Diesel Engines 101. Class 2.

hey guys this is josh with adept ape channel and this is class 2 in our diesel engine course 101 video series and this is actually the second time I've made this video the first one I didn't like how it turned out so I kind of scrapped it and started over hence the delay of an extra week on why it didn't come out thank you to everyone that has click the like button on the first video it's gotten a lot of likes compared to most of my videos per capita it's got more likes per views so thank you very much for that this second video the one we're making now is gonna focus on the air management system and the valve train so the first one we obviously we talked about our piston our piston rings we talked about valves a little bit we talked about the connecting or on the crankshaft in the cylinder this one's gonna be focusing on the air side so how air gets in and how air gets out there's a lot to that ok so I hope you liked the video ok so since this is gonna be focusing on the air management side of the engine we touched on valves in the first video but I didn't really describe what they were i was basically using them as a way to turn off and on air to the cylinder now when most people think of a valve if they aren't around engines they think of something like this this is a hose valve so this turns on and off water almost everyone that's seen this video is familiar with these for the reason of engines and in particular this video series don't think of this as a valve anymore for an engine this is a valve now if you've never seen one of these before might be wondering like well how does this turn on or turn off something I mean it's basically just a stick with a mushroom dent and how does it work there's no knob or anything well we're gonna be talking a lot about these in this video but that's gonna be later in this video I wanted to bring this up because you need to understand how this is shaped to get into the very important subject when our beasts discussing right now and that subject is the first video we were discussing the cylinder and the piston and I talked about a lid well the lid would be the the cylinder it's not part of the cylinder however it needs to seal the cylinder off so it's gonna be exposed to the combustion pressures and heat only that if you saw the little animation clip that I made at the end you have valves going through it remember the valves don't just hang in the air they need to be closing off the exhaust or the intake to the cylinder so something had to be devised that would sit on top of the cylinder to seal it off also to contain all the valve components now since it's allowing intake and exhaust air out in different areas it needs to have ports and this item is called a cylinder head and we're gonna talk about that a lot starting right now now getting back to this super simple illustration here the vertical lines going here would be your cylinder and your cylinder wall that's the lane of the Pistons traveling it above that where it says intake and blue exhaust and red and then injection and yellow that's actually the cylinder head itself and the blue and the red sections are your your ports you can see the the valves there that are moving those are the black lines now that whole section is basically the cylinder head excluding the injector and that's what we're gonna be focusing on in the first part of this video here so what is a cylinder head well this is a cylinder head this is a an automotive design so this is a gasoline engine this is a big-block Chevy cylinder head and this is what they call bear head because it does not have valves in it and the head doesn't have any moving components but what it does have is mostly the ports and what your point what I'm pointing to here are the intake ports they're the rectangular sections here and there are four of them because this is over four different cylinders I can see two other small ports on the ends of the cylinder head as well those are coolant passages we're not going to be talking about the cooling system in this video but there are there is coolant that flows through the cool of the cylinder head now this is the other side of the cylinder head this is the exhaust side of the cylinder head so these are your exhaust ports you can see that these are square shaped exhaust ports and this is an aluminum cast aluminum head most diesel heads are going to be cast iron though I'm using the big-block Chevy because it's a very simple engine design and we're gonna get back to this port location here so now you can kind of see what I'm talking about on intake and exhaust ports if your intake which was the first clip and then the exhaust was the the last clip there now this is the bottom side of the cylinder head this is the same cylinder head I was talking about and as you can see there's no valves in this but if you look closely the ring here is where the cylinder would seal against the cylinder head itself so the head is obviously on top of the cylinder block and the cylinders and then it's just sitting on top there and you can see the valves are in contained within the cylinder area and if you look closely you'll notice that the the valves are different sizes there's a larger and a smaller valve size and we're gonna be talking about that a little bit later explaining why that is now if you look closely also there's an area