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Piston -valve clearances

  
Mopar Muscle
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Piston -valve clearances

 
Spud490 Spud490
User | Posts: 65 | Joined: 01/12
Posted: 10/10/12
10:06 PM

Can you check piston to valve clearances WITHOUT using rockers! Is it possible to just do the math using the specs of the cam & how much the valves-move at the tightest spot? My motor is totally new & I don't have rockers yet and I'm  trying to figure out IF I can run 1.6 ratio rockers or not depending on clearances. I just don't want to buy 1.5 ratio IF I can run 1.6.  
10's or bust!!

Garys69RR Garys69RR
User | Posts: 99 | Joined: 03/12
Posted: 10/11/12
03:19 AM

What piston are you using? What cam? Solid, roller or hydraulic? Maybe some one else has used that combination and can enlighten you. But in the end, always do a final check on assembly.  

69_340_GTS 69_340_GTS
Enthusiast | Posts: 535 | Joined: 06/09
Posted: 10/11/12
04:02 AM

Sure. Put on a light valve spring. Put the piston at the crankshaft (rotation) location of maximum valve lift. Install a dial indicator, making sure the valve and the stroke of the indicator are parallel. Push the valve down until it contacts the piston and take a reading on the indicator. So now you know how far the valve can travel before it hits the piston. Subtract the cam lift (times the rocker ratio) from the total travel, and you have your clearance. Easier and better to do this with all the parts assembled though, and less chance for a mistake.  

451Mopar 451Mopar
User | Posts: 220 | Joined: 07/10
Posted: 10/11/12
08:57 PM

That won't work as described, the maximum valve lift will be the installed lobe centerline, which means the piston will be more than 1/2 down the bore at max valve lift.
The minimum piston to valve clearance is around TDC +/-20 degrees.
You would need to know the distance between the closed valves at the piston when the piston is at TDC as your starting distance (I refer to it as "valve drop" distance.)
Then you can either calculate the piston position, or using a degree wheel advance the crank a degree at a time and record the valve drop distance of both the intake and exhaust.  You did not say what engine, but for example using a 440 engine, +/-5 degrees from TDC, the piston only moves down the bore about 0.006", +/-10 degrees is about 0.0243", +/-15 is about 0.0546", and +/-20 is about 0.0968".
The second part is measuring the cams lobe lift at these points around TDC.
Once you know the cams lobe lifts you can multiply the rocker ratio to get total valve lift at each degree measured, then subtract that from the total valve drop distance calculated from the valve drop at TDC plus the piston position from TDC.  

69_340_GTS 69_340_GTS
Enthusiast | Posts: 535 | Joined: 06/09
Posted: 10/12/12
04:53 AM

I knew how to do it but that 3rd sentence wasn't exactly what I was trying to say! 451 did a much better job.  

Spud490 Spud490
User | Posts: 65 | Joined: 01/12
Posted: 10/12/12
06:46 PM

I'm doing the 490" 383 stroker from Muscle motors w/ Ross piston(9.9 cc dish ). Now using Indy ez heads (cnc port max wedge) instead of the B1/bs heads. Mp .620 solid cam. Ross says they cut the valve reliefs for .700-.750 lift with 9.980 deck height( I have 9.965 w/ 0 piston- deck height. Also .051 cometic gskts). So according to that math I SHOULD be good for the .661 lift that 1.6 ratio results from. Thx guys for the info.  
10's or bust!!