valve train geometry?

[grumpyvette]

IF Im changing just the cam and lifters do I need to recheck the pushrod length?
JUST WONDERING,IF YOU HAVE STOCK LENGTH PUSHRODS,YOU MILL THE HEADS,USE THIN METAL HEAD GASKETS,WOULDN'T THIS PUT THE ROCKER ARM CLOSER TO THE CAM?THEN WHY DO YOU NEED LONGER PUSHRODS WHEN YOU INSTALL A BIGGER CAM THAN STOCK?YOU WOULD THINK YOU WOULD NEED A SHORTER ONE SINCE THE LOBE IS TALLER THAN STOCK AN THE ROCKER ARM IS CLOSER TO THE CAM BECAUSE OF MILLING & THINNER HEADGASKETS.



while your correct! the answers not always that simple because the cam base circle dia. on the new cam is frequently a differant dia. than the stock cam and the lifter seat height varies also, it will require verifyiong the correct valve train geometry.
you want the rocker to exert it force as much as possiable on the valve centerline to reduce friction and valve guide wear
YOULL NEED TO CAREFULLY CHECK YOUR PARTICULAR ENGINE!
heres a simple way to get close to the correct length
BUY ONE OF THESE

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=3567&prmenbr=361

after making sure the valve springs are correctly installed you drop the checker in place on the rocker stud and install your adjustable pushrod
adjust the length to fit and measure the resulting length if its within twenty thousands of the stock length its fine for most applications, if its more than 30 thousands long or short get the closest length set available

<b>btw, if your one of the people that still does not own an adjustable push rod! you can easily make your own by cutting a stock pushrod in 1/2 (2 pieces), removeing 1 inch from the total length an then with about 2 " of a 4 inch section of 3/16 or 1/4" thread rod installed and (in one section epoxy it in place leaving about 2" sticking out thread two nuts onto the thread rod and slip on the other end of the cut pushrod,(no epoxy) use the two nuts to adjust to stock length and let the epoxy harded in the one section[/color] now you can easily measure and order custom push rods useing the pushrod checker and adjustable push rod as tools
AND YEAH IT ONLY WORKS WITH THE CYLINDER HEADS ON AND THE INTAKE REMOVED BECAUSE THE HOLE IN THE CYLINDER HEAD that GUIDEs THE PUSH ROD WON,T ALLOW THE NUTS ON THE ADJUSTABLE PUSHROD TO PASS THRU, UNLESS YOU PLACE THE CUT ABOUT 1" from the UPPER END OF THE ADJUSTABLE TEST PUSHROD BUT I prefer to place the adjusting nuts centered as I like to watch for all clearances with the intake manifold removed while manually checking as I turn the engine over by hand durring assembly, and at that point, while checking all the clearances, I use test springs which apply very little load on the push rod</b>

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=3272&prmenbr=361

HERES OTHER TOOLS YOU MIGHT NEED

SOMETHING TO READ
http://www.compcams.com/information/Products/Pushrods/

CCA-7705 5.800 in. to 9.800 in. adjustment range, Master pushrod length checker 4 piece kit ... $78.69

here

http://www.vetteweb.com/tech/vemp_0703_ ... index.html

http://www.circletrack.com/techarticles ... index.html

http://www.circletrack.com/techarticles ... ckers.html

http://www.compcams.com/Technical/FAQ/V ... ometry.asp

http://www.babcox.com/editorial/ar/eb50232.htm

http://www.customspeedparts.de/content/ ... metrie.php

http://www.hotrod.com/techarticles/cams ... index.html

http://www.eatonbalancing.com/blog/2007 ... -geometry/

 

[grumpyvette]

BTW if you go to change the valve springs with the heads still on the engine, most guys use the hose they use to do a compression check and the spark plug adapter and pump the cylinder up with about 125 psi of air to hold the valves shut while they do it, yeah it usually works just fine.

(yeah there's a different method)
(1)disconnect the battery
(2) remove the spark plugs, and rocker arms
(3)turn the first cylinder to BDC BYE HAND or someplace close to that
(4) insert one end of 5 ft of 3/8" rope into the cylinder thru the sparkplug hole and be sure you tie a KNOT in the other end
(5) rotate BYE HAND,the engine until the rope compresses against the valves holding them in place
(6)REPLACE THE SPRINGS on that cylinder while the valves are held to the combustion chamber roof
(7)rotate the cylinder back to BDC
(8)pull out the rope

(repeat 7 more times) :laughing:

yeah! the air USUALLY works but I don,t trust it EITHER, I want those valves locked from falling into the cylinder PHYSICALLY

BTW youll want one of these or something similar

http://store.summitracing.com/partdetail.asp?part=SUM-906784&autoview=sku

IVE done it both ways many times, Ive never trusted the air alone but Ive used it without problems in the past, the ropes usually not a problem,, and yeah theres the potential for it to tangle but I have not had that happen either
self aligning rockers have ridges to prevent the rocker from moving off the valve stem

http://www.ratwell.com/technical/HydraulicLifters.html

If you think you have a worn cam lobe, it will not open the valve completely, while a stuck or burnt valve won,t close completely, remove the compression tester and , squirt some oil into the cylinder and retest, if it bumps the readings up significantly its not likely to be a result from a worn cam lobe, but it might be from bad rings, detonation damage on the piston, or a burnt or non-seating valve ,
your best course is to pull the valve covers and carefully watch the rockers,and measure the lift at the retainer, with a dial indicator and a magnetic base while you slowly turn the engine by hand if you find a suspect worn cam lobe,when cam lobes wear they usually eat lifters and cause other damage thats measurable at the rocker/retainer

http://www.harborfreight.com/cpi/ctaf/d ... umber=5645

http://www.harborfreight.com/cpi/ctaf/d ... number=623

viewtopic.php?f=62&t=881&hilit=leakdown%E2%80%A6

viewtopic.php?f=52&t=282

If you find a flat tappet lifter that's not pumping oil, you'll need to inspect closer,and try adjusting the preload or lash carefully,flat tappet lifters need to spin freely in their bores to prevent wear,if the cams undamaged (UNLIKELY) yes you can just drop a well lubed (use molly assembly lube)new lifter onto the lobe and adjust the valve preload/ or lash clearance and your good to go, but carefully inspect the cam lobe thru the lifter bore once its out and any resistance to the lifter sliding up out of the bore usually indicates BOTH the lifter base and cam lobe are damaged and you need a new cam/lifter set
then place a high pressure air hose on the cylinder after you bring the cylinder up to TDC on the COMPRESSION STROKE, and listen for air leaking out of the exhaust or intake indicating a burnt or bent valve


http://www.youtube.com/watch?v=DxROQtv7 ... r_embedded

LOOK CLOSELY he OBVIOUSLY had the clearances wrong, look at the inner area where the rocker stud adjustment nut has worn a a significant polished area where it was badly miss aligned, now proform may not be nearly (TOP OF THE LINE) but looking at the evidences strongly suggests a clearance issue or geometry issue with the valve train was a major factor in the rocker failure. I see guys knock the parts manufacturers all the time and at times its valid, but many times when parts fail its improper installation, or lack of knowledge as to proper procedures or how to check clearances or geometry.

btw heres a better rocker design

http://www.youtube.com/watch?v=UrWK73ysF3Y