Tractor has a oil light but no pressure gauge. Oil is filled a beyond the dip stick level. I took oil pan off and cleaned the suction screen (Suction screen wasn't clogged but I cleaned it anyway). Cranked 30 second no oil. I removed and cleaned the oil valve behind the filter. Cranked again with decompression engaged. No oil. I then removed the oil valve behind the filter and cranked it without it or the filter on no oil. Took off the oil inlet pipe crank a little still no oil. Sounds like I have a oil pump problem. I have never tackled a oil pump any advice or cautions? Thanks Dan