A six cylinder four stroke vertical inline engine has a firing order 1-4-5-2-3-6. Firing take place with equal angular interval. The mass of reciprocating parts per cylinder is 2.5 kg, stroke 100 mm and connecting rod length 200 mm. The cylinder centre lines are spaced at 300 mm apart. The crank shaft speed is 300 rpm. Examine the engine for the balance of primary and secondary forces and couples. If the engine is not completely balanced, suggest a suitable firing order to make it complete balance