bearings and oil flow

Discussion in 'Oil and Lube Systems' started by grumpyvette, Sep 19, 2008.

  1. grumpyvette

    grumpyvette Administrator Staff Member

    Bearings and oil flow

    viewtopic.php?f=53&t=88 ... cation.htm

    keep in mind both engine oil temps and trans fluid temps seldom reach operational temps,fluid
    and stabilize , for semi consistent data,in under 12-15 minutes of drive time,temps have a huge effect on lubricant viscosity and durability. . ... stall.html
    Id also point out that, if you properly set up an engine's oil system, open the oil drain holes and use the proper oil pan, windage screen and crank scraper, its virtually impossible , in a well designed engine to run the engine "long enough to pump all the oil upstairs."
    as with a properly designed baffled oil pan, with a carefully fitted and clearanced windage screen and crank scraper, the oil pump simply reaches a flow rate pumping oil out of about 100 or so potential lubricant flow leakage points

    theres zero doubt an accusump oil feed is a good insurance policy to maintain oil pressure at the bearings, but simply having a 7-8 quart baffled oil pan,properly clearanced, windage screen and crank scraper will insure the oil pressure remains consistent , mostly due to the fact that theres always going to be enough oil over the oil pump pick-up, simply because theres really no room to pack most of the available oil volume in the upper engine ,plus the fact that hot oil flows well.
    OIL PRESSURE read on the oil pressure gauge is a MEASURE of RESISTANCE to oil flow, you can REDUCE the pressure the gauge reads by either increasing the engine clearances or REDUCING the oil viscosity (thickness) so it flows thru the clearances faster with less resistance.(OR INSTALLING A SLIGHTLY WEAKER OIL PUMP BYE_PASS SPRING,that limits the pump pressure before it allows some oil to re-circulate back through the bye-pass valve ,from the high pressure back to the low pressure side of the pump impellers, but only the max pressure you reach is limited by the bye-pass spring,in your oil pressure bye pass circuit and its that spring resistance determines the point where the bye-pass circuit, opens and limits max oil pressure, but the bye-pass circuit has zero to do with anything else, if its functioning correctly,
    there are many oil leakage points(100) in a standard Chevy engine.
    16 lifter to push rod points
    16 push rod to rocker arm points
    32 lifter bores 16 x 2 ends
    10 main bearing edges
    9 cam bearing edges
    16 rod bearing edges
    2 distributor shaft leaks
    1 distributor shaft to shim above the cam gear(some engines that have an oil pressure feed distributor shaft bearing.)
    once oil exits the bearings or valve train it flows mostly by gravity back to the oil pan sump, but a properly designed windage screen and crank scraper correctly clearanced allows the spinning crank/rotating assembly to act like a directional pump that drags the vast majority of the oil flow back to the sump, by design.


    A simple modification to the upper thrust bearing may be beneficial in some engines. Install the upper thrust bearing in the block to determine which thrust face is toward the rear of the engine. Using a small, fine tooth, flat file, increase the amount of chamfer to approximately .040" (1 mm) on the inside diameter edge of the bearing parting line. Carefully file at the centrally located oil groove and stroke the file at an angle toward the rear thrust face only, as shown in the illustration below. It is very important not to contact the bearing surface with the end of the file. The resulting enlarged ID chamfer will allow pressurized engine oil from the pre-existing groove to reach the loaded thrust face. This additional source of oiling will reach the loaded thrust face without passing through the bearing clearance first (direct oiling). Since there may be a load against the rear thrust face, oil flow should be restricted by that load and there should not be a noticeable loss of oil pressure. This modification is not a guaranteed "cure-all". However, the modification should help if all other conditions, such as surface finish, alignment, cleanliness and loading are within required limits.

