Bucket Shim vs Valve Sprung

[Smokey228]

Okay so I've been talking to a few ppl and none of us knew the difference so i thought, of a sample of just us 4 ppl, thats 100% of the population who didnt know what the differences were.

So im asking the guru's.

What is the difference between bucket over shim or bucket under shim whichever it is, or both? and Valve Sprung engines?
Do bucket shim use springs?

Thanks,
Jase

+rep will rain from the skies for anyone who can constructively help.

[ed]

huh?

question doesnt make sense

valve and valve spring can be considered a single operating unit

what sits on top of the valve and spring assembly - ie bucket and shim, or rocker, or whatever, is a separate thing altogether

bucket/shim assemblies are just something that sits between the cam lobe and valve stem. the shim is what adjusts for wear and manufacturing tolerances. whether the shim sits above or below the the bucket is a performance consideration, and reflects the shims likelyhood to be 'spat out' by the rotating cam lobe.

there is nothing specifically relative between a shim over or under assembly, with respect to the valve and valve spring, except for the typre of valve spring retainer (which must be designed to suit the bucket/shim etc) that sits on top

[Smokey228]

So a bucket shim assembly still uses a valve spring than?\

Okay that makes sense now
Let me re-phrase the question...

The reason i ask this question is from looking at different head configurations.

With the 1g, you dont see springs, is that because they sit below the shims and inside the head? As opposed to say a nissan motor like the rb30 where the springs are in clear sight?

[ed]

yes

springs are visually hidden under the bucket

[ed]

[Smokey228]

Wonderful, exactly what i was wondering!

Thanks ed, +rep

Is there any advantage to either?

Cheers,
Jase

[mrshin]

Yep, engines with rockers etc. suck! Having cams operating the valves straight up is much better as far as hanging together at high revs goes.

[brett_celicacoupe]

less weight, less moving parts(usually), fewer bearing surfaces, less flexing (pushrods compress to some degree), less power loss.

i love it when people with -GE engines say they have a noisey lifter

[The Real Roadrunner]

Yep, engines with rockers etc. suck! Having cams operating the valves straight up is much better as far as hanging together at high revs goes.

i dont 100% agree, alot of newer generation engines use cam followers for a reason.

in performance applications if its a choice between shim under/over id go for under.(but then again id probly change to shimless)
as theres less chance for a cam to flick a shim out.

what are you thinking of building or was it just a general Q?

cheers
linden

[LeeRoy]

At the same time though with wear on shims as an engine ages the valves gradually open less and less. If you look at your v6 commodore engine they run push rods which move rocker arms which open the valves so they dont run shims. Instead of shims they run hydraulic lifters which as they age they increase in height by oil pressure and actually adjust themselves to make up for engine wear helping keep valve opening distances close to factory.

Even older engines than these though often dont run hydraulic lifters and as an engine wears they need to be adjusted periodically. Old nissan motors like those in 240z's run this setup.

On the otherside though the above posts explain why overhead cam setups are better.

[brett_celicacoupe]

they dont usually get too bad. the valves and seats usually wear at a similar rate to the shims so the wear balances out

[wraith]

Yep, and then at sustained high RPM your hydraulic lifters decide to REALLY readjust your valve clearances (due to sustained high oil pressure) and bad things, like valves staying open happens... apptly our poor Nissan cousins with their fabled SR20 suffer from such things. Wear on shims is bugger all really, and a quick trip to the nick-a-part will get you a pocket full of shims to adjust valve timing.

[The Real Roadrunner]

At the same time though with wear on shims as an engine ages the valves gradually open less and less. If you look at your v6 commodore engine they run push rods which move rocker arms which open the valves so they dont run shims. Instead of shims they run hydraulic lifters which as they age they increase in height by oil pressure and actually adjust themselves to make up for engine wear helping keep valve opening distances close to factory.

Even older engines than these though often dont run hydraulic lifters and as an engine wears they need to be adjusted periodically. Old nissan motors like those in 240z's run this setup.

On the otherside though the above posts explain why overhead cam setups are better.

let the mass neg repping begin

[IN 05 NT]

the ducati bikes have a good setup... its called DESMO..... been a while since i looked into it,

but teh rocker arm is atached to the valve, so there for, you dont get any valve lag at high RPM,

heres a pic, notice how there's NO SPRING, as its not needed, 2 rocker arms per valve, one to push open the valve and one to pull it closed again.....



blake

...

[roadsailing]

yep, ducatis have an interesting system, i like it a lot, and it has been applied to car engines occasionally also.

its actually called desmodromic (desmondromic?)

you can tell a desmo ducati rider at the lights, he's the one trying to work out if his bike is only making the funny noises it's supposed to be making