Use of Melling High Volume Oil Pump in Jeep 4.6L Stroker Engine Build

[JJH]

In putting together a jeep stroker build, I have a question regarding oil pump selection.

I see Moses using high volume oil pumps in engine builds in his books and in the materials presented here.  My intention was to use one until I found several references from Melling and anecdotal that high volume may cause issues with a fresh build.  The reason being that tight bearing clearances on a fresh build could be over taxed by the added pressure.  Some folks mentioned their engine builder would not warranty an engine with a high volume pump.

Moses and Tony Hewes both referred to using high volume Melling pumps in jeep strokers. So , what are the thoughts on these opposing positions?

 

Thanks!

 

JJH

[Moses Ludel]

JJH...Thanks for your interest in my books and the magazine coverage...I have used high volume (not "high pressure") Melling oil pumps since the late 'sixties on every engine I have rebuilt to blueprint standards.  That has been my choice for small- and big-block Chevrolet V-8s, inline AMC/Jeep sixes, AMC V-8s and Buick V-8s/V-6s that require a spacer plate and longer pump gears; big-block Ford FE V-8s, including a 1968 Mustang GT500KR (listed on the Shelby Registry) with a 428 Cobra Jet V-8 big block—plus a laundry list that includes Ford 300 inline six truck engines and a variety of GM and Chrysler V-8 engines.  I have personally never experienced an engine issue related to a Melling High Volume oil pump nor has Tony Hewes.

Here's how I view it:  When I use a Melling high volume oil pump, the pump will bypass at a preset pressure.  Yes, the added volume will push out more oil, but only at or below that pressure threshold.  To protect my engines, I want continual oil flow to the bearings. 

A stock Jeep oil pump's pressure threshold is plenty as we all know from watching the oil pressure gauge with a cold engine.  Added oil flow volume will not increase pressure beyond the oil pump's relief (bypass) valve setting.  The concern with adding higher oil pump pressure would be overloading bearings beyond their ability to bleed off oil at the sides of each bearing.  A presumed threat or risk is "spinning a bearing".  I use Melling High Volume oil pumps and do not use "high pressure" oil pumps in stock or lightly modified engines.

Wear at the crankshaft cheeks, improper rod journal radiusing, bearing wear and other machining issues can allow excess oil bleeding from the sides of rods.  Here, higher pressure might help compensate until the engine can be rebuilt properly.  High volume, on the other hand, will flow more oil in general and help resist cavitation—especially at higher rpm.  At no time can a bearing run on bare journals.  Insert bearing coated layers or old babbitt bearings are relatively soft and will quickly fail from direct contact with a crankshaft journal.

Consider this...When the engine starts up, the oil pressure is high, and oil is less viscous.  This would be the highest risk point for spinning a bearing.  However, we clearance rod and main bearings to allow a normal gap between the crankshaft journals and bearings.  The bearings, if clearance is correct, float on a thin film of oil.  If clearance is too tight, the film of oil may not protect the crankshaft journal.  Friction and heat will make matters worse and score the bearing(s). 

The bearing clearances should allow normal oil bleed-off.  If bearing clearance is excessive, too much oil will bleed from the sides of the bearings and drop the pressure.  Excess clearance can be caused by worn out bearings or a worn/out-of-round crankshaft journal.  In this case, the connecting rod or main bearing will actually create the notorious rod or main knock.  Tight oil clearance problems usually cause bearings to heat up severely or spin.

While Plastigage is suggested as the final check of bearing clearance, I use care with microcrometer readings of the journals and the inside bearing diameter within the rod and cap (secured to proper torque with fresh rod bolts after rod big end machining and the cutting of new tang slots).  This requires inside and outside micrometers.  If the rod big ends are true after rod sizing, and if the bearings are the correct size, and if the journals have been resurfaced or polished to the right diameter and radiuses, there will be proper bearing clearance and oil flow. 

