Is there an up side to running a slightly longer valve? As in .040 longer. Is there a down side? Does rocker geometry go all to hell? Thanks. Kim
Longer valves
- Thread starter oldkimmer
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Wyrmrider
Well-Known Member
Kim
let''s say your motor was designed for a .440 valve lift
and the stock rocker was angled up with the valve closed = flat at mid lift and angled down the same amount of the angle up at valve open
now you stick in a cam with .520 lift?
what happens?
valve closed is in the same place so all the lift angles the rocker tilted down
called overarcing
now put in your .040 longer valve (hope you did not sink the vales that much)
mid lift is right back where you were stock
a little more up==a little more down
cheers
let''s say your motor was designed for a .440 valve lift
and the stock rocker was angled up with the valve closed = flat at mid lift and angled down the same amount of the angle up at valve open
now you stick in a cam with .520 lift?
what happens?
valve closed is in the same place so all the lift angles the rocker tilted down
called overarcing
now put in your .040 longer valve (hope you did not sink the vales that much)
mid lift is right back where you were stock
a little more up==a little more down
cheers
I didn’t get that...
Kim, it Aggravates the Geometry issue. You will have to pick up the rocker and move it back. IF you NEED a longer valve for big lift, then you do it. Otherwise a standard valve in a standard head will handle most of what you need. If not, you probably need an aftermarket head.
Kim, it Aggravates the Geometry issue. You will have to pick up the rocker and move it back. IF you NEED a longer valve for big lift, then you do it. Otherwise a standard valve in a standard head will handle most of what you need. If not, you probably need an aftermarket head.
Wyrmrider
Well-Known Member
sure
the piviot ends up low
so you could move the shaft
but if .040 makes a difference think about what a quarter inch radius roller does
my point was that you have to figure in valve lift as well as the stem
rumble gets it
think about mid arc at mid lift
the piviot ends up low
so you could move the shaft
but if .040 makes a difference think about what a quarter inch radius roller does
my point was that you have to figure in valve lift as well as the stem
rumble gets it
think about mid arc at mid lift
It really depends upon the application. I don't know how many small block LA heads we rebuilt 11/32 bronze guides and hardened seats using longer 11/32 stemmed Chevy valves. The cost of the Chevy valves is what cinched the deal.
replicaracer43
Grumpy Old Man
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Lots of people run screwed up rocker geometry, even some of the well known shops. Youd be surprised.
yellow rose
Overnight Sensation
I'm not. People just let **** go and call it good, then when it eats parts and needs a ton of spring and it won't RPM like it should it needs to be fixed.
Cheaper to do it correct once. But you know...guys have been doing without fixing geometry since the 60's so that means it's ok.
Rediculous really.
Wyrmrider
Well-Known Member
same findings as iQ
MOPAROFFICIAL
Oogliboogli
If you wanna do the best with the worst, raise the valve as much as the added lift to 'try' and combat the rocker nose rolling inward. When the geometry is wrong, many things occur...like less lift, more lift, straight up ...the rocker does not translate to the valve the cams motion...and dont forget valve guide wear accelerates, parts are stressed.
You could do the best with the best solution...and end up with the best result.
Get a geometry kit from B3racing
You could do the best with the best solution...and end up with the best result.
Get a geometry kit from B3racing
Lemme answer the question directly. You can install a .040" longer valve and make things worse. You can install a .040" longer valve and make things better. It depends upon the application. You have to be smarter than your cylinder heads.
Thanks guys. I was thinking that the tip could be shortened if need be. Also I see the installed spring height will be different by that amount. Kim
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Oogliboogli
They can but cut to a point, till they allow aluminum rocker body contact on each side of the roller tip with the retainer...
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replicaracer43
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And typically a longer valve is used to raise the installed height, allowing a taller spring package, required by using higher lifts, to avoid coil bind. Just one reason it is sometimes done.
The valve is supposed to be 5.011. The ones I got are 5.040. .029 though taller. These are the intakes. The ex valves are 5.011. Do u really think there will be a problem taking .029 thou off the top? I do realize that the intake springs will be that much higher. So maybe the spring or retainer will hit the rocker. I’ll see what my head guys says when he sees them. Kim.
MOPAROFFICIAL
Oogliboogli
I have before. That would about max unless the lock groove is lowered or you have a very flat retainer.
I have retainers, locks and springs from Edelbrock heads. I can order the proper intake valves if this is gonna be a problem. They had these longer 1s in stock so I took a chance that they would work. Can a guy have the exhaust seats cut down that amount? Or is that a no no. Kim
Wyrmrider
Well-Known Member
you go through the hardening on the exhaust seats
roller rockers kim? or?
rocker hitting the retainer (a symptom of the problem) is almost always shaft too low
grind the underside of the rocker is not a fix the problem is still there
if the shaft's too low adding a lash cap makes the problem worse
roller rockers kim? or?
rocker hitting the retainer (a symptom of the problem) is almost always shaft too low
grind the underside of the rocker is not a fix the problem is still there
if the shaft's too low adding a lash cap makes the problem worse
Theses are Speedmaster alum heads. He wants to use stock non adjustable rockers. I do have Hughes rollers if nessasary. I can also get valves that are 4.90 which would be .021 shorter than the 5.011. I’m trying not to have to order out of the USA as I already have stuff stuck at the border. My sister ran across the border many times for me as she lives 15 minutes away. She is not allowed now as the border is closed both ways. I was thinking not shorter valves cause it may have too much spring pressure then, but maybe not.kim
Can you assemble this and see where your at now?
I did a measurement with just the valves in the heads. They are the .029 taller than the exhausts. Which doesn’t sound like much but by just eyeballing it’s enough difference. I’ll get a couple shortened to match the the 5.011 length. I’m gonna try order the right length. Kim
Pics. This shows the .029 thou difference in the valves. The short are the right length at 5.011. The intakes at 5.040. Kim
Wyrmrider
Well-Known Member
looks like some lash cps on the short ones
shop around .050>.100
then get the geometry right from there
shop around .050>.100
then get the geometry right from there
The short valves are the proper length. I hear lash caps are not such a good idea. There is .029 thou difference. Kim
Wyrmrider
Well-Known Member
Better get your hearing checked
ran them with Ti valves and 5/16 stems all the time
he could run .100 and .70 or any other combination with a .030 split
shortening the tips that much takes away the heat treat
shim he springs to get almost equal pressures
spring cups if necessary
viton seals if not done already
ran them with Ti valves and 5/16 stems all the time
he could run .100 and .70 or any other combination with a .030 split
shortening the tips that much takes away the heat treat
shim he springs to get almost equal pressures
spring cups if necessary
viton seals if not done already
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