piston to valve clearance

[hotrodfeguy]

I know this is somewhat subjective as to valve size. But lets say a CJ set of valves on Std eye brow cut pistons. I know some Mfg's are slightly off but at what cam lift does one really need to start to looking at this. So far every HYD cam I have run was under .600(my 30507 was small valve A head) and never ran into issues. But I have a up and coming juice that's going to push things here and was wondering where that edge is.

[bluef100fe]

Depends how much the heads/block are milled.... How sunk the seats are... How wide the margin is on the valve... How your valve timing events fall with the chosen cam... I had problems with one that was under 0.600 net lift... With stock replacement cast pistons and stock size valves... Ever since that one I check them all unless it's a comp 268H or smaller going in a stock long block... Just not worth the worry... Good luck

[jayb]

I would check every cam.  Why take chances?

[fe66comet]

Whenever I assemble an engine I bolt the head on just snug and set everything up. Before I place the head on I place some silly putty on the piston and slowly rotate the engine by hand. If all feels well and nothing seems to hit I pull the head and check the impression the valves made in the putty, usually just placing a machinist rule in the impression that is left tells the story. Just don't try it with clay LOL.

[blykins]

I would check every cam.  Why take chances?

Amen.

I've seen some stupid things happen.  My list of "what to check" grows with each engine. 

It doesn't take any time to throw some clay on and check things out, or if you want to get involved, set a dial indicator up on the spring retainer in conjunction with a degree wheel, and "map" out the depth clearance at intervals before and after TDC.  Clay will tell you what your radial clearance is.

With modern forged pistons, I really don't have an issue with depth clearance, even up to .700-.750 lift, but due to the shape of some valve reliefs, radical clearance can get pretty close. 

If you have a cam with a lot of overlap, say for instance a tight lobe center cam, you could run into clearance issues.  Or, if you have a lot of cam timing advance or retard, then you could run into clearance issues on a particular valve.

[hotrodfeguy]

So what would ya do pump up a hyd lifter and check it out? What I am building for this "TRUCK GUY" is a 67 F100 2wd 390 2V cast piston so its 9.5 CR roughly Lunati 30507 230/240 @.050 585/600 LIFT grind CJ valves A heads RPM intake 780 holley Are the particulars. Should be a fun little truck with 3.91 gears. He wanted 3.25 but I told him with the tires he wanted 235/75/15 to grab a bit more gear. Or a bit more stall. As he is still hauling a trailer he went with gear.

 When I cut the 3 angle seats I didn't go far it was more to get the larger valves in.

[blykins]

I use a solid lifter to check piston to valve clearances and then the lifter I'm going to use to get pushrod length. 

You can also take that hydraulic lifter apart, then stack it full of washers and put it back together to make it temporarily solid.

[fe66comet]

I just tighten the rocker to zero on hydraulic lifters, once adjusted while running it ends up the same anyhow. As far as a non adjustable pedestal? Use a solid lifter as suggested I guess, I never have run a completely non adjustable rocker. Must be the hot rod in me LOL.