If your CB 750 engine makes a rattling noise in the lower part of the case, you may have a bad primary chain tensioner. You can check it by removing the oil pan while the engine is still in the bike.
To replace the tensioner, you must remove the engine from the motorcycle and split the case.
Torque the smaller 6mm bolts to 7ft-lb or 9Nm
Torque the bigger 8mm tolts to 18ft-lb or 24Nm
0:00 intro
0:39 split the engine case
1:05 replacing the tensioner
1:38 clean and re-seal the case
2:44 close the engine case
3:26 install the bolts
4:20 torque the bolts
5:07 conclusion