Piston to Valve clearance
Thread Starter
Racer
Joined: Aug 2004
Posts: 482
Likes: 80
From: Florida, Tampa Bay
Piston to Valve clearance
Getting ready for the heads install and trying to select which camshaft i'm going to go with. I'm swapping my cores out with a set of Bob's from precision porting in a couple weeks. The cores are of unkown origin to me and could have been milled without my knowledge. With all that being said what is the largest cam I can use without worrying about piston to valve clearance? I'm doing the install myself and if I pick a cam that doesn't clear, i'll be trying to return a used cam.
Thread Starter
Racer
Joined: Aug 2004
Posts: 482
Likes: 80
From: Florida, Tampa Bay
That's close to what I was thinking. If I go with something very close to 0.600 and the heads have been milled i'll be right on the edge. Does anyone know what the maximum lift with unmilled heads is on a stock engine with stock valves.
Burning Brakes
Joined: Nov 2004
Posts: 822
Likes: 0
From: Grafton Ohio
The only way to be sure is to have your new heads cc'd then compare the results with a stock casting. Then you will know if and how much your new heads have been milled.FWIW I'm running stock .054 gaskets with 317 casting unmilled heads and a comp 581/588 224/228 cam and have no clearance issues at all. Jer. 
Drifting
Joined: May 2002
Posts: 1,607
Likes: 1
From: San Francisco CA
Originally Posted by smittydog
Does anyone know what the maximum lift with unmilled heads is on a stock engine with stock valves.
Since you're pulling the heads anyway, you could always put some modeling clay on a piston then slap a head back on (with the valve train for one cylinder) and turn the engine over and measure the thickness of the clay.
Thread Starter
Racer
Joined: Aug 2004
Posts: 482
Likes: 80
From: Florida, Tampa Bay
When checking the clay thickness, what is safe and is it necessary to check all cylinders?
My ported heads will be CC'd. So I can compare that to a new head and tell how much it's been milled?
My ported heads will be CC'd. So I can compare that to a new head and tell how much it's been milled?
Racer
Joined: Mar 1999
Posts: 413
Likes: 0
From: Pennsville, NJ
Originally Posted by smittydog
When checking the clay thickness, what is safe and is it necessary to check all cylinders?
My ported heads will be CC'd. So I can compare that to a new head and tell how much it's been milled?
My ported heads will be CC'd. So I can compare that to a new head and tell how much it's been milled?
1. Minimum clearances: .080 Intake, .100 Exhaust (with head gasket installed).
2. Only need to check #1 Cylinder if you are staying with .080, .100.
EVERYONE should measure PTV clearance. From my research on this forum and others indicates that a piston can come out of the hole anywhere from .003 - .010. So if someone says cam "X"/gasket "Y" fits for them, they might not fit for you. Are you willing to trash your investment for the sake of a little time?
Good Luck!
Thread Starter
Racer
Joined: Aug 2004
Posts: 482
Likes: 80
From: Florida, Tampa Bay
After I put a thin layer of clay on the piston where the valves come the closest, assemly one head, valve train and turn over the engine a couple times by hand. Then I go to the shallowest part of the clay and measure it's thickness? Any tips on the easiest way to measure the clay? Not many high dollar tools under my tree but I can borrow some if necessary.
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Drifting
Joined: May 2002
Posts: 1,607
Likes: 1
From: San Francisco CA
Here are some instructions from Comp cams: http://www.compcams.com/Technical/Instructions/
Click on “Camshaft installation and degreeing instructions” (This is an Adobe .pdf file so you will need a copy of Adobe Acrobat reader)
Go to page four and there is a section on measuring piston to valve clearance.
Keep in mind that clearances vary with duration as well as lift and a 240 duration cam will likely have less clearance than a 224 duration cam with the same lift but this should give you a better idea of your clearance than you have now. You will want to do this procedure again when you get your new cam to be sure you have enough.
This is the “poor mans” way to check the clearance and it’s simple and pretty accurate. Most engine builders use a cam degreeing kit (approx. $200-250) to accurately degree a cam for maximum performance as well as to check piston to valve clearance accurately at various degrees of crankshaft rotation
Click on “Camshaft installation and degreeing instructions” (This is an Adobe .pdf file so you will need a copy of Adobe Acrobat reader)
Go to page four and there is a section on measuring piston to valve clearance.
Keep in mind that clearances vary with duration as well as lift and a 240 duration cam will likely have less clearance than a 224 duration cam with the same lift but this should give you a better idea of your clearance than you have now. You will want to do this procedure again when you get your new cam to be sure you have enough.
This is the “poor mans” way to check the clearance and it’s simple and pretty accurate. Most engine builders use a cam degreeing kit (approx. $200-250) to accurately degree a cam for maximum performance as well as to check piston to valve clearance accurately at various degrees of crankshaft rotation
Drifting
Joined: May 2002
Posts: 1,607
Likes: 1
From: San Francisco CA
You can take one of your lifters and remove the plunger assembly and spring, and then take up the space with nuts/washers, so you can just get the pushrod cup and clip back in it. Do this with two lifters. Use the stock pushrod.
Thread Starter
Racer
Joined: Aug 2004
Posts: 482
Likes: 80
From: Florida, Tampa Bay
That sounds like it should work! I was planning on reusing my stock lifters and picking up some pushrods. Can the lifter be reasembled after or should I pick up a set of new ones?