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where is the camshaft located in an overhead valve engine Q&A Review

What does a twin cam do?

A camshaft is what opens and closes the engine valves in time with the piston. On yee olden engines they used to be a single camshaft, located towards the bottom of the engine to operate all the valves. The valves are on top the engine, so for the camshaft to move them from the bottom of the engine there would be long metal rod, called a pushrod, that went from the top of the engine down to the camshaft. One end of this rod would ride on the camshaft, the other end would ride on what is called a rocker arm. As the higher part of the camshaft pushed up on the push rod (hence the name), the top of the rod would push on the bottom of the rocker arm. The rocker arm would rock forward (hence it's name) and push down on the valve, opening it. As the lower part of the camshaft came down, the rod would drop, the rock arm would rock back, and the valve spring would pull the valve closed. The problem was as the rod wore down, a cap would form between the top of the rod, and the bottom of the rocker arm. Instead of smoothly pushing up and down on the arm, the rod would have to jump that gap, and slam into the bottom of the rocker arm. This would cause a lot of noise, and if left alone could eventually cause driveability issues. On 4 cylinder engines they quickly switch to a overhead camshaft, or the camshaft sat at the top of the engine, riding right on the valves, eliminating that whole rod and rocker assembly. On a 4 cylinder engine that was fine and easy to do, but on a v6, where you have 2 different heads, and 2 different sets of valves on each side of the engine, it could not be done with one camshaft. So eventually they did the twin camshaft, also know as the dual overhead camshaft, or dohc for short. They would put one cam on each side of the engine, riding right on top on the valves.

What does SOHC mean on a car?

SHOC refer to single overhead camshafts mean the camshaft locates on Engine head and this control both inlet and exhaust valve. You can see it very common in euro 3-or 4 vehicle engines but nowadays all manufacturers using DOHC double overhead camshaft where one for inlet and second for exhaust valve

What does OHV mean on a lawn mower?

It means ‘Overhead Valve’ - the valves are in the cylinder head and operated by pushrod from the camshaft that us located in the cylinder block. You can also have OHC (OverHead Cam’) where the camshaft is in the head and operates the valves either directly or bus rockers. Older mowers have ‘L head’/side valve engines, where the valves are in the cylinder block operated directly from the camshaft, and the cylinder head is basically a flat plate.

Is the Ford Ranger a good truck?

I have an 03 ranger 4.0 V6 manual trnas and 2010 ranger 2.5 4 cylinder, auto trans. The 4.0s of that vintage were built in germany and were pretty well engineered. For example, with the 4WD trucks, the installed engine had a balance shaft run off of the crank, located in the bottom end of the engine. It’s function is to absorb harmonics/vibration off of the crank. Made for smooth running engine. The main bearing caps were 4 bolt, not two, and the oil pan acted as a support/girdle for the main caps. Like I said, good engineering. This was all aluminum. However, the overhead valve arrangement was complicated. Instead of a camshaft within the block, there was a “driveshaft” in that position that had a sprocket on the front to drive the LH overhead cam. The rear of the shaft had a sprocket to drive the RH overhead cam. This necessitated the use of multiple steel chains (rather than belts) to operate the overhead cam shafts. The problem is the chain guides were plastic and off such a grade that around 100,000 miles the guides would start breaking into pieces and dumping plastic into the engine. so this meant a perfectly good engine would have to be pulled in order to clean out the debris and install new upgraded chain guides. Other than that, he 4.0 is a strong running, reliable engine. I notice that the front frame tends to rust, prematurely. The 4WD electronic shift is a bit complicated. There is a motor to shift in and out of 4WD. There is a relay to control shifting between 4WD lo and 4WD high. The relay on my truck burnt out, bought a new one, and to this day I cannot find the location of the burnt out relay. Checked every location various manuals described, and could not find out where it is to replace it. Sad.

What are the moving parts inside an internal combustion engine, and what are their functions?