Crank journals on specification, with rod big ends and their tang slots restored properly, should provide the right bearing shape and oil clearance.  Quality bearing shells, fitted in a properly sized rod big end, should be concentric and on specification.  For normal oil bleed, the shape of the rod journal radiuses is important and often overlooked.  Spun bearings can result from incomplete or incorrect crankshaft grinding or poor connecting rod machining.  These are machining problems that would not be influenced by use of a high volume oil pump.

To be clear, there is no such thing as "break-in" of crankshaft bearings.  Bearings ride safely on a constant oil film in a properly clearanced and lubricated engine.  Over the entire lifespan of connecting rod and main bearings, a properly built and lubricated engine should have bearing wear measurable in the ten thousandths of an inch. Camshaft bearings do depend on block alignment and sometimes require "fitting" with a very light alignment hone or, traditionally, a bearing scraper during engine assembly.  (This is extremely rare with modern engine blocks and should be a last resort.  More commonly, the bearing(s) have been installed poorly and have peened over their ends.)  Unless the camshaft cannot rotate readily when installed, risk of spinning a camshaft bearing is slight.  A high volume (again, not high pressure) oil pump would assure adequate flow to the bearings especially at critical idling. 

Pistons and rings are not "tight" if cylinder walls are clearanced to the piston size.  Valve guides should not seize if silicone bronze inserts or full new guides are fitted properly and oiling is adequate.  A new engine requires nothing more than consideration for seating the rings properly, and in the case of flat tappet camshafts like the Jeep 4.0L/4.6L, the seating of lifter bases-to-camshaft lobes.  This flat tappet demand requires use of ZDDP additive during break-in.  (Jeep inline sixes also require fitting the pushrods to correct length after block deck and head machining as discussed many times here at the forums.  See "CompCams" or "pushrods" in the forums search box.) Rings require moderate acceleration and deceleration to seat correctly.  Over-revving a fresh flat tappet engine is a good way to ruin the camshaft and prevent the rings from seating.  In any case, a high volume oil pump can assure available oil to all of the critical engine parts throughout the engine's life—especially at idle and high rpm.

Today's thinner cold pour motor oils like 0W-, 5W- or even 10W- (for a warmer climate) would never have difficulty flowing through properly clearanced rod and main bearings with crankshaft rod journals machined and radiused properly.  Even today's thinner pour multi-viscosity racing oils can be used with normal bearing clearances. 

An anecdote:  When I was in high school, a good friend had a 283/301 Chevrolet performance V-8 engine built at a machine shop.  In those years, multi-vis oils were not used during break-in, and the shop had recommended a straight 20 weight oil for break-in.  On a sub-freezing morning, the freshly built engine spun a rod bearing at start-up.  Oil weight may have contributed, but I would bet the rod ends were not machined properly.  This is unheard of today.  In fact, I'm amazed engines survive on 0W- oils but the do—largely due to factory high volume oil pumps, improved engine tolerances and better lubrication system engineering.  In the 'nineties, I toured the GM 4.3L L35 engine plant at Detroit on assignment for OFF-ROAD Magazine.  The chief engineer boasted that the block machining was so close that engines no longer required special fitting of lifters and other moving parts.  Emphasis had shifted to uniform tolerance at the machining level.  Today's better machine shops do this.  Engine survival is all about proper clearances, attention to detail, careful fitment of parts and reasonable break-in measures.

As a point of interest, my 4.0L Jeep Cherokee engine pan was down a year ago for a rear main seal replacement (no surprise here!).  At nearly 180,000 miles, I installed a new Sealed Power oil pump and fresh pickup screen (Melling) from Summit Racing.  I also used a pickup tube installation tool, which I highly recommend.  Summit sells the high end Melling professional tool and a cost-effective Proform tool for occasional use.  The Proform tool works if used properly.  Fitting the oil pump screen to the pump is crucial to engine safety.

