It does not compress air. I checked the belt tightness ok. Oil level is good.

Hi,
Symptoms of a bad or failing Engine Oil Pressure Sensor

• Oil Pressure Light comes on, and you check the engine oil level, But oil level is okay, you can blame the false reading on the sensor.
• Oil Pressure Light blinking constantly. This is the normal >check< oil pressure sensor Warning that the sensor is going out.
• If the sensor is giving false readings, Dispite oil level, the sensor could be replaced.

If the Sensor is currently not working, and does not warn you of engine oil level, and oil level gets extremely low, The Engine could burn up/stall due to lack of oil, and may not restart.
Then you could probably blame it on the sensor.
But really would be lack of oil.

Intermittent No Start,
Common causes deal with 3 basic systems/areas of engin

1. Compression, its the build up of air and fuel into the engines cylinders. Then is compressed by the pistons. And is under pressure. FAILURE An Air leak (vacumm leak) will allow pressure to escape.
2. Ignition System, good battery, good relays, wires are not loose or disconnected, good 10volts to starter, 10volts to distributer>gives 20kvolts to spark plugs>has strong spark to ignite compressed air in cylinders. Other sensors need to work. Crankshaft sensor(ccs) Throttle Position Sensor(TPS), +more
3. Air/fuel Ratio, Air Intake Manifold, and Fuel Pressure Sensor *Fuel Injection Pressure Sensor---if car is fuel injected*, air filter is clean and intake manifold hose, Throttle Plate Acuater, Idle Air Contro Valve(IAC). Also vacumm leak cause no start. To much air not enough fuel will cause lean fuel mixter==low power, low idle, no start.......To much fuel not enough air will cause rich fuel mixter==too much fuel could cause engine knock, flooding of engine wet spark plugs, No Start

Scan Vehicle computer for Codes, Places like AutoZone---Discount AutoParts will connect scanner for free, And Code Will say What is wrong with Vehicle,

check the ac compressor mounting bolts for tight the reasoning is that when the ac is off ,the drive belt is relatively loose as the pulley is just an idler but when you engage the ac clutch the belt tightens to drive the compressor and holds the compressor tight against the engine
over heating can be fro head gasket/cracked head---compression test
partially or blocked radiator--replace
low coolant level--check at radiator cap and fill
bad radiator cap--replace
thermostat fault-- check or replace
air lock in coolant system--- bleed air oit
transmission oil overheating putting too much heat in the radiator from the oil cooler (auto trans.)
failed cat converter blocking exhaust--replace
timing --check adjustment

Is this only when releasing the clutch? I assume it runs good other than that? I would check three things first. Compression, spark and fuel. Compression should be at least 50-60 psi. If that's good hook up an inline spark tester and start unit and observe while releasing the clutch, If you loose spark when releasing clutch if probably a safety switch(similar to safety switch on seat that grounds unit out when you get off the seat)
If you have good spark when releasing the clutch and good compression, its probably a clogged carb. This is the route I would take. I hope this helps. Good luck!

I’m happy to assist further over the phone at https://www.6ya.com/expert/layne_0fccff498c319c32

Remove spark plug. Pull rope several times to blow out cylinder. Spray WD 40 in spark plug hole. Pull rope several times. ensure compression is present. Replace spark plug with new one. Spray starting fluid in cylinder before replacing spark plug. Ensure plug wires snaps on tight. Check oil level, fill with 30w oil if required. All mowers have a low oil start cutoff. Clean or replace air filter.

Is there a grease nipple on the air-end? (Screw element) may need a bit of a grease. Otherwise, when you say, the oil level is ok, I guess you mean the needle is in the green? Have a check of the actual level of the oil with a torch, those gauges arnt the most reliable of devices. I always fill these well over the top (to the rim of the filler cap) it will not harm the compressor at all. Sometimes solves the overheating problem. When was the oil last totally replaced? Oil does degrade over time and can cause problems, it should be replaced once per year, or every 2000/4000 hours running time (depending on the grade of the oil)
If this doesnt help, then it may mean that you may have some kind of blockage in the oil lines? Possibly the oil filter? Although you should get a differential pressure fault come up if that were the case.
Is there any excess noise coming from the air-end pulley itself? It may mean that the bearings might be on their way out? Alot less costly than replacing the air-end itself.

Hope these things help a bit

Either air is in system or belt is slipping. Belt may LQQK good, but check to see if it's glazed or contaminated with oil/fluids.

I assume you have an oil pressure guage.If your oil level is normal it is most likely the oil pump,or a loose serpentine belt or tensioner is not doing it's job.Check the belt and tensioner for tightness first since it's the easiest to check.If you pull the tensioner in the opposite direction of the belt side,it should be fairly tough to move.
Good luck! Greg

Spark should be blue and snappy with fresh plug gapped at 0.020. Try putting some fresh fuel mix into the plug hole and try to start--it should pop several times. Does the engine seem to have good compression? If not, remove the muffler and check the piston skirt and cylinder wall for severe scoring. If it is, then the engine has probably be run on straight gasoline or poorly pre-mixed fuel/oil. At the very lean fuel/oil ratios ( 50:1) recommended for today's saws, proper premixing of fresh fuel and a modern synthetic oil made for saw use is imperative plus the fuel container should be vigorously shaken just before each filling. If the compression appears good, then check the fuel filter, air cleaner, and muffler for plugging. Check the fuel lines for any decay or other damage. Make sure the carburetor fasteners are tight. Hope some of this helps!

i use valvoline sae30, and mine doesn;t smoke,
are the rings ok, ie does it bulid up to full pressure in normal time?
just one other thing, these have to be kept level, or they will smoke.

The whining your hearing is the timing belt idler or tensioner pulley. The belt is alittle tight but the whining will stop after a while after you get some miles on it. Try replacing your oil pressure sending unit and see if the light turns off. If not, you'll have to remove the timing covers again and double check your marks. Also, this is a no brainer but I have to ask, is your oil level ok.