Page 2 of 2 FirstFirst 12
Results 11 to 19 of 19

Thread: To Compress or Not Compress?

  1. #11
    Join Date
    Nov 2006
    Location
    Plains of NW Kansas
    Posts
    549

    Default AL Vet Correct

    The AL Vet is correct that the load on the pony from the compression tells one that a lot more heat is being generated by the loaded pony.

    I typically run my pony longer on decom just to warm up the pony and get the oil circulating in the main. When the pony gets warmed a bit, go to full throttle on the pony, flip to compression for a few seconds and hit the main throttle. Usually less than 15 seconds on compression to start unless it is below 30 degrees F. If one thinks about it, the compressed air is heating the surface of the cylinder so that when the air enters and is compressed, it is at a temperature that will ignite.

    That is a good idea Ray to check the head temp with a pyro. Now if I can remember to do that next time I crank up the D4 or 112. I use them all the time to check block and tranny temps on the green stuff.
    Last edited by D4Jim; 06-01-2020 at 05:50 PM. Reason: Added Pyro
    D4Jim
    D47U (1950), 3U 112 Grader (1949), Cat 40 Scraper ACMOC Member 20 years

  2. #12
    Join Date
    Nov 2006
    Location
    Faunsdale, AL USA
    Posts
    4,388

    Default

    Shared oil between pony and main is old news, was standard for a very short time on D7/D8 and maybe others. There was a retrofit kit to separate them again..... not a good idea apparently.

    Your idea that having the decompression pulled lets warmed air recirculate back into the intake manifold may be true, but youíre forgetting that the next stroke UP of the piston, the exhaust valve opens and most of the warm air that has been conserved is exhausted, only to be replaced by more cold air coming in the air cleaner.

    Iím glad your main engine starts right up as soon as you flip the decompression to run, but when the engine and air are cold, cranking it under compression is the fastest way to get it warmed up and started...... Unless you believe in the ether bunny!
    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

  3. #13
    Join Date
    Dec 2019
    Location
    Pouce Coupe, BC Canada
    Posts
    193

    Default Only in the North

    Quote Originally Posted by ccjersey View Post
    Shared oil between pony and main is old news, was standard for a very short time on D7/D8 and maybe others. There was a retrofit kit to separate them again..... not a good idea apparently.

    Your idea that having the decompression pulled lets warmed air recirculate back into the intake manifold may be true, but youíre forgetting that the next stroke UP of the piston, the exhaust valve opens and most of the warm air that has been conserved is exhausted, only to be replaced by more cold air coming in the air cleaner.

    Iím glad your main engine starts right up as soon as you flip the decompression to run, but when the engine and air are cold, cranking it under compression is the fastest way to get it warmed up and started...... Unless you believe in the ether bunny!
    -if you live above the 49 parallel.....you believe in the Easter Bunny...and the Ether Bunny (in moderation)
    Caterpillar D6C 99j

    Tax me, I'm Canadian

  4. #14
    Join Date
    Nov 2006
    Location
    Pittsford NY
    Posts
    4,910

    Default

    The reason your main engine started with no prior "compression" time is just because it's a good starter. That fact doesn't mean that running the main under compression doesn't help any particular engine start. My 5U is not a good starter, and so must take a decent amount of heat before it will start (like 5 minutes), whereas Tim's tractor sitting in the same barn will start after a few seconds of cranking. All forms of heat input will assist starting, you just might not notice it if yours is a good starter.
    Cheers,
    Neil.

  5. #15
    Join Date
    Dec 2019
    Location
    Pouce Coupe, BC Canada
    Posts
    193

    Default higher compression ratios

    -there's quite a large window when it comes to a diesels static compression ratio...anywhere from 13 to something like 22 to one...and it seems the higher compression diesels start better, to me at least..probably harder to crank but that extra heat generated in the cylinder fires off sooner..
    Caterpillar D6C 99j

    Tax me, I'm Canadian

  6. #16
    Join Date
    Nov 2006
    Location
    Pittsford NY
    Posts
    4,910

    Default

    I'd agree based on my observations of other engines, notably the Lister CS series. Those start on 18 or 22:1 depending on model, and run on 15:1. They will start in almost any circumstances, if the piston rings and valves are in good shape. But as soon as the compression drops off (like, I suspect, has happened in my 5U), it gets harder to start and requires more external heat, which, if you think about it, can be a replacement for compression-generated heat.
    Cheers,
    Neil.

  7. #17
    Join Date
    Aug 2019
    Location
    Washington
    Posts
    170

    Default

    My knowledge and understanding with diesel engines has grown quite a bit since i first got my tractor. So, maybe part of it is I am noticing things now that I or most people would have not really noticed before.

    I've got a much better idea of how to start the engine than what I used to have.
    Cat D6 5R

  8. #18
    Join Date
    Dec 2019
    Location
    Pouce Coupe, BC Canada
    Posts
    193

    Default Mechanical Injection

    i think the throttle position when starting is important too, you are injecting cold oil into a cold cylinder....(can you flood a diesel engine like a gasoline engine??, I dunno...)

    -so I usually adjust the throttle to what i feel would be just above idle position when warm...crank it and as soon as it fires up and smooths out a bit, check oil pressure..slowly give it more throttle to warm up...

    -just the way i do it...seems to work for me
    Caterpillar D6C 99j

    Tax me, I'm Canadian

  9. #19
    Join Date
    Nov 2007
    Location
    NW Ohio
    Posts
    4,233

    Default

    NEVER crank engine over with starting engine with the diesel throttle open! Your just loading up the cylinders with raw fuel and washing all the oil off the sleeves and rings. Always leave fuel off until on compression and when ready to start. BUILD UP THE HEAT FIRST!!!!

Posting Permissions

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