Piston Releif

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BeesDad

New Member

Apr 29, 2020

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Edmonton

Apr 29, 2020

#1

• Apr 29, 2020

• #1

Hello everyone, I'm new to the Ford world & was hoping someone would be able to help me out. I have an 89 LX notch that I'm in the process of installing a cam & ported GT40P's
I got the cam in, pushrods measured & purchased but I'm having trouble with PTV clearance on the intake valves. I did the clay method for checking & have almost no clearance. I know it's not contacting the piston because I put paint on the relief of a different piston & had no paint transfer. My question is how much can you take off of the piston relief on OEM pistons?
Any & all help is appreciated

Joe

 

Mustang5L5

That is…until I whipped out my Bissell

Mod Dude

Feb 18, 2001

43,175

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Massachusetts

Apr 29, 2020

#2

• Apr 29, 2020

• #2

You should really use clay and measure how much of a cut the valve makes into the clay and how far it is into the piston. Usually the numbers thrown around are a min of 0.080" for the intake valve, and 0.100" on the exhaust valve. So, until you know what you have for clearance, you don't really know how far to flycut the piston.

Also, take into consideration your springs. What are you running? The intake valve chases the piston down, so valve float tends to not be an issue on the intake side, but the exhaust valve is snapping shut as the piston is coming up. If the spring is weak, it might float at high RPM and delay slightly, taking your 0.100" exhaust clearance down to 0.060" or closer.

 

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BeesDad

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Apr 29, 2020

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Edmonton

Apr 29, 2020

#3

• Apr 29, 2020

• #3

Thanks for the info Mustang5L5
I'm not sure which exact springs the heads have but they are Alex's Parts springs. Like I said the clay gets so thin that it's hard to read. If I had to guess I would say roughly the thickness of a sheet of paper?

 

Mustang5L5

That is…until I whipped out my Bissell

Mod Dude

Feb 18, 2001

43,175

17,876

224

Massachusetts

Apr 29, 2020

#4

• Apr 29, 2020

• #4

That’s probably too close.

This is my engine I recently built and this is about 0.080” which is as close as you want it.



You’ll have to grab a cheap set of calipers and get some measurements, but I am gonna assume you need more

 

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BeesDad

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Apr 29, 2020

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Apr 29, 2020

#5

• Apr 29, 2020

• #5

I’m really confused now
I can see the mark from your valve but it’s not even in the valve relief?!
Did I mention I’m new to this lol

 

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BeesDad

New Member

Apr 29, 2020

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Apr 29, 2020

#6

• Apr 29, 2020

• #6

All I get is a tiny smear of clay in the relief

 

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BeesDad

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#7

• Apr 29, 2020

• #7

 

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BeesDad

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Apr 29, 2020

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Edmonton

Apr 30, 2020

#8

• Apr 30, 2020

• #8

Please disregard that last comment Mustang5L5, I've since figured out that you must be running A/M heads with different valve locations

 

skankin

Member

Jan 18, 2002

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May 20, 2020

#9

• May 20, 2020

• #9

What cam are you using with the P heads?

 

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BeesDad

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May 20, 2020

#10

• May 20, 2020

• #10

It's a Speedmaster hydraulic roller. Intake lift is .513, exhaust .529, intake duration is 282, (230 @ 050) exhaust 289 (236 @ 050) with a 110 LSA