The S55 inline six used in M-Series cars from 2015 – 2020 is a beast of an engine. Producing upwards of 425hp in stock form, it can deliver even more. If you’re looking to make some performance upgrades though, it’s important you attend to the one weak point of this motor, the crank hub.
This blog post will take you through some upgrades we recently made to a customer’s car, and we’ll explain the crank hub fix in some detail. Let’s start with the performance upgrades, then we’ll explain what the crank hub is, what goes wrong with it, and why this is a more complex BMW repair.
Breathing Upgrades
One way of making more power and torque is to improve engine breathing. If it can draw more air in, and there’s less back pressure in the exhaust, the engine will respond faster and produce more power.
On the intake side, a cold air intake and charge pipes let the turbos pump more, and colder, air. These are a relatively easy replacement for the stock items, and they’re accessed from under the hood.
For the exhaust we installed new downpipes and a new exhaust system. By reducing back pressure this helps get the exhaust gases out faster and means less resistance to the piston moving up in the cylinder. Exhaust work is done with the car in the air. Other than removing and replacing various covers, it’s not a particularly difficult job.
The Crank Hub Problem
The two camshafts are driven by a chain that goes around a sprocket at the front of the crankshaft. In the S55 engine there are two sprockets mounted to a hub that installs on the front of the crank. (The second one drives the oil pump.)
The way the engine was designed, if it’s driven hard there’s a possibility of the timing sprocket slipping. If you’re lucky and get just a little slip it results in an engine timing problem that’s easily fixed. If there’s more slip the timing can go so far out that the pistons hit the valves. This is a very costly BMW repair and one you definitely want to avoid.
Clearly, if you modify the engine to make more power the chances of this happening increase. That’s why, if you’re making performance upgrades we strongly recommend installing the new design of crank hub. This incorporates pins that eliminate the risk of slip by keying the sprocket to the hub.
Making the Crank Hub Fix
The front of the crankshaft is reached from underneath the car. To get at it you first remove all the covers and then the subframe. Taking that off means supporting the engine from above. Then you can drain the oil, drop the sump pan and reach the front of the crank.
However, working from the top, you also need to take out the timing chain tensioner and lift the chain off the camshaft sprockets. Getting to that entails removing the valve cover, which in turn means removing the fuel rail and all the intake equipment.
In short, this is a big job that takes a lot of time. Unless you have a lot of experience wrenching on your BMW you might want to entrust your M car to a BMW specialty shop.
Trust Us With Your BMW Work
If you need BMW repairs or are looking for some performance upgrades, the EurAuto shop in Plano TX. Can help. Our technicians are very experienced and we promise they’ll do a quality job. Call (214) 552-4194 or make an appointment today.