I picked a less expensive stock replacement pump although Sealed Power, like Melling, does offer a High-Volume pump option.  I did this because the engine has higher mileage and will not be revved high or placed on ultra-steep gradients between now and the time I rebuild it.  Were I hardcore wheelin' with the risk of dry sumping the oil pick up screen and pump, I would have purchased the High-Volume pump for increased flow as quickly as the pick up screen can find oil.

Here is what Sealed Power/Summit has to say about the High-Volume pumps.  The blurb is available at Summit Racing (https://www.summitracing.com/parts/slp-224-43505/make/jeep/model/cherokee/year/1999).  I highlighted the comments on rebuilt engines in red:

Sealed Power High-Volume Oil Pumps

"Oil volume is nothing to take lightly, so why reuse an old oil pump or settle for something less than great, when you can have a Sealed Power pump? They've been making quality, reliable performance pumps for decades. These high-volume oil pumps have increased rotor or gear section lengths for increased oil delivery to critical areas under extreme conditions. Their sturdy cast-iron pump body handles the stress associated with high rpm and added oil volume. The extra volume is helpful in maintaining oil pressure in rebuilds."

Here is Melling's own explanation of the difference between high volume and high pressure pumps.  Note that the high pressure pump is intended for an engine with lower oil pressure.  This hints that the bearing clearances are excessive, and the oil pump pressure will fill the gap.  On an engine with normal oil pressure (presumably a fresh engine build with correct bearing clearances), there would be no need to over-pressurize, as this could result in spinning a bearing:

 

High Volume Oil Pumps 

Melling high volume oil pumps increase the amount of oil flow by an average of 20% through the engine improving oil pressure at idle providing dependable performance every time in every application. Every Melling high volume oil pump is engineered and assembled to the highest production standards from high quality materials. All Melling high volume oil pumps use the latest in gear and gerotor technology to provide the highest level of quality and performance. High volume gears are machined to close tolerances to ensure proper engine pressure and correct, efficient pump operation. End plates are precision ground for maximum wear resistance. Every Melling oil pump is individually tested for pressure and flow under conditions designed to duplicate actual engine operating conditions.

High Pressure Oil Pumps 

Melling high pressure oil pumps can aid in increasing the amount of oil pressure in engines with low oil pressure. Melling oil pumps provide dependable performance every time in every application. Every Melling high pressure oil pump is engineered and assembled to the highest production standards from high quality materials. All Melling high pressure oil pumps use the latest in gear and gerotor technology to provide the highest level of quality and performance. Gears are machined to close tolerances to ensure proper engine pressure and correct, efficient pump operation. End plates are precision ground for maximum wear resistance. Every Melling oil pump is individually tested for pressure and flow under conditions designed to duplicate actual engine operating conditions.

Note that the Melling high pressure pump is an intended bandaid for engines with low oil pressure.  This would be an application where the tolerances and clearances are incorrect ("loose") or the engine has considerable wear.  Short of a rebuild, the engine may still be operational/serviceable but needs more oil pressure.  A fresh, properly clearanced engine could actually suffer from use of this pump.  Spinning a crankshaft (particularly rod) bearing would be possible with this excess oil pressure pushing through normal bearing clearances.  If the engine builder uses a high pressure oil pump instead of a high volume oil pump in a freshly machined and assembled stroker 4.6L engine build, fear of failure could be justified. 

I cannot find a Melling High Pressure pump listing for Jeep 4.0L engines.  If they offered one, it may have been dropped to save confusion about whether or not to use a Melling high volume oil pump in a Jeep inline six engine.  The High Volume pumps are available for all Jeep inline sixes under part numbers for specific block/engine model years.  Presumably, your 4.6L build has a 242 VIN S core.

Looking in the current Melling catalog shows the 242 VIN S 4.0L oil pumps suitable for "Stock" use are either the standard or the high volume part numbers.  There are no footnotes, warnings or sanctions about using the high volume pump. For more product details and catalogs, visit the official Melling site:  https://www.melling.com/product/oil-pumps/.

