Choosing Jeep 4.0L and Stroker Six Pushrod Length

[jakewalter]

Greetings from Northern Michigan,

I am in the process of building a stroker for a 2002 TJ.

I need to check the pushrod length.

The engine is still on the stand.

Do I need to prime the lifters to get the proper pre-load?

Thanks so much,

Jake

[Moses Ludel]

Hi, jakewalter...Congrats on the Jeep inline six stroker engine build!

You do not want to fill the lifters when checking pushrod length.  Setting pushrod length is actually positioning the lifter plunger at the correct position within each lifter.  The ultimate goal is having each hydraulic valve lifter set to zero valve lash plus a given "preload" of the lifter plunger.

Note for getting this into perspective: When the valve is closed and the lifter is on the heel (lowest point) of the camshaft lobe, zero lash means no measurable valve rocker clearance at the valve stem when the lifter plunger is fully extended under its internal spring pressure only (no oil in the lifter!).  Preload is set by either lengthening the pushrod or adjusting the rocker arm (on engines with adjustable rocker arms) to place the lifter plunger at a specific dropped position in the lifter.  Adjustable rockers like the classic small block Chevrolet V-8 call for X-amount of adjuster nut or screw turns below zero lash.  A typical early small-block Chevrolet V-8 pushrod engine called for 3/4-turn of the rocker arm adjuster nut beyond zero lash, with the engine hot and idling.  The rocker ratio was 1.5:1.  The rocker was set to zero valve clearance, just eliminating clicking noise or any feeler gauge gap with the lifter plunger fully extended.  At this point, the rocker nut was tightened slowly (allowing the lifter to adjust the plunger gradually) at 1/4-turn of the nut at a time, until 3/4-turn was reached with the engine running (and spewing oil everywhere unless you used aftermarket oil retainer clips!).  This placed the lifter plunger down in the lifter X-amount of thousandth's inch.  The rocker nut threads were SAE 3/8", the rocker ratio being 1.5:1, the 3/4 turn of the rocker pedestal nut would likely be close to the 0.040"-0.060" pushrod length preload range that Jeep engine builders describe.  On the Jeep engines, all settings are done with the engine cold (not running) or on the stand like your engine.  

As you know, there is no provision on Jeep rocker arms for adjustment.  It is assumed (by Jeep), that the original pushrod length will set the valve to the right lifter plunger preload range.  On an inline Jeep six without adjustable rockers, the lifter preload is set with either adjustable length aftermarket pushrods or replacement pushrods of the correct length.  There are various length pushrods available HESCO, aftermarket engine parts sources and even adjustable pushrods: Clifford comes to mind, they may still offer adjustable pushrods.

On an engine without adjusters on the rocker arms, the hydraulic lifter pushrod length is tested with no oil in the lifter.  Camshaft lobe on its heel (each cylinder checked with the piston at TDC on its compression stroke), the lifter plunger is allowed to fully extend under its own spring tension.  When it comes to engine rebuilding time, with a decked block and head plus a change in the head gasket thickness,the hydraulic lifter plunger height and lifter preload change.  Milling the block deck and head will drop the cylinder head height, which increases the lifter preload since the pushrod now sets the plunger lower in the lifter.

Fortunately, there is latitude in the lifter preload range.  Jeep is of no help in explaining just how much preload you need, though the aftermarket references call for 0.020"-0.060" preload measured at the pushrod (not the valve stem end of the rocker arm).  I prefer a range of 0.040"-0.060" plunger preload to keep the plunger safely below the retainer clip and well enough off the floor of the lifter...This means that with a given piston at TDC on its compression stroke, with both cam lobes on their heels, and with the rocker arm torqued down, the lifter plunger should be somewhere between 0.040"-0.060" below the plunger's fully extended position.  This would be with a camshaft that has stock or moderate valve lift and stock-type hydraulic lifter.

Note that the Jeep plunger height/preload of 0.040"-0.060" measurement calls for either marking the pushrod and using a straight edge across the valve cover deck to confirm the pushrod drop from a fully extended plunger height to desired preload height, or as I prefer, using a dial indicator with the indicator's stem placed directly above the pushrod at the rocker arm.  In this case, you are not checking valve clearance between the valve stem tip and the rocker arm, as this would not help.  Instead, by measuring the height of the pushrod—first with the lifter's plunger fully extended then with the rocker arm nut torqued down into position—you get an exact measurement of the lifter plunger preload.  The rocker ratio is no concern with this method of setting lifter clearance, more specifically, you are setting the lifter preload to 0.040"-0.060" range.

