One of the most notorious shortcomings of the BMW M50 family of engines (which includes the S52) is the oil pump. The oil pump is basically the heart of the engine and is responsible for supplying oil throughout the entire engine (from main bearings to valve lifters) to keep the engine operating as it should. Unfortunately, the stock E36 oil pump has two major weaknesses that can effect engines operated in racing environments as well as daily driven vehicles:
- The nut securing the sprocket to the oil pump shaft can back off. Once the nut is off, the sprocket will detach from the shaft.
- The oil pump shaft itself can shear in half
I’m going to address both of those issues with a fully upgraded oil pump that’s unlike anything else in the market that I’ve come across for the M50/S52 engine. I’m going to need my newly built up S52 to survive long-term and an upgraded oil pump will help to ensure that!
First, here’s the stock E36 oil pump which clearly shows the single fastener with nut which secures the sprocket to the shaft. Some kits simply supply a new nut with safety wire (which I actually have on my M50 today). Other people will tack weld the nut to the nose of the shaft to keep the sprocket from coming off.
Parkin Racing Developments (aka PRD) out of South Yorkshire, England, has developed what I believe to be the best solution to the E36 oil pump failure. Basically, they were inspired by the oil pump that Greg Smith Racing (GSR) developed for the E46 M54/M52TU engine family. The two main features of the PRD upgraded oil pump are:
- The sprocket is secured by 4 steel fasteners, not one
- The shaft is precision ground and hardened out of EN24 steel
These two features nearly eliminate the potential of the shaft snapping or of the sprocket coming off. Some oil pump upgrades kits will include a hardened shaft but they still stick with a single fastener to secure the sprocket to the shaft.
In the picture above, you can see the individual fasteners and sprocket unattached to the shaft in the oil pump. PRD also fully rebuilds the oil pumps with all new seals and checks/corrects internal pump tolerances.
Here’s a side-by-side comparison showing the stock oil pump (left) next to the PRD oil pump (right). In this view it’s easy to see how PRD milled the front of the oil pump housing down in order to fit in the new hardened shaft with flange.
Here’s a picture from PRD showing a batch of several newly machined shafts that will be sent out for hardening.
Here’s a close-up view of the back of the flange and shaft, also from the PRD website.
However, PRD goes one step further and includes an oil pump chain tensioner in the kit to take the slack out of the chain when the engine is running. BMW utilizes a chain tensioner on their oil pump chain on many racing engines and even some production engines (S50 Euro and S54 for example) but didn’t include it in the production M50/S52 family.
I’m jumping ahead a bit, but in these two pictures you can see me holding back the installed tensioner (left) and then letting the tensioner place force on the chain (right). It’s pretty clear that there’s a good bit of slack in the chain and I can only imagine what the chain is doing in normal running conditions.
The tensioner is an OEM piece (it appears to be used on Audi S3 engines for oil chain tension) and seems to be very similar plastic (if not the same) to the timing chain guides found of the M50/S52 engine family.
In order to mount the tensioner you actually have to drill two holes in the block (the two red circles) and then tap the larger one. PRD includes a template in their kit but I found that it didn’t actually match the pattern on my block. After moving the template around a little bit, the picture above shows my final placement.
You can see in the picture above that the most crucial thing to hole placement in the block is missing the ribs both to the left and below the two holes.
In the picture above, you can see the block fully drilled/tapped and the tensioner mounting hardware fully in place. I think this would be a little difficult with the engine installed in the car but it was very simple with the block on a rotating stand.
The next step was to make sure the oil pump chain was centered on the tensioner. In the picture above you can see how the chain is too far to the left of the tensioner.
By adding one washer between the tensioner and the block, I was able to get the chain very well centered on the tensioner. Much better!
The next step is getting the actual oil pump mounted on the block. Unfortunately, the PRD upgraded oil pump didn’t simply bolt in place of my stock oil pump. After talking with the experts at Seems Legit Garage (where I purchased the PRD oil pump), I learned that the M50 family of engine blocks changed through the years and this issue is fairly common.
You can see in the pictures above that the issue is with the rear mounting location.
Fortunately, there’s plenty of extra material on the oil pump mounting location that you can simply drill it out to a bigger size. I secured the PRD oil pump on my drill press (pretty tricky!) and was able to remove the necessary aluminum to allow it to mount properly.
I’ll feel a lot better when racing my E36 knowing that the PRD upgraded oil pump is humming away on my S52! A crucial upgrade in my opinion.