For a graphic example of the need for oil flow and the highest possible volume of available oil under the most severe off-road driving conditions, my coverage of the 2012 Wheelers for the Wounded Rubicon Super Event makes the point.  In the first video (top of page), check out minutes 9:30 to 12:30.  I filmed this 4.0L Jeep at the Sluice Box.  Oil pressure would be far less concern here than volume.  The fact that this engine still ran after these antics amazed me: 

https://4wdmechanix.com/moses-ludels-4wd-mechanix-magazine-hd-videos-2012-wheelers-for-the-wounded-rubicon-super-event/

I'm sure a teardown would reveal severe stress to the crankshaft and bearings although allegedly this trailered trail-only Jeep and engine had repeatedly "crawled out" on the rocks for years without tossing a connecting rod through the side of the block.  This is a testimonial to AMC's design of the oiling systems and the ability of modern engine oil to cling to journals.  Jeep inline sixes and V-8s ran higher oil pump pressure stock than most other engines of that period.  As illustrated in this extreme example, the oil pump grabbed oil whenever the sump screen dipped into it.

In the case of a Jeep 4.0L/4.6L platform, you would do fine with either a Melling standard replacement oil pump or the high volume pump.  Follow Melling's guidelines.  On a fresh engine, properly clearanced and machined, my choice would be the Melling High Volume pump for the year of the 4.0L engine block, cylinder head, pan and screen.  (4.2L oil pumps are a different design and part number.  The 4.6L stroker with a 4.0L casting core and 4.2L crankshaft will use a 4.0L oil pump, screen and oil pan.)  Quadratec, JEGS, Morris 4x4, Summit Racing, AutoZone, Amazon, Advance Auto and many other 4x4 and general automotive parts sources offer the M167HVS Melling High Volume pump for the common 4.0L/242 VIN S engines.

My focus is always precision engine machining, including balancing, performed by a knowledgeable machine shop with state-of-the-art equipment.  I follow with proper fitting of engine parts during assembly.  For the Jeep 4.6L stroker build, my machine shop and assembly concerns include the block deck height, pushrod lengths after block decking and head machining and, for initial start-up and break-in, the use of ZDDP additive for the camshaft and lifters. 

After assembling the engine with assembly lube on all bearing surfaces, for insurance and long engine life, I always prime the oil pump and lubrication system before initial start-up.  I use a Goodson primer tank although an inexpensive priming tool and 1/2" variable speed drill motor will work here.

Note:  Tony Hewes is an award winning, championship Winston Cup Engine Builder.  In addition to many Jeep customers at the Reno Area, Hewes Performance Machine did machine work and built engines from town car ("utility") types to national championship race engines.  From 2007-2011, Tony did our shop's sublet machine work on valuable postwar and muscle era blocks, rods, cylinder heads and crankshafts, including a 327 Packard straight eight, a vintage 392 Chrysler hemi-head V-8 and a 1957 Chrysler 318 poly-head Plymouth Fury engine.  He has built scores of Jeep inline sixes and AMC/Jeep V-8s.

Moses

[JJH]

Moses,

Thank you for your very detailed reply.  You left no question unanswered.  A high volume pump has been ordered and will be used in my engine build.  And thank you for providing such a wealth of technical info in so many other areas.  It has been a great resource for me over the years.

 

JJH

[Moses Ludel]

JJH...All of us need to follow manufacturers' recommendations, use the correct parts for a given application, and stick with best practices.  If you have access to quality machine work and are assembling the engine yourself, your care during the parts fitment will assure great results. 

What is the 4.0L donor core year and application?  Are you using a complete 1991-1999 Mopar MPI 242 (VIN S?) with ignition distributor, PCM and the OEM wiring harness?

Let us know how the engine build turns out...

Moses

[JJH]

Moses,

I have a complete 4.0L, MPFI, and AX15 from a 1991 Cherokee.  My intension was a transmission swap in place of the T176, a rebuilt 4.0L head and the MPFI from the doner engine onto the original AMC 258.