    from chevy high performance mag




    with the engine up to operational temp.of between about 180f-210f
    and using an oil viscosity that maintains at least 15-20 psi at hot idle in traffic,
    your engine should maintain a MINIMUM of 10 psi per 1000rpm and max out pressure at about 4500-5500rpm at 60psi or higher
    remember the thicker the oil the harder it is to force thru the clearances in the engine, and pressure is how you measure the RESISTANCE to oil flow, but you should use an oil viscosity that at least maintains that 15-20 psi at idle

    one factor thats frequently over looked is that many bearing manufacturers don,t seem to have placed the bearing oil feed holes in bearing shells so they exactly match the oil feed passages in the engine blocks
    example heres a common minor mis-match on the bearing shell/oil passage alignment

    but Ive seen some where over 1/3-to-1/2 the oil feed hole was blocked due to misalignment, thats usually easily cured, by drilling a shallow increased diameter recess in the blocks oil passage to open it to match the bearing or opening up the bearing feed hole, but which ever route you take be sure to carefully clean and deburr both

    increasing the groove, from 180 deg to 270 deg, lowers bearing support, increases oil flow rates and tends to increase wear


    As you'll see in Figure 1, below two different types of grooved upper main bearing shells

    the oil groove terminates before it gets to the bearing parting line. This style of main bearing has accounted for a 15 percent or more increase in hot idle oil pressure. So if you're looking to eliminate some of those unexplained low oil pressure gremlins contact your bearing manufacturer and ask about this style bearing and availability for the engine applications that you are building.

    keep in mind only the upper main bearing shell should have an oil groove, having a 360 degree oil groove lowers the bearing ability to handle high rpm loads

    The main bearing oil groove is required for the sole purpose of supplying oil to the
    connecting rod big end bearing. At one time it was common to have a full 360° groove on the
    main bearing to provide an uninterrupted supply of oil to the big end by means of a single
    drilling from the main journal. This was achieved by having identical upper and lower bearing
    As bearing loads increased this design proved unsustainable as the oil film thickness, on
    which every crankshaft bearing relies, became insufficient for reliable main bearing
    operation. The solution was to increase the bearing area on the more heavily loaded lowerhalf
    bearing by reducing the extent of the groove to around 230° or even 180° in order to
    provide a single bearing land of greater width. Any increase in bearing width enables a
    higher oil film pressure to be sustained as the distance from the centre of the bearing to the
    edges, which cannot sustain an oil pressure, is increased. This in effect allows the
    generation of a thicker oil film with which to separate the shaft and bearing shell.
    The reduced oil groove extent would sometimes be compensated by a cross-drilling on the
    main journal in an attempt to maintain an uninterrupted supply of oil to the big end bearing.
    However, in many cases it was found that the big end could cope very well with the
    subsequent intermittent oil flow offered by a single drilling from a 180° groove.
    Nowadays, with the use of computer simulation and engine testing the optimum extent of the
    groove may be determined. It is not now just a case of allowing the big end to survive but
    that the efficiency of the bearing system can actually be improved by due attention to the
    groove geometry. This is because the big end bearing, like any hydrodynamic lubricated
    bearing, will use as much oil as it needs to generate an oil film for any given operating
    condition. Any less than this amount risks disrupting the oil film and ultimately starving the
    bearing of oil, but equally, feeding excessive oil to the bearing simply results in additional
    leakage, and reduced efficiency. Therefore, the oil groove, like many other features on a
    bearing shell, can be optimised.

    read thru these links ... forman.pdf ... ooving.pdf

    TB 2051 2/10/2000
    Influence of Grooving on Main Bearing Performance
    Various forms of main bearing grooving have been used over the years. We are
    frequently asked what difference grooving makes.
    First, it’s essential to understand that bearings depend on a film of oil to keep them
    separated from the shaft surface. This oil film is developed by shaft rotation. As the shaft
    rotates it pulls oil into the loaded area of the bearing and rides up on this film much like a
    tire hydroplaning on wet pavement. Grooving in a bearing acts like tread in a tire to break
    up the oil film. While you want your tires to grip the road, you don’t want your bearings
    to grip the shaft.
    The primary reason for having any grooving in a main bearing is to provide oil to the
    connecting rods. Without rod bearings to feed, a simple oil hole would be sufficient to
    lubricate a main bearing. Many early engines used full grooved bearings and some even
    used multiple grooves. As engine and bearing technology developed, bearing grooving
    was removed from modern lower main bearings. The result is in a thicker film of oil for
    the shaft to ride on. This provides a greater safety margin and improved bearing life.
    Upper main shells, which see lower loads than the lowers, have retained a groove to
    supply the connecting rods with oil.
    In an effort to develop the best possible main bearing designs for High Performance
    engines, we’ve investigated the effects of main bearing grooving on bearing performance.
    The graphs on the next page illustrate that a simple 180
    groove in the upper main shell is
    still the best overall design.
    While a slightly shorter groove of 140
    provides a marginal gain, most of the benefit is to
    the upper shell, which doesn’t need improvement. On the other hand, extending the
    groove into the lower half, even as little as 20
    at each parting line (220
    in total), takes
    away from upper bearing performance without providing any benefit to the lower half.
    It’s also interesting to note that as groove length increases so do Horsepower Loss and
    Peak Oil Film Pressure which is transmitted directly to the bearing
    Last edited by a moderator: Nov 24, 2017
  2. grumpyvette

