Can,t Adjust The Valve Lash

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
Probably something simple but here is what I have.
496, mutha thumpr hydraulic flat tappet cam, flat tappet pro magnum lifters, both brand new.
Using studs in heads for rockers, poly lock and roller.
Going through the assembly valve lash for zero I have a rocker that the nut is all the way down and cant tighten enough down to set the lash.
Is this a stud issue? Could the pushrod be bent so slightly I cant tell? Maybe a rocker problem?
Never experienced this. This engine has not been run.



step one, ISOLATE AND TEST!
VERIFY, if one cylinders valve train has issues,
locate the component or clearance thats different.
it may be as simple as the wrong push rod length or the wrong rocker stud

verify your valve train geometry, is correct, verify push rod lengths are all the same,
on the exhaust and all the push rod lengths are all the same on intake valves,
and all the rocker studs are the same length and type,
if only one rocker won,t adjust, swap its rocker, rocker jam nut,
and push rod with one in a different location
if the problem moves , with the components being moved,
its the rocker or push rod, if the problem stays in the same location,
its more likely the valve spring height,or clearance issue, worn cam lobe or worn lifter or wrong or improperly installed rocker stud

big block rocker geometry test tools have one side up for intake, the other side up for exhaust
Proform Pushrod Length Checkers 66806 BBC 7/16" rocker studs

pro-66806_w_xl.jpg

heres a bit of useful related push rod length info
Big Block Chevy, Standard Length Big Block Intake 3/8" / .080" 8.275"
295-7941-8 Big Block Chevy, Standard Length Big Block Exhaust 3/8" / .080" 9.250"
295-7969-8 Big Block Chevy, Standard Big Block +.100" Long Intake 3/8" / .080" 8.375"
295-7979-8 Big Block Chevy, Standard Big Block +.100" Long Exhaust 3/8" / .080" 9.350"
295-7951-8 Big Block Chevy, Standard Length Big Block Tall Deck Intake 3/8" / .080" 8.675"
295-7961-8 Big Block Chevy, Standard Length Big Block Tall Deck Exhaust 3/8" / .080" 9.650"
295-7800 V8 396-454 Retro Fit Pushrod Set, Intake & Exhaust, 1965-Present
3/8" / .080"
3/8" / .080" 7.725 Int.
8.675 Exh
295-7913-16 Small Block Chevy, Standard Length Small Block Chevy 3/8" / .080" 7.800"
295-7984-16 Small Block Chevy, +.100" Long 3/8" / .080" 7.900"
295-7934-16 Big Block Ford, Standard Length Ford `72-'78 429-460 3/8" / .080" 8.550"
295-7951-16 Big Block Ford, Standard Length Ford `69-'71 429-460 3/8" / .080" 8.675"
295-7582-16 Oldsmobile, Std Length 455 5/16" 9.550"

you'll want a adjustable push rod and rocker geometry check tool
prctool.png



once youve got the correct geometry checker, and checked clearances
and verified push rod length,
chances are excellent your issues resolved,
obviously reading the linked info below will provide far more details


Proform Pushrod Length Checkers 66806 BBC 7/16" rocker studs

https://www.summitracing.com/parts/pro-66806

http://www.summitracing.com/parts/tfs-9001 (7.5-to-8.7")

http://www.summitracing.com/parts/tfs-9000 (6.125-to-07.5")

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...rdering-correct-custom-length-pushrods.14241/

http://garage.grumpysperformance.com/index.php?threads/stock-gm-push-rod-length.3844/

http://garage.grumpysperformance.co...e-springs-and-setting-up-the-valve-train.181/

http://garage.grumpysperformance.com/index.php?threads/correctly-adjusting-valves.196/

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

http://garage.grumpysperformance.com/index.php?threads/big-block-pushrod-guide-plates.4596/
 
Last edited:
Grumpy he has a Comp Cams MOTHER HUMPER Cam in a Big Chevy 496.
Just a Terrible Sin in the Hotrod World here.
 
I can't deny its a less than ideal choice in my opinion,
but its a free country so far, and people are allowed to make less informed decisions,
the cam selected is not the issue,
its the in-ability to set proper valve lash and valve train clearances,
and geometry thats the issue
 
I can't deny its a less than ideal choice in my opinion,
but its a free country so far, and people are allowed to make less informed decisions,
the cam selected is not the issue,
its the in-ability to set proper valve lash and valve train clearances,
and geometry thats the issue
It probably rounded 1/2 the cam lobes .
 
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