Hey Junglemist,
Thanks for posting some good info about these injectors. My engine makes a little popping sound under load (my imagination or is this normal?) and has a bit of a rough idle. I’m not sure if this is normal as I don’t have much experience with these engines. It also dies unless I give it a little push on the throttle when cold starting; this goes away after the engine runs a couple minutes. I’ve run a bunch of injector cleaner through it and changed all of the filters, but it didn’t change anything. So, I’ve been considering checking out the injectors. I have a local friend with a spare set of injectors and may have them checked out as you have at a local shop. I’ll let you know if I do that and whatever I learn from it.
I poked around on the web a bit and AMBAC used to be Bosch America. Update 5/15/2013: Mark at Diesel Injection Service in Portland, OR informed me that United Technologies actually purchased Bosch NA through a whole string of acquisitions (refer to the YouTube video for details). It’s not particularly important, but kinda interesting
I just called a local injector service outfit and they said they would test my injectors free of charge. I have the truck loaded with dirt now and need to unload, then do a parade Saturday. So, I’ll likely pull my injectors Sunday and have them tested Monday. I’ll update this post with my results.
What problem are you trying to solve? Is there a problem? Does your engine run well? It sounds like you checked them out and simple didn’t get the answer you expected. I’m very curious if someone else on this site has checked out the injectors as you did.
5/15/2013 update. I took two sets of injectors into Diesel Injection Service in Portland Oregon and spoke to Mark. He said they check old mechanical injectors free of charge. How nice, I would like to throw the guy some business someday when I need to as a thank you. Both sets of injectors we tested are two-hole designs. Mark looked up the part number and said they should test at 3000-3200 psi (207-221 bar) per the American Bosch reference book. He also said the reference book had B in the book, not B2. This makes whatever the 2 is a mystery.
On close inspection and test, the two orifices are different sizes! The larger is more to the side and the smaller is close to the end of the tip. The larger orifice also blows a larger cone of fuel that blasts out into a fine mist. I have a couple pics attached. They are not the best pics, but the best I can do just now and good enough. I used a set of minus pin gages and found the small hole to be about 0.015 inch and the large hole 0.018 inch. This confirms the sizes and reason for the spray pattern mentioned below. Also, notice in the pics that the pin gages line up just the way Junglemist’s pic suggests.
The first set we tested were the injectors that came out of my engine. I decided to test them in part to help answer Junglemist’s question and see if my injectors are working properly (curiosity). My injectors are stamped AKN-130SM-6844-B2 (note the 2 is not on some of them), 12354296, 3-8? (where the ? is illegible but sometimes looks like the left side of a 6 or 8, sometime a lower case t) with United Technologies USA in cast raised letters on the flip side. My injectors tested a bit higher than the spec at about 3200-3500 psi (220-240 bar) but did not leak. I supposed the only downside to the high pop pressure is if the injection pump does not reliably produce more pressure than the pop pressure (would it cause a miss?). I noticed these injectors have a brass tip.
The second set of injectors are stamped AKN-130SM-6844-B2, 12354296, 12-86 with United Technologies ITALY stamped (yes different than the 1[SUP]st[/SUP] set) on the flip side. This set was supposedly from a good running engine. They tested from one being OK but lower than the 1[SUP]st[/SUP] set all the way to holding no pressure and leaking horrible, and everywhere in between. Mark offered to rebuild them for $24/each, which I consider to be a fair price to go from a known bad set to a known good set. These injectors appear to have a stainless steel tip.
I posted a YouTube video of my findings also:
http://youtu.be/uUFJ2s6XPlw
Note: This video puts the speculation to rest; injectors that are operating properly make a very fine mist vs. malfunctioning injectors make dribbles or streams.
I’m also planning to go into another local shop tomorrow to get a new set of return lines and compression fittings. I would like to replace mine (they are old and have been painted over). I think some people have clear lines so they can see into them, but not sure.
If any of you have a known "bad" injector that makes the engine run bad, I would love to get my hands on it and see how it acts on the bench. Please PM me if you have one.
Please give me a thanks or some positive feedback if you appreciate me running down all of this info!
May 29 2013 Update:
I checked around in the TM’s (WOW, can you get lost doing that!) and found the Trouble Shooting Manual LDS-465-1 Multifuel Engine by Continental Aviation and Engineering Corporation has some interesting info. If memory serves (forgive me if I goof), I downloaded it from the JA Tonka Site. If you jump forward to page 27 paragraph 5: “If drops of fuel can be observed to form on the nozzle tip at 100 psi below opening pressure or if the fuel seems to just flow from the tip in a solid stream, the nozzle is leaking an d must be disassembled and cleaned…” Paragraph 7: “If nozzle operating pressure does not fall within limits of 2800-2850, it must be adjusted, rebuilt, or replaced.” Paragraph 8: “When rebuilding the nozzle holder assembly and using a new nozzle spring, set valve operating pressure to 3000 – 3050 psi because the new spring will take a working set when the nozzle is operating in the engine.” This manual has a bunch of good info on the multifuel engines if you take time out to read it.
