The short version
- The S55's factory rod bearings last very well. When we've changed them, we've been surprised how little wear there is.
- We'd recommend them on an S55 from around 100,000 miles, compared with 60,000 on the S65 and S85.
- We fit ACL bearings and ARP rod bolts, usually alongside a crank hub upgrade.
- S55 rod bearings are priced on application.
Rod bearings are the job we're best known for. Most of that reputation comes from the S65 V8 in the E9x M3 and the S85 V10 in the E6x M5 and M6, where bearing wear is a well-known weak point. Owners of the newer S55 understandably ask: does mine need them too?
What rod bearings do
Each connecting rod runs on a pair of thin bearing shells around the crankshaft. A film of oil keeps the rod and crank apart. When the shells wear through, that oil film breaks down, metal touches metal, and in the worst case a bearing spins or a rod fails. That's an engine replacement, not a repair.
What we actually find inside S55s
The S65 and S85 are high-revving, naturally aspirated engines, and they wear their bearings in a way that's well documented. The S55 is a different design: turbocharged and lower revving, and it doesn't share that reputation.
Our own experience backs that up. We generally see excellent longevity from the S55's factory shells, and on the cars where we have changed them, we've been surprised at how little wear there was.
When we'd recommend them on an S55
On mileage, we'd recommend rod bearings on an S55 from around 100,000 miles. That's significantly later than the S65 and S85, where we recommend them at around 60,000 miles.
Below that, they can still make sense on:
- Tuned cars, especially with bigger turbos, where the bottom end is working much harder than standard.
- Regular track use, where sustained high load and oil temperature take their toll.
- Cars with a patchy history, where you don't know how the oil has been looked after.
- Cars in for a crank hub upgrade, as much of the work overlaps.
How we do the job
On the S55 we fit ACL bearings, as we do on every other engine, with ARP rod bolts. Clearances are checked where appropriate. Every old shell and bolt is laid out by position and photographed, you get pictures as the work goes on, and every old part is kept for you to look at when you collect the car.
On an S55, we usually do the bearings at the same time as a crank hub upgrade, which is the more common risk on this engine.
Prices
S55 rod bearings are priced on application, as the job depends on the car and what else is being done. For comparison, S65 rod bearings on the E9x M3 are from £1,749 including VAT. We'll always confirm the price for your car before any work starts.