There's an even simpler way to determine the correct pushrod length.  CompCams sells a pushrod length gauge, reasonably priced, through outlets like Summit Racing:  https://www.summitracing.com/search?SortBy=BestKeywordMatch&SortOrder=Ascending&keyword=Comp cams 7704-1.  Piston at TDC on the compression stroke of a given cylinder, adjust the pushrod gauge with the rocker arm installed; adjust the gauge to extend from the rocker arm's pushrod socket to the lifter's cup with the lifter plunger fully extended.  Measure the gauge's length, and choose a pushrod length of 0.040"-0.060" longer than the gauge length.  The determined pushrod length will take up the space and depress the lifter plunger to the desired preload height.

Moses

[jakewalter]

Thank you Moses for all of the information and your quick response,

This is what I’m having trouble wrapping my head around.

Comp Cams recommends to soak the lifters overnight and I have also read that to check the pushrod length correctly you need to check the length of the pushrod before applying the installation lube.

If that is correct than you would need to install the cam, lifters and the head check your pushrod length. Disassemble the components soak the lifters, lube the cam lobes and reassemble the components using another new head gasket.

What am I missing here.

[Moses Ludel]

jakewalter...Filling the lifter(s) with oil may ease extending the lifter plunger while adjusting the CompCams gauge.  You can do the same thing by carefully allowing the lifter's plunger return spring to raise the cup to the retainer clip.  Just make sure you do not push the plunger down while setting the gauge.  The plunger needs to rest against the retainer clip at the top when adjusting the gauge or using a dial indicator.

If you use the CompCams oil filling technique, be certain to drain the lifters before setting the preload height or installing the correct pushrods and the rocker arms.  Otherwise, if the lifter is full of oil when the engine cranks over, the valves may be unseated.  In some engine designs, this creates valve interference with the piston crowns.

A tip from Dana that I gleaned in the 'eighties while writing the tech columns for OFF-ROAD Magazine is that it takes approximately four crankshaft revolutions for the overfilled valve lifter's plunger to drop 0.001".  While trying to stabilize the plunger height and normalize the valve clearance/preload, the valves may be standing open too much during initial cranking if the lifter is filled with oil.

I have heard stories of close tolerance race engines that bent valves on initial start-up because an unknowing tech filled the lifters.  Soaking them overnight with the plunger extended or "plunging" the lifter with a pushrod to fill it with oil on the bench can be a recipe for bent valves or damaged pistons on initial startup.

As for lube on the lifter base, light oil would not create an issue while you measure the pushrod length with the CompCams gauge or a dial indicator.  (You have the piston at TDC of the compression stroke, both valves would be closed, and there is no need to rotate the camshaft during this gauge or dial indicator check.)  Once you determine the correct pushrod length, you simply remove the lifter and lube its base and sides with engine assembly or camshaft lube before installing the correct pushrods and rocker arms.  

If the lifters are "empty" of engine oil, it takes a negligible amount of time for the lifter to fill during initial engine startup.  Once the engine and valve train are completely assembled, with rocker arms torqued in place, you can pressure fill the system or use a priming tool to charge the oil pump and galleys.  This will also fill the lifters without unseating the valves.  Even without priming, oil flows rapidly under high pressure through the lifter galley(s) and hydraulic lifters during initial startup.

Note that new lifters are assembled with a fine oil on their moving parts (plunger bore wall, check valve, etc.).  Do not remove that oil or wash it away with solvent.  This minuscule amount of oil provides plunger bore lube during startup. 

Moses

[jakewalter]

3 hours ago, Moses Ludel said:

Once you determine the correct pushrod length, you simply remove the lifter and lube its base and sides with engine assembly or camshaft lube before installing the correct pushrods and rocker arms.  

On this engine in order to remove the lifters you have to remove the head again or is there a different way?

Do you recommend using the installation lube on the sides of the lifters as well as the base?

 

[Moses Ludel]

Yes, jakewalter, you're correct.  My comment about "simply" removing the lifters after gauging the pushrod length is not taking into account the necessary removal of the 4.0L Jeep inline six cylinder head to access the lifters/tappets.  The Jeep inline sixes do not have relief holes in the cylinder head for removing the lifters with the cylinder head in place—nor is there a tappet cover at the side of the engine block for this purpose, a traditional approach for engine manufacturers.  Thanks for raising this point...