    grumpyvette Administrator Staff Member ... NG-SPACERS
    Part Number Description Price Qty Add
    EB-MB5224AM Chevy 350 to 400 Spacer $49.99 ... K,533.html

    400 sbc block/350 crank main bearing spacers

    theres also TRW MS3110P is the part number for a main bearing set to put a standard pre 1968 small journal (283, 265, sj327) crank into a medium journal (350) block ... index.html

    IT should be obvious that you'll need to pre-prime the blocks oil passages and adjust the rockers so oil flows from the rockers with the engine being pre-primed with a priming tool being used BEFORE trying to start any engine with a new cam to insure oil flow begins instantly on the engines start-up,you WON,T get oil to all lifters equally unless the engines crank & cam are spinning,(so during testing spin the engine slowly with a breaker bar or ratchet), because the oil passages feeding the lifters aligns differently at different lifts,your oil leak at the distributor base is normal, but the clearances and flow may be excessive, with a priming tool, some are not nearly to spec. ID measure the diam. of the oil pump primer and then measure the distributor base, Id bet the distributor base is larger and fits better, which reduces the potential for leakage.
    those bottom two bands form a wall on the oil passage, some guys cut a rounded grove and install an O-RING so the upper band seals too the block, you don,t want to do that to the lower band simply because that's the oil flow source to the distributor /cam gear
    20 psi is about normal for your typical 3/8 drill,max pressure is not nearly as important as checking flow, and for leaks where there should not be leaks, with an engine primer tool,Ive brazed a socket to the top of my oil pump primer and use the 1/2" drive air ratchet to drive it, it won,t heat up and burn up like a electric drill will.
    don,t get alarmed if you get zero pressure or flow for a few seconds,(the oil filter and passages need to fill first) that's one reason WHY your pre-priming, to get oil flow to the bearings instantly on start up , you don,t want them running without oil flow if you can prevent it even for 20 seconds
  3. grumpyvette

    grumpyvette Administrator Staff Member

    IF your having excessive oil heat problems with an engine, my
    first suggestion swap to a decent synthetic oil in the 10w30 range or at least the thinnest viscosity that maintains 20 psi at hot idle temps, as SYNTHETICS don,t generally start breaking down until about 280F PLUS while mineral base oils tend to start degrading after repeated 250F use, and the thinner the oil the faster it circulates thru the clearances, and the faster heats absorbed and transferred out off the hotter components
    and Id need to know more about the complete engine parts list, clearances, etc. but Id sure want to verify the fuel/air ratio is at about 12.6:1 not alot leaner and your ignition timing was carefully checked to not be a couple degrees advanced from ideal., and that your running a 7-8 quart oil pan, heres the oil cooler I use and I had to install a thermal switch or it OVER COOLED my engine oil in FLORIDA where average outside air temps closer to 90F
    oil does most of an engines real cooling and the cooling system allows heat absorbed by the oil and transferred to the block to be transferred to the coolant and removed, but a significant percentage of that heat can be removed if an efficient oil cooler is installed, that maintains a significantly lower average oil temp while the engines under stress., think about it a second. the HOT PARTS like rings, valves, cams, lifters, bearing surfaces and valve springs and pistons get cooled mostly by oil splash or pressurized oil flow not direct coolant contact

    my oil pan looks similar to this ... 88bb985ecf
    Canton Oil Pans
    11-120 and 11-120T Oil Pans

    but I extended the sump forward with 14 ga steel and a tig welder to add 4 inches extra to the sump to get 10 qt capacity ... mage=large


    But I was always under the impression that Chevys liked thicker mineral oils, and I should avoid synthetics? Not true then?