Well here goes nothing, lets start with the output and move our way inward. Bottom end/rotating assembly: flywheel:, A flywheel serves 3 important functions. Internal combustion engines don’t produce power in a steady manner, there are moments when the engine is using power instead of producing. A heavy flywheel stores some of this energy to smooth out the power pulses. The flywheel also makes a great place to connect an electric starter motor to turn the engine over for startup. This is done with a geared ring around the flywheel to which the teeth of the starter motor engage. In a vehicle with a manual transmission it also acts like a big brake rotor for the clutch the grab onto, clutches function just like disk brakes this way. crankshaft:, A crankshaft has a couple of jobs that make an engine work. The first is that it provides a way to convert linear motion into rotational motion. A crankshaft turns the up and down motion of the pistons into rotational motion to send it off to the transmission. It almost always protrudes out of both the front and back of the engine. On the back of the engine it connects to the flywheel/clutch/transmission. To the front there is normally a drive pulley that all the engine accessories connect to. On either the front or the back in between either the drive pulley or the flywheel will be a camshaft timing gear/chain/pulley that we will get to later. The crankshaft also normally has holes drilled through it to provide a path for oil to get to its bearings and also send oil to everything else connected to it. Connecting rods:, Connecting rods connect the crankshaft to the pistons. they take incredible forces in both compression and tension trying to hold on to those same pistons. Some connecting rods also have oil passages drilled into them to take oil from the crankshaft up to the pistons. Pistons:, Pistons are what takes the heat and pressure from combustion and converts it into linear motion. The pistons are up at the top of their travel when this combustion occurs, and as this happens it drives the pistons back down again. The pistons have to keep all of this pressure sealed up to do this and employ sealing rings cut into channels around the head of the piston. The pistons are held onto the rods that connect the to the crankshaft by wrist pins that are basically just hollow cylinders. These pistons take the combustion pressure and hand it off to the wrist pins, then to the connecting rods, on to the crankshaft that converts it into rotation, then to the flywheel and finally the transmission. Top end/Cylinder heads/Valvetrain: Timing chain/belt/gear:, The top end of the engine needs to stay in sync with what the bottom half of the engine is doing for all of this to work. The timing system takes what the crankshaft is doing and relays it to the camshaft. This is done either with a belt, chain or by simply meshing two gears together. Camshaft: ,The top end of the engine is entirely controlled by the camshaft, it is the conductor to its orchestra much like the crankshaft links all of the bottom end together. This is why the camshaft is linked to the crankshaft by the timing system, if these two are in sync then everything is in sync. The camshaft’s main job is to control the opening and closing of the valves that let air(and fuel in Otto cycle engines) into the cylinders and exhaust out of them. There are several more parts in between that can take a few configurations that we will get to later, there is more than one way to skin a cat so to say. The camshaft has small lobes on it that serve to push the valves open, this can be done remotely if the camshaft is in the engine block or directly if the cam is in the cylinder head where the valves are. If the cam is in the engine block it’s called a push rod engine, if it is in the head its called an overhead cam engine. Now there can be one to four camshafts in a single engine. Push rod engines will always have just a single camshaft whether its operating just one bank of cylinders(as in an inline 4 or straight 6) or two(as in a V-6 or V-8). Overhead camshaft engines can either have just one camshaft per cylinder bank or two(thus V-6, V-8, V-10 and V-12 overhead engines can have either 2 or 4 camshafts.) After this point not all components listed will be the same for both types of engine and I’ll make sure to tell you which one they go to if applicable whether push rod or overhead. I’ll start with the push rod since that has more components. Lifters(Push rod only):, The lifters serve to ride on the camshaft lobes and transfer their up and down motion to the push rods. Lifters can either be solid or hydraulic, the solid lifter directly transfers their force to the push rods while hydraulic lifters use motor oil to dampen the sudden force of the cam lobe pushing them up before it sends it to the push rod. There are also flat tappet lifters and roller lifters, flat tappet lifters directly make contact with the cam lobes while roller lifters use a small roller bearing to glide across the cam lobe. Push rods(Push rod only):, Since the cam is in the block (on the bottom end) on a push rod engine it needs a way to transfer the cams force all the way up to the cylinder head. Push rods are simply long hollow tubes that ride in the lifter and connect to rocker arms up top. The hollow section of push rods is a handy way to get motor oil up to the top of the valvetrain as well. Rocker Arms(Push rod and some overhead cam):, Rocker arms are simply levers acting on pivots, just like a tetter-totter on a playground. When the lifters push the push rods up one side of the rocker arm goes up with it, this pushes the other side of the rocker down which pushes the valve down thus opening it. Push rod engines need rocker arms to open and close the valves since the push rods can only push up. Some single overhead cam engines that have the camshaft located in between the valves and not directly overhead the valves also need rockers to push the valve down. These rocker arms can be either mounted on a shaft, a pedestal or a stud. Valves:, This is the device that controls the air coming into an out of the cylinder, for each cylinder there will be separate intake and exhaust valves. Each cylinder can have either just one intake and one exhaust or they can be doubled or tripled up. There are currently engines with one exhaust and two intake valves, two exhaust and two intake valves or two exhaust and three intake valves. Most car manufactures have settled on using either two valves per cylinder or four. Valves are normally made out of either Stainless Steel, Inconel or Titanium (Long lasting,Heat control,fast acting respectively.) They ride in either cast iron(long lasting) or manganese bronze(Heat control) valve guides. Valve springs/Retainers/Buckets:, Valve springs serve to close the valve after the cam is done opening it. Since the camshaft can only push but it cannot pull it has to have something to close the valve again after opening it. These springs are held to the valves with retainers with two little clips that allow you to remove the springs if you want to. On overhead camshaft engines that act directly on the valve the retainer will have a “bucket” over it that performs the same job as the lifter in the push rod engine. That’s it for your standard combustion engine but this is hardly an exhaustive list, there are also quite a bit of moving parts directly connected to and driven by the engine, as well as a few rare engine designs that took a different road to get to the same place. However almost all engines will share most of these 8 to 11 basic components. There are many more stationary components as well that i didn’t mention. I’ll link a few diagrams so you can get a good bearing of where each of the components is located. PUSHROD ENGINE: OVERHEAD CAM:

