Some may remember I have had a few problems with my engine, after having a lower bearing fail on the rear cylinder con rod, I rebuilt the engine and everything was fine until the oil light started flashing on idle, so I fitted an oil pressure gauge and it showed the oil pressure rising and falling, on idle it fell to zero, after trying a few different oil viscosity's (I just didn't want to take the engine out again so soon) a thicker oil seemed to improve the oil pressure but the pressure was still rising and falling, so after many posts on here and much thinking I tried overfilling the engine with oil and adding an extra litre of oil the pressure stabilized so I had her tested for road use and began using her again, but over time I decided I need to sort this properly so out came the engine again. You may remember Cf Moto don't make oversize bearings for the crank but my local engineering shop found out that a certain model Toyota had the same size shell bearing so an over size set were ordered and the crank reground to fit, I had been convinced there was a part missing from the oil pick up on mine and had settled on finding this part missing, I thought I would buy the part and all would be fixed but when striping the engine I found nothing wrong, so looking at the crank the bearings seemed to loose I thought this is were I'm loosing some oil pressure, when I had another shop measure the crank they said it not the best regrind but it would not cause rising and falling oil pressure. so looking at all the parts for a few days and much head scratching I had a idea, when I removed the sump filter screen it had some build up of plastic in one corner which is directly under the passage to the oil pump, as the filter screen is flexible and the oil pick up is only about 5mm from the screen I think this is what's causing my oil to rise and fall, as the blocked part of the filter screen is drawn up by the flow of oil and sealing off the pick up port and as flow has stopped the screen springs back opening the port, I'm now fairly happy that's what's going on, the next question where did all the plastic bits come from and it turns out one of the original cam chain guides was wearing badly (the new ones I have are much thicker and seem to be made of different plastic)the plastic in the screen was from the chain guide, so that's the oil fluctuating sussed out, next was the low oil pressure. The bad crank grind was a factor in the low oil pressure but not the whole story, I have ordered a new crank and bit's from Mortch but they didn't sell all of the parts I needed so the other parts were ordered from a Uk dealer, back when I rebuilt the engine the first time I ordered crank shaft main bearings from Mortch who listed bearing with the red mark for crank shaft marked with a B, Mortch no longer sell these bearings so they were ordered form a Uk dealer for crank B and when they arrived they have a blue mark ?? I'm going to get the red and blue bearing measured but I wonder if the red bearings are too small and with the loose regrind on the crank lower end, I do wonder if this is were the oil pressure is being lost, hopefully the next few days will give me the answer, so it's seems bad luck may have had a part to play in my engine problems