Has anyone ever had issues with valve to piston clearance on a 401 once installing a performance camshaft in it? I just built one and am having issues with exhaust valve clearance to the piston. Using Rebuilder's choice pistons from J&C, .015 factory style beaded steel gaskets, and the block has been decked .020" to get the same piston height with these pistons as the factory pistons had. I would expect clearance to be on the order of .1", so am surprised that decking the block .020" would cause this--especially since these pistons set further in the bore and it was decked to make them equal to stock. .466" total lift/232.6 deg duration at .050" lift on the exhaust valve.
its not as much as the lift that matters but more of the way extra exhaust duration, call Carmen he must know he will pick up the phone on sunday.
How much clearance do you have, and what happens if you advance the cam 2-4*? Is it close on the intake side as well? Might as well give us the intake CL and LS as well. Cheryl
My last build with Zollner pistons and a milder Poston NH400 cam was tight too, around 0.085" IIRC. That's less than the recommended minimum. As mentioned, the duration is the culprit. If you have more clearance on the intake side, move it in that direction (also mentioned). As a last resort, Isky has flycutters to cut valve reliefs in the piston. They replace the valve in the head for the 'machining' operation. I'm surprised more builders haven't had clearance issues with even bigger cams.... or maybe they didn't check clearance.
If you used the "Forged" pistons that I had a hand in designing you wouldn't be going through this now as I have the valve reliefs deep enough for a .700" lift custom designed for YOUR engine specs. Unfortunately it's too late now unless you would be willing to start over.
You can also braze a lathe bit to an old valve and use a stop collar for consistent depth. It's probably not that much to have a shop machine them anyways.. Make sure you don't leave any sharp edges. I'd cut a piston before retarding a longish duration cam, or replace the cam.
False alarm. I figured out the issue. I was focused on the wrong area and also made a mistake measuring the valve to piston clearance. I put a light spring on the valve so I could push down on it and see the clearance, but what I didn't think about was that spring does not pre-load the lifter, so the valve was not closing all the way and opening much further than it should. I pulled the head back off and put clay on a piston and it has over .150 clearance on both valves. The problem is the corners of the piston domes were contacting the combustion chamber in the head. Easily remidied with some tape and a flat file. They don't hit baring it over by hand, but have light contact once it is running and everything is slinging around.
Any sharp edges from filing are not good! BTW, that's not that big of a cam. Tuneable... Switch pitch?? Cool if yes.
It is a 4-speed car. I had this same cam in the 425 I just took out of the car, so I already know it is very driveable and streetable. I am rebuilding and putting the numbers matching engine back in the car. I just drive the car to shows and cruise-ins, and it didnt' make sense to have the original engine sitting in the floor taking up room anymore. Thanks for the reminder. I know not to leave any sharp edges anywhere when I cut the corners off of the piston domes--they create hot spots and stress risers!
I would think you wouldn't have to grind part of the Pistons away if they where made for a nailhead engine. Seem like not the correct parts or combination.
I have EGGE pistons in my 401 and a comp thumpr. Had to machine my pistons for p.t.v. But it also 40 thou knocked off the deck of the block and 5 thou off the heads to get the compression where it had to be. EGGE pistons are junk, get good forged pistons, worth the extra :dollar:. I used EGGE because my budget was really tight at the time.