How hard is it for a non mechanic to fix a head gasket themselves?

Like many others have said, it will take a lot of tools that most non-mechanics do not have. Everyone keeps talking about torque wrenches, but there’s a whole lot more you are going to need. Before you even put a wrench on it you will need to drain the cooling system because when you remove the cylinder head, there will be a flood of coolant gushing over the top of the engine. A big mess. Then you can spend the rest of the day finding all the ,wrenches,, and ,sockets, and ,extensions, and ,screwdrivers, and ,torx sockets, both ,male and female as well as deep and shallow socket sets in either metric, SAE or possibly even both,. Some cars will require the removal of the A/C compressor, which means you will need to recover the Freon before removal. Also keep in mind that in the process of removing the radiator and heater hoses and vacuum lines and electrical connectors, there’s a really good chance that they will crack or break and that just adds to the time and cost of repairs and possibly even more tools to remove the specialized clamps or wire repair connectors and tools. Now it’s time to take off the intake manifold and carburetor or fuel injector rails and intake plenum. I’m sure you’ve already removed the air filter and possibly the intake tube snorkel and mass airflow sensor, which you do not want to touch with a greasy glove or your fingers. Then it’s time to remove the exhaust manifold(s). If its a straight four cylinder engine on a front wheel drive car, you might find that rather than risking breaking off the rusted bolts or exhaust manifold studs where the exhaust pipe is bolted to the manifold. It might behoove you to just let the manifold remain bolted to the pipe and let it hang if there’s enough room, or you might need to get under the car and remove the hangars so the assembly will drop down out of the way. Front wheel drive V6, a double nightmare since the rear manifold is almost up against the firewall and on some models the engine will need to be raised slightly to allow removal. If it’s on a rear wheel drive 4, 6 or 8 cylinder engine, depending on the year and model, it can be packed in the engine compartment so tightly that you might need to remove a whole raft of things like power steering reservoirs and alternators as well as the drive belt(s). Once all that’s accomplished and you can finally get to the cylinder head(s), it’s time to remove the valve cover(s) and whatever brackets and supports are attached. Now you are looking at the top of the actual cylinder head(s) and possibly one or two camshafts. If it’s and older push rod type valve train, you will need to remove the rocker arms and remove the push rods, making sure to note exactly where each one came from. A 4 cylinder will have eight and an 8 cylinder will have 16. If it’s an overhead cam design, you will need to remove the timing belt or possibly the cam chains, which means in some cases , the entire front of the engine, (water pump, crankshaft pulley, mechanical fuel pump on some) and timing cover, then on to removing the camshafts. Once the head(s) are stripped down and the head bolts are all accessible, it’s time to test your strength with a socket wrench and and extensions to “break loose” the head bolts. Take note of the length as well as location of each bolt since many of them may not be the same length. Now it’s time to lift the heads off of the engine. depending on the type of head gaskets used, they may just lift right off or may require a bit of cussing and prying to get the adhesive to break loose from the head or engine block. Cylinder heads vary in size and weight and can run anywhere from about 30 pounds for a small 4 cylinder engine to almost a hundred pounds on a large V8. And just to make it even more of a challenge, you will have to lift them up while leaning forward over the engine compartment, and that will require at least some decent upper body strength. Now it’s time to spend