Why do engines have seperate cylinder heads and blocks

[robinessex]

So why not make the whole engine in 1 piece? Then you wan't have to have that potentialy unreliable cylinde head gasket. And those bloody heads bolts getting in the way of a decent inlet/exhaust port. And the coolant channels. And less bits will make it cheaper.

[J4CKO]

Blocks and heads are fairly complex castings with water and oil channels, valve guides etc so not sure it would be viable to cast it as one piece, sure its possible but really would you want to buy a new engine if you bent a valve and it affected the valve seat or would you prefer to replace the head ? any work to the valvetrain would involve removing the entire engine as well.

I think it has been done but 100 years of wisdom dictates a cylinder head is a good idea.

[Herbs]

You might struggle to get the pistons in

[GroundEffect]

A lot of the time we make the head and block from different materials, as well as what was said above.

Herbs said:

You might struggle to get the pistons in

You can put in through the bottom. It was done in F1 in the mid 80s.

[J4CKO]

Grenoble said:

How would you get the pistons in?

From the bottom end rather than the top, that is sometimes done when someone drops pistons out without taking the engine out, drop the sump, unbolt the big ends, remove the crank and remove the pistons.

[gavgavgav]

You have to think of how to make all the oil ways, coolant ways, angled ports etc, and can you imagine how fiddly it would be replacing a valve ....

edited to add - I'm think the valve stem would be too long to feed in

[thinfourth2]

Not all engines do.

The main problem is getting the valves in as to get a decent angle on the ports then you have to have them so that when the valve comes out of the guide it will clobber the cylinder wall.

Add in the difficulty in casting the cooling channels in the head and it becomes basically unworkable.

There is a few engines which have no separate cylinder heads.

Also a few oddball engines which have no cylinder head with opposed pistons

[Herbs]

Ah i misunderstood, when he said one piece I assumed he meant block, top end and bottom end all combined.

[MysteryLemon]

Was going to post a similar thread recently but with another question involved too. May as well tag it on here instead...

Why do manufacturers use a cam belt over a cam chain? Chains last longer and require less servicing but still, modern engines use belts. Why? What is the advantage of a belt over a chain? Why have manufacturers not done away with the whole belt/chain thing yet anyway? Could valves not be controlled by solinoids or have a totally different system that doesnt rely on a strip of rubber to make it work?

[Rawwr]

I guess once 3D printing technology is sufficient to work with metal and alloys, it wouldn't be unfeasible - in theory - to print a one-piece engine?

</crazythought>

[n1cky]

Herbs said:

You might struggle to get the pistons in

go through the sump.

but a single piece head and block wouldn't be great. i dont know how you would go about replacing cams, valves, cam followers or rockers. unless it was a push-rod setup. and even then how would you cast it?

[John145]

Lotus's range extender engine has no interface between block and head.

[crofty1984]

John145 said:

Lotus's range extender engine has no interface between block and head.

Cast-in exhaust port too. Genius little thing.

[RenesisEvo]

Rawwr said:

I guess once 3D printing technology is sufficient to work with metal and alloys, it wouldn't be unfeasible - in theory - to print a one-piece engine?

</crazythought>

It's already possible - search 'Direct Metal Laser Sintering'.

[Grenoble]

MysteryLemon said:

Was going to post a similar thread recently but with another question involved too. May as well tag it on here instead...

Why do manufacturers use a cam belt over a cam chain? Chains last longer and require less servicing but still, modern engines use belts. Why? What is the advantage of a belt over a chain? Why have manufacturers not done away with the whole belt/chain thing yet anyway? Could valves not be controlled by solinoids or have a totally different system that doesnt rely on a strip of rubber to make it work?

Takes a lot of power to run solenoids apparently.

Plenty of chain engines around.

[wst]

The Merlin 3 has two single piece blocks and heads, they mate onto the crankcase. It weighs a hell of a lot. If the 'head' gets damaged you have to replace the cylinders as well. It takes about 3 people to fit the blocks onto the engine. It's generally a massive pain in the arse.

Eventually they realised this and made the Merlin with separate heads.

[mnkiboy]

I might be wrong but does the Fiat Twin-air engine have solenoid (or some such method) activated valves, rather than being cam driven?

[rev-erend]

I'm pretty sure the Lancia Delta S4 rally car not only had a turbo and supercharger but was also a monoblock where head and block were combined with no had gasket.

So it has been done before but I'm sure others ay have done it too.

[Rawwr]

RenesisEvo said:

It's already possible - search 'Direct Metal Laser Sintering'.

Just watched some YouTube videos. Impressive!

[thescamper]

wst said:

The Merlin 3 has two single piece blocks and heads, they mate onto the crankcase. It weighs a hell of a lot. If the 'head' gets damaged you have to replace the cylinders as well. It takes about 3 people to fit the blocks onto the engine. It's generally a massive pain in the arse.

Eventually they realised this and made the Merlin with separate heads.

What is the Merlin 3?