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Arthur: MJB gave you good advice on the flywheel knock. The 820/30 attachment uses two keys in lieu of crankshaft splines, which I always thought was a superior method as compared to the 70/720/730 models. Look for signs of metal power around the crank/flywheel juncture, and oil and grease that is slung outward indicating movement. Checking the crank endplay can tell you if you have a thrust washer that has disintegrated, and that VERY excessive endplay can lead to a knock. Sometimes the endplay makes a knock on the pulley end, so check for a loose clutch driver as well. Listen to the diesel carefully. You will have two knocking sounds that are correct. One is in the cylinders and the other is the grunt of the pumps, and that sounds more like a "Crack!" than a knock, at least to me, when it is working right and on time. You might need to spiff up the timing to met these sounds back. Then there is always the knock caused by loose main beaings, rod bearings, and piston wrist pin slap. These things can be more likely if your engine has a lot of time on it after the last overhaul, especially if the pin bushings and/or pistons were not measured and if needed, replaced, at the last overhaul. There are a lot of "overhauls" where the rebuilder doesn't even measure the pins and slop, or replace the the bushings, puts rings in worn out grooves, not grind the crank, leave the pumps untouched, not rebore, only grinding the valves and installing rings and calling it overhauled. We used to call that a ring job. Not saying that that is the case for you, but I mention for the prospective "overhaulers-to-be" out there. So, check the crank endplay, then the flywheel tightness (since you might have to loosen it to reset the endplay), then the clutch driver, then the pump timing, and that's about it from my worthless-toolbox-of-two-cylinder-diesel-knowledge. Good luck.
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