BMW E34 engine overhaul: what to replace and what to measure
What needs to be replaced or measured in an E34 engine overhaul?
On the M30, the piston rings should always be replaced and the ring grooves cleaned. Wear of the cylinders and pistons must be measured: if the clearance of the top ring in its groove is within the reference value, the pistons or cylinders do not need to be touched. Worn or scored main bearings are renewed.
When is the oil pump replaced and is it worth grinding the crankshaft journal?
The pump is replaced when it does not hold pressure at low revs. An oil pressure fault is often caused by something else, for example a loose banjo bolt or loose bearings. Grinding the journal without nitriding is a short-term repair; an intact crankshaft from a scrapped car is usually better.
Do valve stem seals cause oil consumption and smoking?
The seals do not usually cause them themselves; the fault is more often worn valve guides. The exhaust-side guides wear faster than the intake side. The valves are reassembled in their original positions if they are not lapped.
Can a leaking valve cover gasket cause uneven running?
Yes. An aged gasket can leak oil into the spark plug wells, and the oil can destroy the ignition coils. The repair is cleaning the oil out of the wells and renewing the gasket. On the M50, gasket sealant is used only between the semicircular piece at the front of the cover and the valve cover gasket.