around with a valves are that's actually machined out of the cylinder head and that's particularly common on gasoline engines because they're trying to reduce the compression ratio of the engine so they have an area there on the cylinder head that's machined away okay so this big old cylinder head is also a solar head except this is for a diesel engine this is off of a caterpillar c12 engine and we're looking at the bottom of it of course and you'll notice that this one has valves in it and if you look closely the valves are the same size not only that there are four valves per cylinder unlike that big-block Chevy which had only two so this one has two exhaust to intake whereas you could see how the big-block Chevy there's only a single intake single exhaust now notice that machined away area I was talking about as well I'm kind of highlighting it here you can see each cylinder has the Machine away area typically on diesel engines that does not have that it's a flat cast-iron cylinder head and the reason for that as diesels are less concerned with reducing cylinder pressures and the compression ratio so usually they'll have just a flat cylinder head so big differences multiple valves per cylinder no machine two-way area also this is a cast iron head unlike most automotive applications currently which have aluminum cylinder heads now the next thing to notice on this is the port so these have very big intake ports but if you notice next to them there's also ports so that on the c12 and this is somewhat caught uncommon on diesel engines it has the intake and the exhaust ports on the same side of the cylinder head now you could do this on a gasoline engine as well it's just not as calm this is kind of a throwback engine design so the intake and exhaust manifolds are both on the same side of the engine you can of course do that they do separate the intake and exhaust air ports they're just on the same side of the engine okay so that's your cylinder head now your cylinder head is fairly heavy on that see 12-1 the cast iron cylinder head talking a couple hundred pounds they can get up to several hundred pounds and those are what seals the cylinder that contains your valves and it contains your intake and exhaust ports now during combustion the engine the cylinder is creating enormous amounts of pressure before combustion when that air is getting compressed they can get up to a couple hundred psi actually combusts it can create in the thousands of psi of pressure now even though that cylinder heads heavy that and that's enough pressure to push the cylinder head off or blow out all the pressure and of course we don't want that what we want is the cylinder head to stay in place in the harness that energy and push it into the crankshaft so to keep that cylinder head in place you need something to hold it there and we haven't talked about them yet but this is a bolt or a fastener and this is a head bolt because it holds the cylinder head to the cylinder block now I'll show you picture of a cylinder block we don't really discuss that yet but the cylinder ball block is basically the main component of the engine that holds all your cylinders and it's typically a large cast iron piece and the cylinder head bolts on top of that and of course seals off these cylinders okay so we've discussed the cylinder heads enough I feel now we have to get into the valve train because the the cylinder head doesn't have any moving components to it it's just a cast piece and it has ports in it it holds components that do move though and of course the most critical of those parts are your valves now there's different sized valves and most diesel engines if they're turbocharged have about the same size valves but as you could see on the gas engine in a most naturally aspirated engine so we're talking non turbocharged engines really almost all early engines were naturally aspirated you'd have two different sized valves now what do I mean by two different size of ours well you can see that this valve is smaller than this valve as far as the area of them it does we're not talking about the length of the shaft or any of that we're talking about the actual valve face itself now the reason you would have different sized valves is because during the intake stroke as your piston is traveling down it's pulling air in but there's nothing mechanically forcing air into the cylinder it's hoping that vacuum pulls enough air in so that's why you would have a bigger intake valve typically than you would an exhaust valve because during the exhaust stroke as the Pistons traveling up the piston is mechanically forcing the air out of the cylinder that's why you can have a smaller exhaust valve than you can in intake valve now we're not going to talk about turbochargers in this video but on turbo Tart turbocharged engine it helps push air in and out that's why you typically don't have big valve differences like you would on a gasoline engine or on a non turbocharged diesel engine okay so I have to thank Stefano for hooking me up with a lot of these valve pieces he gave me and I want to get into what actually holds the valves in place of course there's machined ports in the head that allow the valves to go in them but how they actually work I mean if you look at them there's no threads it's not like they can be bolted into the head is something holding it in well we're gonna discuss