers should be replaced with new. Figure out the diameters and the thickness, and order a box of them from McMaster-Carr.

 

Jon.

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48 minutes ago, RJD2 said:

TTR-Thanks! I have considered both going to copper washers, as well as loctite 518. when you say "reasonable", give me a ballpark. that's really what i need; a top and a bottom. 5 ft lbs on the low end, 20 on the high end? i'm using 1/4" driver for socket, and a ratcheted box wrench, so i'm not cranking away at it with all my might, but i would love an idea of what's "geez no you'll strip it" on a 14mm brass banjo bolt for a carb, in terms of an actual ft.lb number....

1. Based on my (limited ?) experience and that of those with much more than I have, fiber washers (OEM to vintage Webers) seem to work better than copper or teflon (I've never used or tried nylon for fuel sealing).

 

2. As "carbking" said, the torque depends on multitude of variables, including thread length/pitch/width, materials in question, etc.

I've never researched/studied torque specs for this type of application and always used "common sense"(?) & "feel" approach.

 

3. While I do agree, in principal, with "carking's" (2) opinion about sealants in general, aforementioned experiences of my own from past +/- 20 years and those of many others with even longer familiarity with vintage Weber applications on Italian (and other) sports cars, etc has proven "anaerobic" sealant as practical solution to persistent fuel fitting leakage/seepage, especially when involving decades old, used components and parts. But again, it should be applied/used very, very carefully and minimally.

 

And yes, always use new sealing washers.

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A reasonable re - snug should be fine. fibre washers sometimes need a bit of re tightening. And the fuel line fitting threads are quite robust. I have never stripped one yet.

Just use a gentle but firm torque, if it still leaks you can give it a bit more or use a fresh washer.

 

Greg

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Thanks you guys! Great info here. I'll find the measurements and get several sets from McMaster-Carr. And yes, TTR, if you don't mind measuring your torque on the 40 DCN's, that'd be very informative for me. I know that I am looking at a subjective matter with an incomplete set of data, but even a ballpark ft. lbs. reading would be helpful.

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52 minutes ago, 1912Staver said:

I have never stripped one yet.

Me neither, but have seen and heard of numerous occasion of stripped (banjo-type fuel inlet) threads on older Webers, which by the way are quite soft die-cast alloy to begin with and also prone to (severe ?) warpage with decades of aging, heat cycles and/or mishandling (i.e. over-tightening, etc). 

 

 

Edited by TTR (see edit history)
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1 minute ago, RJD2 said:

Thanks you guys! Great info here. I'll find the measurements and get several sets from McMaster-Carr. And yes, TTR, if you don't mind measuring your torque on the 40 DCN's, that'd be very informative for me. I know that I am looking at a subjective matter with an incomplete set of data, but even a ballpark ft. lbs. reading would be helpful.

More likely to be in.lbs.

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1 hour ago, 1912Staver said:

I have to say I have not worked on really old Weber's. But quite a few mid 60's and up Lotus engines. Usually DCOE's.

 

Greg

I’d qualify those old enough. 👍


My experience is mostly on DCN 20/21/21A’s.

Just few months ago had 3 sets (of six) cluttering my work benches in the shop along with cars/engines they were belonged to. Now only one set/car and two more coming in within next couple of months.

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I have very little experience with Webers, so one can decide if the following has any applicability to the Webers:

 

When we were still restoring zinc alloy carburetors made in the USA in the 1930's, it was not uncommon for a fiber washer gasket surface to requiring "facing" due to deterioration of the zinc alloy base metal; in order for the fiber washers to seal. I have not seen this issue on post WWII US-produced carburetors by the major brands.

 

European carburetor makes other than Weber (ie Solex and British Zenith) used a zinc alloy in the 1950's and 1960's that was much WORSE than that used in the USA in the 1930's!

 

Again, I have very little experience with Webers.

 

Jon.

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10 hours ago, ojh said:

Measure the torque on the ones that don't leak.  

 

shocklingly obvious, and good advice. to be safe, i may back one of them out just a TINY bit, and then apply torque while measuring. good idea!