    IVE run a MIX of 90%/ synthetic 10% mineral oil in my race cars for many years

    usually 1 qt MARVEL MYSTERY OIL, 9 qts MOBILE 1 10w30 synthetic ... /Oils.aspx

    obviously these won,t fit all chevy applications but if you have the room for the longer, spin on filters

    The "longer high capacity oil filter" Purolator is L40084.

    "longer high capacity oil filter" N.A.P.A: # 1794

    "longer high capacity oil filter" ACDelco: PF932

    keeping the oil cool basically comes down to having the oil flow thru both the engine and the cooler but having the surface area of the cooler large enough and the number of passes thru the cooler ,allow the oil to transfer most of the heats its absorbed in the engine back out into the air flowing thru the cooler,before its routed back to the engine,and that generally requires ducting cool air into the cooler and placing it where the flows not restricted, on my corvette I removed the rear spare tire, and built a mount that allowed a good deal of clearance and no significant engine heat, with it working all the time I had problems getting the heat over 220 f and it mostly stayed at or near 200f,theres basically about 3 qts in the upper engine and oil passages at any time , absorbing heat so having a similar volume in the cooler, releasing heat during the same time makes sense, and having a similar amount in the baffled oil pan sump and filter sure helps,naturally if you have the oil routed to spend more time with the majority of the oil being heated and less of the oils times spent cooling average temperatures rise rapidly
  4. grumpyvette

    grumpyvette Administrator Staff Member

    theres some confusion as to the correct oil pan size and dip stick markings,, ILL try to keep this simple, basically the oil pan should never be less than a 5 qt capacity in a performance application, and as long as clearances under the car permit a 6-7-8 or larger capacity baffled oil pan with a windage screen is preferred, some guys will suggest restricting oil flow return routes to the sump by installing lifter valley breather tubes, but a decent cranl scraper and windage screen on a high capacity baffled oil pan reduces windage losses significantly, and that oil cools the pistons, rings and cam and lifters so reducing its ability to cool and lube those components by restricting flow is not a great idea

    theres about 2-3 quarts of oil in a running engine thats not sitting in the sump, around the oil pump that lowers the oil pan oil level a good deal, normal 5 qt oil pans still have 2-3 qts around the pickup, but that lowers the oil level in the oil pan in most cases about 2-3 inches while the engine runs, so most dip sticks measure the correct oil level as about 2" up on the crank counter weights, because once the engines spinning that puts the oil level below the windage screen or at least below the spinning crank.
    DIP STICKS are NOT always correctly marked,you should be able to research your oil pans intended capacity, Id suggest running NO LESS than a 5qt capacity oil pan and a baffled 6-7-8 qt is vastly preferable if your not sure add 5 qts to an empty oil pan and start the engine for a minute to fill the oil filter and oil passages, then look at where the oil level is in relation to the indicator band on the dip stick so you know what the minimum level should be, if its significantly lower than the dipstick marks, add the required oil level the pans rated for and pay attention to the dipstick.
    just remember oil levels drop several inches once the engines running and as the rpms increase the level tends to drop slightly more, your very unlikely to (PUMP THE PAN DRY) like you commonly hear as a MYTH with the high volume oil pumps, because hot oil with a well designed oil pan and windage tray drains back into the sump quickly and the vast majority of the oil never makes it to the upper engine as its leaking from rod, man and cam bearings and lifter bores and gets swept back into the sump.
    now it should be obvious that to use a high volume oil pump you need a MATCHING high capacity baffled oil pan and windage screen to CONTROL the extra oil flow rates, and the bearing, and other engine clearances and oil drain holes in the block should be designed to use the extra oil flow.



  5. Grumpy

    Grumpy The Grumpy Grease Monkey Staff Member
    as a general rule as your engine oil viscosity is reduced the effort required to pump the oil thru clearances is lower and the pressure reading on the gauge drops, thats not necessarily an indication of lower bearing protection, as thats generally a function of oil quality and its formula, and basic components used, in its design, and generally its increased flow rate increases bearing cooling, a good quality 10w30 should ideally provide 20-22 psi at 800rpm idle (anything over 15-17 psi at 800rpm is fine) and 60-65psi by 5000rpm which is all you can use

    at times having a long small diameter light that you can stick through the blocks oil passages to check the oil feed to the bearings passage alignment helps





    shop carefully cam bearing tools sell for $40-$300 plus and almost identical tools car vary in price by over $120, and be awre all cam bearings in a single block may be different sizes based on the location, so pay attention as you remove them as to the oil feed hole location(S), how they are indexed or clocked and the outside diameter and be aware in many cases the bearing is beveled on one side to aid installation
    heres some info from napa

    When rebuilding an engine, there is nothing more critical than getting the bearing clearance correct. Every engine has its own bearing clearance specs, but the measuring procedure does not change. There are two main methods used for checking bearing clearance – Plastigage® or gauges.

