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To machine the rockers pedestals of my OEM 4 V Open chambers heads, I had indicated to the machinist that the axis of the studs had to be parallel to the axis of the valves and I had made a sketch BUT I had also provided this shema :


and he only looked at this one without taking into account what I had told him, but this diagram is FALSE because the original surfaces of the pedestals ARE NOT PERPENDICULAR to the axis of the valves and here is the result:


The correct geometry cannot be obtained, the rocker arm shaft is too close to the valve stem and the roller cannot press in the middle of the valve stem



I am currently studying a way to save these cylinder heads but I am not sure I can do it.

So do'nt follow the recommendations of this diagram!

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No I do not think so, to have the minimum of displacement, the line which joins the axis of the rocker arm and the axis of the roller must be perpendicular to the axis of the valve at mid-opening, so it is at this moment that the roller tip is furthest from the rocker arm axis, so it should not be in the center of the valve but a little beyond it.
So, if we look with the rocker arm to the left of the valve as in the picture, when the valve is closed the roller tip should be to the left of the center of the valve stem (0.4 mm for a total lift of 16 mm / 0.63 '') then it moves to the right, passes through the center and goes up to 0.4 mm to the right of the center at mid-opening, then it comes back to the left, passes again through the center and reaches its starting position when the valve is fully open. And he does the same movement again when the valve closes. 
With this geometry the total displacement is only 0.8 mm; with a geometry where the roller passes through the center at mid-opening, the total displacement is much greater.

In my case, the roller is already well beyond the center to the right when the valve is closed, then it moves even further to the right to the edge of the valve stem at mid-open and returns to its starting position.

Last edited by rene4406

The Rocker arm ratio is the OEM , 1.73 and the length of the arm, the distance between the axis of the roller and the axis of the rocker arm, is 40 mm

It is on this basis that I calculated that a vertical movement of 8 mm on either side of the position perpendicular to the axis of the valve corresponds to a total horizontal displacement of:

40 - square root of (40² -8²) = 0.8 mm,

i.e. 0.4 mm on either side of the center of the stem if the rocker arm axis is located 39.6 mm from its axis

The lengths of the valves are:
intake: Manley 11872      133 mm = 5.244 ''
exhaust: Ferrea F6124    128 mm = 5.060 ''

I haven't bought the pudhrods yet but if they are shorter the rockers will be in a wrong position and the displacement on the valve stem will be very important. The more the angle increases, the smaller the cosine.



Last edited by rene4406

I agree- if pedestal machining is not done VERY carefully to make a faux 351-HO, pivot studs can become slightly misaligned. But keep in mind that- unless during full cam lift, the roller rocker wheel runs dangerously close to the edge of the valve stem tip, the overall effect of such slight misalignment only shortens the valve lift by a few thousandths of an inch. On a 450-bhp engine, that might remove 15 bhp, assuming correct length pushrods. Unless you are racing a 351-C for money, missing 1% of the potential horsepower of an engine is trivial. Use a bigger cam or higher dome pistons for more compression and you'll get extra power.

And that's only with roller tip rocker arms. Roller pivot/roller tip rockers do NOT increase power, they only reduce oil heating from sliding friction of the rocker arm sled-fulcrums and at the valve stem tip. And they are fussy to position correctly.  With stock sliding-tip steel rockers, their tip radius is so large that a slight misalignment or non optimum pushrod length makes even less difference in power. Your current heads may work just fine with stock rockers- again, with correct pushrods.

Ford once offered a roller-bearing fulcrum for stock stud-mounted rocker arms, for the 1969 Boss 302 which also fits the 351-C & are legal in most race series. They were sometimes used on Gr-3 cars for endurance events and reduced a main source of friction and oil heating without using an oil cooler. The special roller bearing rocker arm fulcrums are no longer available but a good machinist could likely make some up from tool steel, once you find a local source of the drop-in roller bearings. This is shown, with (obsolete) part numbers in the Ford OHO (Off-Highway Only) books of the '70s, available for download on the POCA Website under 'Tech'.

All this can be avoided by buying today's far more efficient aluminum cylinder heads. They also remove 60+ lbs of needless weight mounted high on your engine. Good luck-

I know aluminum cylinder heads perform better and end up costing less, but I want to stay as close to the original definition as possible with an "all cast" engine. And, a lot of Europeans chuckle at the big, all-cast iron engines, and I find it fun to build one that will still provide a lot of horsepower.

I'm not looking for the last horse, 450, 470, 430 hp, whatever, but I want a reliable engine.

I made a small sketch to illustrate the difference in roller displacement on the valve head between pushrods of the "correct" length and "short" pushrods.



After performing a blank mount with an adjustable length push rod, it appears that:
- for the exhaust valves, the rocker arms have an imperfect but acceptable position because not too far from the center of the valve stem.
- for intake, the rocker arm roller is too close to the edge of the valve stem and it will be necessary to plug the existing holes by enlarging and tapping them to put 16 mm screws, then drill these screws and tap at 7 / 16-14 at the correct angle and distance.
My new machinist can do this on a milling machine.

Last edited by rene4406

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