Even with the head removed, the lifters set awkwardly in the block casting; Mopar recommends use of a Tappet Removal/Installation Tool to remove and install the lifters. Summit Racing listings illustrate this type of tool:  https://www.summitracing.com/search/part-type/lifter-removal-tools?sortby=Default&sortorder=Ascending&keyword=Lifter Removal Tools&kr=Lifter Removal Tools.  The cylinder head and a new head gasket must be in place and torqued down properly before installing the pushrods and rocker arms.  Then you can determine the right pushrod length with the cylinder head at its operating height on the engine block.  You only want to install the fresh cylinder head and head gasket once!

That understood, I would lube the lifter bases and the camshaft lobes with camshaft lube during assembly.  When you're ready to gauge the pushrod length, push down gently on the lifter with either a pushrod or tappet removal/installation tool and rotate the lifter before gauging the pushrod length.  This will reduce the lube film thickness.  A few thousands of an inch of remaining lube film is hardly an issue here.  Select the correct pushrod length accordingly.

Be aware that stock replacement type (flat tappet) lifters have a convex base.  The lifter contact with the camshaft lobe is the apex of that curve.  This is the highest pounds-per-square inch load within an engine since this slight contact point gets the full pressure of the compressed valve springs.  Actual load at the lifter contact point can exceed 200,000 pounds per square inch load in a stock engine.

In addition to lubing the lifter bases, a thin film of engine assembly lube on the outside edges of the lifters is also a sensible practice.  This will prevent scuffing during initial engine startup.  The lifters are running in a machined iron block.  This assembly lube dissolves and disperses rapidly when circulating, pressurized oil reaches these parts.

I like to change the oil filter shortly after running the engine.  Let the engine warm up and circulate oil thoroughly, for several minutes or a short drive.  Then replace the oil filter and top off the oil.  For vertical or tilted oil filters, I like to prime the oil filter with fresh oil before installation.  A horizontal oil filter makes this difficult, sometimes impossible.

Moses

 

[jakewalter]

Hi Moses,

I placed a straight edge across the valve tips and found a significant difference in the length of the valve tips so I took the head back to the machine shop to have them adjusted. Than I followed your advice and after checking the pushrods I came up with a difference .005. The length of the pushrods are between 9.5 and 9.55.

If I’m correct using a pushrod that is 9.6 should give me the correct preload.

Would that be correct?

Thanks so much,

[Moses Ludel]

Hi, jakewalter...I'm guessing you watched my video on valve adjustment (http://www.4wdmechanix.com/jeep-232-258-and-4-0l-inline-six-and-2-5l-straight-four-valve-clearances-and-adjustment/) to reach the conclusion to check valve stem heights.  I'm gathering that you've established the needed pushrod lengths, and that they're varying between 9.5" and 9.55" due to the valve stem height discrepancies.  

The stem heights vary over a range of 0.005"?  With a 1.5:1 rocker ratio, that would be a significant change in pushrod lengths to reasonably match lifter plunger heights.  So you're trying to correct stem heights and reach a uniform pushrod length requirement.  Right?

A concern with valve stem heights is the uniformity of the valve seat depths in the head.  If the differences between valves are slight or at least somewhat uniform, valve stem height adjustment is possible and practical.  If this is the 0.005" difference you note, having the heights uniform will make it much easier to get a matched length set of pushrods. 

Moses

[jakewalter]

 

I ordered some Manley pushrods from Russ Pottenger at Bishop-Buehl Racing Engines so I hope that issue is solved however when I went to put on the oil pump I noticed that the piston skirts are going past the end of the cylinders.

Is this normal?

I’m using a Scat 4.2 crank with custom 4.0 rods and Keith Black pistons.

[Moses Ludel]

jakewalter...Manley makes good products...As long as the piston skirts do not interfere with the crankshaft, this does not look unusual.  If you have a concern, contact the tech folks at United Engine/Keith Black and share the exposed skirt lengths.  

Let us know what they consider "normal".  If the piston crowns reach the block deck height and are designed for the stroke length, there should be no issue.

Which piston part number are you using?   Confirm that United Engine is okay with these pistons for a 4.2L crankshaft application in a 4.0L block.  SCAT may have additional comments...Please share the insights...Thanks!

Moses