Onan P220 oil pressure issue

[Oak 0]

Hello everyone. I'm a new member here and have a question on an Onan P220 that I just rebuilt and I'm having an issue with the oil pressure.

 

Basically, this engine should have went to the scrapyard but I rebuilt it. It has new .20 over pistons and .20 under rods, main and cam bearings were replaced, crank was sent out and reground, both intake valve seats were loose so my engine builder welded the block and made new seats. I reassembled it and used assembly grease. I did not pull the oil pump apart and re-gasket it with the gaskets in the kit, I left it untouched.

 

Here is the initial start I did at the end of last summer.

 

It took a long time but I finally got it put in the tractor.(I know wrong brand but the color is correct)  I cranked it up over the weekend but I didn't like the oil pressure I was seeing so I shut it down and pushed it back in the shop. Here is that run.

Monday I changed the oil (store brand 30W) and replaced the filter(Wix 51348). I pulled the oil bypass spring and checked it. It is in spec at 1.0"(maybe it collapses under pressure, IDK). I'm waiting on the new spring I ordered so I took this one and stretched it to 1.2" and installed it back in the tractor. Here is that run.

 

I liked the pressure better in that run but look what happens after a few minutes of run time.

From what others are saying, 20 psi is where the bypass starts dumping oil back into the timing cover but why is my pressure going to 0 at around 900-1000 rpm? Cub Cadet did not install a pressure gauge or kill switch on the 982 so it's hard to find what others are running on that side of the fence. My new spring should be here this week but I'm not sure that will take care of my issue. Do you think I have a pump problem or pump capacity problem because of an internal leak or too large of tolerances? TIA.

[cleat 4,983]

The engine I just built last winter for my Merkur (German Ford car) runs around 50 PSI warm or cold on the road.

 

However, at warm idle the pressure drops to around 25 PSI.

That is measured with and Autometer gauge (fairly pricey and I hope accurate).

 

I know that is different than zero but you can expect some drop.

 

Do you know your gauge is accurate ?

 

Years ago I had an S-10 with the GM 2.8 liter engine. Dash gauge would read zero at warm idle just like your engine.

However, a mechanical gauge screwed into the block in place of the electrical sender showed some pressure at idle. Not a lot but not zero.

 

Truck ran fine and I learned to ignore the gauge as it simply just did not work properly.

 

Cleat

 

Edited May 24, 2017 by cleat

[Jerry77 1,218]

1 hour ago, cleat said:

Do you know your gauge is accurate ?

Had a chevy truck that started showing a drop in pressure - replaced the sending unit and then it read right - they can be bad..