Adding valve reliefs when there are none

Discussion in 'General Tech' started by cyanide, Apr 16, 2012.

  1. cyanide

    cyanide I love coffee.


    I'm using these pistons. There's a hair's worth of valve relief on the intake side, and absolutely none on the exhaust side.

    I still don't have the cam with me since Crower isn't done with the regrind. However, the regrind is going to be very radical, with the Max Lobe lift being around 0.32x - 0.33x, and duration around 245 degrees at 0.05" lift.

    I'm not sure but I have a nagging feeling that I'm going to need some big valve reliefs with these pistons, since the measurements give me a piston to deck height of 0.006" out. Nowhere near the first ring but the piston will still peek out of the bore. Will be using either a standard Y8 gasket (0.027" thick or a revised A6 at 0.048" as per Matt).

    What is the best way to give some clearance? Where I live, the machine work isn't really anything special, and neither is the general aptitude of the machinists. So it has to be simple.

    I'm thinking of the Endyn rollerwave style reliefs but I'd like to hear some smarter opinions from you guys.

  2. BoneSpec

    BoneSpec The Gambler

    so you are gonna cut a 2.5mm deep valve relief in a 4mm thick piston.

    A .500" lift cam??
  3. cyanide

    cyanide I love coffee.

    I don't know how much I'll need to cut. Yet.

    Surprised about the cam? Dave is taking his own sweet time with it. I presume it'll be "special" :)
  4. cyanide

    cyanide I love coffee.

  5. The_Beave

    The_Beave The Red Tape Avenger

    Look at what Rushi did with his D15. (And look what happened with his modified pistons.)

    I've never done it, so I can't really be much more help than that.
  6. cyanide

    cyanide I love coffee.

    I will have a bigger cam than him, so I'm less worried about deto in the midrange.

    I guess i will have to clay this setup to know.
  7. The_Beave

    The_Beave The Red Tape Avenger

  8. Sweed

    Sweed Helt Sjukt

    I've seen people take a old/spare valve and glue some sand paper to it and use that to cut away at the piston to make valve reliefs. Just push open the valves as need be for clearance while spinning them with a drill.
  9. cyanide

    cyanide I love coffee.

    That is one way.

    I had seen a machinist here who had welded/brazed some kind of a grinding blade onto a valve face and used that through the valve guide with a drill. However I am not sure about the merits of doing it that way since people recommend flycutting.

    I think I'll end up using this method if claying suggests any problems. Cheers!
  10. highlift

    highlift Member

    Damn cyanide, you are a serious cat! Hope all goes well friend...
  11. danz

    danz Member

    id wait until you have everything together and clay it before you lose sleep over how to mod the piston.

    edit; the sweetest way ive seen people do the mods ur looking for is to grind teeth into the valve like little blades and use that!! i think it was rushi that did that, iirc...
    Last edited: Apr 26, 2012
  12. cyanide

    cyanide I love coffee.

    Yes, after reading though multiple builds including yours, it seems like the newer OBD1/2 heads had a favorable valve angle, so no work was required. Since Rushi was using the old PM3 casting, he was already at a disadvantage.

    I will be claying the motor with my cut head, so I can see what's going on inside the bore.
  13. The_Beave

    The_Beave The Red Tape Avenger

    Favorable angle compared to what? I have always been under the impression that the VTEC valve angle is much worse for flow than any of the non-VTEC heads.
  14. cyanide

    cyanide I love coffee.

    Compared to the older heads, when considering piston to valve interference.

    You have seen my port work; The valve angles won't be that much of a problem for me :)
  15. The_Beave

    The_Beave The Red Tape Avenger


  16. DocHudson

    DocHudson Active Member

    This is the best thing to do. This is what we do to 1600 blocks using PM0 pistons (30.7mm CH with a fair amount of mid dome)

    What's good about it is that you don't waste too much material on the piston. Once you've made the raw cuts, just clean up the surrounding areas of the new reliefs and get rid of sharp edges.
    You might want to open them up just a hair for insurance against possible piston rock.

    Clay also. And account for rod stretch.

    Add: If i'd want to take it a bit further, I'll cut a junk head up to just one chamber then cut that piece again in the middle to get a clear side view of one intake and exhaust valve seat. I'll mock it up to the block set to tdc so i can see all the way through.

    I've actually seen this in 2sohc's lab LOL

Share This Page