Beisan Systems has launched an S54 exhaust sprocket hub product.
The Beisan exhaust hub is a replica of the BMW exhaust hub, but incorporates a thicker wall and tabs and a black finish instead of a green finish.
The BMW exhaust hub tabs can break and a replacement hub is needed.
BMW only provides the exhaust hub as part of a complete exhaust sprocket components kit, and thus the hub is expensive.
The Beisan exhaust hub is provided as a separate part and is thus less expensive and a cost effective solution for a replacement exhaust hub.
The exhaust hub is easily installed during the Beisan vanos repairs. Its installation is documented in the Beisan S54 Vanos Rattle Procedure.
The Beisan S54 Exhaust Sprocket Hub cost is $400.
The following is a discussion of the exhaust hub failure, engineering solution considerations, Beisan oil pump disk and exhaust hub solutions, and Beisan hub testing and results.
The BMW S54 exhaust sprocket hub has two tabs that insert into the vanos oil pump disk face holes and rotate the vanos oil pump to provide vanos high oil pressure. The high oil pressure facilitates rapid vanos actuation for precise VVT positioning.
Unfortunately the hub tabs to vanos oil pump disk holes fit is loose and has 1mm play (space).
The hub and vanos disk rotate at differing rotational harmonics (cycle speeds). These differing rotational movements resonate at certain RPMs and due to the excessive fit play allow hitting and often rattling. The rattling usually occurs at ~2,800 RPM.
The hub tabs fatigue over time from the impacts and eventually break.
The solution for the breaking hub tabs is to reduce the play between the hub tabs and vanos oil pump disk holes. This reduces the travel of the hub tabs within the oil pump disk holes and thus reduces the hitting impact forces.
Beisan provides an S54 vanos oil pump disk product with smaller face holes that reduce the play between the exhaust hub tabs and disk holes from 1mm to .05mm, a 95% reduction.
The Beisan oil pump disk resolves the exhaust hub tabs to vanos oil pump disk holes rattling and tab breaking.
Since the launch of the Beisan oil pump disk product in 2013, there have been thousands of disk installs with no reports of a broken hub tab after installation.
Most S54 engines don’t have the Beisan oil pump disk installed and thus are susceptible to experience a broken exhaust hub tab.
The Beisan exhaust hub product provides a cost effective replacement for a hub with a broken tab.
The Beisan exhaust hub tabs are thicker than the BMW hub tabs to improve strength.
The Beisan hub tabs are the same width as the BMW hub tabs. Thus the Beisan hub tabs fit the Beisan oil pump disk with smaller holes.
The Beisan exhaust hub should always be installed with a new Beisan oil pump disk.
Used oil pump disks have indentations in the holes sides from embedding exhaust hub tabs. Due to the increased width of the Beisan hub tabs, new non-indented disk holes are best for allowing proper tab matting and embedding in the disk hole sides.
The Beisan exhaust hub is a combination design of two versions of the BMW exhaust hub.
A small number of early production S54 engines have an initial version of the BMW exhaust hub (pic left hub).
BMW redesigned the original exhaust hub, and the new version (pic right hub) is the one found on most S54 engines and is provided as a BMW part.
The primary difference between the BMW original hub version and the BMW new version is the thickness and taper of the hub wall and wall base curve.
BMW increased the taper (angle) of the hub wall, thus thinning it, and deepened the wall base curve (scoop), thus also thinning it. These changes were likely made to ease the release of the hub from the forging die it’s formed in.
The tapering and thinning of the hub wall implicitly caused the thinning of the hub tabs. This can be visually denoted between the two hub versions (pic).
BMW also made multiple small dimensional changes in the new hub design. The most visually apparent (pic) of the changes is the reduction of the mounting holes dimeter to provide a tighter fit with the mounting bolts.
The Beisan exhaust hub incorporates the thicker wall and wall base curve of the original hub version, and the improved dimensional features of the new hub version.
Due to the less tapered thicker wall design, the Beisan hub tabs are the same thickness as the BMW original hub version tabs, and thus are notably thicker than the BNW new hub version tabs.
The Beisan hub and BMW hub are both made from 4140 steel, through hardened to the same hardness and structure, and FNC (Ferritic Nitrocarburizing) surface heat treated.
The Beisan exhaust hub differs from the BMW hub in its manufacturing process. The manufacturing process differences are primarily due to manufacturing volumes and the need for appropriate corresponding manufacturing methods for such volumes.
The BMW hub is forged. This is primarily performed to reduce the hub machining time. As a secondary benefit, the hub steel is preferentially compacted and the grain lines follow the form of the hub, and this makes for a stronger hub.
The Beisan hub is manufactured from billet steel. This significantly increases the machining time and complicates the heat treating process. But this also reduces the upfront tooling cost and risk of forging and the need for larger quantities production.
The BMW hub splines are machined using a custom helical broach and hydraulic press. This allows for the cutting of the spline valleys in one broach pass. This technique significantly reduces the part manufacturing cost.
The Beisan hub splines are machined on a specialized gear CNC machine. This technique reduces the upfront cost and risk of broaching, but notably increases the part manufacturing cost.
The BMW hub is FNC surface heat treated in a salt bath. This technique is conducive to large volume manufacturing, and allows for creating a chromium oxide green surface finish that is corrosion resistant.
The Beisan hub is FNC surface heat treated in a gas nitriding furnace. This technique is practical for smaller volume manufacturing, and allows for a post FNC steam process that creates an iron oxide black surface finish that is corrosion resistant.
There are pros and cons to each type of manufacturing process. But if performed correctly, the different manufacturing methods produce effectively the same results.
The Beisan hub was tested on an E46 M3 for 10k miles. After testing, inspection showed no wear on the exhaust hub tabs or helical splines, and minimal indentation in the vanos oil pump disk hole sides.
The Beisan hub was installed in four E46 M3 cars ~10 month back and the owners have reported no issues.
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