The last documented UOA of my E34S M5 was performed in September 2015 at 191568km. This UOA already demonstrated elevated wear levels of copper, iron and lead, which pointed towards bearing wear.
Originally, it was planned to replace the conrod bearings in the winter of 2015/2016, however two other car related projects came in between due to which this was postponed to the winter of 2016 and 2017. In the past few months, we took on this project and replaced not only the conrod bearings, but (purely as a preventive measure) the oil pump as well.
When performing the engine rebuild of the M88/3 engine of my E28S M5, I paid less than 10 Euro for a single bearing shell. However that was in 2009. Nowadays in 2017, their retail price has more than tripled.
After some time being out of stock, BMW supplies the ‘short-type’ oil pump again, however these retail at over 500 Euro ex VAT nowadays, but bear in mind that this is a mission-critical part and a single point of failure as well so from that point of view, it is imperative to replace the old pump.
After removing the sump, the oil pump and the crankshaft became visible to the full extent for the first time in twenty-seven years. As can be seen, the bottom end has that nice brown varnish colour; the engine is completely free of insoluble and/or sludge, which is a clear testimony if regular and short term oil changes with high quality engine oil, at least during my watch (since April 1999).
From the historical documentation, it appears as if BK02837 was not given frequent oil changes during its first four years. This is however unlikely as she was then in the inventory of a BMW main service agent in Switzerland and not registered for the first time until June 1994. Given this status, it is very unlikely that in between the first service by Roseg in Pontresina and the first delivery in 1994, no oil changes were performed.
Even though some wear was expected after 195655 kilometres, the extend of which cannot be determined (and documented) without performing a visual inspection. If one takes a closer look to some of them, spot wear down to the steel substrate can be seen
The journals for the conrod of cylinders #1 and #3 showed some scoring marks. Fortunately, the scoring could not be felt and a light polish made them disappear.
Upon disassembly of the original oil-pump, only mild level of wear to its moving parts was observed. Based on its condition, it was perfectly defendable to reuse the old pump, however (1) from a risk management perspective and (2) the current market developments for E34S M5’s in good to excellent condition maintaining the old pump would have been the wrong decision, so it had to be replaced.
The outer rotor showed some scoring, which is normal for these (eaton) type of oil pumps because te pump is situated in between the sump and the filter and thus is subject to unfiltered oil from te sump and thus prone to elements of engine wear and dirt.
The short summary is that any well maintained S38B36 can suffer from conrod bearing wear. In my particular case, I think the engine would have lasted no more than 10k kilometres without dropping a rod. Granted, this particular engine saw some appropriate use during the 94016 kilometres that I have added since April 1999. Using a different type of oil would certainly not have delayed the bearing wear. On the contrary, using a low-weight oil would only have accelerated the bearing wear during the more stressful driving conditions (at least 50% of my kilometres).