S65 Engine Bearings…

E9x M3 S65 V8 Rod and Main Bearings

Rod bearing failure! Oh no my S65 has just spun a rod bearing and it only has 60,000kms. Surely this is a manufacturing problem right? Wrong.

There is are MANY topics and discussions floating around the internet about the infamous E92 M3’s S65 engine spinning rod bearings. How and why does this happen? Well…we need to start by looking at what the S65 V8 engine is, and how it was built. The S65 is a masterpiece of German engineering, and is completely misunderstood. Lets start by talking about the specs of the engine, and what makes it so special. It has been built with very refined machine work and equally tight clearances. Bore finish, crank material and light weight components all add up to the right conditions for this engine to spin up to 8200rpm stock. This is the sort of thing we expect from a 1.6L small Honda engine, not a larger V8 engine. Built back in 2007 and at a small capacity of just 3998cc, this engine puts out more HP than a 2014 6.0L LS V8 engine for 1 comparison. Quad cam, 32 valves per cylinder, CNC ported heads, the bearings also only offering a mandatory 1 thousandth of an inch of clearance around the crank and its rotating accomplices, being the block and con rods.

For all this to work harmoniously, we need to have the correct ‘acute’ oil conditions required for things to stay at the correct friction and heat levels, aswell as correct oil flow. Sure, there is a recommended oil viscosity of 10w60. This is only 1 of the items on the list to ensure the above conditions are met. Warming oil up and making sure the temps are correct before leaning on the throttle pedal are also critical. Another thing that takes the correct conditions away from these engines is rapidly degrading oil quality. Each time you start the engine fuel enrichment causes excess fuel to go into the engine oil. and when the engine cools it can often draw water condensation into the oil. This means the engine would need to run long enough each drive to give the oil a chance to boil off the excess water and fuel that is making its way in.

So what can you do get the most out of your S65 engine? We suggest changing your oil every 3 months or 5000kms. If you do a track day it should be changed before and after the event. It is also highly recommended to not let your engine get past 60,000kms without changing the rod and main bearings. During this process you should measure your bearing clearances to ensure you achieve a 2 thousandths per inch clearance for both rod and mains. This will give a larger buffer for oil conditions being a slightly outside of perfect, and will also offer a harder wearing bearing to take more of a beating before they degenerate and come apart into your engine oil (copper flakes and glitter).