valve to piston clearance?

[Stangman]

I've got untouched GT40P's, with 1.7 cobra roller rockers, heavy doublewound springs, and an E-cam...

All going on top of a '98 explorer block.

am I getting dangerous?

[RACEME]

An e cam at 1.7 is only about .530 max lift. You should take a look using playdough, but I would not worry too much unless the heads or the block has been cut on.

[85_SS_302_Coupe]

Something to think about...


Max lift occurs when the piston is on the down stroke pulling air into the cylinders...so technically lift is not the issue with PTV clearance, duration and when the valve starts to open and close. Theoretically you could have a cam with .999 lift on a stock piston as long as it was designed to open after the piston is far enough down the cylinder and close before it makes it's way back up. Of course this wouldn't make much power but it would be possible because the duration would end up being very low.


Now unless i'm wrong, rocker ratio doesn't effect duration, only max lift right? So with the E303 having 282 duration, you should be safe considering how many people have run F/X303 cams (myself included with the X). I can't say you'll be ok if you advance or retard the cam though...all i know is that the X cleared installed straight up.

[Timido]

Exactly on the duration and Cam degree more than the lift causing piston to valve problems. The best way to check piston to valve clearance is with a light checker spring on a long block with the cam you plan to run in it. With a dial indicator on the valve and the engine at 10-15 Degrees Before TOP Dead Center. Pry the valve open and watch the dial indicator you should have .080 clearance before the valve hits the piston. Doing the same thing on the exhaust side at 10-15 degrees AFTER Top Dead Center you should have .100 clearance.

Good read here
http://www.fordmuscle.com/fundamentals/pistontovalve/

[RACEME]

Most of what I have always gone by on a stock shortblock is that most off the shelf cams with 230-290 duration are usually fine to .550 lift installed straight up. The off the shelf is in there because the lobe seperations and such are pretty tame.

[Stangman]

So would I run into any issues if I started advancing the timing?? If so, how far into it?

[Timido]

You could run into trouble advancing and retarding cam timing. Alot of people degree cams in because they are not allways 100% correct. Your best bet is to check it with clay or the dial indicator. It is one step that can save you alot of money and a big headache.

I dont think you are playing with fire with your combo but I would take the time to check it if it were mine.

[Stangman]

I will. I plan to atleast take the longblock apart and do a hone/re-ring/and bearings just to be sure, and that will be prime time for that.

Now the question is... how exactly do I do that clay deal? I've heard of it before but never saw the same method twice... Go figure, I just put my mean doublewound valve springs on :rolleyes:

[Timido]

http://www.fordmuscle.com/fundamentals/pistontovalve/ Put clay on piston turn the motor over 2 times. Remove the head measure the clay.

[Stangman]

Is there some sort of measurement for the head gasket? I havent read the site yet because I have dial-up haha

[mustangjon]

you mean the thickness of the gasket? you should use an old gasket on the mock up.

[331TwistedWedge]

Is there some sort of measurement for the head gasket? I havent read the site yet because I have dial-up haha

the .80 and .100 clearance will be fine "without" mocking up a head gasket ... the exhaust valve needs a little more clearance, with a little heat ~ it expands ...

[331TwistedWedge]

http://www.fordmuscle.com/fundamentals/pistontovalve/ Put clay on piston turn the motor over 2 times. Remove the head measure the clay.

good find tim :bigthumb ... its easy to notch your pistons (if you dont have the clearance) ...

[Mista Bone]

Exactly on the duration and Cam degree more than the lift causing piston to valve problems. The best way to check piston to valve clearance is with a light checker spring on a long block with the cam you plan to run in it. With a dial indicator on the valve and the engine at 10-15 Degrees Before TOP Dead Center. Pry the valve open and watch the dial indicator you should have .080 clearance before the valve hits the piston. Doing the same thing on the exhaust side at 10-15 degrees AFTER Top Dead Center you should have .100 clearance.

Good read here
http://www.fordmuscle.com/fundamentals/pistontovalve/

Sad fact, same way you check a Honda.

[Stangman]

I had considered notching my pistons incase I went with a bigger cam later... how can I do that? They are just hypers...

[85_SS_302_Coupe]

The right way to do it involves removing each valve in the head and replacing them one by one with a special "valve" that will cut a new relief into the piston. You simply attach a drill to the end of the stem on the top side of the head and go at it. This is pretty time consuming as you can probably guess, since you have to take out your springs and valves to do it and take off the head after each valve. I've heard of guys just hitting the pistons with a Dremel but i don't like that idea. Maybe if you just needed a tiny tiny bit of extra clearance in the corners, but i'd stick with doing it right.