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Question: When you use high lift rocker arms, should you also increase the valve lash by the mount of extra lift that you achive?
Example: 1:1.25 rocker arms increase your valve lift by about 13.6% over 1:1.1 rocker arms.
Should you increase the valve lash from .006" to .0068"?
Example: 1:1.5 rocker arms increase your valve lift by about 36.4% over 1:1.1 rocker arms.
Should you increase your valve lift from .006" to .0082"?
Scott Novak
No. The only reason you should change your valve lash is to match the pushrods your using, Chromo, Steel, or Ally. --Ryan
Any change in the length of the pushrods, no matter what material they are made of will be multiplied by the ratio of the rocker arm.
So lets say that the pushrod could change as much .00545" due to thermal expansion. The stock rocker will increase that amount by 10% which will equate to .006" at the valve.
Add a 1:1.5 ratio rocker arm. The 1:1.5 rocker arm will increase that .00545" thermal expansion by 50% to .00818" at the valve.
So wouldn't we have lost our valve clearance if we didn't increase our cold valve lash over the recommended .006"?
Scott Novak
That's true, but it isn't the lash that's important, it's the amount of time the valve spends on the seat, and that will not change. This 'seat time' has a dramatic affect in cooling the valve, and that's what's important. --Ryan
Any change in the length of the pushrods, no matter what material they are made of will be multiplied by the ratio of the rocker arm.
That is true but it doesn't affect things here, because you measure the lash between the rocker and the valve stem. One of the reasons the valves are adjusted cold is to remove the variable pushrod length from the equation. If the pushrod was hot, and longer, yes, you would have to change the tappet setting(assuming you would want to adjust the valves on a hot engine.) The shims under the rocker assy. are used to correct any changes in rocker geometry.
Last edited by John N (2005-11-04 16:34:19)
Think about it. If the cold valve lash is determined to be adequate for a paticular engine configuration, and you then add high lift rocker arms, the rocker arm will travel further at the same cam position and contact the valve stem eariler and and the valve will come off of the seat earlier and set down on the seat later. Your valve will spend less time cooling on the valve seat, unless you also increase the valve lash proportionately to the increase in valve lift.
Scott Novak
You didn't start talking about seat time until Ryan brought it up. You were talking about valve lash.
Ok I give up, do it if you feel it important, but I've never heard of anyone else doing it.
Last edited by John N (2005-11-05 06:56:51)
"I've never heard of anyone else doing it."
Often when folk go to high-ratio rockers they also go to chrome-moly pushrods for added strength due to the greater forces on the valve train. With the lower expansion rate than aluminum it becomes a non-issue.
I like keeping the mass of the valve train low to minimize forces and wear, but then I like the feel of a stock 1200 anyway, so nevermind.
E=mc2 Think The answer is .006 Thousandth,s Slight drag on the feeler gauge ! Make sure the Valve guide hasnt raised up ! Then Make sure ya build Solid shaft Rockers ! Make sure Valve adjuster Is off Sett On The Stem of the vlave as too spinn the valve ! Check Valve Geometry ! 11/4 ratio,s turn 110 engle camm,s intoo screamers ! Bout all I know ! Sean
Tom,
Actually I had always heard that the aluminum push rods expansion more closely matched the expansion of the cylinders. Granted, aluminum has a greater coefficiant of expansion than Chrome Molly does, but the cylinders get much hotter so the expansion comes closer to matching.
With Chrome Moly push rods, when your engine starts running too hot, the valve clearance increases and starts making a lot of noise.
Even with an otherwise stock engine I'd use chrome moly push rods. Every engine that I've owned has shown some signs of the stock aluminum pushrods contacting the pushrod tubes making me believe that the aluminum push rods bend too much.
I've also tried aftermarket heavy duty push rods. Unfortunately, the ball ends pounded into the aluminum rods and mushroomed them. I don't think the heat treat on the aluminum was correct. Another crappy aftermarket product.
Right now I'm using Gene Berg Chrome Moly pushrods and they are working very well.
Scott Novak
John,
I hadn't thought about valve seat time either until Ryan brought it up.
I've never heard about anyone else considering rocker arm ratio when determining the optimum valve lash.
It seems like something that should be considered, so that's why I brought the subject up, to get different persepectives on issue.
Scott Novak
With your steel pushrods, lash increases from cold to warm engine. The lash will increase to over .015" This is why you should not increase your lash from stock, but decrease it. Set the lash to .000". That's right zero. This only applies to steel pushrods.
Gene Berg recommendeds a cold valve lash setting of .004" exhaust and .006" intake when using their cams and chrome moly pushrods.
I think his claim was that if you use these settings and your valves start clattering, your engine is overheating.
I'm using a stock cam with 1 : 1.25 rockers made from VW forgings, Berg Rocker arm shafts, Berg elephant feet adjusters, & Berg 80,000 PSI chrome Moly push rods.
I've been using .005" exhaust and .007" intake valve lash settings. I haven't heard any excessive valve train noise when the engine is at operating temperatures.
Does anyone know what the ideal hot valve lash is supposed to be?
Scott Novak
Ideally it is no lash when hot ! Pushrods like Bearings should runn on a film of oil , Or acheive a hydraulic affect , between expansion and oil pressure ! Least that,s my understanding on it . Yeah also it,s not just Berge rccomends .004 on the exhaust . Volkswagen manual,s call for this .004 valve lash on the exhaust . What im told is too runn .006 and sett the exhaust with a lil more dragg on the feeler gauge ! And Remember that stock camm , s runn lil differently than say an engle 110 or 120 . But It,s a confirmed .006 from guy,s I deal with for exh and Int. on all camm,s . But will admit im not sure why they all say this ! Need an opinion ? Solid rocker shafts ! I have Auto Craft Rocker shafts <, These shafts are machined from Solid Billet And the center spacer Is machined intoo the Shaft . Now I have a Box full of solid rocker shafts from Taiwanneeese Theey all have the Aluminum Spacer that ya just slide on the shaft . With the exception of this one sett ! This sett has a Metal spacer , rather than the aluminum spacer ! Im Wonderin If this is something Somebody made ? Or If these were Sold this way ? And who Sold Um ? And If anybody has any experience Runnin these Metal spacerd Shafts ? Sean
Sean,
VW recommended .006" cold intake and .006" cold exhaust valve lash for 1966 engines through 1979, at least in the two Bentley manuals that I have.
But that was for aluminum pushrods that have a different coefficient of expansion than chrome moly pushrods. VWs recommendations are not valid for chrome moly pushrods.
Gene Berg makes a rocker shaft with a separate STEEL spacer that you lock down with set screws and locktite, when the rockers are set where you want them.
I'm also following Berg's recommendations and grind my vavlve keepers so they lock the valve stem to the valve keeper. Then I adjust the spacing on my rocker arms so the swivel feet contact the centerline of the valve stem. The wrap of the valve springs is supposed to be enough to rotate the valve.
The valve guide wear should be reduced because there is less side force on the valve stem. The keeper groves on the valves should not have any wear on them like stock vavles normally do.
I do have steel shims under the valves to prevent chafing of the aluminum cylinder head, and to adjust the spring pressure.
Scott Novak
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