    Plastigage® has its place, as it serves a purpose for backing up and verifying your bearing clearances. Plastigage® is a special plastic that expands a specific amount when squeezed. Sold in sleeves of threads for specific thickness ranges, Plastigage® works really well in situations where the components are not being completely removed, such as in-engine bearing replacement, and other non-automotive uses. Originally put on sale in 1948, Plastigage® is fairly accurate and the method of choice for many DIY enthusiasts.

    Plastigage® is quite useful, so don’t automatically throw it out. It is a good way of verifying your measurements.
    In reality, the right way to check bearing clearances is with the proper tools. In order to check the clearances for rod and main bearings, you need a set of micrometers and a dial-bore gauge. These are readily available at budget prices, but if you are going to use them a lot, better quality tools are advised.

    This looks like a horseshoe with a round handle attached to one leg. Micrometers typically only adjust 1”, so you need multiple sizes to get the job done. A 1-6” set usually has the sizes you need for most jobs.

    This a complete micrometer set that will cover just about anything you could need for automotive work.

    Dial-Bore Gauge
    This tool uses a dial indicator on a post with a small wheeled measuring apparatus. These are adjustable through graduated post extenders that increase the diameter of the measurement circle.

    The dial bore gauge measures the inside of round holes, such as the bearing journals.

    This one tool can measure 2″ up to 6″ diameter holes.

    Both tools are needed in order to check the interior and exterior dimensions of the crankshaft, rods and engine block journals, as well as the thickness of the bearings themselves. Making all of this happen can be tricky, so here are a few tips to help you work through the process.

    Using a micrometer means following a couple of rules. The key to a micrometer is not to tighten it too much. There are two knobs – a large knob and then a smaller one. The smaller knob clicks when the micrometer is in contract with the part. DO NOT use the larger knob to tighten the mic onto the part as this can damage the tool.

    Reading a micrometer can be confusing, they are graduated differently than rulers. The inside barrel is marked in .100” (large) and .025” (small) notations. Once you reach those marks, the scale on the thimble (large rotating knob) comes into play to get the finite measurements. The thimble is scaled in .001 divisions from .000 up to .025”.

    The hash marks are how you read micrometers. It takes some practice, and unless you use them daily, you will forget over time. Just be patient.

    Outer Diameter Measurements
    These are fairly simple, just choose the micrometer that covers the range needed and measure. It is a good idea to check the part in three different locations, staying away from the oiling holes as they can throw off the measurements due to the chamfers.

    Measuring Bearings
    Even though bearings are flat enough, they cannot be accurately measured with calipers, instead you need a micrometer. There are special micrometers available for measuring round inside surfaces, but you don’t have to have one of those. Instead, you can use the shaft of a drill bit (good quality, and use the smooth part, not the fluted section). Place the drill bit on the inside curve, and then measure the bearing. Subtract the thickness of the drill bit (measure, don’t assume), and you will have the thickness of the bearing.

    An tube mic is useful for measuring bearings and over inside-curved pieces. In a pinch, you can use a drill bit or pushrod and an outside mic.

    This is how bearings are measured. DO NOT use calipers, you can easily scratch the babbit material and ruin the bearing, plus they are just not accurate enough.

    Using A Dial-Bore Gauge
    Setting up a dial-bore gauge requires using a micrometer. You need the base measurement of the bore, rough is enough. Set the gauge to just over the diameter, using the correct extensions. Set the micrometer to the bore size you need, then place the gauge between inside the mic and rock the gauge back and forth, and side to side. Note the minimum reading, and zero the gauge to that reading.

