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Can you have to much oil pressure????

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Fred

11-27-2000 14:44:17

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Is it possible to have to much oil pressure? My 42 c had no pressure until I found the oil tube in the filter was gone so I make one and now my needle gauge pegs on the high side, past the L in Normal ,when throttle pulled back all the way it will drop to just between R & M in Normal. Does anyone have any thoughts on this??

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Paul from Michigan

11-27-2000 18:14:54

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Re: Can you have to much oil pressure???? in reply to Fred, 11-27-2000 14:44:17

The oil pressure you see on the gage is actually the amount of pressure at the pump side of the filter. The oil pump discharges oil thru the hollow camshaft to oil the rod & main bearings. Oil passes thru two holes in the pump body into the camshaft when the pump is putting out less than 15 PSI, such as with hot oil at idle. When the pressure rises over 15 PSI the relief valve in the pump opens and discharges the excess oil into the camshaft to add to the amount passing thru the two holes in the pump body. This is the normal operating condition. The oil filter is designed to pass oil at less than 15 PSI and under normal conditions about 1/6 of the oil will pass thru the filter and 5/6 of it will lubricate the engine. This is what is known as a bypass filter system vs. full flow where all of the oil passes thru the filter before being pumped into the various passages to lubricate the engine. If the oil filter in a bypass system becomes plugged, all of the oil will flow thru the engine. However none of it will be filtered. This is an advantage of a bypass system in that the engine will receive oil even if the filter is plugged, even if it's dirty oil, it's better than nothing. Full flow systems usually have a bypass valve built into the filter or the engine to accomplish the same thing if the filter becomes plugged. What you may have done by making an oil tube is to restrict the flow thru the filter too much, resulting in the same condition as a plugged filter element. That is high apparent oil pressure, but no oil passing thru the filter. I would suggest finding an original oil tube and probably the readings will return to normal. I know this kind of long winded, but the oiling system on these little Allis engines is hard to describe in words. The best explanation I have read is the one on pg. 53/54 of the reprint service manual for B & C tractors. Just as an aside, the rod bearings are not pressure lubricated, only spray from the camshaft. The mains are pressure lubricated. When I replaced the original bearings in my 1948 B the rods were in much better shape than the mains. So much for the theory that you have to have 30 PSI to lubricate an engine bearing. Good Luck, Paul

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Dick L

11-28-2000 08:02:28

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Re: Re: Can you have to much oil pressure???? in reply to Paul from Michigan, 11-27-2000 18:14:54

Paul, you are correct as usual, but I think that something could to be restricting the oil pump relief valve to see that kind of pressure. The hole through the center of the cam should dispense all the oil the pump would be able to put out without going through the filter.

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