a couple of hours cleaning the heads and engine block with your ,collection of de-greasers and solvents and scrapers and razor blades and scotch brite or wire brushes and wheels,. Never use a steel brush or even certain types of brass on any aluminum parts, and make sure the solvents and cleaners you are using are safe to use on aluminum and that they won’t damage anything else like the plastics or hoses and wires under the hood, cause it will splatter all over the place when cleaning. Then you can take the cylinder head(s) to a reputable machine shop and they can (and generally will) clean them before placing them into their multi thousand dollar surfacing machine. And it’s also a good time to have them check the valves and valve seals at the same time. Next comes the really confusing part of which head gasket set and possibly a front conversion set (if you had to remove the timing cover) as well as intake and possibly exhaust manifold gasket sets. The prices and quality vary wildly, so don’t try to “cheap” this out, or you’ll be right back doing the whole thing over again. You will also need to buy some new coolant as well as oil and a new filter, and installing a new coolant thermostat as well as any possibly old, cracked or tired hoses and new belt’s. It would also be the time to replace the cam belt or timing chains and tensioners since you’ve already gotten down to them at this point. Check the timing gears for excessive wear and replace them if needed. And don’t forget to maybe replace that old water pump if the engine has more than 50 or 60 thousand miles. If you are working on a newer car, you might also need to purchase a new set of head bolts if they are of the “torque to yield” variety. (Use once, throw away) Now that your cylinder head(s) have been checked and surfaced it’s time to reassemble the engine. Every part should now be cleaned and dry and organized and ready to go back together. It’s time to open your new repair manual and see what, if any, type of sealer is required before placing the new head gaskets in place. Install the gaskets and gently lower the head back in place, and if you miss or it slips, you might have already damaged the gasket. With the head in place, reinstall the head bolts and thread them in by hand before using that well mentioned torque wrench and angle gauge and follow the manual directions as to what order to torque each bolt. With the head(s) now properly bolted in place, it’s time to reassemble that massive pile of parts that’s lying all around the garage. The factory labor times can run anywhere from as little as six hours to well over 60 hours depending on the year and make of the vehicle. The cam(s) must now be properly “timed” and then install all of the other items And when it’s fully assembled, assuming you’ve made it this far, and haven’t called the junk yard, and you still have enough skin and knuckles left. It’s time to change the oil and filter and refill the cooling system and possibly the power steering reservoir. Some vehicles require that to bleed all the air from the cooling system that the car be placed on an angle because some of the coolant filling caps are actually lower than the engine so the car must be angled so that the radiator or coolant fill reservoir is higher than the cylinder head(s) and/or there can be “bleeder” valves on the engine to let out excess trapped air. Then once it starts and is running smoothly, you can vacuum down the A/C system and recharge it with Freon and see if it still works. Bingo!, Viola!, Hot Damn!, Yay, it lives again. “It’s Alive!” So, as an auto tech instructor for Honda, GM, Porsche and Ford, I would ,NOT, recommend that a non-mechanic/tech attempt to try this job especially at home. It is considered a job for an advanced mechanic at the factories and tech training centers. And if the vehicle in question is equipped with a turbo or supercharger, don’t even think about it, unless you are willing to take the risk of destroying the engine completely.

