Hot answers tagged

18

Valve float means the valve doesn't fully close at the proper time, because the return mechanism (usually a coil spring) isn't strong enough to close it. This usually happens at high RPM. It can damage an interference engine if the valves make contact with the top of the piston. This can bend the valve stem, or chip the edge of the valve. In addition, ...


16

Between the engine and transmission assembly (or part of the transmission assembly) there is a set of gears called the differential. Its purpose is to enable the outside wheel faster rotation when performing a turn. With both wheels off the ground, turning one of them forward will cause the other to rotate in the reverse direction. Safely block the rear ...


15

Valves can bend, break and/or burn. If the valves don't provide a complete seal, for whatever reason, the hot gases are forced past the valve which eat away or burn away the edge of the valve due to concentration of heat and pressure. Causes that I can think of - Anything that causes incorrect valve seal Cooling issues (improper cylinder head cooling)? ...


13

A piston engine is deemed to have an interference design if the normal regions of valve travel and piston travel overlap. In such engines, collision (and damage) would occur if any of the valves is fully open and its corresponding piston is at the top-most point of travel (Top Dead Center) as they share the same physical space. In contrast, the regions ...


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 ...


11

Human Error I have firm belief that the cause of burned valves with short pipes is due completely to human error, lack of understanding and poor judgement. I believe this myth has been perpetuated by actual 'evidence' of having burned valves but the attribution of the cause is incorrect. Guy with burned valves story He has a hot rod he builds. He uses ...


10

The simple answer to your question is: They rotate all the time. This happens during the open/close cycling and not while closed. This is the reason why we have to lap the valves so the entire face of the valve will seal with the seat and not just one little part.


10

Most valves are opened by the cam lobes, and closed by springs. However, it takes time for the spring to 'unwind' and push the valve back. If the engine is going fast enough, this time is longer than the time it takes for the cam lobe to rotate from 'fully open' to 'fully closed', so the valve doesn't follow the cam - a gap appears momentarily. This means ...


9

Yes, the valves do rotate under normal operation albeit slowly. Some valves have rotate mechanisms to ensure they rotate at a predictable rate. http://www.cdxetextbook.com/engines/comp/vlves/valverotation.html http://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Valve%20Train.htm The rotation action helps keep the valve and seat ...


9

Not sure if this is what you were asking, but there are several configurations where there are no lifters (or at least, no push-rods) in an engine, where the valves are driven either through rocker arms or directly by the camshaft(s). Such a configuration is an OHC (overhead cam) configuration. SOHC are higher performance and lighter (and so typically have a ...


8

A burnt valve can happen for one of many reasons, but the underlying issue is, the valve is not sealing correctly and allows hot engine gases during the combustion phase to leak past the seal which is formed by the valve and seat. When the seal is lost, the hot exhaust gases escape past the valve (can happen to either the intake or the exhaust valve, but is ...


7

Exhaust valves are hotter because they are venting the combusted hot air. This causes them to not collect deposits or burn of any thing that tries to deposit on them. Intake valves are constantly receiving a cold charge of air/gas coming in. They run cooler and deposits tend to collect on them and you'll get a nice dark carbon layer on the bottom. If you ...


7

Under normal use (non-performance type use), the valves, both intake and exhaust, should last the life of the engine. If and when they do leak, it will not take long for the valve to become a burnt valve. In your case, I doubt they were leaking prior to pulling everything apart. If the exhaust valves had leaked, they would have been fried. If valves do not ...


7

tl dr - It absolutely matters. All of these parts need to go back into the same spot in the same positions for two reasons: Sympathetic wear - Let's just say parts get used to each other. Once they have been meshed together for a long time, they are broke in together and work together. When you mix-n-match after the fact, unexpected wear can occur. ...


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, ...


6

Valve lapping compound is an abrasive. As you rotate the valve and apply pressure towards the seat, you are wearing both valve contact face and valve seat at the same time. This action makes both surfaces match each other exactly, which when valve spring pressure is applied, allows the valve to completely seal with the seat.


6

In the image below notice that there are no rocker arms or push rods. The cam acts directly on the shim and bucket which acts on the valve stem. You adjust the valves by changing out different shims to get the appropriate valve clearence. In this image, the shim is over the bucket. This is what your Yamaha has. You have an Over the Bucket Shim to adjust ...


6

The main reason the intake valves show more carbon buildup is because in most fuel injected engines (newer direct injected engines excluded), the fuel injector fires right at the back of the intake valve. This means some of the fuel gets stuck on there and you get a build up of it over time. As @elmerfud said about the exhaust valves is spot on. They are ...


6

Yes it absolutely can happen like this. Many valves are actually created in two pieces (head and stem). They are "welded" together (I use the term "welded" loosely here). They can and do fail. There is a write-up on this page which talks about it: Breakage ... can happen to either intake or exhaust valves. Valves break in one of two places, where the ...


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

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

Yes, debris will cause damage, however the valves cover gasket doesn't stick that hard and if it is the original, they come with some kind of rubber material, very easy to take out even in one piece almost always. Some gaskets are made of cork material, those would break but still won't generate much debris neither. The tip is: take time, warm up the engine ...


5

Generally: Cork - always replace. (this includes rubber covered cork) Rubber - replace if deformed or damaged. On newer vehicles with the molded rubber ones which fit into a slot (I've seen on valve covers, intake manifold runners, etc, etc, etc) are good as long as they are pliable (still feel soft/subtle ... not hard or brittle) and are not damaged. So ...


5

There is an old adage which say something to the effect of, "If it ain't broke, don't fix it." If the valves are sealing fine and look relatively clean, there is no real reason to go through the hassle of doing a valve job. By doing the valve job or even just cleaning them up and lapping them, you may cause more damage than good. It is, however, a good time ...


5

If I were to suggest to use thick honey, you would quickly respond that honey will not find very small leaks. That is the answer really, since we are trying to find a gap where exhaust gasses under pressure could leak from, we need to use something with very low viscosity and is visible to us, to find the leak for us. Look at this chart, you will see that ...


5

Regular valve springs won't cut the mustard in F1 That's why pneumatic valve "springs" have no springs. Instead, they use a chamber of pressurized nitrogen to return the valves back into the "closed" position after the cams have run their course. The diagram below (from this webpage) shows a comparison of regular valve springs on the left to the pneumatic ...


4

Attempting to do this will very likely damage the valve seat, valve itself and potentially the valve guide. Lapping is about finely honing the seat and face together. Power tools at this stage and in this method will introduce greater chances for error. There is a better way than lapping valves by hand, it's call doing a valve job. You recut the seats, ...


4

Will cleaning the valves improve performance? Yes. Will you feel the difference? It really depends on the present state of the valves but the answer is probably "no". Is it worth going them while one's in there? That really depends on the end objective and the availability of resources like time and tools. Just to give an idea of the worth involved, here ...


4

According to this User Manual on Page 53 (section 6-3) a Valve Clearance check should be carried out every 26,600 miles (42,000km). It also highlights any other maintenance that should be done and at what intervals. I think checking is relatively simple (assuming you are handy with a toolkit. I found a site that gives this method of checking your valve ...


4

The short answer, no. I can only speak for cars but the industry almost as a whole gone to hydraulic lifters. These lifters take all the slack out of the valve train and compensate for wear and temperature. In the cars that still don't have hydraulic lifters the valve train is already adjusted for maximum efficiency. The adjustment is compensated for ...


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