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Old 08-11-2011, 10:20 PM
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valve guide cutting, dual valve springs

Why do I need to run dual valve springs? I'm looking at lunati 60203 and comp cams XE274H and they both recommend dual valve springs. I can't get away with a single??

I doubt very much the machinist has the correct tool.

While I'm at it if I was to use comp cams positive seal (teflon) and got the tool to machine it (p/n 4726) and the arbor (to many sizes to choose, dunno what one to get) what does it go into? A drill press?

Kinda frusterating putting a motor together from scratch.


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Dual/multiple springs can give spring compression rates more suited to the cam.

A automotive machinist would use a guide and seat machine or mill/drill press of some type to drive the many profiled and straight cutters required for the work. I believe I have over fifty at $$$$ per each. You can get by with a drill press, patience and common sense.

Sbc pilot would most likely be an 11/32"
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Old 08-12-2011, 05:50 AM
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Dual valve springs

1955 - 1985 SB Chevy V8/V6 heads:
If you do not have 1986-up Vortec heads, you can avoid machining the valve guides for dual valve springs by using the Comp Cams 983-KIT. This is a kit that contains 983-16 ovate valve springs, 10* retainers and 10* locks. The 983-16 valve springs are single ovate (not beehive). They set up at 1.700" at 110 lb. seat pressure, and will have 306 lb.. open pressure with your camshaft. The CC 983-16 valve springs are 1.260" O.D. and .836" I.D. You will l have to machine the valve guides to .530" to fit the Teflon (or Viton) positive stop valve seals. That cannot be avoided if you want to use positive stop seals. I don't know if you can use the valve guide cutting tools without a drill press, my machinist didn't.

1986-1999 SB Chevy Vortec V8/V6 heads:
My 1986-1991 4.3L V6 TBI is equipped with a Comp Cams camshaft with .500" valve lift. I used the CC 983-KIT with my 1994 4.3L V6 L35 TPI heads. The engine builder machined the Vortec .900" OD inner valve spring locators (guides) to .830" OD to fit the CC 983 ovate valve springs. He also machined the valve guides to .530" OD to fit Teflon positive stop valve seals. The 1986 and later Vortec heads have a .900" OD valve guide boss that serves as a inner valve spring locator. I also left .080" un-machined between the bottom of the Teflon positive stop valve seal and the valve spring locator boss to serve as a seat for the positive stop seals. I used Teflon .530" ID x 11/32" valve stem seals because I did not want any (zero) oil past the valve stems.

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Old 08-12-2011, 06:39 AM
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valve seals

BTW...You must use K-line Bronze Bullet "self lubricating" valve guide liners to use Teflon positive stop valve seals because no oil gets past those type seals. Viton seals will allow a little oil past the stems and into the combustion chamber.

My engine builder set the valve stem tight at .001" I and .0026" E stem clearance for accurate valve seating. If you use positive stop Teflon seals without K-line phosphor-bronze guide liners with that stem clearance, you will likely gall and seize the valve stems in 20 miles. I feel the port flow improvement and accurate valve seating with tight valve stem clearance is worth the cost of installing K-line valve guide liners. The positive stop Teflon seals is worth the cost in order to prevent oil contamination of the intake fuel air mixture. Oil contamination of the combustion chamber raises the fuel octane requirement. My machinist has been setting up tight stem clearances on GM engines since at least 1969 with no come-backs.
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