All shops have their own methods and idealogy as to how they do this. Since your installing OS valves, they may likely do a clean-up surface on the head and do all the valve work, guides, etc... and then place the head back in the resurfacer and take a cc reading. Its only after they cut the seats for the larger valves and do the valve job that they can establish a true baseline for the chamber volume they will be starting from.

Often, they just fill a chamber at random, or even the 2 end one's to the desired 48cc volume, since they know they should be well above the 48cc target with your head, and just measure down to the fluid level inside the chamber from the machined head surface with a dial indicator. They may stop .005" or so shy of the amount to machine and refill the chamber, just to make sure they are on track. And then take the final cut for the target you are wanting.

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There's no such thing as too much cam....only not enough engine!

It seems as if 1930 is after the same thing I am. We are both using a mid 80's hydraulic truck engine. So a relevant question for both of us is how much can you plane the head without destroying the hydraulic valve lifter/push rod relationship. If there is .190" preload on the lifter, does taking .060 off the head go beyond the limits for the lifter? Will we need a shorter push rod by .060, or is the tolerance of the preload enough to allow it to function well still.

1930 I am eager to hear what your guy Russ at ERson. Let us know. I would not mind calling and talking to him myself.

Thanks for digging on this subject some more. I may eventually learn something.

Sam

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Hydraulic lifters only require between .025"-.045" of preload after zero lash to be adjusted. This info is on most all of the cam sites like Crane, Isky, etc...Preloading beyond that amount isn't necessary or advisable. With non-adjustable valvetrains, it becomes needful to switch to an adjustable rocker or pushrod when milling the block or head to help retain proper lifter preload or by determining what length custom pushrod is required to do this, all while restoring pushrod geometry to an acceptable level.

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There's no such thing as too much cam....only not enough engine!

I can't find the threads now, but I know hydraulic lifter plunger travel, pre-load, and head milling was discussed a while back and the consensus was that quite a bit could be milled form the head before new pushrods or rocker arms were necessary. I believe it was on the order of .100 inches.

Once you reduce the deck and/or head thickness by more than .050", you have already changed the rocker geometry enough that it needs to be corrected. Even though the plunger inside the lifter can compensate for this to a degree, it is well known inside the other brands(Chevy, Ford, etc...)that compressing the plunger beyond the initial amount needed to adjust lash(.025"-.045") introduces other problems like geometry issues, reducing peak RPM...etc if not held to this minimum preload.

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There's no such thing as too much cam....only not enough engine!

Why? All you are doing is shortening the distance between the rocker arms and the head. I think the concern about rocker geometry and head milling would be applicable to V design engines, but the slant six isn't built that way. Milling the head on the slant just brings the rocker arms closer to the cam but doesn't change the geometry of the valvetrain. In a v engine where the pushrods are shorter and the change in angle between the rocker arm and the tappet will be more pronounced when the head is milled I can see there might be a problem, but I don't see the same problem occurring in a slant. I have personally run a slant six heads that had been shaved .0100 without having to change any of the valve train. Granted it was a mechanical lifter motor so I could take the difference out of the rocker arm adjusters, but I don't see why it would be that bog of a difference in a hydraulic lifter slant.

Then again, I am not a trained machinest, so I might be talking out of my butt. But I just don't see how milling the head on a slant six engine would ever require chaning the rocker arm geometry. Shorter pushrods, yes, but rocker arm geometry no.

Reed, this is an issue that involves every engine that has rocker arms irregardless of it being V, inline or oppossed cylinder like a VW, stud mount or shaft mount. Once a baseline of adjustment and geometry is established at the time of manufacture, altering this adjustment upsets many things. If you cut a head .050" for instance, and don't change your pushrod length to compensate, the now "long" pushrod moves the rocker contact point on the valve tip away from its original starting contact point significantly, because now the ratio of the rocker is also playing a part in motion transfer, and can quickly compound the problem to the point of excessive guide wear and/or valve tips being chewed up or worse, dropped valves if the rocker tip runs off of the valve tip. Also, all the major cam companies have pages and pages of instruction on how to correct and avoid this on their websites to help visualize and explain this better.

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There's no such thing as too much cam....only not enough engine!

on the 83 D150, I cut .041 off the head, .010 off the block
and used an Oregon reground cam

hydraulic lifter preload is nearly where it started, I have this info listed in the low rpm high torque hydraulic cam thread.

Your cam being a regrind helped out because of the smaller base circle that is created by doing this. It compensated for the decking that was done on the head and block.

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There's no such thing as too much cam....only not enough engine!

I don't understand this statement, either. The relationship of the rocker arm and valve tip does not change just by milling the head, on a shaft mounted rocker system. If you mill the head/block .050 (no other changes) then all you need to do is "unscrew" the adjuster screw .050, and every thing stays the same.
If using a "stud" mount rocker system, then you are changing the hight of the rocker pivot, and yes, the geometry does change.
Now if you install longer valves, then all kinds of stuff changes. Most likely you would have to raise the rocker shaft, and move it closer to the valve to keep the arm centered over the valve tip. Then you would need different length pushrods.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
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I can see where milling the head or block COULD lead to alignment problems where the pushrod contact the cup end of the rocker arm or could force the "slide" ende of the rocker arm that rides on the tip out of alignment with the valve stem. I just don't see how this would happen on a slant six.

