Checking valve clearance question

[turbo36]

New to this so be nice:icon_blackeye:

Can you check valve clearance with this method?

1. roll motor to TDC

2. assemble the heads with an exhaust and intake valve, but no spring

3. pull up on the valve to establish a closed position

4. push down on the valve until it contacts the piston and measure the travel- this distance should be the maximum cam lift at contact???? I would guess there is some over travel of the valve due to inertia??

I'm sure there are variables in this method that I overlooked , so fire away!!

thanks, Bob

 

[Cranky]

That is not the correct way to check it. These articles have useful info....
http://www.carcraft.com/howto/116_0701_valve_to_piston_clearance/viewall.html
http://www.racingheadservice.com/Information/Technical/PistonToValveClearance.asp

 

[turbo36]

That is not the correct way to check it. These articles have useful info....
http://www.carcraft.com/howto/116_0701_valve_to_piston_clearance/viewall.html
http://www.racingheadservice.com/Information/Technical/PistonToValveClearance.asp

The links you sent where very informative, thanks. But perhaps I need to ask my question a different way. Is there a way to get a starting point without having a cam installed?

 

[IQ52]

No

 

[67 B-body]

The issue is that the valves aren't open at max lift at TDC... The valve will chase the piston untill it gets to max lift, and if along the way it does go further than the pistons current position you have strike.
If you simply put it to TDC and drop the valve down to the piston and measure, you'll cheat yourself out of available lift in the real scenario of your 4 cycle sequence.
I hope this helps you understand a little better...

 

[Meep-Meep]

The issue is that the valves aren't open at max lift at TDC... The valve will chase the piston untill it gets to max lift, and if along the way it does go further than the pistons current position you have strike.
If you simply put it to TDC and drop the valve down to the piston and measure, you'll cheat yourself out of available lift in the real scenario of your 4 cycle sequence.
I hope this helps you understand a little better...

Exactly! Well said.

 

[451Mopar]

I posted a response on Moparts that trys to explain this.
http://www.forbbodiesonly.com/moparforum/showthread.php?t=31674

If you had the cam profile data, showing lobe lift for each degree of rotation, you could calculate the piston to valve clearance for each degree of crank rotation.
Note that in addition to the cam profile, you would need to know the "valve drop" P-V clearance from the valve seated to the piston at TDC, the crank stroke, and rod length.
With the crank stroke and rod length, you can calculate the piston position, Then add the piston position to the "valve drop" number to get the total distance from the seated valve to the piston, repeat for each degree of crank rotation for about +/-30 degrees around TDC. With those numbers, subtract the cam lobe lift, times the rocker ratio, when the lobe is at the same crank degree. This is where you would need to know the lobe profile, and the cams installed centerline.

 

[turbo36]

I posted a response on Moparts that trys to explain this.
http://www.forbbodiesonly.com/moparforum/showthread.php?t=31674

If you had the cam profile data, showing lobe lift for each degree of rotation, you could calculate the piston to valve clearance for each degree of crank rotation.
Note that in addition to the cam profile, you would need to know the "valve drop" P-V clearance from the valve seated to the piston at TDC, the crank stroke, and rod length.
With the crank stroke and rod length, you can calculate the piston position, Then add the piston position to the "valve drop" number to get the total distance from the seated valve to the piston, repeat for each degree of crank rotation for about +/-30 degrees around TDC. With those numbers, subtract the cam lobe lift, times the rocker ratio, when the lobe is at the same crank degree. This is where you would need to know the lobe profile, and the cams installed centerline.

Thanks, this gives me a pretty clear picture of the complexity of this process, so now I understand all the "put it in and see what you get " responses.