    Setting the dial bore gauge uses both the bore gauge and a micrometer. Make sure the measuring ends are square inside the micrometer’s anvils (not as shown)

    Inside Diameter Measurements
    With the dial-bore gauge set to the correct size, place the gauge inside the journal or rod end and rock the gauge back and forth and side to side, just like the setup process. Note the smallest diameter, that is the size of the journal. Just like the outside measurements, take the reading in three different places. One note – the bore must be as it would be in use, so torque the caps to their correct specs and they need to be clean, no oil at all.

    Place the gauge inside the journal and move it slowly till you find the largest measurement. Take readings in three places.

    if your serious about building engines as a hobby or even as a part time side business,
    you'll be forced to either buy or borrow some decent quality precision measuring micrometers,
    simply due to the need to check clearances accurately (ABOUT $250 a set)
    (ABOUT $415 a set)
    (ABOUT $877 a set)
    dial bore gauges are about useless without a set of accurate mics, in the sizes of the bore diameter your checking as you use a dial bore gauge to measure consistency in a given bore size and basically how consistent or "ROUND" a bearing is but you use the mics to verify dimensions.
    in my opinion you,ll also be smart to cross check ,bearing clearances with plasti-guage

    [​IMG] [​IMG] [​IMG]


    yes I use both micrometers and snap gauges and cross check with plasti-gauge
    and yes when you compare the crushed width of the plasti-gauge youll find it rarely falls as an exact match to the bar chart tape that is packaged with it so you can judge clearance based on crush width


    Last edited: Jan 14, 2018 at 1:49 PM
    Strictly Attitude likes this.
  6. Grumpy

    Grumpy The Grumpy Grease Monkey Staff Member

    IF you find metallic glitter in your oil during any oil change that metal came, from someplace,and things are likely to get worse over time, if the engines still driven, ,if you pull it down for a close detailed inspection NOW, you might find its fairly cheap and easy to repair,
    COMPARED, too what it will be inevitably if you continue to drive it in its current condition,
    as all that metallic trash in the oil WILL constantly continue to do ever more DAMAGE
    shop carefully the exact same set of mics from the same company can cost $270-$900 depending on where you buy the set

    read through these links, the time spent will be well worth the effort anf knowledge gained should help

    moroso sells plug kits
    be sure only one oil passage plugs drilled, generally only the pass side oil passage plug with a single .025-.030 hole, many guys use a 1/32" drill bit because its easy to locate, I prefer the smaller #72 drill



    btw I got asked how I apply the 50%/50%
    I generally spray crank journals and bearing surfaces with moly spray first , then paint on the mix linked below.

    Preference on assembly lube?

    50% marvel mystery oil
    and 50% crane moly lubes
    what Ive used for decades
    but this works
    I have used J&B WELD EPOXY on a large magnet

    on the base of an aluminum 1/2 cup measuring cup I purchased at a yard sale for 25 cents to mix up the mixture, the magnet allows me to stick the cup to the block oil pan rail or engine stand where its handy too get at, and I simply brush on the mix with a 1" paint brush, with synthetic bristles that won,t shed

    OH! slide it off the block don,t try to just pull it off , its going to be much less messy that way trust me!
    when your done , wipe it clean and stick it inside the lid of your tool box , after placing it in a ziploc bag to prevent it from picking up trash while in storage


    Crankshaft Thrust Bearing Failure - Causes & Remedies
    For years both transmission and engine rebuilders have struggled at times to determine the cause of crankshaft thrust bearing failures. In most instances, all of the facts concerning the situation are not revealed at the onset of the failure. This has led to each party blaming the other for the failure based only on hearsay or what some "expert" has termed the "cause". Some of those explanations have led to an argument, that ends up in litigation while the truth lingers uncovered in the background. This document is a group effort of combined information compiled by the Automotive Transmission Rebuilders Association (ATRA), the Automotive Engine Rebuilders Association (AERA), the Production Engine Rebuliders Association (PERA), the Automotive Service Association (ASA) and bearing manufacturers. This group of industry experts has assembled the following information to consider and offers solutions that may prevent a similar thrust bearing failure.

