Can someone red pill me on valve adjustments? Why do they need

>>17079531
>Why do they need to be adjusted?
Because they get out of tolerance.
>What exactly is "tightening" up over time?
It becomes out of tolerance after a certain point.
>Also, why do motorcycles need valve adjustments and cars don't?
Some cars do need a valve adjustment. It depends on the type of valvetrain.

>>17079531

>Also, why do motorcycles need valve adjustments and cars dont?

Cars use hydraulic self adjusting lifters.

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>>17079531
but cars do

Clearance between parts changes over time, and if valvetrain components get out of spec you can end up with valves that open too soon, don't close all the way, or whatever.

Many cars DO need valve adjustments. They're necessary on pretty much anything made before the '90s and on many cars into the 2000s, for example E46 M3s need them regularly. There are setups that don't need adjustments, most commonly hydraulic tappets, but those are more complicated than traditional cams and spring tappets, and so they're avoided on bikes for size, weight, and cost reasons.

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it's really the rocker arm that gets adjusted

>>17079542
>>17079546
>>17079547
>>17079548

Ok but isn't it just a rod with a plate on the end moving up and down? I still don't understand what is "tightening up" over time. Like I understand if you told me a spring is losing rigidity over time, that makes sense, but what is the mechanism causing this in valves?

Also, what does it mean when they run out of adjustment?

>>17079548
>so they're avoided on bikes for size, weight, and cost reasons.
Nope. Flat tappets have a much lower reciprocating inertia than those self-adjusting hydraulic tappets - which means you can safely take your valvetrain up to a higher RPM, very important on a motorcycle that's doing 15K RPM.

>>17079531
>forgetting air pumps are all about flow

>>17079567
You're talking about moving parts that go through a lot of mechanical and heat cycles. Metal wears or warps and things shift around a bit over time and adjustment screws or cams can move around. (Those adjustment bits are necessary from day one, by the way, because making exactly perfect parts is impractical and so things have to be adjusted to spec.)

>>17079572
Gotcha, I stand corrected. I'm a car guy and tend to forget about how crazy bike engines can be.

>>17079572
>Flat tappets
I obviously meant solid tappets. Roller vs. flat tappet is a whole other shebang.

>>17079605
>I'm a car guy and tend to forget about how crazy bike engines can be.
Not really, it's still just basic phyiscs.

If you take a good small block V8, give it a very small stroke (like a 4x3 302), and add a great set of heads with solid tappets, you can still end up at 9000 RPM.

https://www.youtube.com/watch?v=oeps18chvC0

>>17079671
Crazy in terms of how high they rev and the demands that places on components, not in terms of basic engineering, if that makes sense. Nothing I deal with goes much over 8k and I'm by no means an engine specialist anyway. (My last industry job was with a firm that did 3rd party R&D for suspension and aero parts and only worked on engines to keep our mules running.)

>>17079567
Its usually the valve seat that wears, meaning the valve has to close more to reach the worn seat surface.

The result is the valve is now further up in the seat when closed meaning the clearance between the top of the valve stem and the cam/rocker is now smaller.