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ok, so this is an inexact science, but by backing a few bolts out one "skip" in the wrench, and then backing it back in with a torque measuring wrench, it looks like i am somewhere in the range of 15-20 ft. lbs. on the bolts that don't leak. so, maybe i should start at 15 and work up to 20 if i need. i think i'm going to stick with fiber washers, and maybe hit them with a 200 grit sandpaper first, this seems to be a used technique. thanks for the help! getting this problem out of my head and exposed to air definitely helps.  from experience, i'd much rather overthink this issue now, than have to helicoil a 50 year old carb.

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6 hours ago, RJD2 said:

i am somewhere in the range of 15-20 ft. lbs. on the bolts that don't leak.

 

Foot Pounds? How big are these bolts and the thread pitch?😲

 

That's like the torque for a 3/8 Grade 2 or a 5/16 grade 5 coarse thread pitch bolt into steel.

 

Not saying it could not be, just surprising if true.

Edited by Frank DuVal (see edit history)
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On 2/18/2021 at 12:54 PM, carbking said:

I have very little experience with Webers, so one can decide if the following has any applicability to the Webers:

 

When we were still restoring zinc alloy carburetors made in the USA in the 1930's, it was not uncommon for a fiber washer gasket surface to requiring "facing" due to deterioration of the zinc alloy base metal; in order for the fiber washers to seal. I have not seen this issue on post WWII US-produced carburetors by the major brands.

 

European carburetor makes other than Weber (ie Solex and British Zenith) used a zinc alloy in the 1950's and 1960's that was much WORSE than that used in the USA in the 1930's!

 

Again, I have very little experience with Webers.

 

Jon.


 

Part of our normal rebuilding process is re-machining the gasket surfaces of the unit. Also the air horn, jet seats, ect. Often times, people over tighten the main jets to try and seal them.........and they crack the fuel bowl. Many people call installing a gasket kit rebuilding the carburetor........and they never get all the channel plugs out.........and they wonder why their cars run like sxxt. 

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I used a "bendable" torque wrench to measure; it is fundamentally imprecise. When coming off, I would guess it was around 7-10ft lbs, but again, that's just a guess. I don't have a digital torque wrench. I can guarantee I haven't stripped the threads yet, but yes, the drive for a number in ft. lbs(inch lbs, whatever) here is so I can avoid potential stripping. If I know my torque number is right, than I can rule out lack of torque as a cause of leak. thanks!

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Had a chance to deal with this earlier today and while not claiming any authority or science on the issue, here's my observation or results I achieved:

Using recently (calibration) tested, high quality (+/-2% accuracy), US-made 0-300 in. lbs. torque meter with "follower" and my experience of "feel" to snug all 6 banjo bolts, all readings averaged between 125-140 in. lbs.

All were assembled using (12) new fiber washers with (very) thin coat of Loctite "518" anaerobic sealant.

 

 

637B7661-8EEE-483F-8BE4-56E2BB254C48.jpeg

Edited by TTR (see edit history)
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4 hours ago, RJD2 said:

the drive for a number in ft. lbs(inch lbs, whatever)

 

Not whatever!  A foot is 12 inches, so the numbers of foot pounds and inch pounds are different by a factor or 12. No small difference!

 

TTR's numbers seem better, as that is 10 to 12 FT-LB of force. 

 

And, a bendable torque wrench is a good tool for measuring take apart torque. As long as the reading is between 25 and 100% of the full scale reading.

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Thanks guys! Forgive my language; when I said "whatever", I was not disregarding the difference between inch lbs and ft. lbs; I meant "whatever", as in 10ft. lbs. or 120 inch lbs, either one. No conflation! Sorry if I spoke poorly.

 

TTR: that's great info. Thanks. Since there really isn't much empirical data on the net around fuel lines, banjo bolts, and torque in this usage, me being able to gather several anecdotal pieces of info is very helpful!

