Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - 351 W Intake Choice
View Single Post
  #32 (permalink)  
Old 12-08-2018, 12:56 PM
ericnova72's Avatar
ericnova72 ericnova72 is offline
More for Less Racer
Join Date: Jan 2007
Location: S.W. Lower Michigan
Age: 53
Posts: 17,994
Wiki Edits: 0

Thanks: 280
Thanked 3,339 Times in 2,795 Posts
Originally Posted by Fang16 View Post
Found this at
Is it a good way to do it?

For the dial indicator method, follow all the previous setup steps except placing clay on the piston top. Again, use solid lifters, install the rocker arms and set zero lash. Rotate the crankshaft clockwise until the degree wheel indicates the Number 1 piston is at 10 degrees ATDC on the intake stroke. This is the crank angle where interference is most likely to happen--not at TDC or at maximum intake-valve lift. At this point, the piston on its way down and, depending on the cam lobe profile, the intake valve is trying to chase it down. Mount the dial indicator on the cylinder head and position it over the retainer of Number 1 intake valve. Set the dial indicator to zero. Make sure that the plunger on the dial indicator has plenty of range to move up and down. Use a small screwdriver or pick to push tip of the rocker arm downward until you feel the valve contact the piston. Observe the dial indicator to determine the actual piston to valve clearance. To measure the clearance on the exhaust valve, rotate the motor clockwise until the timing wheel is at 10 degrees BTDC on the exhaust stroke. Again, this is the crankshaft position most likely to see P2V interference as the piston moves up and draws a bead
This does work, but I'll add a little info about it...

You'll want to check every 2 from 5-15 to find the point the piston and valve are the closest, as 10 is not going to be right in a lot of cases, so best to sneak up on it and locate the closest contact point for your build and go with that for the reference.

This method will tell you if the piston relief is deep enough....but it won't tell you radial clearance(whether the eyebrow relief is big enough in diameter to clear the valve diameter.....clay is still about the only way you can get that measurement.
Reply With Quote
The Following User Says Thank You to ericnova72 For This Useful Post:
techinspector1 (12-08-2018)