I referred to V engines because those are the engines I have seen have more extreme angles of intersection between the pushrod and the rocker arm. I.E. the magnum smallblock engine heads that require clearancing on the pushrod holes to be mounted on an older LA block with the LA valvetrain. The pushrods on the V engines come off the lifter at an angle and make contact with the pushrod at an angle. Shortening the distance between the rocker arm and the lifter without compensating with shorter pushrods or other alteration to the valvetrain gerometry will lead to an exaggeration to the angle of intersection between the pushrod and the rocker arm and potentially the rocker arm and the valve stem. This would, indeed, cause more problems at high RPM with potentially disastrous consequences of the pushrod popping out of place and grenading the engine top end.

However, on the slant six the pushrods are (a) longer and (b) nearly perpendicular to the lifter and the rocker arm. The distance between the rocker arm and the lifter will minimize any change to the angle of incidence of the pushrod to the lifter and the rocker arm. Also, the fact that the pushrod intersects both the lifter and the rocker arm at nearly a 90 degree angle also minimizes the potential for a reduction in disctance between the rocker arm and lifter to cause problems.

I don't have the actual specific angles of intersection for a slant six rocker arm and pushrod and the slant six pushrod and lifter, but I know the angles aren't as large v engines or other engines.

Again, I am not a machinisst and have never measured any of these angles. I am basing this on my high school and college geometry classes and my observations of how slant six pushrods are set in the slant six engine. I would be happy to admit I am wrong if someone comes up with data that proves it. Maybe the next time I build a hydraulic lifter slant motor I will take the time to measure the angle of intersection between the pushrod and the lifter and rocker arm.

Better yet, if somone has a slant sitting on a stand, set the engine with the block perfectly vertical, pull a pushrod, and drop a plumb line from the center of the pushrod side of a rocker arm to the lifter. I bet the plumb line will be almost perfectly vertical.

Here is a tech article written in Mopar that might explain it better. The third pic down lists all the things that contribute to geometry problems in shaft mouinted rocker setups, decking the heads/block is one of them.
http://www.horsepowermonster.com/2013/s ... alvetrain/

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There's no such thing as too much cam....only not enough engine!

Yes, but again, in a slant six engine that doesn't have roller rockers (99.99% percent) I don't see how the concern about centering the roller on the valve stem is a concern.
That quote addresses exactly what I am talking about with V engines. The cam is set high in the block and requires the pushrod to intersect the rocker arm tip at an angle. A change in the cam profile or distance between the rocker arm and cam will change the angle at which the pushrod intersects the rocker arm and lifter, unlike the slant where the pushrod contacts the lifter and rocker arm at a near 90 degree angle. Changing the size of the cam or the thickness of the head or height of the block has an exceedingly minimal affect on the angle at which the pushrod contacts the rocker arm on a slant six.

I agree with you with regards to other engine designs, but I still don't see how a slant six builder needs to be worried about milling a head or installing a high lift cam requires modification to the valve train to correct a change in the angle of incidence between pushrod and rocker arm.

I would like to hear from the serious racers and gurus on this. And 1/4 mile racers ever have a problem with valve train geometry running big cams and milled heads? I am just picturing things in my head and have no real world experience with this issue, so I would love to hear from someone who has actually done those mods to a slant.

that is exactly what I was saying...as the question at that point in time seemed to be about lifter pre load. Also note, the stock lifter preload was around .090, which would put it in the center of the .180 available plunger travel.

concerning the rocker tip location with respect to the valve tip, regardless of pushrod length, the location of the fulcrum, (the rocker shaft pivot point) remains unchanged, so the rocker ratio does not change but the exact relationship of the rocker tip to valve tip can change. The normal valve opening movement has the rocker tip moving across the valve tip, that is because the valve stem tips are at an angle with respect to the rocker arm shaft. That is done by design, so that the wear on the valve tip and rocker arm tip is spread over a larger surface than if the rocker arm end continiously worked the exact same spot on the valve.

this article has a visual that shows the movement of the rocker across the valve tip.
http://www.compcams.com/Pages/417/valve ... metry.aspx

a second concern with improper pushrod length is side loading at the pushrod to rocker interface. That can accelerate wear. The load needs to centered above the column of the push rod or additional push rod flex and loss of lift can be encountered.

For what its worth I was able to get ahold of the tech guy at Erson today and was told that the cam is the second to last thing anyone should buy ( if building a street engine ) when building an engine, he said buy it right before the air cleaner.

He said that if one were planning an all out balls to the walls engine than yes one would want to make sure that everything was copacetic and cam details should be in order but for a mild build engine that would be seeing street duty build the engine how one would want and tailor the cam to fit/ help all other things perform more efficiently.