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What is valve float and how does it impact engines?

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 ...
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16 votes
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What exactly is a "burnt valve" and what causes it?

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 ...
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16 votes
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Why when I turn the front wheels by hand, the crankshaft doesn't rotate?

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 ...
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13 votes

Interference vs non-interference engines

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 ...
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13 votes
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Why did Ducati decide to use the desmodromic valve train rather than a more tradition valve train?

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; ...
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11 votes
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Do straight/short pipes burn out valves?

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 ...
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10 votes
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Do valves rotate over time?

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 ...
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10 votes

What is valve float and how does it impact engines?

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 ...
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10 votes
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What are the various kinds of tappets / lifters and the advantages / disadvantages of each

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 ...
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9 votes

Do valves rotate over time?

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/...
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8 votes

What exactly is a "burnt valve" and what causes it?

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 ...
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7 votes
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Effects of leaky exhaust valves

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 ...
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7 votes

Why are intake valves dirtier than exhaust?

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 ...
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7 votes
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Should I care about valve order or are they interchangeable?

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 ...
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7 votes
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Formula 1 valve trains

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 ...
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7 votes
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Are valve shims re-usable?

Yes, shims are reusable. Since they are between two pieces of metal and suffer no fatigue or wear, as long as they look good and measure out good (are concentric), there should be no issue using them. ...
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6 votes

Why are intake valves dirtier than exhaust?

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 ...
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6 votes
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What does valve lapping compound actually do?

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 ...
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6 votes

XJ600 1994 Seca 2

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 ...
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6 votes
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Can a valve suddenly break in half? Versys 650 destroyed engine

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 ...
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6 votes

Why did Ducati decide to use the desmodromic valve train rather than a more tradition valve train?

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 ...
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6 votes
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Camshaft problem not sure what needs replacing

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), ...
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6 votes
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Preventing debris from falling in engine while changing valve cover gasket

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 ...
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6 votes
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Reusing valve stem seals

Well, if you believe the seals are in good shape, there's nothing saying you can't reuse them. However, considering you have it all apart and the seals are relatively cheap considering the amount of ...
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5 votes
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Do valve cover gaskets need to be replaced every time you reopen the valve cover?

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 ...
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5 votes
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Lapping valves with a drill

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 ...
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5 votes
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Should I lap my valves if I have easy access?

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 ...
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5 votes

Lapping Valves - Using Water as Test Medium

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 ...
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5 votes
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Pneumatic Valve Spring Operation in Formula 1

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"...
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5 votes

Reusing valve stem seals

As inexpensive as those seals are, and as hard as they are to get to, you should absolutely replace them. Do not reuse them.
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