What is the function of an engine block?
Daniel Becker, Patent Attorney and Early-stage Engineering (2013-present)
This is a curious question. How many people are introduced to the word “engine block,” in a context in which it would not be explained? Well, anyway… The block … is basically the entire engine… less every single thing that does something.
What it does… is a list of many things. Structurally, it’s core job is to ensure the relative spatial constraints of the crankshaft and the reciprocating components.
The block is primarily composed on the bank (s) of cylinders and the upper part of the crankcase.
The pistons must move coaxially with the axis of the cylinder. Because the motion of the connecting rods will be at some degree of offset from the centerline of the cylinders throughout their reciprocating motion (the length of a connecting rod are only aligned with the central axis of a cylinder when it has reached the end of its motion), the piston is only able to move coaxially within the cylinder by the strength and fit of the cylinder, etc., being adequate to absorb the component of the connecting rod’s force that is not contributing to the translation of the piston within the cylinder.
The crankcase, and specifically the “main bearings” of the block are what locate the crankshaft. The crankshaft must resist the bending and torsional forces from the cylinders, and that can only be managed if the crankshaft is constrained against moving away from its intended rotating axis. Therefore, the block also but be of a particular precision of shape and strength of construction to constrain the crankshaft against these forces, and provide features that define the limits of the crankshaft’s movement.
More specific functions of the block include conducting heat, allowing the passage of fluids, and having strength and shape to locate all of the other components of an engine from deflecting relative to the block. A ~soft block can warp, and then heads or manifolds don’t fit. A brittle block can crack, and make the engine incapable of performing combustion on all cylinders. A block which cannot adequately conduct heat can warp and seize up.
From another perspective, what does a block do WITHIN a car? It is the heaviest single part. A lightweight block can save a lot of weight, and have a marked effect on the entire vehicle’s performance. I can’t remember the model year, but The S197 GT500 had a 5.8L steel block until the midcycle freshening, maybe in 2011. Thereafter, it had an aluminum block. It apparently saved 100 lbs over the steel engine. Because the mustang does not locate its very large engine very far back in the chassis, the engine contributed almost all of its weight to the front axle. In fact, I wouldn’t be surprised if the center of gravity of the engine was in-front-of the front axle. Losing 100 lbs there would mean that MORE than 100 lbs’ -worth of weight shift would be appreciated, in considering the change to front-to-rear weight distribution, because weight in-front-of the front wheels effects a moment about the front wheels that decreases the load on the rear axle!
At any rate, I remember that several of the car magazines lauded the changes for that model, and I think that Car and Driver said that it was the weight shift, rather than the extra 50 hp was what made it so much better than the previous version.
Also… In the case of several racing cars, the block is actually used as part of the middle of the car’s chassis! The only road car that I can think of, that used the engine that way was the Ferrari F50. In that case, the block would also have to be designed to provide the bending and torsional and vibrational performance that would normally be handled by engine cradles, suspension mounts, and engine-bay walls.
Huh. That was a lot more than I was expecting to say. I hope that was helpful!
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