What is an overhead valve engine?

It's an internal combustion, 4-stroke engine where the valves are located in the cylinder head(s), directly above and opposite the piston crowns, thus the the term “overhead valve". Contrast this with other engines that have the valves located in the engine block and adjacent to the cylinder(s), commonly referred to as “flathead". Engines whose valve trains employ a single camshaft in the block operating the valves through pushrods and rocker arms, as well as engines that use overhead cams are correctly called “overhead valve" engines.

My old V8 engines had large rocker covers over the valve lifters. My newer truck just has a flat plate where the rocker covers were. What makes the valves work in these newer engines?

Though very little has changed with respect to the mechanisms by which intake and exhaust valves are actuated in overhead valve engines, there are a variety of related variables that can influence the orientation and overall dimension of your valve covers. Whether the cylinder heads are cast from iron or aluminum dictates casting shapes intended to achieve necessary stiffness, whether or not your engine utilizes ent of direct port fuel injection, or either single or dual overhead cams or more conventional tappet, pushrod and rocker arrangements all potentially impact upon the relative dimension or orientation of whatever access cover is needed to conceal it all and render the space within which all related components operate oil tight. If your engine is a V8 with a single, centrally located camshaft and overhead valves, then without exception of which I am aware, it still relies upon the same lifter -pushrod - rocker arm arrangement of yesteryear. In these cases, some sort of valve cover is still required for access to valve train components. If your engine utilizes single or double overhead cams in each head, then the valve actuating components can potentially be much more compact, and if all centrally located, such arrangements enable a much smaller inspection opening (valve cover). But in the absence of any descriptive information about your particular truck engine Richard, this is all pure speculation. If you can get your hands on a good cutaway illustration of the engine in your newer truck, which I am sure is readily available over the internet, I am quite confident that you can answer any questions whatsoever as to the inner and outer anatomical details.

My 2006 dodge grand caravan is ticking bad and the lifters are barely dripping oil. I have changed the oil and oil filter. What else can I do? Where is the oil pump located and can I replace it?

Get a factory manual - I know the earlier ones (Mitsubishi engines) had the oil pump in the timing cover, the later ones may have it there as well. Besides, you’ll need the manual for the torque specs putting it all back together anyhow. A Factory Service Manual is best, you can often score these on eBay secondhand for a decent price. If you have to get an aftermarket manual, get a Chilton’s. How’s your oil pressure? If you don’t have a gage in the IP, you want to get a diagnostic gage (mechanical gage with a long rubber hose,) then remove the OEM oil pressure sensor and screw the gage in in its place. Then, restart the engine and go around to look at your mechanical gage. Blip the throttle a couple of times, to make sure that oil pressure responds to engine speed changes (it should “jump” a bit, then probably settle down.) If you have good pressure, you may have a clogged gallery. If you have bad pressure, you’re in for more than a lifter replacement, since your bearings are probably wiped out, or close to it, with bad oil pressure (slipper bearings for the crank and cam depend on a pressurized oil film for proper operation.) Also, note that you may not have the cam in the block with conventional tappets - you may have an overhead camshaft by that model year, that may have hydraulic lash adjusters (somewhat fewer parts, a bit less complex, and much less likely to wipe out the camshaft.) Or, an overhead cam with a roller follower actuating the valve on one end and with a hydraulic lash adjuster on the other (either way, there ,will, be a hydraulic component in the system to allow the system to operate with “zero clearance” to reduce noise.) Either way, you may want to pull a cam saddle or two to make sure oil is making it to the head to lubricate the cam bearings…

Why do we need rocker arms in overhead camshaft engines? Can't the camshaft directly push on the valves?

You don’t. Overhead Cam engines don’t use them. Rocker arms are used with pushrod engines where the cam is located inside the engine block. EDIT: Some OH Cam engines do use a cam follower, which some people call a rocker arm. They function slightly differently from a conventional rocker arm in that the fulcrum location and direction of action are different. It’s a question of nomenclature.

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