Idling Oil Pressure

[Mad Max (TX)]

I am in the process of having my TO 20 rebuilt at a repetable tractor repair shop. The mechanic told my that he replaced all bearings, plastigauged all journals and rebuilt the oil pump. However he seems to be having trouble getting the oil pressure to get any higher than 5 to 10 psi while hot idling. At higher RPMs pressure is good. Is this normal for these old engines?

 

[jjinga]

I had my TO20 engine rebuilt earlier this year.
My oil pressure was doing that before the rebuild.
My oil pressure now is 34psi cold and hot idling and 39psi hot at working rpm's.
The low OP reading are probaly the oil pressure relief spring and valve in the oil pump.
That's my 2cents worth, any other thought's would be welcome.
ps: I am using 10w30 oil.

 

[Richard L]

according to the TO 20 parts book on page 2 item number 66 is a pressure adjusting washer part number 15 326 A. If you have a parts book let them see this page and they should be able to get it higher in PSI. If I remember correctly the high pressure should be 27-30 PSI.

 

[Jim in OH]

Max, it is acceptable, but I wouldn"t say that it was normal.. what you describe would normally be attributed to larger than normal clearances somewhere. Did he refit the cam bearings too? changing the relief valve setting will not change the low idle pressure, it would only afect the maximum (at high idle) which you have said is already okay.. If that is low also, then it should be adjusted higher.. but if high idle pressure is okay, I"d probably let it go and put the tractor to work..

 

[Jerry/MT]

Check the relief valve( tuck open or too soft spring). A new rebuild should have almost constant oil pressure independednt of hot or cold oil and rpm. My TO-30 has probably 600 hrs since it was rebuilt and my oil pressure is a constant 27 psi hot or cold, lo idle rpm or high idle rpm..

 

[Texasmark1]

Certainly the type/viscosity of the oil you use will influence this. I used to think that my oil pressure had to be constant over the temp/rpm range.

Thinking through it over the years, the oil pump is a gear pump that is turned by the camshaft or other part of the engine. As the engine rpm's increase so does the volume of the pump. If the pump supplies oil at a rate faster than it can be consumed, the pressure raises.....pv=kt. k is constant and t is the temp. If the pressure gets too high, the pressure relief valve opens and allows an increased volume thus lowering the pressure.

If your oil viscosity changes dramatically between low and high temp, at high temp it could be very thin and accordingly flow out through the ports easily and as a result reduce the pressure. Yes the pressure setting washers can change it and overhauling an engine with some clearance larger than spec can change it also.

If your engine runs 30 psig at operating rpm's then you are good to go in my estimation and I have spent a bunch of time studying it. If you want it higher get a higher viscosity, like using a 30w rather than a 10w-30 which seems to become thinner at higher temps even though it is rated 30w.

Case in point is the idiot light. It goes out at around 7 psig and with the light you don't have any idea where your oil pressure is. How many millions of engines, of all types, have been supplied over the years with this setup and have run for 100's of thousands of miles without overhaul.

HTH,

Mark

 

[Bruce(OR)]

When I did the wife's engine I replaced the seals in the pick up tube to prevent it from sucking air and lowering the pressure. I also ran some very close tolerances on the bearings.
Your rod and main bearings are the primary sources of oil pressure. Excessive clearance will give you lower pressure. So, once the engine warms up, the pressure reading will be lower than a cold engine. Unless your running a newer engine with a tighter bearing clearance.

 

[2tractors]

I don't think the cam has bearings but the wear will probably affect the pressure, I've rebuilt both a 20 and 35 and am wondering what effect the cork like stoppers in the end of the rocker shaft have on pressure. If they allow too much oil to escape out the ends then it would seem to lower pressure along with reducing the oil going to the tappets.What effect would everyone think occurs if you use RTV and completely stop up the shaft end?

 

[Anonymous-0]

If you are using 10 w 30 automotive oil ( M ) , you run the risk of scrubbing the lobes off of the cam , and scoring the lifters . As has been noted in this forum , automotive oils have been altered over the past few years . You should be using diesel rated oils ( c ) .
Most newer vehicles have roller lifters , and don't need the additive that was removed . It was removed because it was poisoning the cat. converter .
Wal Mart has Shell , Mobil , and one other deisel rated ( c ) oil at a fair price .

 

[jjinga]

Then what do I use in my diesel truck that has a catalytic converter?

 

[John(UK)]

At 2200rpm and at working temperature (not just warm)the oil pressure should be 20-30psi @ 400rpm it should be 15psi. It will depend on the grade of oil and the air temperature as well. You should be using SAE30 above 50F and SAE20 below. If oil is leaking out of the end of the Rocker shaft then this will lower the pressure, what you should check out, is the oil getting to the Rockers at all times. If it isn't, then the pressure is escaping, whether it is the ends of the Rocker shaft or from the Camshaft Bearings, these do wear but are always neglected and rarely repaired. Has the Oil Pump been checked, running at speed the oil pressure is maybe OK and it can't produce more pressure than the relief valve will allow, but when it is running slowly the pressure will be escaping rapidly and the Pump cannot keep up with the leak because it is worn. Just as a matter of interest, the Z129 Engine from the TO30 has the same pressures, for anyone who would like to know. John(UK)[email protected]

 

[2tractors]

JJinga, good question!!