Valve reliefs

[frederick]

Can you cut valve reliefs in the original cast pistons?
Problem I'm having is inadequate piston to valve clearance on one cylinder.(0.080")

Cheers,

Frederick

[Challenger340]

Is it an Intake or Exhaust Valve ?

I've personally run as tight as .060" Int & .080" Exhaust.
BUT !
Make sure EVERYTHING is right, Valve Lash, etc., and especially Valve Spring pressures, are set correctly for the application/Camshaft Requirements.

Yes, you can machine Flycuts in stock cast Pistons, just make sure they will have no less than .150" thickness at the root depth of the Flycut.

[frederick]

Thanks for the reply Challenger340.

I was worried the cast pistons might not take flycuts.

The problem is the intake valve to piston clearance which is 0.080" instead of the recommended 0.100"

I have got ali heads, don't know if that makes a difference to the clearance you have to run.
Camshaft is a flat tappet hydraulic Lunati 60302 voodoo.(262/268-0.475/0.495)
Comp Beehive springs, setup to 130lbs seat, 290nose pressure.
Got all installed heights within 0.005", haven't got a spring pressure checker.
Hydraulic cam so no lash.

I checked the crown thickness on an old piston: 0.31" and I'm not going to make the reliefs deeper than 0.03"

Reason it's just one cylinder is that the pistons are not all at the same height.
7 are 0.039-0.043" down the hole, but one is 0.023".
Don't know yet wether it's the crank,rod or piston that's the source.

I could retard the cam 4 degrees, this gives 0.099" clearance, but then exhaust is down to 0.113".

Frederick

[frederick]

Cut one very small relief.

Tested p/v clearance again 0.0105"
I tested with a hydraulic lifter shimmed up to make a solid.

One question: should you adjust to give 0.030" preload or adjust for zero lash with the "solid lifter"?
I've found some contractionary info on this.

Cheers

Frederick

[frederick]

One question: should you adjust to give 0.030" preload or adjust for zero lash with the "solid lifter"?
I've found some contractionary info on this.

Figured it out myself.
Lifter plunger diameter=0.62"
Area=1/4*pi*D^2 = 0.311 square inch

Suppose oil pressure is 100psi
100*0.311=31.1lbs

Seat pressure = 130lbs , so no way will the plunger go up in the lifter when the valve opens.

Cheers,

Frederick

[Challenger340]

Apologies Frederick, I wasn't paying attention, but seems you've got things figured out anyways.

Aluminum heads "grow", hence typically why Guys drop the Head Torque by 10%.

Intake Valves, do not "grow" as much as Exhaust Valves(more Heat exposure and expansion length-wise).

Either way, I wouldn't sweat the .080" Intake Clearance, as long as the Valve Spring Pressure is up to snuff.

Bob out.