Claying Pistons

[red94fiveo]

I'll be doing my headswap (actually just the installation part) this weekend and had a quick question about claying the pistons to check PTV clearance. This may seem real obvious but what kind of clay should I use? I can run over to the Art department at school and pick some up, will that work ok. I think its just generic clay used for ceramics. When I clay the pistons and bolt up the heads to check clearance should I do this with or without the head gasket on? Any other helpful tips for doing this. I have the solid lifter ready to go, I think other than that I should be OK.

 

[Killercanary]

I used playdough. I can't remember if I put saran-wrap around it though to keep it from sticking to the pistons... I think I did.

 

[Killercanary]

BTW- do it without a head gasket first, if it doesn't clear without a headgasket, it probably won't clear with one either as most standard replacement head gaskets are aroun .050" or so. You can get thinnier or thicker ones. Check with the manufacturer of your gasket to see what the advertised compressed thickness is of their gasket. I do not remember what the minimum clearances are for PTV clearance for the intake and exhaust... the exhaust typically requires more if memory serves me right, I think its because the exhaust valave is typically hotter and therefore expands more than the intake valve.

 

[tmoss]

.080" intake and .100" exhaust are base points that will keep you out of trouble. Most gaskets compress to .039" thick, so do it without new gaskets and add in the .039" to the measured clearance.

 

[str8stang036]

How far down the clay got compressed is the PTV clearance ?

 

[Rootus]

How far down the clay got compressed is the PTV clearance ?

Basically. The closest point of contact will probably be the edge of the valve, not the face. Use a razor blade and cut across the clay, and peel one half away, then you can see & measure the thickness.

Dave

 

[Joes95GT]

If you told Ed that you had the stock shortblock, he would have designed the cam so it doesn't wack a piston. I know your just being safe, but it's just a thought...

Joe

 

[str8stang036]

is claying an accurate measure? Because if the clay is hard the Piston and Valve cant push it down enough to get an accurate measure right? Just a thought.

Are there other ways of checking PTV clearance?

 

[RIO5.0]

red94fiveo...I helped Jesse install his FTI combo last weekend...we clayed the pistons and had like .160 or so on the exhaust side...plenty of room...we checked it just to be on the safe side...Ed prolly gave you the same package...he wouldn't sell a kit otherwise...BUT....there is a statement on the invoice stating to verify PV...
Dont go wild on the clay..dont go much beyond the valve reliefs with you clay..

We stopped at an arts/craft place and got a little 1.99 square of modelers clay...

 

[Rootus]

is claying an accurate measure? Because if the clay is hard the Piston and Valve cant push it down enough to get an accurate measure right? Just a thought.

That would have to be some pretty hard clay -- the seat pressure of the valve spring is probably about 135 lbs, and that's when it's all the way *closed*, it goes up as the valve opens. And the piston isn't going to give any. So I think you can assume the clay is giving a pretty accurate measurement.

Dave

 

[str8stang036]

Your right Hairy. Now, if there is not enough PTV clearance what needs to be done to make it work?

 

[Rootus]

Your right Hairy. Now, if there is not enough PTV clearance what needs to be done to make it work?

Choose a cam with less overlap, or cut the pistons (or get new ones).

Dave

 

[rockin_rick]

How big of a ball of clay should you put on the piston? I'm imagining a sphere about 1/2" to 3/4" in diameter, then squishing it down some. Is this about right?

Rick

 

[red94fiveo]

How big of a ball of clay should you put on the piston? I'm imagining a sphere about 1/2" to 3/4" in diameter, then squishing it down some. Is this about right?

Rick

That should be OK. Just don't use too much. I did this today and I used a little too mch, then I spent about 30 mins cleaning clay off pistons and valves.

 

[rockin_rick]

Here's a tip for those who haven't done this before. Don't use soft playdoh. Take the time to get modeling clay. I tried the playdoh and since it is so soft, it got inside (above) my valves so now I have to pull out the valves and clean it out. It was also so soft that it was hard for it to maintain it's shape after cutting and removing from the piston. I then had to go and get the real stuff and do it again...

I don't know, perhaps old, hard playdoh would be ok, but the modeling clay cost less than $2.

Rick

 

[fords2fast4u]

PTV Clearence is nothing to mess around with. Most of this has been answered, but use modeling clay, it will hold better when you cut it and pull it off the piston to measure it with micrometers. The amount of clay you need should not exceed much past filling the valve relief, which is a very small amount. As stated, .1 on the exhuast and .08 on the intake - I put together an engine once that pushed the envelope - something like .48 on one side or the other i don't remember - but that was the second measurment - the first what like .6 (on another pistion) - the owner said to put it together (with my hesitations) and it ran fine - 6 months later - #8 went south with bent valves and pieces of valve train all over the place -

needless to say, getting the pistons cut is not that much, and I think it cost me like $14 a piston - it took a little extra time to get them back, but i know they'll never touch - piece of mind - I'd cut the pistons before i went after a whole new cam to match my setup.