 

Ok, last question here: TTR is reading around 10ft. lbs. of torque on a secured, non-leaking, Weber banjo bolt. I seem to be seeing somewhere in the 8-15 ft. lbs. range. When I re-assemble, I will start around 8ft. lbs, and work my way up to 10-12 ft lbs. Where should I set my "cap" on a torque wrench, if I've got a leaking banjo bolt, and am attempting to rule out nut torque? 15 ft. lbs? 

 

Oh and yes, for the record, I have several ratcheting torque wrenches, one beam, multiple click type, both in inches and ft lbs., so I can dial this in to the inch. Thanks again folks!!!

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20 hours ago, edinmass said:

Many people call installing a gasket kit rebuilding the carburetor........and they never get all the channel plugs out.........and they wonder why their cars run like sxxt. 

Yep, sadly true and that “Many” probably equates to 99+% of the individuals who work on carburetors, be they enthusiast/hobbyist or so-called professionals.

20 hours ago, edinmass said:

Part of our normal rebuilding process is re-machining the gasket surfaces of the unit. 

While this ^ is often necessary, it is also worth noting that “re-machining” should also be approached with careful consideration and understanding any/all consequences. Once any material has been removed, it is difficult to reverse the process.

 

Of the older Webers I’ve ever worked on, including ones in my photo above, almost all have been plagued with warped bases AND main bodies, along with accelerator pump &  top covers and as part of normal rebuilding/restoration process have required straightening which involves special fixtures/tooling and one or more heat cycles in oven to bring them back to “square”. Some, due to previously performed amateur/hack work have required more intensive metallurgical “surgeries”. 

Unfortunately, I’ve seen a few occasions and heard of countless stories where someone had resorted to address the warped base by block sanding or machining it flat without realizing the rest of the carburetor body remaining warped with throttle bores out-of-round, shaft alignment off, etc, all which will make any future efforts to correct them much more difficult, if not impossible and may be OK for carburetors that are plentyful and readily available, but for the types I’m familiar with, I’ve heard of owners having had to pay tens of thousands of $$s for a used set + another $10K+ for rebuilding/restoring them.

 

@RJD2 First, on something like this application, I wouldn’t use any torque wrenches, per se.

On anything critical/precision like this I’d use torque meters, which are usually much more accurate than “typical” torque wrenches. I have several different scales, ranging from 0-6 in.lbs to 0-600 ft.lbs 

 

I also have various click-type, twin beam torque wrenches, but use them mainly on things were repetition is the objective (like head bolts, etc.).

Lastly, I will not be able to offer any recommendations on your particular case. Only thing I can suggest is the use of common sense.

Edited by TTR (see edit history)
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Common sense........Isn’t very common today. 
 

We make individual fixtures to work on our carburetors. Since we do 95 percent Stromberg, it isn’t to often now that we haven’t made the tooling already. The entire carburetor is often distorted.......and many can be saved, but some can not. Every year at Hershey, we are offered carburetors to purchase as “good cores”, and we often tell the sellers they are beyond repair......and have no value. Usually several hours go by, and a new purchaser brings the came carburetor by to look for parts and gasket kits. It’s unpleasant to tell them they bought a paper weight............especially when I know the guy who sold it to them knew it was junk.....and stuck it to them anyway. Happens EVERY year.

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I am a foolish man, but I am not foolish enough to think I can rebuild a carburetor. Luckily, I have a great local shop that rebuilds carbs/starters/alternators.

 

I just grabbed a digital torque wrench that will go down to 2.2 ft lbs. I'll use it to test my wrenches against, and come in with precision when it's time for re-assembly. Thanks folks.

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3 hours ago, edinmass said:

Common sense........Isn’t very common today.

While I, sort of, agree, I can't say it applies only on "today". Based on my (limited to few decades of) personal observations, I've grown to believe it's almost like a myth in human endeavors throughout all ages. 

Edited by TTR (see edit history)
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I don't think cmomon sense was all that common even in the days of yore.  When working on the really old cars you often times run into "vintage" repairs.  Some of them are strange but highly thoughtful and others can be rather jaw droppingly stupid.  It is best to never be surprised at anything anybody does for a repair.  

