Valve pockets in pistons

[winr1]

How deep are yalls valve pockets and at what lift, duration ??

Curious as I have not mocked my mill up yet to check for clearance



Ricky.

[GJCAT427]

Mine are TRWs popups from the muscle parts program L2299s They are modified on the domes about .060. The valve reliefs are about 3/16" as measured with a tape measure. The cam is a C8AX-6250-D with .600 lift and 330* duration as per spec sheet in the blueprint specs from Ford. This is a pretty rad cam in its day but what the he!!. I`m gonna try it. Hoping to start assy this week if the garage and the weather cooperate.

[gt350hr]

  What cam are you using?

[winr1]

Thanks GJCAT427



gt350hr, not sure till I mock the block up


428 crank in .040 390 block, late model SP pistons, shaving around .087 off the tops

Hankering to get it together to check ....  bench racing at the moment :-)



Ricky.

[gt350hr]

     Cutting the piston that much will also ( obviously) shallow the valve pocket by .087. Anything more than 230 @ .050 on a 108*lsa should be CAREFULLY checked. Hopefully the "deck thickness" of the piston is still more than .200 or it will likely cave in in the center.

[winr1]

Looks like the deck where the valve pocket is the deepest is around .465

The deepest part of the pocket is around .190, so deck is .275 thick at deepest part of pocket

Top ring land is around .316

This is as the piston is now, not milled .087

Will not be going over .220 @.50 or .500 lift .. 108

Where is the piston in the bore when the piston and valve are the closest ??




Ricky.

[CaptCobrajet]

Check the exhaust from 12° btdc to 6° btdc.  Check the intake from 6° atdc to 12° atdc.  Most any usable cam with 108 to 114 separation will get closest within those ranges.  I check in 2° increments unless they are really close.  Sometimes on aggressive cams you have to check every 1° through there.  For a 220 at .050 cam, the 2° increments are fine.  Be sure to zero your indictor on the retainer after each move of the crank, then push it down until it bumps the piston.  If you have the heavy springs on,  you can do it with the adjuster if you lube the threads and pushrod cup prior.

[gt350hr]

   Your cam should only have .119 lift "at the valve" at 10* ATDC. This should still be safe with a valve pocket depth of .100 or more. As Blair suggested check to be sure . The piston should have moved about .010-.014 off of TDC at the checking points he suggested. Piston motion is still "kind of" slow but is ready to speed up quickly around 20*S ATDC and why many of us aren't bothered by "total lift" numbers because the piston is often 1" away from the valve at that point.
   Randy

[TomP]

Never hurts to put clay or a cutaway head that allows you to see the valve fit. Sometimes the valve notch is not in the right spot.

[winr1]

Thanks much guys :-)



Ricky.

[gt350hr]

Never hurts to put clay or a cutaway head that allows you to see the valve fit. Sometimes the valve notch is not in the right spot.

      Tom ,
         The cut away head is THE most valuable tool there is for piston to valve checking. Tough to do on an FE with the rocker shaft  but a bolt on plate can be fashioned to hold the shaft in place along with a  normal stand.  Crane Cams had a display of a small block Chevrolet that featured the front cylinder , a single cylinder crank , rod and piston and cutaway head. I was able to "play " with it for an hour or so waaaaay back in '75 and it has stuck with me all these years. I was able to borrow it 15 years ago to teach a class I had at a company I used to work for. It opened allot of eyes as to what actually happens between valve and piston. I was able to show the effect of lash change not being direct to piston to valve clearance that was a big surprise to most of my "students".
     Randy