720d, how long to crank w/o oil pressure?

Ok, just put a new crank in my 720d. The tractor has been apart, with oil drained, for a year. I finally got it back together. Followed the JD service book. Lots of assembly lube on the rod and main bearing journals. Today I'm cranking it over with the pony engine for the first time. Have the diesel throttle all the way back, just cranking it over with the pony until I see oil pressure. But the gauge barely goes up. It's down in low.

I stopped and checked the oil level, it was now low, I guess from filling the crank, and timing cover, and all the other passages. So I filled it back to full. Still reading very low on the gauge. It's a new gauge. Also, I had replaced the gaskets in the oil pump while it was apart, trying to stop a leak.

I'm going to try my old gauge, just to trouble shoot the new one. But how long do I crank before oil should be fully circulated and I show pressure?

I think if you have that question you probably have already cranked enough.

Ok, update. I tried again after supper. First I popped the valve cover off. Oil came out, so I knew it was pumping oil at least. I hooked the old oil pressure gauge back up, and it read the exact same as the new one. Moving just slightly off the bottom. Checked out the oil pressure adjustment screw. Turned it in, (A LOT), and got my oil pressure back. I thought, being a fresh crank, that the tolorances would be tighter, and therefore oil pressure higher than before. The machinist mic'd the crank right in front of me, and showed me how it was all at specs. And the bearings were all stamped with the right size, I had double checked. So I know that's correct. The only thing I can think of is that the crank I replaced had been welded on, and pretty roughly, around the center main. Which is why I replaced it with a N.O.S. crank. I wonder if the old crank's oil passage was messed up some, or filled in some, when it was welded on. I don't know.

If the oil gauge has been replaced the new ones don't read correctly. If you have a john deere gauge that comes on the tractor when it was new and replace it with a aftermarket one it will read at low. That's just the way they are made , the only gauges that read correctly are the ones you buy from deere at about 80 bucks.

"<font color="#6699ff">[b:654c4848f0][i:654c4848f0]But how long do I crank before oil should be fully circulated and I show pressure?[/i:654c4848f0][/b:654c4848f0]</font>"

Reviewed the [b:654c4848f0]OPERATOR'S MANUAL JOHN DEERE TRACTOR MODEL 70 DIESEL (GENERAL-PURPOSE AND STANDARD)[/b:654c4848f0] under the [b:654c4848f0][i:654c4848f0]STARTING THE DIESEL ENGINE[/i:654c4848f0][/b:654c4848f0] topic the second paragraph on page 29.

"Allow the cranking engine to motor the diesel engine [b:654c4848f0][i:654c4848f0]until oil pressure registers on oil gauge.[/i:654c4848f0][/b:654c4848f0]"

For both our Model 70 diesels it is only a couple of seconds.

Hope this helps.

I worked on a lot of these old girls . With a master gauge I would let her start up. If you used pre- lube grease it will run at idle for a long time . Now if it doesn't come up right away shut her off!, and find out why. Oil pump could be worn out and /or a oil line cracked or not tight etc.

Throttle all the way back? You mean the way it is supposed to be cranked with Zero fuel rack because the stop knob was pulled and the throttle all the way back shut down postion?
Or just back to slow idle ?
Cranking is supposed to be done with the decompressor activated however there is no mention of doing such ?
Operators manual says zero compression and zero fuel until oil pressure appears on the gauge . When oil pressure appears , add compression. After a couple of rotations with compression and zero fuel, NOW push the throttle ahead.

Yep, I was doing as the book said. I should
have listed my procedure completely. I had
the decompression lever pulled, diesel
throttle completely to shut off position,
even had the diesel fuel bowl shut off. I
wasn't trying to start the diesel yet, just
spinning it over for the first time since
putting the new crank in, getting oil pumped
back through everything.

What I didn't like was I was spinning it
over for what seemed like too long to me,
and wasn't seeing the oil pressure come up
yet. I was wondering how long you spin it
over on just assembly lube, without oil
pressure building, before you decide
something is wrong. It made sense to me that
it would take longer than normal to build
pressure since everything had been
completely drained. But I didn't know where
to draw the line.

If you see my follow up post, a few more
turns and the pressure came up slightly.
Then I was able to use the pressure
adjustment screw to get the rest. The only
other time I put a crankshaft in was my "G".
It's pressure was basically the same before
and after its rebuild, so I guess I wasn't
expecting such a change. I read today in the
JD service manual, in the lube system
section, I'm to recheck the pressure after
overhauls and after working on the oil pump.
Well I just did both, so I guess that's was
my answer.

Thanks for all the responses. I appreciate
the input.

(reply to post at 03:06:13
01/15/17)

Click to expand...

Rick is right. Had this same problem with new gauge on my 720. Even the expensive ones from John Deere don't always read right. Get yourself a good test gauge and adjust your oil pump once you warm it up. Then you hook up your new gauge and try and remember where in the L your normal is. Anyhow that was my experience.