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Discussion Starter · #1 ·
Hi guys,

Back again with another question as my build goes along.
Today I was checking for pushrod length and PTV clearance.

How I used to do it was with the clay method (However I use playdoh which is definitely not as good as it's less dense and doesn't stick well to the piston).

I initially tested the PTV clearance, I cycled the motor through 3 rotations.
The exhaust valve was never an issue and barely made any impression in the playdoh however the below is what I have on the playdoh for my intake.

I was concerned because it has gone through at the valve relief which I was immediately concerned about (My new heads have 2.25 intake valves)

The one thing I didn't like about this method is that I see the three imprints of the valve and am wondering if in the course of three rotations the playdoh had been pushed out of the pocket of the piston to the top and then has been flattened at the top of the head causing the playdoh to split.

So then I decided to set the dial indicator up and check using that method.
I got true top dead centre and attached my degree wheel.

I tested the valve in multiple locations and got the following results (Metric dial indicator - put conversion next to it).

20 Deg BTDC - 5+mm
10 Deg BTDC - 4.4mm (0.173)
5 Deg BTDC - 3.80 (0.149)
TDC - 3.42mm (0.134)
5 Deg ATDC - 3.88mm (0.152)
10 Deg ATDC - 4.5mm+

Going off the dial indicator method I have more than enough clearance, however I was just concerned about the tear through the playdoh.
Anything to be concerned about or has the playdoh just pulled forward on the piston after each rotation and is the dial indicator method accurate enough for clearance on around the valve pocket?





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I dont think the valve reliefs on that piston is big enough for a 2.25” valve.
 

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Using play doh to check P to V clearance is a complete waste of time. That's the worst thing you could've used. I like the clay method since it also will show you the radial clearance too, (ie. how close the edge of the valve is coming to the outside edge of the valve relief "eyebrow" in the piston). You want at least .030" to .050" radial clearance, (and most pro engine builders will tell you that they like to see .050"). The vertical clearance minimums are .080" for intake, and .100" for exhaust. I've always used modeling clay that I bought from here....

Sandtastik® Air Dry Modeling Clay - 1.1 lb (500 g) It's only $9 and it works a whole lot better than play-Doh ever will.

If you open it up and expose it to air, you have to take what you need, and seal it back up good and air tight since it lasts only a few hours once it's exposed to air, and then it gets too hard to work with. I also spray a light coat of PAM cooking spray on the valves so the clay doesn't stick to them, and clean off the piston top with acetone or brake cleaner so the modeling clay sticks to the piston real good without moving. But don't even bother trying that with play Doh.

BTW, what size engine is this you're working on?
 

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Using play doh to check P to V clearance is a complete waste of time. That's the worst thing you could've used. I like the clay method since it also will show you the radial clearance too, (ie. how close the edge of the valve is coming to the outside edge of the valve relief "eyebrow" in the piston). You want at least .030" to .050" radial clearance, (and most pro engine builders will tell you that they like to see .050"). The vertical clearance minimums are .080" for intake, and .100" for exhaust. I've always used modeling clay that I bought from here....

Sandtastik® Air Dry Modeling Clay - 1.1 lb (500 g) It's only $9 and it works a whole lot better than play-Doh ever will.

If you open it up and expose it to air, you have to take what you need, and seal it back up good and air tight since it lasts only a few hours once it's exposed to air, and then it gets too hard to work with. I also spray a light coat of PAM cooking spray on the valves so the clay doesn't stick to them, and clean off the piston top with acetone or brake cleaner so the modeling clay sticks to the piston real good without moving. But don't even bother trying that with play Doh.

BTW, what size engine is this you're working on?
According to the piston part nr he is working on a 030 over bore 454.
 
