Concepts: Why do you need a 2 piece engine? (Head vs. Block) Why not 1 giant piece?

I know this is going to sound like a very very stupid question…

Why are engines designed with a top and bottom half?
By necessity? Why not have it just be 1 giant part?
One giant block with valves on top, and crank on the bottom.
This would eliminate the need for a head gasket…

Obviously, there is a very good reason for this…But what is it?
Is this b/c of assembly issues?
Can’t get the piston inside?
Or is it for maint. issues?

There was such an engine built in the US; the 4 cylinder Offenhauser (“Offy”) racing engine use at the Indianapolis 500. The engine was assembled through the crankcase. It was not a cheap engine to manufacture. You still needed an oil pan, of course.

Assembly cost is the main reason for having a THREE piece engine; head, block and oil pan. However, many small aircooled engines have no separate heads.

Most of the head gasket problems started with the use of dissimilar metals of engine and block. An all iron or an all aluminum engine has fewer problelms due to the absence of the differential expansion rates.

When the block and head are different pieces it also makes it possible to put different heads on engines destined for different vehicles. A V-8 could go into a sports car with high compression, DOHC 4-valve heads, and the same V-8 could receive slightly lower compression, SOHC heads with different intake runners for a pickup truck that needs better low-end torque and is designed to run regular gas.

In the beginning…

Henry had to start somewhere.

The one piece design makes engines very reliable…No high-pressure gaskets to fail. But very high cost to manufacture and maintain if a valve job is needed…Aircraft engines frequently combined the head and cylinder into one casting. The cylinder was then bolted to the crankcase…

It seems simpler and faster to place the valves into the head if the head is free of the engine block. I suppose the valves could be inserted through the cylinders, but there would have to be sufficient room in the crankshaft cavity to insert the valves. And simpler and faster means it cost less. Also, I think a one-piece casting would be more expensive.

I’m kind of surprised that the one piece hasn’t made a comeback. I can think of a way that it could be made cheaper to manufacture, but it absolutely would not be rebuildable. The technology exists, but the retooling costs would be staggering.

And it would be limited to inline engines only. No v designs.

Wasn’t the (original) Bugatti also 1 piece?

After you insert 8 pistons and rods through the crankcase, it would be tough to fish the rod ends up to the crank so you could bolt the caps on. Plus, the pistons don’t fit through there any way. Then, you would have to get thr piston ring compressor off. It’s easier to put the crank in and then put the pistons in. Once the piston goes into the hole, the ring compressor is off. More parts makes for easier machining too.

Interesting post. I am envisioning the complexity of that casting, and the machinery necessary to machine the cylinder bores and the valve seats. That would be tough. Cylinder sleeves would help, but that would defeat the purpose.

It’s a concept that was tried and finally rejected . Lots of old ideas sound good till somebody tries to put them into practice .

If you stamp the basic frame of the engine in aluminum instead of casting, then cast the cylinder liners, insert the pistons into them, attach the crankshaft, then insert this assembly into the block, it would work. The top of the engine would be stamped in layers and then cold welded together.

The valves could be inserted before the piston assembly, or screw in valves could be used. The crank would be held in a cradle that bolts to the bottom of the block, the pan below that. Once assembled, it would be very difficult or impossible to rebuild, but it would be cheaper to make a new one than rebuild an old one.

@keith - the Crosley CoBra (Copper Brass) engine is pretty much what you describe - but the corrosion issues compared to cast iron did it in.

Mine would be a lot simpler to make.

Mostly it’s a manufacturing issue but maintenance would also be difficult. A present day OHC engine with a non-detachable cylinder head would be a nightmare if not impossible to machine and assemble including the needed ferrous valve seats and also valve guide inserts made from metal other than aluminum. Combustion chamber volume if not a machined shape, would be difficult to control. The casting cores would be complex to put it mildly. Removal of casting core sand from water passages would be difficult. Maintenance would be difficult too as the entire engine would need to be disassembled to work on the valves; even just one valve. Maintenance is not entirely ignored by mfrs. in their constant quest to reduce cost. With a four valve engine the maximum valve angle would be limited by assembly access only through the cylinder bore.

For mass production auto and truck engines, the non-detachable cylinder head concept was discarded so long ago that there is little information found with Google.

Present motors given the cost of manufacturing are MORE reliable then a one piece motor. The restrictions on the design of the internal parts for prop[er assembly would create huge problems in the way of combining engineering, performance, reliability and cost. Trust the manufacturers on this one. If it could be done better the other way…it would have. Wha Who and others have it absolutely right, Today’s motors generally outlast the rest of the car given reasonable maintenance anyway…why bother ? This is just another over indulgence we can’t and shouldn’t make a part of today internal combustion motor.

If we re-introduced a one piece engine…They would be “disposable power units”…The cost of any type of internal component failure to repair would negate the cost of ownership… You need to be able to get at certain things from time to time…Head gaskets dont fail all by themselves…the loose nut behind the wheel usually has a MAJOR hand in their failures. The reasons against a one piece design are too numerous to list to be honest…and I guess you need to be a Gear Head to fully understand this… Kinda like “Its a Jeep thing” comment…ya know?

The boys here answered this question adequately in my opinion.