    Although thrust bearings run on a thin film of oil, just like radial journal (connecting rod and main) bearings, they cannot support nearly as much load. While radial bearings can carry loads measured in thousandsof pounds per square inch of projected bearing area, thrust bearings can only support loads of a few hundred pounds per square inch. Radial journal bearings develop their higher load capacity from the way the curved surfaces of the bearing and journal meet to form a wedge. Shaft rotation pulls oil into this wedge shaped area of the clearance space to create an oil film which actually supports the shaft. Thrust bearings typically consist of two flat mating surfaces with no natural wedge shape in the clearance space to promote the formation of an oil film to supportthe load.

    Conventional thrust bearings are made by incorporating flanges, at the ends of a radial journal bearing. This provides ease in assembly and has been used successfully for many years. Either teardrop or through grooves on the flange, face andwedge shaped ramps at each parting line allow oil to enter between the shaft and bearing surfaces. However, the surface of the shaft, as well as the vast majority of bearing surfaces, are flat. This flatness makes it more difficult to create and maintain an oil film. As an example; if two gauge blocks have a thin film of oil on them, and are pressed together with a twisting action, the blocks will stick together. This is similar to what happens when a thrust load is applied to the end of a crankshaft and oil squeezes out from between the shaft and bearing surfaces. If that load is excessive, the oil film collapses and the surfaces want to stick together resulting in a wiping action and bearing failure. For this reason, many heavy-duty diesel engines use separate thrust washers with a contoured face to enable them to support higher thrust loads. These thrust washers either have multiple tapered ramps and relatively small flat pads, or they have curved surfaces that follow a sine-wave contour around their circumference.

    Recent developments:

    In the past few years some new automotive engine designs include the use of contoured thrust bearings to enable them to carry higher thrust loads imposed by some of the newer automatic transmissions. Because it’s not practical to incorporate contoured faces on one piece flanged thrust bearings, these new engine designs use either separate thrust washers or a flanged bearing whichis a three piece assembly.

    Cause of failure:

    Aside from the obvious causes, such as dirt contamination and misassembly, there are only three common factors which generally cause thrust bearing failures. They are:

        • Poor crankshaft surface finish
        • Misalignment
        • Overloading
    Surface finish:

    Crankshaft thrust faces are difficult to grind because they are done using the side of the grinding wheel. Grinding marks left on the crankshaft face produce a visual swirl or sunburst pattern with scratches - sometimes crisscrossing - one another in a cross-hatch pattern similar to hone marks on a cylinder wall. If these grinding marks are not completely removed by polishing, they will remove the oil film from the surface of the thrust bearing much like multiple windshield wiper blades. A properly finished crankshaft thrust face should only have very fine polishing marks that go around the thrust surface in a circumferential pattern.


    The grinding wheel side face must be dressed periodically to provide a clean, sharp cutting surface. A grinding wheel that does not cut cleanly may create hot spots on the work piece leading to a wavy, out-of-flat surface. The side of the wheel must also be dressed at exactly 90° to its outside diameter, to produce a thrust face that is square to the axis of the main bearing journal. The crankshaft grinding wheel must be fed into the thrust face very slowly and also allowed to "spark out" completely. The machinist should be very careful to only remove minimal stock for a "clean-up" of the crankshaft surface.

    In most instances a remanufactured crankshaft does not require grinding of the thrust face(s), so the grinding wheel will not even contact them. Oversize thrust bearings do exist. Some main bearing sets are supplied only with an additional thickness thrust bearing. In most of those instances, additional stock removal from the crankshaft thrust face surface may be required. Crankshaft end float should be calculated and determined before grinding additional material from the thrust face.

    Crankshaft grinding wheels are not specifically designed for use of the wheel side for metal removal. Grinding crankshaft thrust faces requires detailed attention during the procedure and repeated wheel dressings may be required. Maintaining sufficient coolant between the grinding wheel and thrust surface must be attained to prevent stone loading and "burn" spots on the thrust surface. All thrust surface grinding should end in a complete "spark out" before the grinding wheel is moved away from the area being ground. Following the above procedures with care should also maintain a thrust surface that is 90° to the crankshaft centerline.

    When assembling thrust bearings:

        • Tighten main cap bolts to approximately 10 to 15 to seat bearings, then loosen.
        • Tap main cap toward rear of engine with a soft faced hammer.
        • Tighten main cap bolts, finger tight.
        • Using a bar, force the crankshaft as far forward in the block as possible to align the bearing rear thrust faces.
        • While holding shaft in forward position, tighten main cap bolts to 10 to 15 ft.lbs.
        • Complete tightening main cap bolts to specifications in 2 or 3 equal steps.
    The above procedure should align the bearing thrust faces with the crankshaft to maximize the amount of bearing area in contact for load carrying.


