fe570 lower oil screen DOH!

The oil pump draws oil from the sump directly through the lower screen so, in effect, it acts like a 'magnet' for any non metallic rubbish in the sump. Anything small enough to get through the screen will be trapped by the filter. If the lower screen became clogged to the point that it seriously restricted oil flow then you could get oil starvation and parts of the engine could suffer, typically the top end first and then main bearings if the blockage was severe enough. In addition to cleaning the lower mesh filter I'd check and clean the upper one in the oil pipe from the head although, intheory at least, any debris shouldn't reach the head.

As regards any damage your engine has suffered only a complete strip down would tell you for definate. You could remove the tappet cover and look for any obviuos scoring etc. but if it's still running OK with no abnormal noises then I'd just give it fresh oil and a new filter (after the screen cleaning) and use as normal and maybe check the oil screen again after a few hours use.

FYI I would stop using silicone gasket sealant, that stuff will squeeze out, get hard and then plug the oiling system.

Loctite 515 or 518 is much better, it's an anaerobic sealant. If some gets into the oil, it just stays liquid and mixes with the oil. Next oil change you flush it out.

MrX: I did a full engine rebuild, and after running the rebuilt engine for an hour and extra noise started coming from valve cover area. Opened valve cover, the left side intake rocker arm had no oil, it had been running so hot that it had burned all the oil from rocker arm surface. Other areas of the valve cover and valve mechanism were oily as they are supposed to be. Shim's surface was destroyed and rocker arm's counter-surface also. Valve gap was over 0.2mm, and it was in spec when the engine was rebuild an hour earlier. Then I drained the engine oil, it looked fresh. Oil screen next to oil plug was covered, not totally but seriously with mainly little fibres and some tiny debris size of a fly's dumb that I believe must have come from the rebuild process despite blowing the parts with compressed air and despite good general "hygiene" when working with the parts. I didn't use any dirty rags or paper like toilet paper that flints but good solid "woven" paper with long fibres but obviously I should have chosen the materials even more carefully. A lesson learnt. The screen in valve cover was totally clean, also main oil filter looked totally clean. I put in new shim, new rocker arm and then refilled with fresh oil. Ran the engine for a few minutes, then drained the oil checked both screens which were totally clean this time. Also measured oil pressure as specified in the manual and it was in spec, 1.5-1.9 on idle. Ordered an oil pressure alarm sensor so this won't happen again, hopefully, for a reason or an another.

Try using Loctite 5910 as specified in manual for assembling case halves. The gasketing material used by the factory when assembling the engine had not become brittle, it was elastic as it should and relatively hard to remove from the case sealing surfaces so I suppose it is good for this purpose.