that so if you think of the bottom of the head this is a valve insert here this would be the port where air would be coming in or out of so your valve would sit against it and this would be the closed position and when the valve opens it would typically be like this of course because your cylinders below the valve the valve would open like this and it would seal this port off in the head so the valve is opening allowing air in or out if it's an exhaust and then it closes and it then seals off the port which allows no air in or out of that cylinder for that particular valve and that the amount of travel that the valve does is called lift so if you have one inch of valve lift that would mean the valve opens one inch and then closes one inch so that's basically what we're talking about with the valve the valve itself is just a piece of metal it doesn't know when to open when to close and what's holding it in place well let's talk about that so you have those holes and we'll use our valve seat here as an illustration once again and you insert the valve through the bottom of the cylinder head and then it sits against this foul see and then this top portion of the valve is called the stem the valve stem and the valve stem extrudes past the cylinder so or the cylinder head so your cylinder head would basically bits be this area here and you need a way to retain the valve where it is in a way to retract it when it's done doing its job of opening of enclosing so sorry about that there's something that helps it from moving all over the place and that's called a valve guide so this would be a valve guide this gets pressed into the cylinder head and that keeps it from moving basically laterally and it makes it just move very tightly in its bore now this doesn't hold the valve in it just keeps it from moving really any direction around and all these parts of course can wear over time the most important parts of the valve train are something called a valve spring and as you can guess it's a spring now these Springs you can compress it a little bit but they're very tight you need a mechanical system basically to compress these so if the top of your cylinder head were to sit here this valve spring would sit on top of the cylinder head and then you need a way to connect it to this valve so the valve doesn't just fall into the cylinder and of course destroy everything so the valve spring will sit on top of the cylinder head a little clumsy but you kind of get the idea it sits on top of the cylinder head and then you have this piece which helps the valve rotate and it holds the top of the spring in place and then you have these really little pieces that if you see these grooves on the valve itself these are called keepers and you can see they have two ridges in them and those ridges are real pain to get on you put them on correctly you can see they're tapered slightly this top portion here is tapered as well and once they're in place they can't be removed because they're they're compressed together and that top port is called a rota coil and then the valve spring sits up against it so you have your machined piece so if you think of my hand as the top of the cylinder head you have your spring you have your rotor coil which allows the valve to rotate as its opening and closing and then your keepers there theoretically this is a complete valve now though they're usually be a seal here to help the valve not any oil get into the Soner not any air get out of the cylinder into the crankcase but that's basically what the valve system looks like you have your valve seat your valve guide your valve spring your rotor coil and your keepers and then of course the valve itself and that is basically the valve and how it works okay so you're now an expert on cylinder heads and valves okay not an expert but at least you understand how they work now the valve itself we discussed how it's in the head but we still haven't determined what tells it when to open when to close and how much so what pushes it down and allows it to well what comes back up is the spring the spring tension forces the valve back up after it goes down so something pushes it down and that items typically called a rocker arm this is actually something called a lifter but a rocker arm is very similar to this and what it is it's usually bolted to the top of the cylinder head and it sits on top of the valve and when something tells it to it pushes down and opens the valve now we're gonna go back to thinking like we're designing our first engine here and we need something that tells this valve whether it's an intake or an exhaust valve when to open and close because if you remember from the first video they have to open and close at a specific time the intake valve has to open when the Pistons traveling down on the cylinder during the intake stroke and the exhaust valve needs to open when the piston is traveling in the exhaust stroke and of course then they need to close before the combustion stroke so what-what would open and close that valve and keep it so that it's always at the right time in comparison to the piston so basically we need something that's connected to the crankshaft because if you remember the crankshaft connects to the piston and the crankshaft rotates and it is basically controlling the Pistons up-and-down motion so we need something connected to the crankshaft that we could