The brief
Mr Clarence's 520i had picked up a vibration, worst on cold start and still there while driving, so he brought it in. A vibration like that, especially noticeable cold, usually means the mounts that hold the engine and gearbox have given up. And with the battery getting on for five years, that was worth dealing with in the same visit. The engine and gearbox sit on rubber mounts that carry their weight and soak up the shake, keeping it out of the cabin. As the rubber ages it sags and cracks, and once it does the drivetrain moves around more than it should, so the vibration comes straight through, worst when the engine's cold and lumpy on start-up. Sagged mounts don't recover, so they get changed as a set. The battery, near five years, is about when they fail, so renewing it now beats a no-start later, and a new BMW battery needs registering to the car.
The diagnosis
On the lift each mount got a pry-test. The engine mount had sunk and the gearbox mount was worn, the play obvious under load, which is the vibration on cold start and on the move. The battery, at close to five years, was on borrowed time. The rest of the car was sound. So it was an engine and gearbox mount replacement as a set, plus a new battery with registration, the vibration fixed and the battery sorted before it caused trouble.
The work
The engine and gearbox were taken onto transmission jacks to carry their weight, the sagged engine mount and the worn gearbox mount removed, and new genuine BMW-spec mounts fitted, every fastener torqued to the manual figures and the drivetrain checked sitting square. The old battery was removed and a new genuine BMW battery of the correct type fitted, then registered to the car's power management so the charging strategy is set for a fresh battery. A road test confirmed a smooth cold start, no vibration on the move, the battery holding charge, and no warning lights.
The outcome
A smooth cold start, no vibration through the cabin, no clunk on shifts or over bumps, a fresh battery properly registered, and no warning lights. Mr Clarence got the 520i back smooth again and the battery sorted before it left him stuck. Doing the mounts as a set resets the drivetrain's refinement, and renewing the ageing battery now is far less hassle than a no-start later.
