17

To understand the question at large, it is first good to know what the application is and how it came about. The engine in question is the older type of 4-cylinder engine used in Series-A Minis (not the modern BMW manufactured one, but the one produced by the British Motor Corporation). This Mini used a specific head design which has a Siamese port ...


17

The Wikipedia article on VTEC should be good at helping you understand it all. VTEC is a trademark of Honda's patented technology (the original patents have expired but Honda have patented newer implementations such as A-VTEC). So no other manufacturer's production engine can do exactly the same thing. However, that doesn't mean they can't be similar. This ...


13

Ducati use desmodromic valve systems because it provides for; A more faithful adherence to both; (1A) Not just high speed Valvetrain timing. (1B) But also high acceleration Valvetrain rates; regardless of what weight/material the valve is made from. The latter (1B) - which can provide an advantage over the pneumatic Valvetrain design approach - allows ...


12

Obviously any physical damage; cracked, broken, bearing surface damage, sheared gear, etc... Any catastrophic failure warrants cam replacement without possibility of repair. A warped cylinder head could theoretically also warp the cam shaft but i would not just replace it, i would check it first. Place the cam in a set of V blocks. Put a dial indicator on ...


12

VTEC is what Honda are calling their implementation of variable valve timing. Each manufacturer has their own version of it, each with their own name. See here for a list. So, you are right in saying only Honda's have VTEC. But other makes have a system doing essentially the same thing, they just call it something else.


11

Crank shaft has a pulley or a sprocket at the front end, which turns a cam shaft/shafts through a cam chain or cam belt (timing belt). 1 turn of a cam shaft = 2 turns of a crank shaft. At the other end of a crank shaft is a flywheel which being turned by a starter motor for a start. Crank shaft is the first shaft in the whole engine which turns everything ...


10

Degreeing a cam is process for installing a camshaft and then verifying it's proper alignment with respect to the crank shaft. If a camshaft is being replaces due to damage or malfunction with another OEM camshaft generally the degreeing process is not performed. When the camshaft is installed a set of timing marks is lined up and this lines up the ...


9

During the exhaust stroke as the piston is pushing the burnt gases out of the cylinder the stream develops speed. Since the stream of gas has mass it will develop momentum. This momentum follows Newtons first law a body in motion tend to stay in motion. As the cylinder empties the exhaust stream will actually pull a slight suction on the cylinder. If there ...


9

I'm struggling to find the question you are asking here but taking the literal question "Would you assume the mechanic broke your camshaft if your car would not start due to broken camshaft around 30 miles after they repaired a different issue under the hood?" my answer would be "No." If a camshaft were broken by a mechanic or anyone else, the car would not ...


9

There are a number of different engine designs and these govern not only the location, but also the number of camshafts within an engine. Some terms you will encounter include OHV which means Over Head Valve (the cam is usually in the block, below the valves and acts upon the valves with pushrods and rocker arms) An example of this being the Austin Morris ...


8

Lobe separation angle is affects overlap between the intake and exhaust valves which can effect emissions, performance and efficiency. Example of Lobe Separation Angle Measurement of Lobe Separation Angle Measurement would be done with a degree wheel on the crank and dial indicator on the cam. The measurement occurs between the MAXIMUM lift of the intake ...


8

What things could happen to a camshaft that warrant its complete replacement? There are couple of things which I can think of off the top of my head: Performance Gains: The user wants some gains in performance so will replace the camshaft so the engine can breath better (more air in = more power out). Cam failure: A cam can fail for many different reasons ...


8

A cam... in its most generic sense converts rotary motion into linear motion or vice versa using solid egg-shaped actuators (lobes)¹. An engine camshaft... refers to the shaft which houses a series of cams that actuate the opening/closing of the intake and exhaust valves on a four-stroke engine. A performance camshaft... is just a camshaft whose lobe ...


8

Much of the information in this answer is adapted from this excellent forum post In the generic sense A jackshaft refers to an intermediate shaft that transmits rotation/power from one shaft to another. Per Wikipedia: A jackshaft, also called a countershaft, is a common mechanical design component used to transfer or synchronize rotational force in a ...


8

@Zaid Thanks for contributing this knowledge! I just want to post my own description because it took me more than one read-through to understand your answer. My understanding of the situation: Ford had invested in manufacturing the original 4.0 block several years ago. There was no reason to design and invest in a new block. There was already a hole in ...


