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valve protrusion

Started by evofatboy, February 25, 2019, 11:17:19 AM

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evofatboy

Picked up a set of Screamin Eagle evo heads. I want to run a T-man 625. I am checking my valve to valve clearance and I need to sink the valves. Sinking the valve is going to raise the valve protrusion. What is the maximum Valve protrusion allowed? Will I need to use a shorter valve if I exceed valve protrusion limit? I also read about front cutting the valves to get added valve to valve clearance. At what angle would you face cut the valves. thanks for any help.

jsachs1

Base line average protrusion is 2". I don't like to go above 2.030". Biggest problem becomes rocker geometry.(Where the rocker arm tip hits the valve). If it's to far out, and you have stock guides you will wear them rather fast. You can get a little more life from a good bronze guide.
John

Hillside Motorcycle

A man can also tip the stem, and grind the valve to gain a little here, and gain a little there.
Sinking the valves to establish valve to valve at TDC lift, will also increase chamber volume, requiring a good re-surface, and then, valve to piston may be an issue, as well as intake manifold fitment.
Otto Knowbetter sez, "Even a fish wouldn't get caught if he kept his mouth shut"

aswracing

Quote from: evofatboy on February 25, 2019, 11:17:19 AM
Picked up a set of Screamin Eagle evo heads. I want to run a T-man 625. I am checking my valve to valve clearance and I need to sink the valves. Sinking the valve is going to raise the valve protrusion. What is the maximum Valve protrusion allowed? Will I need to use a shorter valve if I exceed valve protrusion limit? I also read about front cutting the valves to get added valve to valve clearance. At what angle would you face cut the valves. thanks for any help.

Take half the amount you're increasing the lift over stock, and add that to 2", and you'll be pretty close on the target stem protrusion. Basically what you're doing is incorporating half of the additional lift in how high up the rocker tip comes, and the other half in how far down it goes. Therefore the arc that the tip travels in remains centered in the same position, and theoretically you're still have a 90 degree angle between the valve stem and a line drawn between the valve stem tip and the center of the rocker arm shaft, when at half lift - which is the definition of correct geometry.

If you want to angle the margin at the perimeter of the valve, well, the stock valve angles are 27 on the intake and 31 on the exhaust. So if you cut the margin at those angles, you'll gain the maximum possible v-v clearance. Just keep in mind that if you reface the 45's in the future, your valve gets a little smaller.

jsachs1

Quote from: Hillside Motorcycle on February 26, 2019, 05:40:00 AM
A man can also tip the stem, and grind the valve to gain a little here, and gain a little there.
Sinking the valves to establish valve to valve at TDC lift, will also increase chamber volume, requiring a good re-surface, and then, valve to piston may be an issue, as well as intake manifold fitment.
Be careful grinding the valve stem tips. Some aren't hardened more than .025" deep.  :wtf:
John

Hillside Motorcycle

And some are not, correct.
Arbitrarily tipping the stem, without knowing what you are working with, would be a foolish move, I agree. :wtf:
Otto Knowbetter sez, "Even a fish wouldn't get caught if he kept his mouth shut"

Benjie40

Or you can order shorter length custom valves from AV&V. I was told they are $70 each... Just make sure they aren't to short and cause cool bind...