BMW S55 Engine Crankshaft Hub

  • X55 HUB

Project Description

OBJECTIVE: To design a crankshaft hub for the BMW S55 engine which will prevent engine failure at higher horsepower levels than the factory design. The factory engines are reportedly failing at 500hp.

PRELIMINARY ANALYSIS: The factory Crankshaft hub is multiple pieces. The sprocket that drives the camshafts is slipped onto the hub along with the oil pump sprocket. The 2 sprockets are sandwiched against the hub and the outer face of the crankshaft. The assembly is held onto the crankshaft with 1 stretch hex bolt. There is no key of any kind to prevent slippage.

FIRST APPROACH: To make a stronger bolt that will hold the assembly tighter and raise the failure point. Also to remake the hub one piece with the camshaft sprocket.  After consulting with the top automotive racing fastener manufacturer, I decided to make the bolt out of 8740 steel. I machined the blanks myself, sent them out to get heat treated, ground, threaded and zinc coated. As for the hub, I decided to go with 8620 steel. I had to reverse engineer the piece including the sprocket profile. I machine the hub blank on the lathe. Since I was only making a few test pieces, I chose to machine the sprocket teeth myself. The sprocket teeth were then induction hardened and then the entire hubs were zinc coated.

RESULTS: The test bolts were tested with stock hubs on a few modified engines and did hold up well. The hub and bolt were installed on a high horsepower engine. They eventually failed.

SECOND APPROACH: I decided to remake the entire hub including the 2 sprockets 1 piece and incorporate a key. I went with 8620 once again. This time I added a key at the tip of the hub where it engages into the crankshaft. I had to make a drill tool to drill a keyway into crankshaft in the correct place. After the hub blanks were machined, I took them to Gerhardt Gear in burbank to cut the sprocket teeth. Since the new design featured 2 sprockets fairly close to each other, I was unable to mill them. I am now awaiting the new hubs to be returned so that I can send them to get heat treated and then zinc coated.

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