Compression fittings are rarely seen in aircraft. The big #1 fitting arrangement is the 37 degree flared fitting and tubes. Unlike the the Automotive 45 Degree flared fittings and tubes.
If you look very close to that aircraft primer pump you will note that the 37 degree flared male fittings are cast with the body.
To this day I always have to look close and check twice my flaring tools when I grab one to use since I have at least 3 of each 45 deg. and 37 deg.
At any rate there are several very good web sites that explaing how to assemble 37Deg flared AN fittings and tubing as well as those explaining the difference.
You can use the original 1/8" tubing weather aluminum or copper makes no difference. The correct fitting nut is AN 818-2D and the correct sleeve is AN 819-2D .
Joined: Oct 02, 2014 Posts: 1955 Location: South Carolina, Dorchester County
Posted: Fri Jun 07, 2024 9:14 am Post subject:
Wes,
I'm guessing......use aluminum fittings on aluminum or copper tube and steel fittings on steel tube?
Need to use a 37-degree flare tool because automotive flare tool is 45-degree?
Is the 37-degree also a "double flare"?
Is there difference between commercial 37-degree and AN or military 37-degree --- or is it all interchangeable (tools, fittings, tube sizes, etc)?
Thanks! _________________ Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51
“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari
Joined: Oct 02, 2014 Posts: 1955 Location: South Carolina, Dorchester County
Posted: Fri Jun 07, 2024 10:32 am Post subject:
Reading the Hemmings article (link posted earlier) there's three design features of the YS carb that the author says are intended to "prevent flooding" either the engine or the carb itself.
While the dash primer pump seems capable of circumventing at least one of those three features (engine).
And the pump priming lever seems like it could circumvent the other two (carb).
More likely if either is used excessively or improperly?
Did I read a post where somebody flooded the intake so badly that gas went down the exhaust pipe and blew the muffler off when the engine fired?
Also found it interesting that the YS is purposely designed to continue operation (doesn't say how well) should the air filter become "plugged". _________________ Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51
“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari
Last edited by RonD2 on Fri Jun 07, 2024 10:55 am; edited 2 times in total
Ron those questions are all answered in the links in my post above. Military and Civilian Aviation industry both use the Mil-Spec AN 37 Deg system. The commercial system has slight differences. The 37 deg. system is used in both single or double flare. The norm in aviation is double for fittings exposed to very high pressure and motion.
It's a very simple 10 minute job to clip off thecompression sleeve on the original primer tubing, slide of the original compression nut, slide on the new AN nut then the new AN sleeve, single flare the 1/8" copper tube and screw the new nut onto the appropriate nipple on the new used pump.
As for the fittings, Steel is more expensive and is used on copper, aluminum and steel tubing in very high pressure applications where a lot more torque is applied to the nuts on installation. Which, by the way, will be on a steel nipple since they are not to be used on an aluminum nipple. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Oct 02, 2014 Posts: 1955 Location: South Carolina, Dorchester County
Posted: Fri Jun 07, 2024 11:38 am Post subject:
Thanks Wes,
Yes, the links are informative, but not really geared to somebody unfamiliar and considering using aviation parts and fittings on the M38 (the topic at hand).
So, if I understand what you said and the link info, best practice would be:
Yes, use aluminum fittings on aluminum or copper tube for aluminum nipples and use steel fittings on steel tube for steel nipples. Don't mix them.
Yes, use a 37-degree flare tool, single or double flare is ok.
Yes, there's a difference between commercial or industrial 37-degree and AN or military 37-degree fittings. Don't mix them. _________________ Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51
“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari
Since he is replacing the original style dash hand primer then he already has all the tubing needed and it is already plumbed where needed. The aircraft type primer will fit the same place on the dash. All he needs to do is clip the tips of the two copper tubes at the edge of the compression sleeves. Slide an aluminum nut and sleeve in that order on each 1/8" copper tube, flare the tube with a 37 degree single flare and scew them together.
As for which fittings and sleeves can be used with which tubing, Steel only with steel. Aluminum with aluminum or copper. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Oct 02, 2014 Posts: 1955 Location: South Carolina, Dorchester County
Posted: Sat Jun 08, 2024 3:09 pm Post subject:
Maybe I'm confused, but don't think he has one.
JeepdaddyRC wrote:
I’ll admit the M38 and A1 carbs are somewhat confusing to me. I’m used to a conventional mechanical accelerator pump that gives you a squirt of gas before starting,
Because of this, I’ve considered adding a cold weather primer kit to give a shot of fuel directly into the intake manifold.
This recent experience has me revisiting that idea.
Anyone add a dash mounted primer pump? Seems like a good a way to prime the engine prior to starting - instead of relying on the vacuum actuated accelerator pump?
Is my thinking reasonable?
_________________ Ron D.
1951 M38 Unknown Serial Number
1951 M100 Dunbar Kapple 01169903 dod 5-51
“The only good sports car that America ever made was the Jeep."
--- Enzo Ferrari
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37 degree flared fitting nut.
37 Degree flared fitting sleeve
37 degree flared fitting flared tube with nut & sleeve.
