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H Oil Pressure Problem

D

Doug Kieta

Member
I am trying to bring a 49H back to life. Just had the rod bearings replaced and the engine tuned and it runs really well. However, even at full throttle, after running for a while the oil pressure drops from
about 60psi to about 5 psi. This seems abnormal to me. As part of the rebuild, the mechanic installed a salvage oil pump and sanded the base plate. Didn't improve from the original which acted the same.
For you guys that run H's, what is the range of oil pressure you experience from full throttle (bush hog work) to idle? Also, is there a way to test the performance of the oil pump on the bench? Any
suggestions or insights you can offer will be most appreciated. I love this old girl and want to take care of her as long as I am around to do so (am 80). Thanks for the help
 
The pressure drop is below normal expectations. An H usually has a pegged pressure needle all the time at full throttle, and 30psi at Idle. Running thin oil can reduce pressures, I recommend diesel grade 15W-40. Oil pressure loss can also be from bad cam bearings, and out of spec main bearings. Jim
 
Sounds like the gasket on the oil pump might be partially blown or leaking some. Or maybe your mechanic didn't put the right size bearings in it. Could also be the oil you are using. Several things to ponder over.
 
When I acquired my '53 Super H it exhibited oil pressure readings similar to yours.

I replaced the main and crank bearings, carefully flat sanded out wear grooves in the oil pump cover and switched to 15W-40 oil. Now at cold startup it shows about 30 psi and idle and 60 at speed; fully warmed it drops to about to 5 psi at slow idle and 30 at speed. I suspect worn cam bearings (which I have not replaced) are the cause to low oil pressure when hot. However it's been running like this 20+ years with no issues - I am inclined to continue using it as is.

Incidentally long time tractor mechanic (my late father in law...) shared these old engines will keep running fine as long as any oil pressure at all shows on the gage at idle. What is important is oil is circulating, not its absolute pressure.
 
One of my H's reads about half guage on a cold engine. Once warned up, it drops down to really low on the guage. Tractor has a lot of hours on it. I suspect worn bearings outside of tolerances. I'm not to concerned with it. I figure if it's getting oil up to the upper engine and the guage, that it's getting oil. No pressure at all up above, I'd be concerned about the crank being dry, and that would definately not be good.

If I had to guess, I'd guess you'd probably have to replace all the bearings in your engine (cam and main bearings included), and get everything within tolerances to get high oil pressure back, and maintain it when engine is hot. Just doing rod bearings is like saying you did a complete overhaul, when you actually just did a partial overhaul.

If it's say, worn cam bearings, there really isn't any magic tricks for that. You can play around with the pump if you want. But if there isn't any issues found there, there really isn't anything there to fix. And if not, it's back to worn bearings that you did not replace.
 
I had a 350 (very similar to an H) and when cold the oil pressure was about 60-70 range. When it warmed up at full throttle it would still make just under 50 - at creeping idle (picking up bales) it would dip to 20 PSI - when you opened the throttle the oil pressure would immediately climb back up to almost 50 PSI. I always ran 10W 40 motor oil.

Can't help on how to test an oil pump on the bench. But if you had two oil pumps in a row give you the exact same readings and if you can trust your mechanic the issue probably isn't the oil pump.
 
If pump check pump drive shaft and housing wear. Oil from pump gears goes up through housing to oil passage. Worn shaft causes some oil loss. Sometimes material needs removed from pump housing so bottom plat will be close enough to gears. If gears are out of spec or damaged the above could be useless.
 
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