S85 rod bearings: what the M5 and M6 actually need

We have grown accustomed to the intense maintenance BMW Motorsport engines require. On the S85 V10 in the E60 and E61 M5 and the E63 and E64 M6, the rod bearings do not last anywhere near as long as they do in a standard 5 or 6 Series engine.

The good news is that the labour to replace them on this V10 is straightforward, which is why we offer it as a service. The better news is that there are three other things worth doing while the engine is open, and two of them are problems most owners never hear about.

When to do it

This is preventative maintenance, not a repair you wait for. Do it at your next oil change interval, and then every 60,000 to 100,000 miles.

If you are wondering whether to inspect first and decide afterwards, see the questions at the end of this page — the short version is that inspection gets you most of the way to the cost of doing the job.

The bearings: custom clearance, not off the shelf

We use a custom-sized ACL rod bearing set.

Standard bearings run a little tight for our liking, so we worked directly with ACL to develop a solution that produces the rod bearing clearance we want to see. It is not a catalogue part we resell — it exists because we asked for it.

It is also economical. The clearance is similar to other options on the market, at a lower price point, without giving up quality. If you want the wider comparison between the options, we wrote that up separately: which rod bearings to use for the S65 and S85 — WPC, BE, or ACL.

Rod bolts: stock or Carrillo

We have found the Carrillo WMC bolt for the S65 rod to be a good aftermarket replacement for this rod as well. But it needs care, and here is why.

On this rod you cannot measure rod bolt stretch the way you normally would on another engine or on an aftermarket rod. That removes the check most engine builders rely on. So we determined the correct torque procedure ourselves, through careful in-house measurement, specifically to find the procedure that does not distort the roundness of the big end bore. Torque a bolt wrong here and you have an out-of-round bearing surface, which is a far worse outcome than the bearings you were replacing.

The interesting part: the stock bolt is at yield at the torque figure BMW specifies for this rod. The Carrillo sits well within its stretch specification, which means it can be reused next time the job is done.

That said — we will be straight with you. The stock rod bolts have not been failing in these engines, and they are economical. We stock those too, and they are the more popular choice for this service. The Carrillo is an option, not a requirement.

The VANOS oil line almost nobody finds

This is the one worth reading twice.

The S85 has a high pressure VANOS line that runs inside the engine. It can develop a leak, and because the leak is internal it is almost undetectable — nothing drips, nothing shows on the floor. What it does is quietly reduce your oil pressure.

On an engine that is already hard on its rod bearings, losing oil pressure to an invisible leak is exactly the wrong problem to have.

So when we are doing rod bearing work we typically remove the VANOS oil pump and replace that line as a matter of course. Reinstalling the pump requires setting the valve lash on the VANOS oil pump gear, which is why it is sensible to do during a job where the engine is already apart rather than as a standalone visit.

While we are in there

Two more things, both of which cost very little extra at this point and a lot more later.

Engine mounts. They are extremely easy to access with the engine opened up. If yours have not been replaced recently, this is when to do it.

The oil pan. We very commonly find that S85 oil pans have taken abuse over the years and had their drain plug threads stripped, partially or completely. With the pan off the car, we mount it on our in-house mill, resurface the sealing face, and then drill, tap and Heli-Coil or Time-Sert the drain.

Doing it on the mill rather than by hand is the whole point: it ensures the drain plug ends up perfectly flush with the sealing surface, so it will not leak in future. A drain repaired at an angle with a hand tap is a leak waiting to happen.

Common questions

Should I have them inspected first, then decide?

Honestly — if you are going to pay to have them checked, you are already halfway to having them done. The labour to get to the bearings is the labour. It is more cost effective to simply replace them.

If you want some idea of what is going on in there before committing, a cheaper first step is an oil change with an oil sample sent for a Blackstone report. That will tell you something without opening the engine. We can help with that.

Can I fit something stronger while it is apart?

Yes. There are upgrade options — OEM BMW rod bearings with the WPC surface treatment, or BE Bearings. We cover the trade-offs between those and our ACL setup in the rod bearing comparison.

What does it cost?

We price parts at the time of the job rather than publishing a figure, because parts pricing genuinely moves — WPC-treated bearing pricing, for one, has jumped sharply at times. Send us a quote request and we will give you a current number for your car.

Related reading

• Which rod bearings for the S65 and S85: WPC, BE or ACL — the comparison, if you are choosing.
• S65 rod bearing service — the V8 sibling in the E90, E92 and E93 M3.
• The S54 rod bearing problem — the same failure on the straight six, and what we did about it.

Book it

Tell us the car, the mileage and whether the bearings have ever been done. Send us a quote request or call (949) 667-4397.

Daily-driver European service — BMW, Mercedes-Benz, Audi, Porsche, Volkswagen & MINI — is handled by our sister shop, Pinnacle Auto Repair.