How do they make the non-circular holes in an engine block?

I’ve always wondered this. Take a look at the photo in the link below. See how some of the smaller holes that go through the top of the block are round? And some, the larger ones, 4 each surrounding a cylinder in this case, are not round? These holes in question – I presume they are for the coolant as they are the largest holes – these holes are sort of an oblong “D” shape.

I can understand how the engine manufacturer could make a round hole in a block with a drill, but how do they make the “D” shaped holes?

Sand core casting, not drilled

You might be surprised at the intricate shapes achieved with sand core casting.

Mrpete222 has a few basic casting at home videos that is a good primer to how casting is done in general, then onto the very complex castings. Spent a summer in the foundry and it was hot but interesting.

I always get a kick out of the ‘How It’s Made’ type shows when they show casting. Fire hydrants, engine blocks, bells, man hole covers, you name it.

Those are cast as mentioned. Sometimes castings need to be refined. A milling machine or grinder can be used to dress a casting. Billet blocks are fabricated with CNC milling machines. They can excavate any shape.

Casting provides a near net shape, but machining is required for precise dimensions. Rectangular holes are often machined with a milling machine. A bar is pushed through the hole and machine tool bits on the bar remove the metal.

If I’m not mistaken that is a process called broaching.

Look up the “How It’s Made” show that shows how they make engine blocks. I think they have them all on Netflix.

Milling machinery can easily make non circular holes with great precision. In automotive blocks & heads they’re almost always cast in and then finished on a milling machine as required.

The most beautiful machining job I’ve ever seen was on a turbocharger impellar hogged out of a hunk of billet as a school project. I’ve always been fascinated by that piece. It was beautiful work.

Those holes are net cast, that is they are not machined after casting. They aren’t precision holes, just passageways for the coolant. The deck of the block is milled flat, but the holes themselves are as cast.

The neatest trick I’ve heard of is how turbine wheels are made. The hub and blades are seperately formed, then BRAZED together at temperature and held there until the braze metal migrates sufficiently to effectively form an alloy. The part is put into service, reaching temperatures higher than that required to initially melt the braze metal!

(And people wonder at the cost of turbine power…)

@meanjoe75fan … what is the motivation to braze rather than MIG weld for attaching the blades to the hubs on turbines? Are you talking about the kind of huge turbines used by the power company generators to generate electricity for cities? Steam turbines? Or are you referring to exhaust driven turbo-charger turbines for increasing the hp in automobile engines?

I imagine he’s referring to jet engine turbines. MIG welding wouldn’t be strong/precise enough for that, I’d guess. And may not be possible with the materials involved.

@Texases … I’ve never heard of the show “How It’s Made” until now. If it is on cable tv, that is why. I’ve never had access to cable tv. But I’m interested in seeing how the engine casting technique is done. I think found a source for a dvd. Double checking. Is this the show you mean?

How it’s made (Television program)

Summary: Collection of episodes about the manufacturing of various personal transportation vehicles and their parts.

Gaiam Americas, Inc
Discovery Communications, Inc
ISBN: 9780766253056 0766253058

Yep, that’s one of the episodes in the series. They recently had a series about how various exotic cars are made. VERY interesting.
Here’s their web site:

Too bad the only episodes on the web site are about making food…

I’m on it @Texases , the vdo is in the mail, thanks for the link.

Hey, if you have a minute, take a second look at the photo from the link in the OP. I’m curious about something (else). Does it look to you like that particular head gasket fits the head shown? To me they look like they don’t match up.

I see what you mean (the holes on the gasket don’t match all the holes in the block), but I think that was intentional. Not all the passages have to connect to the head. So many of them do match exactly, I think that’s what’s going on here. But it could be the wrong gasket, I guess.

There’s one of those auto-enthusiast speciality books titled “How to Rebuild Your Small Block Ford” or something like that, and in there they show in photos how they rebuilt a Ford engine. It turns out – they discovered during the rebuild – the reason the engine had to be rebuilt in the first place is because the time it was rebuilt before, the rebuilder had installed the head gasket on backwards, the front towards the back & visa versa. So at the rear of the engine, the coolant passages were completely blocked, and it fried the engine in short order.

I was thinking the rebuilder must not have been paying much att’n to what he was doing. Installing the head gasket backwards? But if the gaskets don’t always match with the holes in the block, maybe such a thing as accidentally reversing the gasket is possible even for an experienced rebuilder.

You mean they don’t use square bits ?