Piston VS. Valve

i,m sure someone has morer smarts about valve to piston clearance. i need some help, and advice- when do i worry about clearance between the two. my new hyd. roller weighs in at .533/.548 lift 236/242 dur. i've installed the correct springs per specs. the heads are torqued down already and i would like to leave it that way (52.99gasket+soreback=sucks). 400 block with 5.565 rods

You should have no problems with piston-to-valve interference.

tom

There's a hundred ways to skin a rabbit, but I think I'd start by pulling out the spark plugs and turning the engine over by hand. If it stops when you turn it over you have a serious clearance problem and you'll need to start pulling the engine apart. If it doesn't lock up you could call the people you bought the cam from, tell them what your combination is and they should know if there's potential for a problem. They'd probably want to know the deck clearance and the shape of the piston crowns, ie, flat, dished, raised and by how much if they're dished or raised. They'd probably also want to know if you installed the cam straight up or if you retarded or advanced it when you installed it.

F-BIRD'88 had a good tip on this. WAY easier than the clay method.

Pick a cylinder in each head, tighten all 4 rocker nuts 2 turns past zero lash. Turn motor over very slowly by hand to feel for any bind.

BBP

That doesn't tell you anything. It's just telling you that you have no interference. It doesn't tell you if you are .002" from interference or .200" from it. You can actually have interference and not feel it. The best way to tell what you actual P-V clearance is to clay it.

tom

Don't it tell you that at normal rocker adjustment, that the valves don't contact the piston?

BBP

thanks for the help everyone! the combo stands as a 400 2 bolt studded align honed 10/10 cut crank(stock) rebuilt 5.565 rods w/arp bolts hyd. roller at(i'm looking at card) .533/.548 lift 234 242 at.050 rpm airgap 750 annular speed cam installed strait up- oohh pistons are kb hyper 18 cc dished w/valve reliefs - everything is balanced

another thought- could i get the lifter at full lift w/checker spring, get piston tdc and push the valve stem down until it hits the piston- then measure the difference? i know the lifter must not be allowed to "pump down".

With rocker studs of 24 tpi, 2 turns = 1/12" (0.08333') with 1.5:1 rockers, you have the valves .125" further open than 0 lash.

This seems like a meaningful clearance to check for?

BBP

You can do it any way you like. As someone who has to stand behind my work and to insure that my customer has a quality build, I use clay so I can tell him EXACTLY what he has. That is called documentation. Not guessing or estimating.

tom

With the clay method, How much time does the head torquing & then taking them off take? Do you throw away the head gaskets each time or reuse them?

BBP

With the clay method, you don't torque the head down. You use 4 head bolts to hold the head in place. You don't have to use a head gasket either. You just add the compressed gasket thickness to the value you get from the clay.

tom

Tom, what about bringing the piston to TDC, putting a dial indicator on the valve and gently depressing it manually until it comes into contact with the piston then subtracting the valve lift? I've never actually done it this way but I've always been curious.

The valves aren't opened all the way with the piston at TDC are they? The intake valve definitely wouldn't be and I thought the exhaust valve wasn't either. The clay method is the best way and the way good engine builders measure the clearence.

Unless the valve timing is way out of whack, the valves are not open at the same time the piston is at TDC. That is why doing it as you describe doesn't give you a real idea of how close the piston-to-valve relationship is while the engine is running.

tom