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720 difference in diesel noise

J

jdfamily

Member
Curious, my friend and I both have 720 JD Diesels, one is electric start the other a pony start.
our question is when idling one makes quite a bit of the knock of the diesel, the other is so quiet
it does not even sound like a diesel. Any thoughts on why that is?
 
The quiet one may have worn injection pump cam lobes, injecting fuel later. Care must be taken when setting the timing and checking the full stroke of the pump tappets. Each timing line at full cam lift MUST NOT disappear from the timing window. If it does then cam lobes and/or roller follower arms are worn, or cam timing is late. If the pump timing is set at the pushrod on a worn lobe then pump damage can result when at full lift. When setting each pump timing I purposely start with the tappet line 1/8 inch back from where it should be, roll the flywheel to full cam lift and make sure tappet line is still short of the window end opening. If all is well then I set it as it should be..
 
Depends on where the knock is ? I suspect the quiet one is worn out. Once you rebuild one they get noisier, but the noise moves from the crank area to the cyl. head area. The flywheel could be loose too and an extra source of noise like the other guy stated.
You will also note if a narrow front end ones that run and make good power will bounce the front end at idle some.
 

Pull the injectors from the wimpy diesel and check the pop pressure and spray pattern.
Also as previously stated check the pump timing.
A restricted air intake system with lower the compression pressure .
Outside of that , it's an overhaul $$$z
 
Thanks. will do some checking on the quiet one, your comments make sense. Not a mechanic, but usually can figure things
out with the help of the manual
 
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