S54 Exhaust Hub Inspection
By now just about every single E46 M3 owner out there has either heard of or experienced a broken exhaust hub, but if you're a new M3 owner you may not have had the pleasure of dealing with this all-too-common problem, so we would like to address a few questions we frequently receive about the S54 'Exhaust Hub'.
For starters, the name is a bit misleading. It really has nothing to do with the exhaust system, but gets the name from the fact that the hub is mounted to the exhaust camshaft. There is a hub on the intake cam as well, but only the exhaust side hub has the failure-prone tabs. The tabs on the hub fit into a (nearly) matching set of holes in an oil pump on the back of the Vanos (aka, Vanos oil pump disc) and as the camshaft spins, the hub in-turn spins the vanos oil pump, building pressure within the vanos unit to around 1200psi.
The reason that the tabs fail is due to the oversized holes in the oil pump. The holes are just a couple mm larger than the tabs, so the tabs are constantly banging back and forth inside the holes as you accelerate and decelerate the engine, until eventually one or both of tabs snap off. Now here's the dilemma. When only one tab fails the other tab is still turning the oil pump, making 1200psi and the vanos is happily oblivious to the failure, but that broken tab is now lodged in the spinning disc and is prone to falling out at the worst time (is there a good time?) and potentially damaging the engine. This is why it's important to check your hub even if you don't have any vanos issues. You don't want to wait for a failure! The tabs can be checked fairly easily by removing the valve cover and physically looking at them.
Let's be honest here. Just address the problem now before it's too late. If you're on a budget you could just have the oil pump disc modified with smaller holes and that will buy you some piece of mind. We can drill your oil pump disc for you for $150 and turn it around the same day.
A better solution would be to replace the hub with something more durable in addition to the modified pump disc. Combining the two upgrades will allow you to abuse your M3 without fear of retribution.
We offer 2 solutions for replacing your weak exhaust hub. First is our Cryo Hub. The Cryo Hub a is brand new hub that has been cryogenically treated (duh). Now, without getting all technical, Cryo treatment makes the hub 30% stronger than stock, and that's really all you need to know! :) Second is our D300 Hub. These are the used and broken hubs that we buy back from you when you purchase a modified hub from us. We take these and have them machined down, then oversized tabs are welded on. Both hubs are equally good options. Collectively we have about a gazillion miles on them without a single reported failure!
So, If you have Vanos fault codes along with poor performance and misfires on all cylinders, then you probably have a broken hub, but even if you don't have any fault codes at all.... check your hub ASAP!