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Ok, at risk of asking an "adjacent question"-but definitely related to torque and stripping threads:

 

Is there an elegant, low-risk means by which to test if a stud has been pulled on an intake manifold? My initial thought was to put a few copper washers on the stud, fasten a nut, and torque it to spec. In this instance, I do have an advantage, in that I have a reliable metric to go by: 22n M. Is there a better technique for this purpose?

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Why copper? Common steel is fine, since you are limited by the torque specification of 22 n-m.

 

Yes, this is  a good method. Corvair engine rebuilders use the same method to check the long head studs that might be starting to pull out of the block. We use steel conduit (typically 1/2" EMT) for the "washer" since the studs are what, ~ 7" long? Torque the head nut to 30 to 35 ft-lbs and the Corvair head stud will be good to go when the head is installed. No fun to remove the head to Helicoil the block after everything is assembled. BTDT several times.....😡

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When I expect a problem, I will retorque bolts or studs on disassembly. The "feel" tells you as much as the torque wrench does. Better to heli-coil it early than after you have cleaned everything up and put new gaskets on.

 

The thread was about fuel fittings. I don't think I could ever get comfortable using a thread insert on a fuel fitting.

 

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8 hours ago, Bloo said:

I don't think I could ever get comfortable using a thread insert on a fuel fitting.

Why? Thread inserts are stronger than treads in aluminum and other non-ferrous metals!👍 

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Facts like that will make no difference if it fails. What if it leaked and caught fire and you were the guy who put the heli-coil in? It was strictly prohibited at every shop I ever worked at, and I suspect that is the reason.

 

Fuel can go up the threads of course, and the threads are a larger diameter once you put in a thread insert. If you were going to do it you would have to be doubly sure that your washer and fitting would effectively seal all the way out to the larger diameter of the heli-coil threads. On some carbs that fitting may not have much of a shoulder on it.

 

Edited by Bloo (see edit history)
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What if the original threads that you thought were good also failed?  Same result. Of course if the seal does not cover the repair area it should not be done. That's obvious.  Common sense, not blanket statements of fear. If the bolt is properly torqued into a properly installed thread insert, what would go wrong? The original post was about banjo fittings. These are much larger than the bolt that holds them together.

 

I have not seen pipe thread thread (NPT) inserts. I was answering for standard bolt thread inserts. Hey, a quick Google and, they do make them! But, and here I see your point of a second layer of threads. How do they seal? 🤔 Not good to rely on a "glue" for gasoline applications.😲

 

 

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If the original design burns the car down that is much less my problem, and more the problem of the car manufacturer, although I would not send it out the door knowingly with bad threads.

 

Banjo fittings in my opinion are a likely place for trouble. It needs a close look no matter what. It might be fine. On the other hand you might have a nice big fiber washer (some Webers do) but what is pushing on it? A banjo fitting with hardly any surface area like this one? Probably.

 

img_2D_0001.jpg

 

Here is another common banjo setup with copper washers:

 

tbr41.jpg

 

I wonder how close the OD of that copper washer is to the OD of the heli-coil? I wonder how tightly the copper washer centers on the banjo bolt? It might be fine, but I think I will leave that determination to others.

.

Edited by Bloo (see edit history)
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awesome info here, folks. for the record, i have not stripped any of the threads on my carbs. the question came about cause i don't have a torque spec for the banjo bolts, and i'm fighting a fuel leak at both the banjo bolts, and the 19mm flat faced brass screws. if you see these images, you'll see the washers are "OEM Weber", but don't look like the greatest fitment to me. I've got several sizes in hand from McMaster-Carr, and may end up just figuring it out through trial and error.

 

I DO however have at least one intake manifold stud that needs to be helicoiled. Still kicking myself over this one. My local classic car tech will be doing the job, as he's got decades of experience on it. I didn't have a torque spec on it at the time I first did the rebuild, at least now I do.

IMG_0094.JPG

IMG_0074 3.jpg

IMG_0075.jpg

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