Midway I discovered my doner was not a 250,000 mile engine, but was in fact freshly rebuilt.  A 4.0L swap then became in order.  I then discovered hopelessly damaged keyways on the 4.0L crank.  Since the 4.0L block needed little more than a hot tank and a light hone, and needed a new crank anyways, I decided to combine my existing components into a stroker.  I am doing the long rod version with the 4.0L rods and custom pistons. The crank is from the existing AMC 258.  All of this is going into a 1984 CJ7.

JJH

[Moses Ludel]

Perfect, JJH!  You had the excuse to build the 4.6L, everything to gain with limited expense!  The rods with custom pistons will work well for deck height...Are you changing the camshaft and injectors?

Regarding the build of your 4.6L, many will find this Tony Hewes formula helpful.  This engine included the customary Melling High Volume pump.  For the record, the 4.6L ran flawlessly from the initial startup.  My friend Brent, the 1998 Cherokee's owner, added a HESCO water pump and high flow thermostat housing with a large Griffin radiator.  See the list of parts and machining in the article:

https://4wdmechanix.com/moses-ludels-4wd-mechanix-magazine-vlog-road-testing-jeep-4-6l-stroker-inline-six/

CompCams has a variety of contemporary camshafts, some similar to the 252 grind.  We have discussed the newer camshaft profiles in recent Jeep 4.0L/4.6L forum topics.  Regardless of camshaft maker, my simple formula for low end and mid-range power with decent fuel efficiency is more valve lift than stock with mild duration, a camshaft advertised as good for (normal) idle speed to 4,000-4,500 rpm.  This will provide substantial bottom end torque and drivability.

Moses

[JJH]

Moses,

Yes, I plan to use the comp cam 68-232-4 (https://www.compcams.com/xtreme-4x4-206-212-hydraulic-flat-cam-for-amc-199-258-4-0l.html).  I'm aware of your advocacy of the 252 grind.  In the absence of obtaining that grind, the 68-232-4 has had positive reviews, provides a bit more lift, is purported to be efi friendly, and good for the 800-4800 rpm range.  Your thoughts would be welcome.

Since I did not set out to build a stroker, I acquired new 12 hole upgrade injectors rated at 240 cc (not sure of the pressure rating, but probably less that 24lbs).  I expect I will give them a try and then upgrade to 24lbs injectors if necessary. I do have an adjustable fuel pressure regulator for fine tuning.

The rest of the jeep is as follows: 1984 cj7, AX15 Trans, D44 full float rear, D30 front, ARBs, 4.27 gears, 33x10.50r15 tires.  I don't expect travel speed to ever be more than 55-65 mph travel speed, so it should spend most of its time below 2200-2300rpm.  We live 10 miles out of town and 55mph is plenty of speed to get us there.

JJH

 

[Moses Ludel]

The camshaft is a fine contemporary choice, JJH.  Fuel efficiency will be optimal, the bottom end torque ample.  The 252 grind did not work with coil on plug (C-O-P) engines (1999-up Grand Cherokee 4.0L, 2000-up for Wrangler and XJ Cherokee).  CompCams likely dropped the grind to avoid continually explaining why the camshaft threw engine codes in late 4.0L engines.

If good quality, the injectors are worth a try for this engine rpm range despite the added cubic inches.  24 pound injectors would be a safe bet, but test these first.  I invested in a fuel injector testing and cleaning machine to test for uniform fuel flow per injector.  Not sure where you sourced the injectors, but brand-x "off-shore" injectors can be all over the board for flow rate. 

If the injector source is questionable, test and compare their flow rates.  A set of cleaned and flow tested used OEM Ford 302 H.O. injectors would be better than mismatched, cheap injectors.  You can get "rebuilt" OEM Ford injectors for a reasonable cost.

I like your axle and transmission choices!  You'll like the stroker power, especially the torque rise and torque peak at a relatively low rpm with that camshaft. 

Moses