So preparing to start my top end build-up and I am planning out my steps and one question I am battling with: Do you verify valvetrain geometry first / verify pushrod length first and then check for valve to piston clearance or vice versa?

Seems like if you verify VT geometry first, you run the risk of caausing aa collision with your valves and cylinder. But if you verify valve to piston clearance first, you may not have thaat right either as a incorrect pushrod could also skew results.

Current set-up and planned upgrades below

Current Set-up
383 (Jasper Class II)
Blue Racer Crane Cam WG-1173
• .050 Duration: 224° Intake; 234° Exhaust
• Advertised Duration: 298° Intake; 304° Exhaust
• Cam Lift: .290 Intake; .300 Exhaust
• Valve Lift: .465 Intake; .488 Exhaust
• Lobe Center: 107° Intake; 117° Exhaust
Edelbrock Performer 2101
Hooker Headers and Sidepipes w/ Max Flo inserts
Speed Demon 750 Carb
Dart S/S Iron Eagle Heads (10024267)
- 76cc combustion chamber, 165intake/65exhaust and
2.02intake/1.60exhaust
1.5" Rockers
TKO-500
3.55 gears

Planned Upgrades
Edelbrock Air Gap 7501 (already purchased and verified will fit under hood)
AFR 195 aluminum cylinder heads with 75cc chambers (part #1036)
1.6" Rockers - (#1301-16)
Pushrods (part #7944-16) - I have the tools to measure as well but this is my initial guess.
COMP Cams Xtreme Energy Retro-Fit Camshafts CCA-12-433-8
Cam Style: Hydraulic roller tappet
Comp Cams High Energy Roller Lifters (part #853-16)
Head Bolts (part #134-3601)
Rocker Studs (4500-16)
Guide Plates (4808-8)
Various Gaskets
Autolite Platinum Plugs AP3924 w/ .4 gap
Blue & Black RTV, Assembly Lube, Break-In Oil

Thanks
Shane

 

Your valve to piston clearance is based on your cam shaft lift and duration and has nothing to do with the valve train geometry. Checking valve train geometry simply makes sure the rocker is centered in the center of the valve stem during its motion.

 

Pushrod length has no effect on valve lift.

 

once you establish your clearance, use a manley pushrod length checker and try to achieve these results...easy to do ......

 

Folks, thanks.
So maybe I have a misconception of checking valve to piston clearance....

My understanding was that you installed pushrods, lifters, etc and THEN rotated the engine to ensure that as the valves moved they did not interfere with the piston.

So do you actually just rotate the engine with our the pushrods, lifters, etc installed? And look for clearance between a dynamic piston and static valves?
Shane

 

Correct.

 

You are correct that you rotate the engine with the lifters, push rods, and rockers installed but the push rod length has nothing to do with the piston to valve clearance.

 

So then I am really confused....
If you have everything assembled then, wouldn't a longer pushrod cause a greater movement of the rocker and therefore a greater movement of the valves into the combustion chamber?

Oh wait, I think I just figure it out. If, when I am going through this procedure, even if the pushrod length is not ideal, I am setting it to zero lash and the actual amount of movement through the valvetrain will remain the same. <slaps head>

Do I got it now?

 

 

Shane

Make sure the cam is degreed in when checking. If your using the tool with the radius make sure you check the center line of the intake which should be 106 center line with your cam, Don't check it a .050 unless you knopw the radius on the tool has he same radius as the roller lifter you are using or it will throw you off, Thats why the center line method is the safest method to use.

Or you could measure how much the pistons are in the hole, valve pocket depth, gasket thickness and measure how much your valves are below the deck and add all that up and we call this valve drop and call Compcams and give them this info with your cam info and they can come pretty close on how much clearance you will have.

Its going to hard to check everything with a hyd. lifter as it will colapse while checking giving you a false reading.

 

You have to measure your piston to block deck clearance and do the math based on the valvetrain geometry to determine whether it's safe to install a different cam or rocker system than was originally designed for an engine. Hand turning the engine over after assembly is just a sanity check to make sure you didn't installed the cam chain on the totally wrong teeth and to help push some oil through the galleries.

 

Any good "for Dummies" guides on this?

 

The only way to be sure about this is to assemble a piston and the valves, rockers, pushrods and lifters (must be solid lifters) for that cylinder and check it with clay.

 

This is exactly what I was planning on doing.....But some of the other folks seem to indicate I shold be doing a series of advanced pre-calculations.

Is the spin & clay method ok for a mildly aggressive street engine but the truly "correct" way is in depth calculations? And is that really only necessary with a race / strip engine with smaller tolerances?

 

I don't know of any calculations which would give you a reliable answer.

 

The short answer to your last statement is yes. Pushrod length has nothing to do with valve lift or clearance. No mater what length the push rod is, the motion is the same (duration, lift, etc).