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another weird one: valve spring shims ?


PatAllen
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I believe those shims are used between the bottom of the valve spring and head to increase the installed spring pressure and they may also protect the head from the steel spring cutting into the aluminum.

there is a cup already at the bottom on all m10 heads so the spring doesnt touch the alu...i am just wondering if this is common or just very old school

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I believe they are use to get the correct valve spring pressure at the correct spring height.

Say, for example, your valve springs should have 100 lbs of pressure at 1 inch, but your "installed" spring height is 1 and 1/16 inch(the springs would have less than the 100 lbs of pressure). The shim(s) would be used to get the correct installed height(and spring pressure)for the valve springs.

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Guest Anonymous
I believe they are use to get the correct valve spring pressure at the correct spring height.

Say, for example, your valve springs should have 100 lbs of pressure at 1 inch, but your "installed" spring height is 1 and 1/16 inch(the springs would have less than the 100 lbs of pressure). The shim(s) would be used to get the correct installed height(and spring pressure)for the valve springs.

+1 couldn't have said it better myself.

You can also use a valve spring pressure gauge.. and you'll find some springs don't have as much umph as others.. so you might shim them..

Many times on a stock motor where the customer has no intension of building it up but plans to put 14psi of boost on it, you can remove the spring on the motor.. and shim it to counter act against the boost trying to push it open. IE.. SBC 2" valve 3.14 Sq inches * 14psi = 43.96 lbs of force trying to push it open or essentially 44 lbs of lost seat pressure. Gotta shim or they'll float at revs.

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well, thats what i expected...band aid for weak springs...

thanks.

Well, not really. As fishhead stated, it is mainly used after a valve grind to set the spring pressure to the correct value. If you had new seats and new valves, you might get it right without shims, but using the shims is the standard on many engines. If you use it as a bandaid for a weak spring, you can end up reducing the valve travel too much and get spring bind. I would normally measure my spring force not installed to verify the springs, then use the shims to set the correct installed height, then use the gauge to measure the closed spring force. You do NOT want to just shim to maximum before bind unless you want to wipe out a cam or rockers.

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well, thats what i expected...band aid for weak springs...

thanks.

Well, not really. As fishhead stated, it is mainly used after a valve grind to set the spring pressure to the correct value. If you had new seats and new valves, you might get it right without shims, but using the shims is the standard on many engines. If you use it as a bandaid for a weak spring, you can end up reducing the valve travel too much and get spring bind. I would normally measure my spring force not installed to verify the springs, then use the shims to set the correct installed height, then use the gauge to measure the closed spring force. You do NOT want to just shim to maximum before bind unless you want to wipe out a cam or rockers.

re-quote please. i stand correct, thats exactly what i meant.

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Toby, don't you just shim to just before coil bind? I mean, I know there is a clearance.

I don't- I add inner springs to add pressure! It's remarkably effective,

as there are quite a few little springs you can use to get a better range of adjustment.

But I try like death to stay a good ways away from bind- when you get close,

some of the coils are already contacting, and the rate can rise pretty

darned quickly.

t

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I always use them on VW aircooled engines. Stops the springs from wearing into the much softer aluminum head material. As stated earlier, also useful for setting up spring pressure equally. Even on new springs there is often a "range" of actual pressures. VW and BMW engines - vastly different, but some techniques do transfer over...

Best Regards,

Jeff in Yakima

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I always use them on VW aircooled engines. Stops the springs from wearing into the much softer aluminum head material. As stated earlier, also useful for setting up spring pressure equally. Even on new springs there is often a "range" of actual pressures. VW and BMW engines - vastly different, but some techniques do transfer over...

Best Regards,

Jeff in Yakima

would that realy matter on a "stock" engine ?i mean, i rebuilded gazillions of engines in my life, all kind you can think of, i never spent the time to measure spring rate pressure, never got faillure or bad performing engines. I visulay inspect them and make sure they follow some height logic in between them, thats its...

btw i would be more than worried to have to shim the spring height that much after a valve job, isnt it ? that means

1-the valve has been cut beyond logic (there isnt much you can cut until you reach teh edge of the valve)

2-the seat has been ground down way too much, i would prefer replace it

btw2 i just acquired a Neway valve seat reseater (gizmo named one, old model), now i can perform 45deg cut and 30 deg back cut myself.

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Probably not much.

I only check the race car's... and like you,

on everything else,

just make sure they don't 'look wrong'.

(same height, not canted, etc)

And as to cutting into the aluminum, as noted above, BMW already uses a steel washer... I suspect it aids valve rotation, too.

t

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