Eaton Balancing

A unique feature with the shaft mounted rocker arms such as those found on the Y-Block (as well as the FE, MEL,  and LYB) Ford engines is that the solid lifter or lash adjusting versions can be measurably variable in the rocker arm ratio depending upon where the lash adjusting screw is positioned within its range of travel. Where changing the pushrod length on the stud mounted or trunion type of rocker arm affects the geometry of the rocker and not the rocker arm ratio, changing the pushrod length on the shaft mounted Y-Block rocker allows for some deviation from the advertised amount of rocker arm ratio. This in turn allows some flexibility in rocker arm ratio tuning without having to purchase specific rockers for this purpose. What makes this possible is that the contact point for the pushrod at the bottom of the adjustment screw changes in relationship to the center of the pivot point (shaft) as the adjusting screw is moved up or down. (see illustration)

Depending upon the year model, Y’s can be found with rocker arms that have an advertised ratio of 1.43:1 or 1.54:1. Measurements performed on these rockers shows that the advertised ratio is more closely achieved when the adjusting screws are approximately half way down or midpoint in their adjustment travel. When the rocker adjusting screws are taken towards their extreme ends of adjustment, then the ratios do deviate from this advertised value. This same phenomenon is also seen on the aftermarket roller rockers that are available for the Y.

This rocker ratio variability can be measured several different ways. In the past, I have used an adjustable length pushrod so that the rocker adjustment screw could be varied and then measuring the net lift at the valve while maintaining zero lash. With the cam lobe lift being known, it’s just a simple matter of dividing the lift at the valve by the cam lobe lift to obtain the real time rocker arm ratio. This particular measurement is performed after achieving optimum rocker arm geometry which is effectively done by altering the rocker stand heights. Rocker arm geometry will also affect the net valve lift if the rocker shafts themselves are not at their optimum height. This has been covered in detail in a separate technical article.

To facilitate an easier method of rocker arm ratio measurements, a simple fixture with two dial indicators was fabricated that would simulate the rocker as mounted on a head. This would facilitate much quicker back to back testing of the different rocker arms without having to dry assemble the rockers on a workable head in order to simulate their movement through the various scenarios. Based on measurements taken on several different rocker arms, some trends in the observations become apparent. If the adjuster is at the top of its adjustment range, then an increase in rocker ratio would be observed. Conversely, if the adjuster is at the bottom of its range or screwed all the way in, then there would be decrease in rocker ratio. The following chart summarizes the measurements and are converted to rocker arm ratio values.

Having the ability to change to different rocker ratios opens up more tuning options regarding performance and/or efficiency of an engine. There are instances where it would be ideal to either increase or reduce the rocker ratio on either or both valves depending upon the camshaft and the specific application that the engine is being used. This myriad of combinations would be another chapter in itself so that will be left for another day. What must be remembered at this time is that the net valve lift is greatly affected by changes in rocker ratio as well as the speed in which the valve is being lifted from its seat. As an example for a particular scenario, I’ll use the Isky T-505 camshaft for the Y which has an advertised valve lift of 0.505”. This is calculated using a 1.5:1 rocker and if a 1.43 rocker is utilized, then this lift drops to a nominal 0.481” lift and reduces even further to 0.461” if the pushrod is shortened as much as possible. On the other side of the spectrum are the aftermarket 1.6 rockers for the Y which would allow the gross valve lift on this same camshaft to increase to 0.539” lift and if the pushrod is lengthened as much as the rocker adjustment will tolerate, then 0.562” lift. The valve lash would be subtracted from all these equations for actual lift at the valve.

This range in rocker arm variability does create some interesting scenarios that can keep an engine from running at its peak potential or become a potential source for breakage or engine damage. An example is an engine that has one head milled more than the other but has not had the pushrods adjusted appropriately in which to compensate can effectively be running different rocker arm ratios from side to side. And yet another instance is where mismatched heads from different years are on the same engine with a subsequent different height of the rocker shafts on each side. Although either of these scenarios could be checked by just visibly insuring that the rocker arm adjustment screws are sitting in approximately the same location on both banks of rockers, it is advisable to do an actual check of the net valve lifts at the valves. Milling the heads to increase the compression ratio also effectively increases the rocker arm ratio in that the adjustment screws must be moved up in order to use the same length pushrods. In this particular case, if the valve to piston clearance was already marginal then the valve is automatically positioned closer to the piston by the amount the head was milled. What compounds this is that the rocker ratio also increased if the same length pushrods are retained which effectively puts more lift at the valve which left unchecked could ultimately be just the amount that allows the valve to contact the piston.

As always, I hope this topic did not thoroughly confuse you but instead did help to enlighten you on just another nuance with these engines.

Until next time, Happy Motoring. Ted Eaton.

Originally published in the Y-Block Magazine, Nov-Dec 2005, Issue #71.

Rocker arm geometry is an area that’s very often overlooked when modifying an engine for increased power output and/or efficiency. Besides the obvious advantage of reducing valve stem and guide wear by minimizing the “scrubbing” action that can take place when the rocker arm geometry is optimized, the maximum or advertised lift at the valve for a given camshaft profile can also be obtained. The method in which the rocker arm geometry is altered will vary depending upon the valve train design. There are basically two rocker arm support designs where the rocker arms are either a ball (fulcrum) and stud arrangement or are shaft mounted. To adjust the rocker arm geometry on the ball and stud style, the length of the pushrod itself is altered in order to change the pivot point but when dealing with a shaft mounted rocker arm such as on our venerable Y-Block or an Fe Ford, then the height of the pedestal stand holding the rocker shaft must be altered.

In the case of the Y-Block, rocker arm geometry whether it’s good or bad, doesn’t change when the heads and/or deck is machined. The relationship of the rocker shaft to the valve stem tips remains the same and the pushrod length only needs changing when required by lieu of the lash adjuster being outside of its usable range. On an engine using the ball and stud arrangement for its rocker arms, any machining done to the head or deck surfaces can necessitate a change in pushrod length to maintain the existing rocker arm ratio.

Rocker arm geometry is generally optimal when the travel or movement of the rocker arm tip on the valve stem is minimized. To understand how to achieve correct geometry, it must be understood that the rocker arm tip itself travels in an arc. At zero lift, the rocker arm tip is expected to be closer (or inboard) to the plane of the pivot point and as the valve starts moving down, the rocker arm tip starts moving outboard. If the geometry is close to ideal, then the rocker tip will be at its most outboard position at half or mid lift at which point the rocker tip starts moving inboard again as the valve reaches full lift. Simply put, ideal rocker arm geometry is achieved when the rocker tip is sitting on the valve stem tip at the same position at both zero lift and full lift. In a perfect world where the rocker shaft pedestal stand locating holes, the valve guide, and the rocker itself are all machined to exact specifications, the rocker tip is expected to be sitting slightly inboard of the valve stem center at both zero and full lift while the rocker tip will be sitting the same distance outboard of the center of the valve stem at exactly mid-lift. But because of variances in manufacture, getting the rocker arm to sit on the valve tip in the desired location while optimizing the rocker arm geometry doesn’t always happen. In these cases, lash caps may be utilized to increase the area on the tip of the valve stem in which to increase the working area but in other cases it may require another style of rocker arm of the same ratio. Depending upon the scenario, compromises may be made in which optimum geometry is not achieved in order to allow the rocker tip to be sufficiently located on the valve stem tip.

Now that it’s clear that the rocker tip must be sitting on the valve tip at the same location at both zero lift and full lift, then it’s easy to assume that the rocker arms pivot point most be raised or lowered if the rocker arm tip contacts the valve stem too far inboard or outboard at zero lift in relation to where the tip resides at full lift. In the case of the Y-Block with its shaft mounted rockers, this involves altering the height of the pedestal stands so that the rocker shaft can be moved in the appropriate direction. If the rocker arm tips are sitting too far inboard or closer to the shaft versus where the tip sits at full lift, then the pedestal stands need to be longer or sitting taller. Conversely, if the rocker arm tips are sitting too far outboard as compared to where they reside at full lift, then the pedestal stands need to be shortened. In extreme cases, altering the height of the shafts can require an appropriate change in pushrod lengths to insure adjustability at the rocker arm for valve lash adjustment.

There are several different methods in which to measure rocker arm geometry. Without any measuring tools available, a visual observation of the rocker arm movement while the valve is going through its range of motion can prove quite adequate. Using a dye or magic marker on the valve stem tips to indicate the path or length of travel on those tips while varying the height of the rocker shaft can also indicate better or worse rocker arm geometry. Measuring the actual valve lift can also be performed as maximum valve lift occurs at “perfect” geometry and if the rocker is above or below this ideal point, then the valve lift starts decreasing logarithmically by the amount that the geometry is incorrect. There are tools available to facilitate measuring rocker arm geometry and one of these is a dial indicator on a fixture that actually measures the relationship of the rocker tip and with the edge of the valve stem at both zero and full lift. Regardless of the method used, the end result remains the same where the contact point of the rocker tip with the valve stem at both zero lift and full lift are being made the same.

As delivered from Ford, the rocker geometry on the Y engine is reasonably close with the stock lift camshafts. As the stock camshafts are replaced with those with increased lift, then it becomes necessary to machine the rocker shaft pedestal bases so that the shaft itself sits lower to re-achieve a more ideal rocker arm geometry. Because of the variability in the various rockers from the different manufacturers, it would be difficult to have a set amount that would need to be removed from the stands for a given amount of lift. Even using aftermarket or replacement valves with different than stock valve stem lengths will dictate checking the rocker arm geometry and correcting as deemed necessary. Due to all the variables involved, it would be prudent to at least check the rocker arm geometry on an engine as it’s being assembled especially when new valves, rocker arms, and possibly rocker shaft assemblies are being replaced.. T.E.

Originally published in Y-Block Magazine, Sep-Oct 2005, Issue #70.

When Randy Gummelt and I set out to build a Y engine for his rear engine dragster, the plan was to have an engine combination that would run an eight second quarter mile. And Randy also had his sights on the Australian Y record and with a target of an 8.99 or better et, that plan would achieve both goals. By now, it’s pretty well known that Randy ran a best of 8.15 @ 162mph at the Y Shootout during this past Labor Day weekend at Columbus Ohio so the plan was definitely a good one. But to back up a bit, in order to accomplish this it was necessary to figure out a workable combination and then to start gathering up the necessary parts that would make this combination work. Thus the plan starts to take shape as follows.

For the basic foundation, it was decided to use a C2AE-C block due to these particular castings being known for their consistent thicker cylinder walls as well as the additional main support webbing that is already present in these blocks. For an aspirated version, I normally have no issues in boring these particular blocks out to 3.860” (+0.110” over) but because this was to be a serious blown effort, the finished bore was targeted at a smaller 3.800” bore to maximize cylinder wall integrity and in turn reduce any chance that cylinder wall flex would potentially kill or hurt some of the power. Part of the reason for going with a 3.800” bore versus a 3.810” bore was being able to get in on a special run of Total Seal brand 1/16” wide gapless rings for a 3.800” bore that were being made for one of the Nascar teams. The 3.810” bore 1/16” wide rings were already available as an off the shelf item but being in a position to make the bore and stroke ‘square’ was more conducive to the overall plan. Because of the supercharged nature of this engine, the top ring would be gapless by design as opposed to normal practice of using a gapless style ring in the 2nd groove in a normally aspirated application.

It was determined early on to use a Moldex crank in order to get the desired 3.800” stroke. To facilitate this much stroke and free up some much needed clearance at the camshaft , 2.000” rod journals were specified to bring the rod bolt area of the connecting rod inboard and away from the camshaft. To permit the use of an economically priced SFI approved flywheel, a scrub bolt pattern on the flywheel flange was called for and the face of the flange was spaced ~0.420” further to the rear or away from the engine. This additional spacing was to eliminate any spacers between the flywheel and the torque converter while still maintaining the pre-requisite 0.100” freeplay in the transmissions front pump. The C2 block already incorporated 292 main bearing sizes and so the main journal dimensions were sized as standard 292 size which at least kept main bearing selection both simple and inexpensive. The crankshaft is fully counterweighted which means eight counterweights versus the normal six and even with the additional weight afforded by the extra counterweights, lightening holes were needed in the crankpins to facilitate balancing without an extreme use of heavy metal or tungsten. Both the leading and trailing edges of the counterweights are bullnosed or rounded in shape; no knife edging on this crankshaft.

Going to the front end of the crankshaft, the snout was mandated as 1.600” diameter as opposed to the stock 1.250” diameter normally seen on a Y. This allowed the use of the more readily available BBC blower hubs and drive hardware while also reducing significantly any deflection that occurs due to the blower belt pulling heavily on the crankshaft snout. Through the use of a Y marine cover, the crankshaft snout was shortened even more which reduced any potential deflection even further. Although 3/16” woodruff keys (#9 if you’re ordering them) were employed for the timing gear and basic drive hub allignment, an additional groove was machined into the crankshaft at 180° from the other keys so that ¼” keystock could be employed to insure no key failure at the drive hub for the blower.

The 2.000” rod journals made it possible to use the considerably less expensive Eagle 6.125” long H-beam connecting rods that were available as an off the shelf item. Even though the connecting rod cross-section was dimensionally smaller by using the 2.000” journal, there was still less than the required minimum of 0.050” clearance to the camshaft. Although only a pair of connecting rods actually had interference issues with the camshaft, all the connecting rods were subsequently modified to insure that they would clear the camshaft in the event of a catastrophic camshaft timing failure.

Pistons were a custom order item from Wiseco. These pistons maintain a minimum of 0.260” thickness in their decks for the blower application and incorporate an inverted dome (dish) that adds 27cc’s to the total cylinder volume. Because of the unavailability of a pair of usable 471 heads while gathering up parts, it was decided to use the 113 castings which were attained through and already ported by John Mummert. Because the pistons were going to be custom built regardless of the head being used, the particular head in regards to the chamber size being used was not a major player as the piston dish size could be altered in which to compensate and still maintain the targetted 7.5:1 compression ratio. But had 471 heads been available, then a more desirable ‘D’ shaped dish in the piston would have been used. The particular piston blank that was being used to make the pistons only had a given amount of deck thickness which limited dish design when using the smaller chambered 113 heads. The compression height (pin location) for the pistons is 1.715” which places the top of the piston at a calculated 0.010” in the hole for deck clearance.

This basically takes care of the parts required to put a rotating assembly together for the bottom end other than the main support girdle and that’s already been covered in a previous article. Future articles will go deeper into blueprinting and camshaft specifications as well as some of the other modifications that were required to put a final assembly to the engine.

T.E.

Originally published in the Y-Block Magazine, Mar-Apr 2006, Issue #73