7

To answer your questions, if there is a real leak, then yes, there is a problem. The oil will cause the belt to deteriorate and possibly slip. When it does, it is catastrophic. Pistons slam against valves and the head is toast (in most cases). This does happen suddenly. Get a different shop to look at it. If the belt appears dry, I would bet there isn't an ...


7

In addition to Zaid's answer. VTEC - Variable Valve Timing and Lift Electronic Control) In essence, it selects between two different cam profiles depending on the RPM. Here's an animation - This is how a cam controls poppet valves. Read about cam profile here For volumetric efficiency we want the intake stroke to fill the cylinder with the max - air-...


7

First, it's probably important to review what valves do and how they're supposed to work on a four stroke internal combustion engine. What valves do Essentially there are intake valves and exhaust valves with a minimum of one of each per piston, but F1 cars (and many modern road cars) use two of each. The following description will use "valve" singular, ...


7

The two primary bearing types found on a crankshaft are roller bearings and plain bearings located on the main journals of a crankshaft. There are two types of journals on a crankshaft. Main Journal - Where the crankshaft main bearings would be located Rod/Offset Journal - Where the connecting rod bearings would be located Crankshaft Components Image ...


6

The goal was to prevent valve float at higher rpms. Given the metallurgy of the day it required a lot of spring pressure to ensure that the spring was push the valve closed. The desmo unit mechanically forces the valve closed as opposed to using spring pressure. This would allow an engine to run at a higher rpm then a unit with a conventional spring poppet ...


6

Other answers have well covered how cams are inspected. This case history makes me wonder if the tech who took this engine apart damaged that cam in some way. The quick discount is suspicious. Dealer techs are mostly paid per job and they move fast. This is a low pay job that would not have been wanted in the shop. Explaining why the service dept has to buy ...


6

This diagram does a decent job of explaining VTEC: In a nutshell (paraphrasing the Wikipedia article), you have two cam profiles, one designed for low-RPM operation and fuel efficiency, the second (taller cam) for performance. The ECU decides when to select which profile based on several engine parameters by actuating the locking pin that runs through the ...


6

Surely, to get a Subaru (or any true boxer engine) to run in this kind of configuration is relatively easy. Bear in mind that you are talking about an engine with two horizontally opposed cylinder heads and a four stroke so for each revolution of the camshaft, there are two revolutions of the crankshaft. Each piston hits it's "top" of it's travel twice, ...


6

I believe this is the part you are looking for: If so, it's called a rocker arm. The most probable reason for its demise is metal fatigue or maybe it just broke. Looking at this forum (and others), it appears that these were designed to fail in case of catastrophic cam belt failure. With that in mind, it's not inconceivable that one of them has broken just ...


6

Your explanation of the application in the Ford motor is spot on. To answer the original question of "what is a jackshaft?" in a broader context: a jackshaft is simply a shaft that transfers rotational movement from one path to another. Basically, it's a spacer between chain and/or belt drive circuits. Here's a few pictures that illustrate the concept.


6

From the same site, an explanation of the differences between the two types of valves shows theres still a valve seal. I suspect this is the only part where clearences have to be tight.


6

It's either in time, or it isn't. You can rotate cams on a non-interference engine in any direction, all you want. However, in general I'd suggest it's best to only rotate only in the natural engine direction. If you are off by one tooth, backing up one tooth on a cam is not going to get you into "interference" territory. I always crank the engine over ...


5

First, remember that we are talking about four different engine cycles here: Intake; Compression; Ignition/Combustion; Exhaust. Top dead center (TDC) happens between two of these cycles: between Compression and Combustion, then again between Exhaust and Intake. The reason the piston and valve do not come into contact is because either the piston is following ...


5

Do any of the four cylinder car guys out there run this configuration? Not that I can find, with the simulated exception of some "scatter cams" referenced by @Steve Matthews, and given a great answer by @Paulster2. Although these are not really "Big Bang" by strict definition. Here is a link to a really good read even though it's only marginally appropos! ...


5

Performance cams have various cam lobe configurations where the valve lift and duration are changed from OEM to provide better efficiency for the combustion process. I would like to make a distinction between efficiency for the combustion process and efficiency of fuel consumption. Combustion efficiency can be related to how much air and fuel can get into ...


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