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82 720 very low oil pressure


wlf89

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Yes! The hole in the block is fairly large and the tensioner block has a small hole in it.

 

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I once worked out the oil pressure on the piston as about 7 pounds if the oil pressure was at 50 PSI. Much much less if 20 PSI @ idle

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Yes all tensioners will have the oil feed to them, I meant the oil jet just above the crank sprocket. I think Nissan figured out that enough oil gets on the chain from the cam spray and the tensioner leakage. 

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 the timing chain tensioner bolts had backed loose, one was pretty much all the way out and the other was loose. it looks like it bolts over a oil hole so im hoping with it loose and not sealing the oil was leaking around it and loosing pressure and this is my problem. would everybody agree?

 

Time to smack the person on the who assembled the engine along side of the head, like my second grade teacher would do when I was being a brat.

A practice I carry on nearly 60 years later, when ever I screw something up (mentally of course).

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put it back together this morning and put the oil in and left the coolant out just to crank it and make sure was gonna have oil pressure, let it run about 45sec and only got around 18-20psi. i dont know what in the heck is wrong with it. about ready to take it to the crusher.

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put it back together this morning and put the oil in and left the coolant out just to crank it and make sure was gonna have oil pressure, let it run about 45sec and only got around 18-20psi. i dont know what in the heck is wrong with it. about ready to take it to the crusher.

 

Before you crush it give it to somebody here that will just put in a motor :).

 

Have you checked to ensure there is not a rag or something on the pickup tube? Stranger things have happened.

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Well you can drop the oil pump and remove the spindle then assemble it again. Use a long screwdriver blade and an electric drill to spin up the pump. I've done this to pre lube an engine before. Now you don't have to start it for oil pressure.

 

 

If the tensioner was loose.... maybe something else was left off or loose.

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didnt see nothing else missing or loose inside the engine, this morning i was emptying my drain pain and putting up tools before it rains and did find a sliver of aluminum in the catch pan about 3/4in long and 1/4in wide maybe,  i dont know where that would have come from but could be something to do with it i guess but wouldnt think it would be from nothing that important?

 

what all is aluminum on these engines though? the timing cover and valve cover is about all thats coming to mind. havent had the valve cover off but the timing cover didnt look to be broke anywhere.

 

below are 2 links to the picture of the metal piece

 

https://postimg.cc/image/l1coaky1n/

 

https://postimg.cc/image/gurtv363v/

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Head, timing chain cover, valve cover are aluminum and have access to the oil pan where this part was found. That's about all. Intake, carb, oil pump, distributor, alternator are all on the outside. Cam and valve train, timing sprockets, tensioner and guides are steel. 

 

Pistons are mostly aluminum and very brittle. If this engine was rebuilt there could have been a piece but I can't see how it would be left in the oil pan. Is it slightly curved?

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Looks like part of a piston to me. The "paint" could just be burned on oil sludge.

 

If it's not a piston ring land or skirt, it had to come from the timing cover or maybe even from the inside of the valve cover.

 

To me, finding that piece warrants removal of the engine for a comprehensive inspection. Make sure the oil galley plugs are in the front and back of block. Pull a rod cap and make sure the oil psi didn't ruin a bearing. Check the crank thrust. Look into the bores under the pistons and inspect the piston skirts. Etc.

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Piston skirt. Cracked or damaged when installed but not the cause of low oil. 

 

Engines will run very well on very low oil pressure. 30 would be enough when revved up. The low pressure light is set for under 8 PSI so...

 

It would have to be the front plug or it would spill out the clutch end.

 

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The 1/2" hole above the 13 should have a press in plug. If it was missing I doubt you could build any oil pressure.

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wish i had of took some pics when had front cover off, but i remember thinking to myself that my block only had 2 holes there where yours had 3 in the pic so maybe the plug was still there. i really hate to put much more money in the truck, the body is rotted and falling apart and not worth it.

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If I was you, I would try to get the rebuilder to fix it and put it back in your rotten truck.

 

Then watch CL and fakebook for a not rotten 720 that needs a new motor.

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That is a shame.  I guess you will have to either tear it down and fix it your self or find another engine for it.  I do not beleive that I would have that machine shop do any more work unless you tear it down and find it is total un related to the engine rebuild.  Please keep posting and let us help if we can.

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If you fill out your location and what vehicles you have you mind find someone on Ratsun lives in your area and might have an engine for a reasonable amount of money.

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took the valve cover off this morning and that is for sure where the chunk of aluminum came from, it was the little rib on the front of the cover near the fuel pump arm,(probly from changing the pump 3-4 times last year before i finally got a good one, and hit it somehow with the arm). anyway bolted the crossmember and idler arm back up and filled it with water so i could drive it out the road and see what happens, once i rolled it off the tall ramps i had it pulled on to work on the oil level was fairly low vs the slightly over full it was while on the ramps. so topped it off and put the water in and cranked it up and got about 23psi idle and 45-50 going out the road. maybe the tensioner was the problem all along but still less psi than used to be, think im gonna put the original sender and gauge back in and see what it shows since i think it was still ok.

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23 is ok for idle and 45-50 driving. I would expect top 20s at idle if that's the high output pump. Mine is 29 (ish) idle but I shimmed the pump relief for closer to 60 running.

 

The high output pump will have the rotor inside showing clearly when looking down into the inlet....

 

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This is a normal pump. The rotor is barely visible...

 

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This is because of the 13% longer trochoid rotor. Externally they are identical.

 

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