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John Deere Tractors Discussion Forum
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Looking for solution to "Diesel knock" in JD 4020

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03-20-2017 14:25:26

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I have a John Deere 4020 Diesel that developed a miss. The first step to cure miss was to remove the pencil injectors and have them tested. All cracked/popped adequately, however, 2 of the injectors test pattern was not real good if pressure was added slowly so I replaced them. This did not cure the miss. Turned out miss was a broken rocker arm on # 1 intake valve. After replacing rocker arm started hearing a ping in upper part of motor and isolated it to # 3 cylinder and suspected a wrist pin. When I was getting an estimate on what an overhaul would cost the mechanic asked if i had checked injectors. When I explained what i had done and that #3 cylinder happened to have one of the 2 new injectors, he suggested that I swap the injectors and see if the sound moved. He said if there were significant differences in pop/crack pressure between injectors it could adversely affect injector pump timing. Swapped #3 injector with #6 and the sound moved with the injector. Took all injectors out again and had the pop/cracking pressure checked. The originals cracked at 2000 psi and the new ones at 2800 psi. All 6 were set to 2800 psi (at Injection shop's recommendation). Now I have even more unwelcome "Diesel knock" chatter. Quiet at 600 rpm. Most notable between 1200-1700 rpms. Any suggestions? Looking at having all the injectors setback to 2000 psi and see if solves problem even though the mechanics say pressure should be in the 2600 to 2800 range. Tractor starts and performs OK, just noise is driving me nuts to the point I don't want to use it. My local "experts" don't think the change in pop off pressure would significantly change the amount of fuel allowed through the nozzle to cause or cure "Diesel Knock". Thanks!

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03-22-2017 09:16:53

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 Re: Looking for solution to in reply to toopoor2fix, 03-20-2017 14:25:26  
The higher injector crack pressure is preferred as it breaks the fuel up more to get more power and fuel economy . The new nozzles are set to 2800 because the springs and seats wear in and will drop the 200 psi or so in just a few hours . The old nozzles should be set to 2600 psi. otherwise its harder on the pump to run off balance . As far as knock goes the better shape the engine is in the more knock there is . I've overhauled many a 2 cyl. diesel and some of them sounded like the head was ready to come off .

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03-21-2017 10:17:02

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 Re: Looking for solution to in reply to toopoor2fix, 03-20-2017 14:25:26  
I once owned a JD 730 Diesel, and yes Diesel Knock was extremely loud, but expected when 180 cu in were coming up on compression in each cylinder. You could run the 730 all day and listen to the ringing in your ears all night.

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03-21-2017 10:11:41

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 Re: Looking for solution to in reply to toopoor2fix, 03-20-2017 14:25:26  
I know changing the static timing is not the way to change the injector pump timing advance, however, based on other forum discussions, I changed the static timing a fingernails width worth. It helped immensely. No bothersome "Diesel knock" at 1000 rpms and after it runs for an hour or so, the "Diesel knock" is tolerable at the 12-1700 rpm ranges as well. It did change the way it cold starts. It now blubbers for 5 seconds or so before it smooths out.
Thank you for your replies to my question. Before messing with something that has not been changed to address a new problem, it has been helpful to get advice from people that have been down that road before.

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03-21-2017 07:51:29

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 Re: Looking for solution to "Diesel knock" in JD 4 in reply to toopoor2fix, 03-20-2017 14:25:26  
A good running diesel will have a crisp rap to it.

As experience indicated , all injectors have to be a matched set and up to spec.

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David G

03-20-2017 17:53:14

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 Re: Looking for solution to in reply to toopoor2fix, 03-20-2017 14:25:26  
I would check the timing.

It should be quiet @ 0 degrees, and have a crack and a little lope at idle @ 10-14 degrees.

We run @ 10, boy does it pull, but a little noise.

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Tim S

03-20-2017 15:49:13

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 Re: Looking for solution to in reply to toopoor2fix, 03-20-2017 14:25:26  
A "quiet" running 4020 will not have as much power as one with a little pre-ignition knock...the timing is probably advanced a bit more than needed..for it to be quiet..

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Mike M

03-21-2017 05:14:47

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 Re: Looking for solution to in reply to Tim S, 03-20-2017 15:49:13  
A 2 cyl. diesel will also end up being noisier after being overhauled ! But the noises move from the crank up to the cyl. area where the power is made. Seems like the gain a little hop to the narrow front ends when idling too.

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03-20-2017 15:34:30

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 Re: Looking for solution to in reply to toopoor2fix, 03-20-2017 14:25:26  
Sounds more like injection pump timing instead of injectors,or possibly a bad fuel problem.

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