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Note I don't mean flushing out the cooling system, I mean the actual block.

I've got an air-cooled Yamaha XS400 engine whose cam shaft sprocket and chain got chewed up. In taking the cam out, I saw you can see right down to the crank (the timing chain is in the middle of this engine between the 2 cylinders). I was thinking it might be good to flush out the engine of any possible metal shards or remnants, pouring liquid in from the top between the cylinders and draining it out the sump plug.

Does anyone know if theres a product or right chemical to do this?

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    If you've got metal shards, it would probably be a better idea to pull the engine apart, check for damage, and most possibly put new bearings in it. You have no idea what damage may have taken place in there without some kind of inspection. You probably also want to change this question ... as it sits, it's a shopping question and will get closed. Maybe you want to know what you should do with it? – Pᴀᴜʟsᴛᴇʀ2 Jun 14 '17 at 23:19
  • I always use Naptha for flushing in this situation, it will not harm seals or other components. Can be bought at the hardware store. Flush it several times (half oil and half naptha) run the engine (idle only) for a 30 seconds with this flush recipe, after draining the last time fill with Only oil and run a few minutes, drain and refill oil. – Moab Jun 19 '17 at 0:35
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You can use a thin oil to flush the system out - something like 3-in-1 or other solvent (like WD40) then you would have to remove those residues which can be done with brake cleaner or carb cleaner.

The thing is though, if your cam sprocket and chain got chewed up you probably want to take everything apart to inspect it anyway. Did the timing jump/skip a tooth and cause damage to the valves, cams, valve seats, piston crowns etc? Only through careful inspection will you be able to tell how serious the "chewing up" was.

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