Oil Pressure Question

I have a Jinma 254 tractor here that needs split for an oil leak. When the owner dropped it off, he also told me that the last time he used it he got the oil light after warmed up at idle. He had assumed it was out of oil, but when he checked it to load it and bring it to me that was not the case.

So, before I split it, I put a gauge in the port to verify what was going on. The needle on the gauge flutters very quickly, probably coinciding with engine rpm. Cold idle it swings between 40 and 60 psi. Warm is between 10 and 30. The higher the rpm, the faster the flutter. I assume the drop in overall pressure is most likely general wear, but am a bit lost on what would cause the flutter. It almost seems like an oil port on the crank is exposed for a portion of revolution and just dumping oil, but I'm not sure how that would be possible. I did pull the pressure relief valve and it looks fine.

Any ideas what would cause this? I'd like to have some idea what I'm looking for or if there's anything else I can check/test before I pull the engine. The parts breakdowns are pretty crude drawings, so not much help there.

Thanks in advance, Jeff

What is the oil leak you are going after?

If it's the rear main, good chance the reason it is leaking is because the main bearings are loose. That could explain the fluttering oil pressure, the crank bouncing up and down at low speeds.

Still, from your readings, that doesn't sound like low enough pressure to turn on the light. Was it thoroughly warmed up? It takes the oil longer to heat up than the coolant and the top end of the engine.

And possibly, not knowing the oiling sequence of the engine, there may be metered oil moving through a open-close port based on rotation of the crank or cam. That is a common method to meter oil to the rocker shaft so not to flood the top with excess oil. If there is a loss of flow resistance beyond the metering device, it could cause a pulsed drop in oil pressure, or that may be the way it is designed. If it is, it would sure be hard on the gauge!

A service manual would be handy to look through, if it can be found.

There could be a design feature of that engine allowing that pulsing. I would get info from a dealer service tech first. Ticking pressure reading in time with RPM is a very bad sign (opinion). As you surmise, a failed bearing oil passage alignment with pressure. Depending on the owner's wishes either fill it with 15-40 oil, and see how far it gets before failure, or rip into it now. Find a bearing set before ripping into it. I have seen it several times. In one instance the tractor lasted for 5 more years, sold and gone. Another lasted 8 minutes, but began pounding at 4 minutes and was shut off. Others disappeared into the future away from me. Jim

Ok guys, I'm going to reach out here and say that posibility exists of there being a suction leak between the oil sump and the pump. I have seen rapid fluctuations in pressure where the guage bounces 30 to 60 psi multipule times within a few seconds.

Beagle, Yea I once left the pickup tube loose on a Cat 3116.

Owner originally thought it was the rear main, but its actually the gasket between the rear of the block and the bell housing. Obviously will still get a new rear seal also.

That thought had crossed my mind also, but from the parts diagram it look like the pump itself is right down at the bottom of the oil pan with a screen on it. No suction tube to speak of.

Also, I believe the bearings are getting loose. When revving the engine there is a slight drop in oil pressure before it rises with the rpm. When decelerating there is a slight rise in pressure before it drops as the engine slows down. I take that as the engine pushing against the worn and not worn halves of the rods and mains.

I would check the oiling of the rocker arm assy. That is easy to do and it could tell the story.

Jeff NWOH,

I would check the pump pick up real close. If you don't find anything, I would then check the pump. A stiking pressure relieve valve could be the problem. Engine wear does not make the oil pressure fluctuate like that, it just gets lower then normal,

Guido.

Have you tried putting the gauge on a couple ft long hose, many gauges flutter bad from engine vibration especially if not liquid filled