Does Different Pushrod Length Change Valve To Piston Clearance

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
Guys, I went from an incorrect length (8.950) to a correct length (9.034) pushrod. Does that change valve to piston clearance? I compensated for the shorter pushrods with the lash adjuster screw. In fact I "compensated right out of oil circulation" with T&D Rockers. Now that I have the correct pushrods I'm wondering if the valve will open wider. Clearance was already tight @ 0.70 with zero lash. Anyone?

If you change pushrod length on a stud mount rocker,
like the big block or small block chevy or Pontiac engines
you'll change the rocker geometry and that can affect valve to piston clearance.
in the example you posted, you changed the push rod length about .080
this will effect the proper rocker geometry ,
without checking you can,t be sure it improved or got worse and the same thing applies to the piston to valve clearances,
you can.t guess, you need to verify.
always deal in facts, never guess.
yes the difference should be minor, total lift may not change all that much,
but the point in the piston to valve clearance between the components in their respective rotation where the valve comes closest to the piston might change a degree or two, so its well worth checking out.
you really need to degree in any cam and check the valve train clearances and piston to valve clearances carefully,
never assume, it gets expensive when you're wrong.
its well worth the cost to own and know how to use a degree wheel and a dial indicator and any mechanic should have some plastic clay for verifying.
yeah pulling a head to checks a P.I.T.A. but its far better than bouncing valves off a piston because you were not willing to check carefully, the piston to valve clearances
yodam.jpg

this is something that anyone with experience will take the time and effort to check & verify simply because the potential cost in, damaged parts and machine work, if you get it wrong can be very high!
he truth is your only guessing unless you accurately measure the internal clearances with your engine set up correctly with the cam and rotating assembly correctly installed.
sure there are software programs that can predict what clearances you'll have but they are never precise. you need to verify the clearances.
you really need a dial indicator and a degree wheel and some modeling clay
clay6.jpg

yes I use BOTH the push rod checker tools to get the quick check on length, and the adjustable length push-rods and a marker too method verify the correct length with a cross check by looking at the wear/sweep and location, on the valve tip
valvetip.jpg

if your within .050 away youll generally be ok, if your within, .030 or less that is ideal,
at some point your effectively "SPLITTING HAIRS" and yes ideal length is preferred
if you have adjustable length push rods you can play with the length to find ,
what gives you the best and most consistent and ideally narrow and preferably centered,valve tip wear pattern
that way your not guessing , you see what minor changes do to the wear pattern
get as close as you can, and it does not mater much if its a bit over or under length as long as its reasonable close
http://garage.grumpysperformance.co...rect-custom-length-pushrods.14241/#post-72353

http://garage.grumpysperformance.com/index.php?threads/pushrod-length-tolerance.15189/#post-86918



03313a.jpg

don,t put absolute trust in a cam cards info, thats one factor I constantly find where the printed info, that comes on the cam cards , varies so much, from reality , that the only way you can know exactly what the truth is, is with a dial indicator on YOUR engine with YOUR cam.

dialretainer.jpg

RockerGeometry.jpg


GRAPH SHOWING VALVE AND PISTON LOCATION, ,USUALLY AT ITS CLOSEST BETWEEN 10-20 DEGREES BFTDC and USUALLY AT ITS CLOSEST BETWEEN 10-20 DEGREES AFTDC
PtV3.jpg



related threads
yes as usual, much of the info you need is in links and sub=links:rolleyes::D


http://garage.grumpysperformance.com/index.php?threads/checking-piston-to-valve-clearances.399/

http://garage.grumpysperformance.com/index.php?threads/valve-train-clearances-and-problems.528/

http://garage.grumpysperformance.com/index.php?threads/rocker-push-rod-wear-issues.9815/

http://garage.grumpysperformance.co...ectly-and-get-it-to-last-cam-install-info.90/

http://garage.grumpysperformance.com/index.php?threads/check-cam-valve-lift.15893/#post-95551

http://garage.grumpysperformance.co...-pushrods-and-check-info-you-might-need.5931/

http://garage.grumpysperformance.com/index.php?threads/pushrod-length-tolerance.15189/#post-86920

http://garage.grumpysperformance.co...ng-combustion-chambers.2630/page-2#post-54342

http://garage.grumpysperformance.co...train-clearances-and-problems.528/#post-79273

http://garage.grumpysperformance.co...mble-and-swirl-quench-squish.4081/#post-12283

http://garage.grumpysperformance.com/index.php?threads/valve-to-piston-clearance.16349/#post-99047
 
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