time to it so that it would open and close the valves in the right timing to the engine now this would have to be something strong it would have to be something mechanical because remember we have to overcome that valve spring tension and the valve spring tension can be a lot it can be hundreds of pounds to compress that fully not something you're gonna compress with your hand especially a diesel valve spring like this they do get very small if you get to a very small gas engine but still to compress these as much as you're going to as often these are like you need something strong and mechanical now it can't be an on and off because the valve remember sits up against that seat and if you were doing something where it just slams it in every time it would damage the valve or the seat or cause them the we're very early so basically you want something that will slowly start to open the valve and then quickly towards its full lift open it fully and then come back up rather quickly and then as it gets close to the top where it's gonna touch that valve seat slow down so it would need to be something that instead of a square would almost have to be kind of an egg-shaped item because remember you're dealing with a rocker arm that's gonna be riding on this device so that rocker arm would need to ride on it and as it's pushing the valve down it would need to be some sort of design item that would be kind of an egg-shaped well this item if you haven't thought about it yet it's called a camshaft and the reason it's called a cam shape aft is because it's full of cam lobes and if you've ever seen a cam lobe it's basically an egg-shaped lobe so it's mostly circular and then it has a rounded tip on the end so I've got a couple pictures of a camshaft here by itself so it is a little hard to see but you can see that there's an actual rise on each lobe and that is what I was talking about where it's not an on/off it's actually a gradual increase that helps push that valve open and then it slowly tapers off so you're not slamming the valve open and closed and the camshafts typically about the length of the engine and it has a lope for each intake and exhaust and this particular engine actually has an injector low but we'll be discussing that later all goes according to plan here is a valve train in action now this engine is actually idling about 700 rpm this is how fast your intake and exhaust valves are opening at idle now imagine when you're going down the road the 15 mm well BM they're going very quickly okay so now we know what a camshaft is one thing we need to realize about the Camp Chef though is it spins at half the speed of the crankshaft and why does it do this you have to remember that the piston goes up up and down twice for every time the intake or the exhaust valve opens if the camshaft was spinning at the same speed as the crankshaft so for every rotation of the crankshaft the camshaft spun one time your intake and exhaust valves with open every time the piston went up and down of course we don't want that because the piston needs to go intake compression power and exhaust for one complete cycle now it only needs to open the intake valve once and the exhaust valve once for that time so when you're timing your crankshaft and your camshaft together you need to reuse what they call a reduction now how you time the crankshaft typically on a diesel engine is done with a gear drive so you have sets of gears and typically the cam gear is much bigger than the crank here it's about twice as big and that's because it needs to spin at half the speed of the crankshaft in order for the valvetrain to work properly I'm only gonna touch on this briefly but there's basically two different styles of camshaft engines as well there's what they call an overhead cam so that means the camshaft sits in or on top of the cylinder head and it basically opens and closes the rudder it forces the rocker arms open and close the valves directly now there's disadvantages and advantages to this but there's also what they call push rod engine this is where the camshaft typically sits very close to the crankshaft in the cylinder block and then something called a push rod which would be this sits in a lifter and this opens or pushes the rocker arms up and down to open and close the valves now each end does engine design has its advantages and disadvantages because if you move the camshaft up you get rid of the push rods but then you have more gears and the cams further away from the crank shaft so it creates its own issues of course you're getting rid of the push rods which are these can Bend they can break so there's really no perfect engine design that I just wanted to touch on briefly now we've covered a lot in this video and hopefully it helps you to better understand what the cylinder head is how the valves work how they're seated in the cylinder head with the camshaft is cam lobes cam timing all that stuff basically how the air management side of it okay hopefully enjoy this video I try to get a lot of information in there hopefully a tune in for the next episode we're probably going to be focusing on the crankshaft and we might get into the oiling system okay so thanks for watching [Music]

Channel: Adept Ape

Views: 206,762

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Id: C_3JDp0CDvA

Length: 23min 35sec (1415 seconds)

Published: Thu Feb 13 2020