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Discussion Starter #1
Hi.

When installing valve springs the seat pressure has to be equal on all intake/exhaust seats.

How accurate must it be??
Whats the margin of error? 1lbs? 5lbs? 10??

People say they have to be as equal as possible, but nobody knows how much 'as equal as possible' is.

Share your experience....

Doc
 

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Here's my experience when I switched the stock heads on my mildly built 1970 302 (RV cam, 4bbl, headers) for a pair of stock 4bbl heads. All I did was find approximate TDC (feeling for piston upstroke) and then torque down the first cylinder valves to 15 ft/lbs. Then I manually cranked the engine a quarter turn and torqued the #2 cylinder, cranked again and torqued the #3, etc. This was definitely not very accurate but I have 60,000 on the heads now and have no problems and made no adjustments. I don't think it needs to be too accurate for a fairly stock motor. I'd use a degree wheel on a race motor.
 

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Discussion Starter #6


Anyone else got anything?

A little bit more info: A high revving (7500++rpms) engine with approximately 160 - 180 lbs seat pressure.

The question is still how accurate.......
 

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Well, I'll take a stab at it. I would think that you should be more concerned about the spring height when there installed. If they call for 160lbs @ 1.5 and it checks out to be 150 @ 1.5 then I would say buy a new spring. If it's a little over 160 I would think your getting your moneys worth. Just don't ever install them below what the manufacture suggest. You'll lose the valve lift capacity of the spring and that's called coil bind!!

Are you having a problem with some spring you are installing?
 

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I just took a spring out of the box and checked it for ya. This spring calls for an installed height of 1.800 in. Its supposed to have 195 lbs of seat pressure. Its got about 187 lbs. on my spring checker. Within 10 lbs. is ok. They are new springs also.
 

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Discussion Starter #9
We are a little off the issue here. I'll try to explain.

(This is an example)
When setting up a head, the spring seat load should be 162lbs @ 1.900 with CompCams #953 springs. When I measure them at my spring tester with height mic, they're a little off. Always, any springs. So i shim it up to (or off to) correct spring pressure. It's never much. (And yes, I know about coil bind)

The question is: How much difference in spring pressure is acceptable? Do I have to shim them to exactly the same seatpressure or is 2 lbs difference okay? What about 5 lbs? And so on....

I hope I made sense this time.

Doc
 

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Doc,
You'll find most companies will say 10lbs either way is not an issue. Personally, if you have the space (in terms of not coil binding) I would shim a another say 0.010 to be on the safe side. Its better to start with a little more pressure than required than less or on the edge.

Every spring will lose as much as 10% of its advertised pressure once it goes through the first heat and load cycles.
 

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On 2002-02-15 15:24, V8740 wrote:
Do you think the cam companies take that into consideration?
yeah, to an extent... i mean they are supposed to ship out cams without any flaws or degree errors too.

Unfortunately cam companies cannot predict the amount of shimming your head will need, or the level of consistancy between the valve pockets or seats on your heads, or how well you will set up the installed height. the Edelbrock performer rpm heads we used in the 5.0L EFI articles came with different depth intake and exhaust pockets. I'm sure many novice engine builders would have simply installed new springs without bothering to check that measurment.
 

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[/quote]

Ahhhh?? Did I say something funny? Fill me in please. Thanks.

[/quote]

I think Tom was try'n to say, Your talk'n 'bout apples and they'er talk'n bout oranges.

Dan
 

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Most cams have a suggested valve spring by specific part number or spring pressures.Spring's values are usually available and are given as specific numbers.Is there a need to stray from these numbers? If so,why worry about specifics!
 

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Discussion Starter #16
67stang,

Thank you!!!

I love this site..........
 
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