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Discussion Starter · #5 ·
Bought some clay and re tested it looked good but on the radial was very very tight to the edge

My cam was 103 degreed advanced when I installed, I retarded it to 105. It's 106 by the cam card

What would 2 degrees further retarded to 107 give me in terms of clearance?
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You want .050” clearance
 

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For the radial clearance on the valve, I would just put a think piece of clay on it was like .050 or so along the relief edge and see if the side of the valve hits it. On this method you can just use the valve drop method (with no spring) assuming piston is a TDC.
 

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If you need to borrow an Isky 2.30 valve notch tool I have one you can use just pay the round trip ride
 

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Discussion Starter · #10 ·
For the radial clearance on the valve, I would just put a think piece of clay on it was like .050 or so along the relief edge and see if the side of the valve hits it. On this method you can just use the valve drop method (with no spring) assuming piston is a TDC.
I will do this tonight and if it's still too close I'll retard the timing 2 degrees and re test.
2 degrees retarded from where I am will put me 1 degree retarded from standard cam specs
 

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What you're supposed to do with the clay after the valves have made their impression, and you pull the cylinder head back off of the block, is the take a plastic knife and cut the clay in half right down the middle, and measure the radial clearance thickness as well as the depth/vertical clearance thickness of the clay with a set of dial calipers. You don't want to just eyeball the radial clearance. You have to try to cut the clay in half without distorting it's shape, so that your measurement is accurate.

What I do is use a plastic knife to cut the clay in sections while it's still on the piston, and then I take a plastic spatula, (when the Mrs. isn't looking :D ) and I use the spatula to gently and slowly scoop the sections of clay off of the piston before the clay hardens. And then I take several measurements of the thickness of the clay at the edges where I made the cut
 

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Single edge razor works good too, small hotel/motel bar soap size modeling clay from a hobby mart works great and its cheap, cut a slice off with the razor flatten it out some like 1/8" thick and press on valve relief, cycle engine over and cut across valve imprint with razor
 

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Bought some clay and re tested it looked good but on the radial was very very tight to the edge

My cam was 103 degreed advanced when I installed, I retarded it to 105. It's 106 by the cam card

What would 2 degrees further retarded to 107 give me in terms of clearance?
View attachment 749736
I don't know if anyone can tell you for certain exactly how much more or how much less clearance you will have given any specific amount of retard or advance, but retarding the camshaft will decrease your P to V clearance on the exhaust valve side, and advancing the camshaft will decrease the P to V clearance on the intake valve side.
 

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Discussion Starter · #17 ·
Changing the cam timing won't change the radial clearance any.
The only way to add more radial clearance is with a smaller valve diameter or piston machining
Clayed it one more time and you can see where it just passed through the clay, it's right on the top of the valve pocket, the valve doesn't go down into the valve pocket but kisses it from the top from what I can tell.
I'm gonna retard it two degrees and see what happens, because it's just kissing the valve pocket I think if the valve raises slightly it could clear the valve pocket entirely.
That's the theory in my head anyway as the valve is barely going into the valve relief at all.

Anyway I'll test it and if it's no good, I might be looking at getting a different cam :/


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Discussion Starter · #18 ·
Okay so here's my results of retarding the timing a further 2 degrees which theoretically would put me at 107 degrees intake centreline (cam is 106 on cam card).
It's definitely picked up clearance, however I probably wouldn't feel comfortable running it and further retarding the cam would change the profile of the cam too much I would say.

So I'm thinking about stepping down in cam. My current cam is 231/239 at 600 lift lunati. 106 ICL
I have to work off what's available in to me being in Australia but I'm looking at the 224/230 at 510 lift. 106 ICL

What part of the cam grind will effect the PTV clearance and would I have any issues stepping down to this cam?

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Hard to tell for sure but you might be able to take a die grinder with a sanding roll and give it a little more room. You would almost have to take one of the pistons out so you could look at the underside to see how thick it is.
 

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Discussion Starter · #20 ·
Hard to tell for sure but you might be able to take a die grinder with a sanding roll and give it a little more room. You would almost have to take one of the pistons out so you could look at the underside to see how thick it is.
I did think of this, then I thought would it be better to just down size the cam?
 
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