Valve Clearance on Larger Camshaft and Flat Top Pistons

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famous bob said:
you need to clay check it , that way you`ll get the closest reading at the tightest of stage of rotation , fail proof !!
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Checker springs and a dial indicator will give you the most accurate readings. The indicator will show you where the tightest stage is. Just a degree at a time until you find the inflection point. If you are close enough with valve to piston to be concerned, clay won't get you an accurate answer in my experience.
 
DC 340 said:
Checker springs and a dial indicator will give you the most accurate readings. The indicator will show you where the tightest stage is. Just a degree at a time until you find the inflection point. If you are close enough with valve to piston to be concerned, clay won't get you an accurate answer in my experience.
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The accurate way is the springs you run and clay.

Checking springs will show way LESS clearance than you actually have.

Using checking springs is a bad short cut.

I’ve seen guys notch pistons when they didn’t have to.
 
Newbomb Turk said:
The accurate way is the springs you run and clay.

Checking springs will show way LESS clearance than you actually have.

Using checking springs is a bad short cut.

I’ve seen guys notch pistons when they didn’t have to.
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So tell me, how do you get an accurate reading from clay? Do you jam a caliper depth gauge into it with a flashlight and eyeball the reading? Do you peel it off and hope you haven't changed it? Then measure it with a caliper hoping you haven't compressed it?
 
DC 340 said:
So tell me, how do you get an accurate reading from clay? Do you jam a caliper depth gauge into it with a flashlight and eyeball the reading? Do you peel it off and hope you haven't changed it? Then measure it with a caliper hoping you haven't compressed it?
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Yup. I can measure clay.

This is why I constantly have to cover the same ****.

The way you teach makes everything show LESS clearance than you actually have.

The way you do it you don’t have a clue what the actual clearance is.

You can bet on that.
 
Probably have a mile of clearance, let us know what you end up with.
 
Newbomb Turk said:
Yup. I can measure clay.

This is why I constantly have to cover the same ****.

The way you teach makes everything show LESS clearance than you actually have.

The way you do it you don’t have a clue what the actual clearance is.

You can bet on that.
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I am not teaching anything for sure but I do have a clue what my piston to valve clearance is. I still don't know how you measure clay. :(
 
DC 340 said:
I am not teaching anything for sure but I do have a clue what my piston to valve clearance is. I still don't know how you measure clay. :(
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If you can’t measure a piece of clay to .005 you are qualified to check p/v. That’s the truth because your method is off way more than that.

I can prove that easily.
 
Newbomb Turk said:
Using checking springs is a bad short cut.
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Won't show the additional .025" clearance when using the camshaft springs.
The checking spring is just a guide not very accurate, will show way less than the actual clearance.
 
Newbomb Turk said:
How the **** do you expect me to TELL you how to use a caliper or a machinist rule?

I’d have to SHOW you. And I’m not making a video for that basic **** right now.

I have more important things to video than that.
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Alright. I still don't get it. But I guess you beat me up enough. I'm done here.
 
mygasser said:
cut the clay with a modelling knife across where the valve imprint is and peel away one side of the cut. then measure the thickness of the half still on the piston. not rocket science and definately not worth argueing over :thumbsup:
neil.
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EXACTLY. If he can’t figure that out I can’t help him. I told him that several posts back. But he keeps on keeping on.
 
DC 340 said:
Alright. I still don't get it. But I guess you beat me up enough. I'm done here.
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Beat you up? I told you and I’ll say it again, how can you NOT do it.

Can you use dial calipers. Can you use a machinist rule?

If so you can do it. If not, keep doing it your way.

Makes no difference to me.
 
mopowers said:
How is that? Do checking springs add additional valve movement? I'm having a hard time picturing that in my head.
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Because ALL rockers worth a **** are not built to the nominal ratio.

That means for example a 1.5 rocker SHOULD be 1.56-1.58ish, not 1.5.

That’s because ALL rockers flex. All of them.

It’s the engineers job to determine the flex based on rocker geometry and other things like adjuster offset and even pushrod to lifter angles.

You can test this easily.

Measure your lobe lift (accurately, like with a dial indicator on the lobe, not calipers but you can drop a lifter in and use a pushrod and dial indicator just make sure everything is in line when you do it) and then calculate the lift at a nominal ratio.

I can give you my numbers because I know them.

My lobe lift is .3875 and that’s measured. It matches the cam card. With a 1.6 ratio I should have .6200 lift. That’s at zero lash.

I have measured my rockers with checking springs and they measure at the valve .6374 and that’s a 1.645 ratio and sadly, it’s too low.

With the spring I use, lift at the valve is .6123 which is 1.58. That pisses me off.

PRW has now corrected that issue by adding MORE unloaded ratio so that loaded they measure 1.6 like they should be.

I can tell you that that small ratio difference absolutely changes p/v clearance by a bunch, especially if the geometry is correct because that makes the valve get off the seat faster and the ratio change makes everything open sooner and quicker.

It’s all about rocker flex and accounting for it.

I’ve seen good engine builders absolutely jack up build by notching pistons because they measure p/v with checking springs, think they don’t have as much clearance as they do and they give up compression for no reason.

