Is there an easy mathematical way to figure this?

What might be a minimum clearance spec.?

 

Depends on what rods you are using. Aluminum will stretch far more than forged steel. With my 406 with steel rods I am running about .110 of an inch.

 

.100 on intake and exhaust on a street engine.In a trailer queen you can run whatever you feel safe with.
The only way to really check it is mock it up and use a degree wheel and dial indictor.You can use clay also,if you do it right.

 

Clay in the cylinder, Correct?

 

In the valve reliefs of the piston.

 

I also put it around the valve reliefs. if you do it right you can get piston to head clearance as well. You just might be suprised when and where the valve get closest to the pistons

 

Depending on cam the valves are closest at overlap between 300-400* of a 720* rotation.Or about 60* BTDC & 40*ATDC on the overlap cycle.

 

There is no easy mathematical way to figure it out. You could have a .700 lift cam in a SBC that never touches the pistons. You could also have a .500 lift cam that will easily smack the pistons. It all depends on duration, LSA, cam timing and overlap.

If you install race pistons with deep valve pockets, the chance of a piston hitting a valve greatly decreases.

 

Thanks for the info.

 

the best way is to use a dial indicator on the spring retainer. With the rockers all lashed, bring the engine to 10* BTDC and put the indicator on the exhaust side. Push the valve down until it hits the piston which watching the indicator. If you use a checking spring (like you would use on a flowbench) then .100 is a good distance to shoot for. With a real valvespring installed you can get away with a larger number. After you get the exhaust side, move the engine to 10* ATDC and check the intake side the same way. You can get closer on the intake because that valve doesn't get near as hot, so it doesn't expand as much.

 

Trouble is you need to use solid lifters to check the clearance. Hydraulic lifter bleed down and won't give a true reading. Adjust the solid lifter to zero lash since that's how the hydraulic will work.

 

using a light spring lets you use HR lifters with no problems

 

sump'n like this Ellis http://www.iskycams.com/votc.php
Hows it been swing'n ?

 

Great link Jeff!

BTW a left one today

shoot me a call dead beat

 

excellent link. I'm installing my heads this Friday night and was going to use the clay method since I'd have the heads off, but I may try this as well since it's all apart.