No piston to valve clearance!

[80Camaro]

Well I finally got as far as degreeing my cam tonight and all went well. Then I checked the valve clearance with playdough... you've got to be kidding me!
At the top of the valve relief ramp, at the ridge, it cut it so close you can see through it! I didn't feel any resistance turning the engine.

Now, I know part of the problem is that my pistons are between .006 and .008" OUT of the hole. The machine shop was supposed to zero the deck when I had it built in '04... now I'm finding it.



I have a 350 with Speed Pro Power Forged 4 valve relief flat tops
Vortec heads that have been milled twice
Comp 276 roller cam 534/544" lift with 1.6 roller rockers (502/510 with 1.5)
1044 gaskets (.050")

Any words of comfort?

[Matt@RFR]

Vortec heads that have been milled twice

Angle milled?

[80Camaro]

No,

[Matt@RFR]

Reason I ask is because you said,

At the top of the valve relief ramp, at the ridge, it cut it so close you can see through it! I didn't feel any resistance turning the engine.

If I'm reading that right, it sounds like the valve isn't perpendicular to the valve relief in the piston. Was the clay a uniform thickness in the entire valve relief?

Are you sure the cam is degreed correctly? Correct valve lash or preload?

If that checks out OK, you allready have pretty thick head gaskets on, it may be time to do an extra deep valve job on the heads. Or new pistons if you're game for that.

[80Camaro]

Well, I don't believe the heads have been angle milled. seems like my machinist would have informed me when I told him they weren't.
But the valves are not perpendicular with the reliefs. As you come up the ramp from the bottom of the relief, the valve gets closer to the piston.
I degreed the cam with no problem coming up with 107 (This cam recommended 106), close enough.
As far as lash, I made a solid lifter out of a hyd flat and tightened the rocker until I just couldn't turn the pushrod.

[Matt@RFR]

Hmm. Seems to me like something is up with the pistons. With the angle discrepency in the valve relief, it sounds like fly cutting the pistons at the correct angle, and down the where the relief starts would probably get you good clearence.

Are the Vortec heads a 23º head? I think so, but am not sure. Wow, something aint right. Look into the piston part number and make sure they're what you need.

[80Camaro]

I've pretty much decided to flycut the pistons. An engine guru buddy of mine says that those pistons weren't really meant to be used with too much cam lift. And he says it doesn't surprise him that the valves and reliefs don't match. But they are a good, durable piston and could stand to be cut.

[Matt@RFR]

Well it sucks you've got to tear it down, but I'm glad to see you'll be fixing it correctly.

If you don't mind me asking, how much money will you have in those pistons after they're machined?

[myclone]

80Camaro,

You'll find that the relief in the piston dont match the valve angles on those Speedpro/TRW pieces. This is normal but as you found out when piston to valve clearance is tight there can be issues. Youre guru buddy is correct in that these pistons are fairly beafy on the crown (heavy too) and there isnt an issue with fly cutting them as long as you dont go wild with the cutter.

Matt,
Unless the heads are bow tie stuff a production vortec head (non LSx based) will have 23* valve angles.