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Hello guys, brand new to site

Not seeing this problem anywhere else.

I have a gravely 252 zero turn with FH721V, about 750 hours. Engine is homeowner unit, one owner, and has seen aggressive maintenance schedule with filter changes and synthetic 10w30 its whole life. Starts and runs fine, makes good power, no operating sympoms

Engine oil pressure light has slowly become more illuminated over the last couple years.
This summer it has decided to fully illuminate, even at high idle
Changed oil pressure sender, no change.
Checked oil pressure, and its really low. On hot engine, its down to 8psi, at high idle.

In the last 30 hours the engine oil has taken to blackening the oil quickly. More specifically, we change the oil and filter, and in about 14 hours, it was black like it had a superfine black particulate in it. Change the oil and filter, did the same thing by 11 hours. Change the oil and filter again, switched oil brands this time. After 1 hour the oil is black again, still with what seems like ultrafine black particles.

Dumped oil again. The oil looks like a black metalic paint. In the oil drain pan, it seems to have swirls of silvery something in it, like a black metalic paint would look. Or if you have ever seen an aluminum or silver paint. I have the oil out for analysis now.

Anyway, enough is enough, and we have to do something about the oil pressure, so we pulled the crankcase cover off last night. Cant find any thing serious. Oil pump rotor and cover have some light swirl marks, showing some slight wear. I checked all the wear specs against the manual and none of the parts are anywhere near the service limits. Oil pressure relief valve spring is .870" and the wear limit is .770". The only thing I would say is the oil pressure spring rests below the top of the hole its in, so that with the cover installed, there will be no preload on that spring. The pressure regulating ball will be well off the seat at all times. Thought of putting some washers in there to preload the spring.

Also the crankcase cover has some wear on the boss that carried the crankshaft. The oil pump drive gear rests on the crankcase cover boss. The boss is wearing down.
There is fine metal shards in the oil residue in the crankcase. Running a finger around the crankcase walls leaves metal flake on your finger. It may be from the worn boss, it may be somewhere else.

I'm wondering if the worn boss is allowing enough crank endplay to create an exit path for the oil in the galleries, thus dropping the oil pressure.

Reaching into the cylinder liners as far as i can, the cylinders feel ultra smooth. Crankshaft journal areas show no sign of wear, measure exactly the spec in the manual.

Oh, and one last thing, the oil pump cover had one loose bolt. Two were tight, the last one wasn't finger tight. Had it out before I thought about it, so cant say how loose it was, but it wasn't tight for sure. It would have been leaking oil for sure.

Any thoughts on any of this?

Ken

I would suspect excess wear due to the oil used. Pistons, aluminum bearing surfaces, possible powdered metal in the oil pump gears, etc. Most newer automotive oils have reduced or eliminated the needed barrier lubrication materials that are believed to contaminate cat. converters. Read up on ZDDP for one such additive. Cylinder walls might be cast iron sleeved that will withstand the wear of the pistons. Real problem with certain engines these days. Might be too late for this engine but there are additives that will help this situation, not real expensive for the small engines.

And today's auto engines are designed to run on this oil. Roller cam followers, coated pistons, low tension moly rings, super finished crank journals, tight exact clearances, etc. etc. Seem to run forever. Do see timing chain failures if not replaced exactly on spec, hard to make those things with very low friction I suppose. I would run the recommended Kaw, brand oil, or Amsoil small engine syn. oil, or use an additive in the off road stuff. Maybe too late now though.

UPdate,

Engine number is FH721VC06454
ENGINE CODE IS FH721V-FS21-R

I just did a compression test. Both cylinders rise quickly to 121psi.

Crank endplay I would estimate at .050-.060" without a dial indicator. Its seems like a lot for sure. Can't find that spec in the service manual.

Crank journals are exactly on spec 1.571"

Low oil pressure arises from too much space for the oil to pass through
This can be between the oil pump rotor & the sidewalls, lower crank journal & bottom bush, which will be the sump housing in most cases or between the con-rods & crank journal.
Oil pressure bypass valves rarely give grief but you could replace the spring if you like.

Black oil and low pressure are not connected to each other.
Black oil is products of combustion making their way into the oil.
A single reading of the compression will tell you absolutely nothing of any use.
Regular compression tests ( annually ) would have allowed you to plot drop over time and when it starts to accelerate then it is time for new rings.
Once it starts fouling the plugs it is too late.

Have you smelled the engine oil as it begins to darken? Has it taken on a gasoline smell, or does it smell as though it has hundreds of hours on it? These are indicators that can help diagnose your situation as well.

The loose gerotor cover would be my guess as to low engine oil pressure and could be a big part of the minute aluminum particles.

Update:

We put her back together with new gasket. Tightened up those oil pump cover bolts and added lock washers.
Oil pressure goes to 75psi initially, drops to about 25 when working hard. Pretty happy with that.

Waiting to see what the oil does in time. If it still gets black it will still be a mystery.

And of course, we must have weakened the electic pto clutch because the tractor started blowing the main fuse an hour after it back into service. Pinned it down to the clutch. Waiting for a new one.

OK, it sounds like you've made some progress.

What did you do about:

The too-short pressure relief spring

The excessive crankshaft end play

Finding a source of the metal particles?

Black oil is the result of carbon being held in suspension in the oil. Not necessarily a bad thing; diesel oil is almost always black but not so much with gas engines, especially if it turns black quickly. Fuel is the source of carbon, through leakage of combustion gas into the crankcase. Check your spark plugs to see if they look normal.

tom3 said:

I would suspect excess wear due to the oil used. Pistons, aluminum bearing surfaces, possible powdered metal in the oil pump gears, etc. Most newer automotive oils have reduced or eliminated the needed barrier lubrication materials that are believed to contaminate cat. converters. Read up on ZDDP for one such additive. Cylinder walls might be cast iron sleeved that will withstand the wear of the pistons. Real problem with certain engines these days. Might be too late for this engine but there are additives that will help this situation, not real expensive for the small engines.

Click to expand...

Good call on the anti-wear additives that have been removed from automotive oils. Mower engines are subjected to extreme and dirty service, especially during the hot summer months. Rislone make an additive with ZDDP(zinc) that helps with excessive wear on the cylinder walls/pistons/cam lobes etc. My personal oil choice for my FH580V is Valvoline VR1 40w oil that has zinc and friction modifiers. I add a little Rislone during the oil/filter change at every ~35 hours. BTW, this particular Rislone additive is not sold at Walmart. The one they sell does not have ZDDP. I get mine from an auto parts store. Also in my opinion, attentive maintenance is the key to longevity with these engines, no matter the manufacturer. I work on these engines and mower as a side business and I consistently find that the most neglected task is the valve lash check/adjustment. I find that most owners don't know about valve lash check/adjustment. Most use the mower until it either quits running or want start. They ignore symptoms that there is a problem until the mower stops working.