Results 1 to 10 of 10

Thread: D2 D3400 Compression Release Mechanism Question

  1. #1
    Join Date
    Jan 2007
    Location
    Kerrick, Minnesota
    Posts
    1,164

    Default D2 D3400 Compression Release Mechanism Question

    So the YouTube comments section has raised a good question from my latest video and I don't have any answers to reply back with so I wanted to ask the folks here to see what a good response would be - the question is why did Cat decide to hold the intake valve open to decompress the engine and not the exhaust valve like others did? This is regarding the D3400 in the "J" series D2's but I know Cat also held the intakes open to decompress other engine models as well. So is there any specific reason/benefit in using the intake valve? Or is it just as simple as the old saying that "there's more than one way to skin a cat"?
    D2 5J2115SP
    D2 5U7066
    RD6 2H1768
    RD6 2H3072
    No.9 Auto Patrol 8A331
    No.9 Auto Patrol 8A340
    No.9 Auto Patrol 8A539
    Ten PT3037
    Twenty PL134 (Yard-Art)
    Minneapolis-Moline prototype crawler X253
    1945 Farmall H

  2. #2
    Join Date
    Nov 2007
    Location
    NW Ohio
    Posts
    3,694

    Default

    Good question.
    Last edited by Rome K/G; 01-25-2020 at 06:56 PM.

  3. #3
    Join Date
    Dec 2006
    Location
    victoria australia
    Posts
    3,179

    Default Filtered Air

    Hi Toby,
    a good question,
    I once asked that question at The Dealer in early days of working in the engine rebuild shop as an Apprentice and I was told it was because you can have loose soot, water and other crud in the exhaust pipe/manifold.
    The exhaust system is basically unfiltered air that water can sometimes get down the pipe too and some of that crud would get drawn into and out of each cylinder via the dirty exhaust system, whereas utilizing the Inlet system the air transferred in and out of the cylinders would essentially be clean.
    Or words to that effect.
    Cheers,
    Eddie B.

  4. #4
    Join Date
    Apr 2007
    Location
    Elkhorn, WI
    Posts
    3,827

    Thumbs up

    Thanks edb!
    I learned something today!

  5. #5
    Join Date
    Nov 2006
    Location
    Faunsdale, AL USA
    Posts
    4,169

    Default

    I think itís obvious that moving filtered air in and out of the cylinders is preferable to the carbon and other crud that could be in the exhaust system. Iíll grant the point that the efficiency of sucking anything back in from the exhaust would be pretty low, but still possible for chunks to fall into the open valve and get stuck.
    D2-5J's, D6-9U's, D318 and D333 power units, 12E-99E grader, 922B & 944A wheel loaders, D330C generator set, DW20 water tanker and a bunch of Jersey cows to take care of in my spare time

  6. #6
    Join Date
    Dec 2006
    Location
    victoria australia
    Posts
    3,179

    Default Pony Exhaust Heat

    Hi Toby,
    credit where it is due here, as I thought that Rome K/G had posted just before me (I saw his post after I posted mine above) about the Pony motor exhaust heat being circulated thru the Inlet system to help heat the main engine's combustion chambers etc.--he is correct for later engines fitted with the pony exhaust heater tube thru the Inlet manifold.
    Cheers,
    Eddie B.

  7. #7
    Join Date
    Nov 2007
    Location
    NW Ohio
    Posts
    3,694

    Default

    HA! lol yea i thought maybe you guys thought my answer was out in left field!!! lol so i deleted it.

  8. #8
    Join Date
    Mar 2015
    Location
    north idaho
    Posts
    677

    Default

    Quote Originally Posted by Rome K/G View Post
    HA! lol yea i thought maybe you guys thought my answer was out in left field!!! lol so i deleted it.
    I love your left field answers

  9. #9
    Join Date
    Jan 2007
    Location
    Kerrick, Minnesota
    Posts
    1,164

    Default

    Thanks guys, utilizing the heat generated by the pony exhaust as Rome K/G mentioned had ran through my mind as well, although like edb said this early D3400 I'm working on is one of the first generation units that just dumped the pony exhaust straight out instead of running it through the diesel intake - I always found it strange that they did it that way when you consider the time when this D2 was built they were already utilizing the pony exhaust heat on the bigger models with the upright starting engines. I would've thought that small displacement D3400 would've needed all the help it could get from the pony but it took a little while before they started running the exhaust pipe through the diesel intake on the D2's.

    Several viewers questioned whether holding the intake valves open during cranking might cause intake air to be blown back out through the air cleaner, but obviously that has never been an issue. My thoughts on this were that the combination of an engine that has reduced breathing capacity due to being decompressed combined with the fact that as cylinders are coming up pushing air back past their intake valves, there are other cylinders that may be scavenging this displaced air due to their valves also being held open while those pistons are on their way back down creating an easier path for the air to go than back through an oil bath air cleaner?

    At any rate, the preference of clean filtered intake air being pushed around over the dirty exhaust source makes perfect sense - I much appreciate the help!
    D2 5J2115SP
    D2 5U7066
    RD6 2H1768
    RD6 2H3072
    No.9 Auto Patrol 8A331
    No.9 Auto Patrol 8A340
    No.9 Auto Patrol 8A539
    Ten PT3037
    Twenty PL134 (Yard-Art)
    Minneapolis-Moline prototype crawler X253
    1945 Farmall H

  10. #10
    Join Date
    Nov 2007
    Location
    NW Ohio
    Posts
    3,694

    Default

    Quote Originally Posted by d2gary View Post
    I love your left field answers
    Thanks Gary!!!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •