Why oil restrictors? Is there a general rule as to how much the roller tip will move per .050 inch change in pushrod length? I am going to measure mine but I am just curious.
thx
-jbojo
Oil VOLUME doesn't change with pushrod length..The INSIDE diameter of the pushrod is what changes volume..So a 5/16" pushrod with a 0.80 wall will flow more oil than one with a 0.118 wall..So using a restrictor in the pushrod is one way to limit oil to the top end of the cleveland..Because I went to a larger pushrod with a larger inside diameter it will flow MORE oil to the top end hence the restrictor.. Don posted up a great article on the 351 cleveland & heres some great info about rocker arm geometry & pushrod length by George Pence.. I would check all your installed valve stem heights FIRST before anything else..if there not the same you need to correct that
Correct geometry at the rocker tip will place the sweep of the rocker tip nearest the rocker arm at fully closed and fully open, the sweep will be furthest from the rocker arm at 50% open, and the rocker tip shall be in the middle of its sweep at approximately 25% and 75% open. This geometry will always result in the narrowest sweep pattern, although there is nothing beneficial about a narrow sweep pattern, it is just a method of evaluating the rocker arm geometry. This description of sweep pattern will be in direct opposition to many of the rocker geometry instructions you shall run across. A few of the camshaft companies are notorious for promoting bogus rocker geometry instructions. The hot rod industry teaches home mechanics (and professional mechanics too) to focus on setting the rocker arm's contact patch on the valve tip, by manipulating the rocker arm's height and the push rod's length, at the expense of other concerns. This may achieve the most rudimentary aspects of rocker adjustment, and it may be convenient, but it cannot possibly result in an ideal adjustment. The most rudimentary aspects of rocker arm adjustment simply keep the operation of the rocker arm within four parameters; (1) the rocker arm should not contact the valve spring retainer when the valve is fully closed, (2) the rocker arm should not contact the push rod when the valve is fully open, (3) the rocker arm slot should never contact the fulcrum, saddle or stud at either extremity of its motion, and (4) the rocker arm tip should never bear down upon an edge of the valve tip; its sweep pattern does not have to be perfectly centered on the valve tip but it should contact the valve tip in the middle half of the valve tip's surface.
As you assemble a cylinder head you can detect rocker geometry and push rod length problems early on by paying attention to the valve stem heights; the valve stem heights should be equal across the cylinder head. If the valve stem heights are unequal, or if one particular valve stem is higher or lower than all the others, you SHALL run into problems.
There are two types of rocker arm designs to consider, the first is the stud mounted, push rod guided type of rocker arm. The height of stud mounted rocker arms is set by the lash adjusting nut (aka the poly lock). Adjusting lash with this type of rocker arm alters the rocker arm's height, and impacts the rocker arm's geometry. In order to maintain consistency in push rod length stud mounted rocker arms are best adjusted mounted on the engine in conjunction with a fixed length push rod.
The other type of rocker arm is the fixed-pedestal mounted type of rocker arm that fastens securely to the cylinder head's rocker arm pedestal. A fixed-pedestal mounted type rocker arm can provide lash adjustment just as easily as the stud mounted variety, by employing a push rod cup style adjuster. The factory rocker arm and the two Yella Terra rocker arms are all of this second type of rocker arm. The high-end T&D and Jesel shaft mount rocker arms are also fixed-pedestal mounted rocker arms. All fixed-pedestal mounted rocker arms are in fact a type of individual shaft mounted rocker arm; they are more stable and contribute fewer rocker arm induced problems to the valve train as long as the saddle/fulcrum is rigid enough. The height of a fixed-pedestal mounted rocker arm is raised by shimming the rocker arm fulcrum/saddle; it is lowered by removing material from the fulcrum/saddle or by removing material from the pedestal cast into the cylinder head. Increasing valve length also has the same effect as lowering the rocker arm. This type of rocker arm makes it possible to adjust the relationship between the rocker arm tip and the valve tip independent of the push rod, with the cylinder heads sitting on your work bench.
If you are using the factory rocker arms and determine their geometry requires adjustment, a good starting point is to set the height of rocker arm to position the fulcrum’s pedestal approximately in the middle of the rocker arm slot at 50% valve lift. Do not Tufftride the factory rocker arm parts until after the rocker arm geometry has been sorted out.
It is popular to test rocker arm adjustment with the heads assembled on the short block by coloring the valve tips with a felt tip marker, assembling the valve train with the push rods set to zero lash, hand rotating the crankshaft through two revolutions and inspecting the contact patch pattern on the valve tips. As far as I am concerned, the contact patch does not need to be centered on the valve tip, it just needs to stay away from the edges.
Push Rod Length
Sorting out the rocker arm geometry is a prerequisite for determining push rod length. Due to the age of Cleveland series motors, (1) the original manufacturing tolerances can result in dimensional differences, (2) parts have been mixed and matched over the decades, or (3) some parts have already been refurbished once or twice and worked on by many hands of various skill level. For these reasons you may find each cylinder head requires a different push rod length. The actual length of the push rods you shall order for the engine shall be the sum of the length of the longest or shortest “zero lash” push rod plus a small additional amount. This small additional amount added to the length of the push rod establishes the hydraulic tappet adjustment; i.e. the amount you plan to compress the hydraulic tappet plunger.
The factory fixed-pedestal mounted rocker arms, and stud mounted rocker arms require consistency in rocker arm height amongst the all the rocker arms on each cylinder head (both cylinder heads if possible) so that the push rod length required to set all of the rocker arms at zero lash is within a few thousandths of an inch per cylinder head. The length of the longest push rod required to set all of the rocker arms at zero lash shall be the basis for determining what length of push rods to order.
The fixed-pedestal mounted rocker arms equipped with push rod cup adjusters (such as the Yella Terra rocker arms) do not require as much consistency because the adjustable push rod cups will make up the differences. Start with the push rod cup adjusters screwed all the way into the push rod tips and find the rocker arm requiring the shortest push rod to achieve zero lash. The length of this shortest push rod shall be the basis for determining what length of push rods to order. There is a limit to how far you can screw the adjusters out, so keep an eye out for big differences and resolve any problems.
Hydraulic Tappet Adjustment
One rule of thumb for adjusting hydraulic tappets is to compress the plunger 1/2 of the plunger’s available travel; however it is important to measure the travel of the plunger if that’s your plan. The plunger of a modern hydraulic tappet does not compress as much as the plungers did decades ago. The plunger travel of a Crane roller tappet is only 0.062”. The plunger travel of a 1995 Johnson HT900 tappet I have on hand is 0.125”, whereas the plunger travel of a 1970s vintage HT900 is tappet is 0.187”. I am told the plunger travel of a typical modern hydraulic tappet is in the range of 0.060” to 0.080”. Nowadays the recommended range of hydraulic tappet adjustment when using stud mounted rocker arms is 1/8 to 1/2 turn of the adjusting nut beyond zero lash when the engine is hot (adjustable rocker arms are usually mounted on studs with 3/8-24 or 7/16-20 threads). Decades ago the spec for adjusting small block Chevy tappets was one full turn beyond zero lash, which was supposed to set the tappet plunger in the middle of its travel! This means the plunger in Chevy’s tappet had 0.145” of travel.
The amount to adjust a stud mounted rocker arm beyond zero lash – engine hot
1/8 turn = high performance motors with adjustable valve train
1/4 turn = high performance motors with non-adjustable valve train
3/8 turn = sets many modern tappets at half collapsed
1/2 turn = maximum adjustment, do not exceed 1/2 turn
The relationship between stud mounted rocker arm adjustment and tappet plunger compression
Turns on Adjusting Nut | Adj. Nut Movement | Actual Compression of the Tappet Plunger
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1/8 turn ______________ 0.005” to 0.006” ______________ 0.009” to 0.010”
1/4 turn ______________ 0.010” to 0.012” ______________ 0.017” to 0.021”
3/8 turn ______________ 0.015” to 0.019” ______________ 0.026” to 0.033”
1/2 turn ______________ 0.020” to 0.025” ______________ 0.035” to 0.044”
The length of a cold push rod or the cold adjustment of a rocker arm must be altered to compensate for the thermal expansion of parts and achieve the proper amount of plunger compression when the motor is hot:
(A) Iron block and iron heads: ____________ Subtract 0.002”
(B) Iron block and aluminum heads: _______ Add 0.006” (additional 1/8th turn)
© Aluminum block and aluminum heads: __ Add 0.012” (additional 1/4th turn)
Some tappets (such as the Morel HLT hydraulic roller tappets) utilize intentionally limited plunger travel as a method to increase the rpm capability of the tappet. This requires adjustable valve train, and push rod length should be determined following the instructions of the tappet manufacturer.
Longer Valves
Longer valves are sometimes required (or at least convenient) for solving 3 problems that crop up when installing a higher-lift camshaft. Longer valves (1) increase the distance between a valve spring retainer and the top of the valve guide, they (2) provide the additional height needed for valve springs which have an installed height that is higher than the installed height of the OEM valve spring, and they (3) raise the height of the valve tip which can be a better choice than lowering the rocker arm when adjusting rocker arm geometry.
Manley severe duty stainless steel valves for the 351C are available off the shelf in +0.100” lengths;
*Manley Performance severe duty intake valve, 2.08" dia. x 5.34” lg. (+0.100”); #11764-8, 132 grams
*Manley Performance severe duty 2V exhaust valve, +0.100” length, #11853-8, 105 grams
* Manley Performance severe duty 4V intake valve, +0.100” length, # 11822-8, 140 grams
* Manley Performance severe duty 4V exhaust valve, +0.100” length, # 11857-8, 111 grams
Manley’s titanium intake valve is also available in +0.100” length;
*Manley Performance titanium intake valve, 2.25” dia. x 5.35” lg. (+0.100”) #11490T-8, 90 grams
This valve has the requisite hardened steel tip as indicated by the “T” in the part number, but the valve head is 2.25” diameter. Machining the head of this valve to 2.19” shall make this valve a +0.100” length replacement for the Cleveland intake valve that weighs 87 grams.
Push Rods
Standard 351 Cleveland push rods are 5/16” diameter and 8.41" long, but when the block is decked, when the heads are milled, when factory head gaskets are replaced by gaskets having a different compressed thickness, or when parts like the camshaft, lifters, valves or rocker arms are changed the required length of the push rods shall change as well.
Push rod deflection can cause many seemingly unrelated engine performance problems; they are the weakest link in an overhead valve type valve train. It is important to use push rods in any application that are stiff enough for the spring forces, for the weight of the valve train components, and for the engine speeds involved. Push rods should be manufactured from seamless chromoly tubing. 5/16” push rods made from 0.080” wall thickness tubing are considered adequate for a relatively stock motor and are readily available from companies such as Crane Cams, Manley Performance Products and Trend Performance. For higher performance 5/16” push rods with 0.105” wall thickness and 3/8” push rods with 0.080” wall thickness are more appropriate; the 3/8” push rods have been a common recommendation for 351C applications for decades.
My preference however is to use 5/16" push rods made from 0.120" wall thickness tubing. The push rod manufacturers will question the need for such strong push rods, but using push rods that are “overkill” for their application is my way of insuring the push rods are perfectly stiff and there’s no possible way they contribute to any valve train related reliability or performance issues. Remember, the canted valve Cleveland valve train splays the push rods off to either side of the intake port; these push rod angles expose the 351C push rods to angular bending forces not encountered in the valve train of in-line valve motors; the 351C needs a sturdier push rod. The push rod is not the appropriate component to use for reducing valve train weight or saving money. Since the passage in the middle of the push rod is only 0.072" diameter it also acts as a restrictor to control the amount of oil flowing to the valve train. This has always been a secondary benefit in using these heavy wall 5/16” push rods. Of course, restricting oil to the valve train via the push rods is not a concern if a motor is equipped with tappet bore bushings having 0.060” orifices.
Finding 5/16” push rods with true 0.120” wall thickness in 351C lengths is becoming difficult. Smith Brothers of Redmond Oregon (800-367-1533) now sell 5/16” push rods with 0.116” walls. Manton Pushrods of Lake Elsinore California (951-245-6565) sells 5/16” push rods with 0.118” walls. These small differences in wall thickness will not weaken the push rods, but a little more oil will be metered to the valve train, which is something we wish to avoid with the 351C.
![IMG_2609[1].JPG](https://cdn.imagearchive.com/7173mustangs/data/attachments/17/17264-eac2155188b47aca6bb0e4d421251c42.jpg "IMG_2609[1].JPG")