Not only do you lose compression but any time the notch is deeper than it needs to be, you lose power because the piston dampens some of the incoming air/fuel and if the notch is too big you lose that.

I always knew it lost power having notches too deep but I never knew why. I just knew it was true and provable on the dyno.

Billy Godbold explains it better in his cam book. It’s worth the read.
 
It seems to me that no body has mentioned the most important component and it specs.
The Valve springs. If you have weak springs the valves will float/bounce of the seats at high rpm.
 
Newbomb Turk said:
Because ALL rockers worth a **** are not built to the nominal ratio.
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This and
mopowers said:
How is that? Do checking springs add additional valve movement? I'm having a hard time picturing that in my head.
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Light springs can't duplicate deflection and load the valvetrain experiences with stiffer springs
 
My reasoning for measuring first with a checking spring and dial indicator before clay and heavy springs is to gauge (1) if there will be piston-to-valve contact during checking and (2) if a clay check is even necessary for my level of build. The thing that keeps me from starting with the heavy springs and clay on a solid roller cam is that the spring pressure doesn't allow you to creep up on piston-valve contact like you can with a checking spring. Using the checking spring, I can stop rotating the crank just before I run out of valve drop where the piston and valve will bind. With the heavy springs and clay, the only way I know I have contact is after the contact produces enough resistance through the valve, rocker arm, pushrod, and timing chain to where I feel more resistance in the breaker bar than the spring and rotating assembly resistance I've been feeling. Going as lightly/slowly as I'm going on the breaker bar, I don't know that the binding would bend the valve or mar the piston, but the chance is there whereas it isn't with the checking spring method. If clearance with the checking spring confirms no piston-valve contact but shows clearance is under minimum, I move to a clay test with the heavy springs for the more accurate measurement.

If the checking spring and dial indicator shows minimum or greater clearance, there's no need for me to then check with heavy springs and clay since I know there will be added clearance with the heavy springs. The exception here where I proceed to clay and heavy springs even with minimum clearance is if I'm concerned about clearance between the relief wall and valve. I'm not building engines to the performance level that I'd want to adjust parts to decrease valve clearance down to the minimum, but I'd measure with clay and heavy springs after the initial checking spring measurement if this were my goal.
 
Fish Bite said:
My reasoning for measuring first with a checking spring and dial indicator before clay and heavy springs is to gauge (1) if there will be piston-to-valve contact during checking and (2) if a clay check is even necessary for my level of build. The thing that keeps me from starting with the heavy springs and clay on a solid roller cam is that the spring pressure doesn't allow you to creep up on piston-valve contact like you can with a checking spring. Using the checking spring, I can stop rotating the crank just before I run out of valve drop where the piston and valve will bind. With the heavy springs and clay, the only way I know I have contact is after the contact produces enough resistance through the valve, rocker arm, pushrod, and timing chain to where I feel more resistance in the breaker bar than the spring and rotating assembly resistance I've been feeling. Going as lightly/slowly as I'm going on the breaker bar, I don't know that the binding would bend the valve or mar the piston, but the chance is there whereas it isn't with the checking spring method. If clearance with the checking spring confirms no piston-valve contact but shows clearance is under minimum, I move to a clay test with the heavy springs for the more accurate measurement.

If the checking spring and dial indicator shows minimum or greater clearance, there's no need for me to then check with heavy springs and clay since I know there will be added clearance with the heavy springs. The exception here where I proceed to clay and heavy springs even with minimum clearance is if I'm concerned about clearance between the relief wall and valve. I'm not building engines to the performance level that I'd want to adjust parts to decrease valve clearance down to the minimum, but I'd measure with clay and heavy springs after the initial checking spring measurement if this were my goal.
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You’ve over thought it to the point you are going down the rabbit hole.

There is no way clay will bend a valve. You’ll have so much clearance it’s silly.

I don’t have the time to screw around and do it twice.

I knew where this is where you’d end up.
 
You'll be fine Fish Bite.

How to check piston to valve clearance

My combo - 263/268 @ .050" solid roller with .665" valve lift, advanced 4º. Diamond shelf flat tops with a -5cc or so valve relief and a Cometic .039" gasket. I don't remember the exact number I got but it was basically double the minimum clearance.

I tried the clay method at first but could not get it right. Not sure what I was doing wrong but it turned out using the degree wheel was actually easier and is 100% accurate. Cam should be degreed first.
 
This cam with the intake at 102* will have about 0.200" valve lift with 1.5 rockers at TDC.
The exh in at 110* will have about 0.165" valve lift at TDC.
I would suggest the tiny amount [ if any ] of 'rocker flex' at 0.200" lift would be almost unmeasurable.
 
Newbomb Turk said:
That’s because ALL rockers flex. All of them.
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The entire valve train can deflect.
" When you change stiffness with a better rocker design, something like a stud girdle, stiffer rocker stand, or stiffer push-rod, the deflected lift is higher with less deflection."
Newbomb Turk said:
Because ALL rockers worth a **** are not built to the nominal ratio.
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"Most are cheated up about a quarter to a half point so that the deflected lift checks very close to the advertised ratio."
Newbomb Turk said:
It’s all about rocker flex and accounting for it.
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The entire valve train can deflect.
 
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