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nothing to mark on the plastic no engraving. The tensioner is ok a redessassemble it for check it a pictur effect
History of the bike. I bought the 1300 from a museum in Terrebonne, Quebec, a museum of motorcycles. She had been there for two years with oil and prestone in. the man who sold the bike to the museum claims to have rebuild the engine back from a pro kawa 6. bring it back home, I cleaned carburetor and change the fluid. and it starts like a new one no valve or crank noise nothing.last Summer I haved not been able to ride bike as I want, haved some break leak, master cylinder problem,carb,fire on 2 and 5 cyl speedo has broken twice and now all that work has been done. that noise occurs. I do not know what work was done before in the engine. See nothing yet I'm now investigate

0h, so it is plastic after all? For sure a riddle that can't be ignored since obviously it's not just some little flake. And the amount of metal you found is huge. It came from somewhere and it wouldn't make me feel comfortable at all! It's also very interesting how smooth and quiet the bike ran otherwise, with this noise happening randomly.
Something definitely got ground.

Again - what area of the engine do you think the noise was coming from?

Could you post a picture of the back side of the half moon circular piece of debris and also a side view of the piece so we can see how thick it is and if it is flat or has a slight curve to it?
Thanks

Hi Kawboy and everyone, thank you for your interest. the half moon is hard but malleable plastics or rubber like 2,5 mm thick. I do not see any metal with this one, but many in my fist oil change. Clutch disassemble stator and all the cover that goes on, nothing has suspected, oil pump to. Casing is beautiful everywhere I see and parts in perfect condition. my dad have a 1300 79 and wanted to hear the sound. So the next day of that noise poping we restart it and wow there no sound at all we let it heat and run marvelous, redone the oil change and the oil was good no aluminum or metal in.I am at the point where I wonder if the previous owner has not forgotten something in or something minor and if I go back put it together fingers crossed while praying for a road test and oil change again?? What do think?

The only thing I can think of is the water pump mechanical seal. But I can't see how it would enter the oil and the engine!... Hmmm......
Unless the oil seal was gone as well, but then you'd have coolant in the oil and oil in the coolant.

Yet there were noises so something was grinding, and this plastic and the metal were the outcome. 0r maybe the reason? Can you think of anyone dropping 'something' into the engine? Maybe by accident and didn't bother to let you know?

So, one possibility would be this is a part of a piece that stayed out of trouble except when it did happen to be in the wrong place. Got chewed up making noises and finally all the pieces fished out when you removed the oil pan. And it does remind me to be a part of the mechanical seal.

You came this far so I'd remove the side covers and check on things regardless. If you find nothing, I'd probably put the bike together, fill with fresh oil, let it run and see what happens. I can't think of anything else at the moment.

If I were in your situation, I would want to know what the piece of debris was and where it came from before running the bike. At this point I would call the previous owner and ask for some history on the repairs the bike had in the past. That might clue you in to what's going on. I personally am not one for crossing my fingers and hoping for the best.

Let us know how you make out please.