Piston to valve clearance wisdom

Hello,

I have a freshly decked head that i am trying to check piston to valve clearance.

Using helper springs and some modeling clay, I was able to get a sample to measure but dont have a spec.

Engine is Mazda Skyactiv 2.5L, high compression engine means extra concern here.

Questions:

1. How would I compensate for VVT for this test?

2. The service manual doesn't have a piston to valve clearance requirement. How do I know what is acceptable?

Thanks,

Phil.

Generally 0.080in intake and 0.100in exhaust, but race engines might reduce this to 0.060in or less. With a Variable Valve Timing, you would typically check at both ends of the adjustment range. You will probably need to temporarily pin or block the adjusting mechanism to hold that position.

BTW there is a module specifically on this topic in the Engine Building Fundamentals course.

Hey David, appreciate the quick response.

Regarding the cam phasers, Is it safe to assume that the mechanical limit of the phasers is the maximum cam timing the engine will command?

The exhaust VVT is hydraulic, the Intake side is electric.

Yes, there has to be a mechanical stop -- so you don't rely on software to prevent a piston to valve interference. If you find your new decked block has insufficient clearance in the maximum position (advanced for intake, retarded for exhaust), you could modify the phaser to prevent that. Then tune the ECU to only use the available range.