I got my cam degreed today, and I also check for piston/valve clearance. The cam is within 1-2 degrees, and the piston/valve clearance is fine on the exhaust side, but it's cutting it close on the intake side (about .050). On my timing chain set, it says if I advance the cam 4 degrees, it will lower my RPM range by 200 RPM (which is fine with me) and the intake valve will gain clearance, but the exhaust side will lose. How much clearance are we talking here? The cam is a 230/236 at .050, .510/.520 lift. Anyone know?? Thanks in advance.

 

The amount of lift and duration have nothing to do with valve clearance. It all depends on when the valves open and close. Cams may have identical lift and duration but one opens the intake valve at 45* and the other opens the intake valve at 41*. The first one opens the valve sooner. Advancing a cam decreases the amount of intake valve clearance. Retarding the cam decreases the exhaust valve clearance. How much will vary with the cam grind since the ramps are not all the same.

The amount of lift means nothing to valve clearance since the valves are closed when the piston is at TDC however the valve timing determines when the valves actually open in relation to where the piston is in the cylinder. Having a long con rod engine keeps the piston at TDC longer because of the increased dwell. This can affect piston to valve clearance also.

.050" is a little too close. General rule is .100" minimum on the intake. Exhaust is .125" minimum. You're going to risk hitting a valve. I'd recommend retarding that cam 4* or finding a different grind. Your other option is to pull the engine apart and have the pistons fly cut.

 

It is unlikely that your interference point is between the valve and piston. Unless you've done something really different during your build up.

Many people have installed cam much bigger than yours and had plenty of clearance. Something is wrong.
In any case advanceing the cam will -DECREASE- intake valve to piston cleareance as Steve stated.

 

yeah i'm thinking either you messed up checking the clearance or something is wrong. i've never saw a valve to piston clearance problem till around or over .6 lift and that's without a gasket so you could add.035 more to the numbers for a gasket.

 

Yeah I read the thing wrong about advancing the cam. I think I'm going to try the clay method tonight to get another measurement for my clearance. The other thing too is that my new intake valves are 2.02", so they are much bigger than stock, and that would cause less clearance as well. Thanks for the replies.

 

You should have .200" clearance with that setup, at the very least.

2.02" valves are only .08" larger than "normal" 350 valves. They do not normally cause a clearance issue, except with the diameter of the flycut in really tall-domed pistons.

You have something else going on, or you're not measurign right, or something. Lots of people use cams a hell of a lot bigger than that one in 350s, with no problems whatsoever.

Just FYI, I am running that very cam in my 400 with 1.6 rockers... no clearance issues.

 

You're going to need a pair of solid lifters to check it properly. Hydraulic lifters won't give you a proper clearance reading.

 

How do the hydraulic lifters affect the clearance checking?? Will it read higher or lower? I just tried the clay method and I am still around .050" clearance. My block was zero decked if that makes a difference. Thanks.

 

Oh, and I also have the checking springs in place of the valve springs. Thanks.

 

They will increase your measured clearance and give you a false sense of security.

Something's wrong. That cam doesn't come that close.

 

I don't see what can be wrong. I have everything installed correctly, and all my measurements are being taken at the proper spots and everything. Like I said though, the block was zero decked, so that will decrease my clearance. Also, my Speed Pro pistons don't look like they have large valve reliefs. Any other ideas?? Thanks for all the replies.

 

There is a chance that your piston valve reliefs are machined wrong. Or the head is mis-located on the block Offset dowel pins.
Are the heads exessively milled or angle milled? What heads are they. Try checking a different cylinder.
Your timing gear set may be mismatched. Wouldn't be the first time.
What are your timing points (.050") and what does the cam card call for.? The cam could be ground wrong or mislabled.

hummm....

 

i don't like the clay method. try using an indicator on the valve, it'll give you a lot truer reading of the clearance.

 

Well, I tried both the indicator and clay method and got similar similar results. I called the guy at the machine shop who did my block, who is a friend of mine, and he said just to take a Dremmel and lightly shave a little of the valve reliefs. I tried it and I gained about .050". Thanks for the replies.

 

with dish pistons and a 500lift cam, 230/236, I shouldn't have any clearance problems \right?

 

A method I've learned is to take a set of junk lifters and take them apart, put a heavy spring inside so the lifter is fully expanded. Or you can get a solid lifter like suggested in this thread.

Quote:

On my timing chain set, it says if I advance the cam 4 degrees, it will lower my RPM range by 200 RPM (which is fine with me) and the intake valve will gain clearance, but the exhaust side will lose. How much clearance are we talking here? The cam is a 230/236 at .050, .510/.520 lift. Anyone know?? Thanks in advance.

Duration has a huge effect on piston to valve clearance. Without looking at it, I can't recall the numbers but I think it was something like 10 degrees on either side of the overlap that has the least clearance.

-- Joe

 

I think I know what you were meaning to say, but your opening statement may confuse some people..

-- Joe

 

I'd hope not.

Here is how you check max lift on a setup:

Bolt head on with teh gasket you plan to use.

Replace #1 cyl intake and exhaust valve springs with checking springs.

Get a dial indicator and mag base. Set it on top of retainer.

Set motor to top dead center using a piston stop, or your fave method.

Push down on the valve until it contacts the piston lightly.

Subtract .100 for min clearance. You now have your max possible lift.

I don't trust the clay method.

-- Joe

 

yeah, I could check it, but I already had the valvesprings installed on the heads and shimmed. I'd rather not take them apart.

 

It takes two minutes totake the spring out.. ??

-- Joe

 

yeah, I just don't hav the spring compressor and don't like the mallet method......but maybe i will, like you said, it only takes a minute,

 

Mallet method?? Care to explain, I've never heard of it. The clay method seems pretty accurate and I will have to go that route since I do not own any checking springs.

 

it was just regarding taking the springs off, I think you can smack the springs witha mallet to let the retainers off,..i think they even do that in some engine builders,...i think it's okay just quicker...but i don't know.