Starter grinding timing conundrum

have you tried taking 3 plugs out the three taking out put leads back on plugs earth them down then turn over to try to start it if no kicking back move plug to next cylinder and try that do this until you have tried all cylinders this may which cylinder is causing problem after checking tappets measure the amount each valve opens in case you have a cam lobe going flat also turn engine over by hand till roter arm starts to move then turn engine backwords to se how much movement there is befor points move