    A number of factors may contribute to wear and overloading of a thrust bearing, such as:

    1. Poor crankshaft surface finish.

    2. Poor crankshaft surface geometry.

    3. External overloading due to.

    a) Excessive Torque converter pressure.

    b) Improper throw out bearing adjustment.

    c) Riding the clutch pedal.

    d) Excessive rearward crankshaft load pressure due to a malfunctioning front mounted accessory drive.

    Note: There are other, commonly-thought issues such as torque converter ballooning, the wrong flexplate bolts, the wrong torque converter, the pump gears being installed backward or the torque converter not installed completely. Although all of these problems will cause undo force on the crankshaft thrust surface, it will also cause the same undo force on the pump gears since all of these problems result in the pump gear pressing on the crankshaft via the torque converter. The result is serious pump damage, in a very short period of time (within minutes or hours).

    Diagnosing the problem:

    By the time a thrust bearing failure becomes evident, the partshave usually been so severely damaged that there is little if any evidence of the cause. The bearing is generally worn into the steel backing which has severely worn the crankshaft thrust face as well. So how do you tell what happened? Start by looking for the most obvious internal sources.

    Engine related problems:

        • Is there evidence of distress anywhere else in the engine that would indicate a lubrication problem or foreign particle contamination?
        • Were the correct bearing shells installed, and were they installed correctly?
        • If the thrust bearing is in an end position, was the adjacent oil seal correctly installed? An incorrectly installed rope seal can cause sufficient heat to disrupt bearing lubrication.
        • Examine the front thrust face on the crankshaft for surface finish and geometry. This may give an indication of the original quality of the failed face.
    Once you are satisfied that all potential internal sources have been eliminated, ask about potential external sources of either over loading or misalignment.

    Transmission related problems:

        • Did the engine have a prior thrust bearing failure?
        • What external parts were replaced?
        • Were there any performance modifications made to the transmission?
        • Was an additional cooler for the transmission installed?
        • Was the correct flexplate used? At installation there should be a minimum of 1/16" (1/8" preferred, 3/16" maximum) clearance between the flex plate and converter to allow for converter expansion.
        • Was the transmission property aligned to the engine?
        • Were all dowel pins in place?
        • Was the transmission-to-cooler pressure checked and found to be excessive? If the return line has very low pressure compared to the transmission-to-cooler pressure line, check for a restricted cooler or cooler lines.
        • If a manual transmission was installed, was the throw out bearing properly adjusted?
        • What condition was the throw out bearing in? A properly adjusted throw out bearing that is worn or overheated may indicate the operator was "Riding The Clutch".
    How does the torque converter exert force on the crankshaft?

    There are many theories on this subject, ranging from converter ballooning to spline lock. Most of these theories have little real bases and rely little on fact. The force on the crankshaft from the torque converter is simple. It is the same principle as a servo piston or any other hydraulic component: Pressure, multiplied by area, equals force. The pressure part is easy; it’s simply the internal torque converter pressure. The area is a little trickier. The area that is part of this equation is the difference between the area of the front half of the converter and the rear half. The oil pressure does exert a force that tries to expand the converter like a balloon (which is why converter ballooning is probably often blamed), however, it is the fact that the front of the converter has more surface area than the rear (the converter neck is open) that causes the forward force on the crankshaft. This difference in area is equal to the area consumed by the inside of the converter neck. The most common scenario is the THM 400 used behind a big-block Chevy. General Motors claims that this engine is designed to sustain a force of 210 pounds on the crank shaft. The inside diameter of the converter hub can vary from 1.5 inches up to 1.64 inches. The area of the inside of the hub can then vary from 1.77 square inches to 2.11 inches. 210 pound of force, divided by these two figures offers an internal torque converter pressure of 119 psi to 100 psi, respectively. That is to say, that depending on the inside diameter of the hub, it takes between 100 to 119 psi of internal converter pressure to achieve a forward thrust of 210 pounds. The best place to measure this pressure is the out-going cooler line at the transmission because it is the closest point to the internal converter pressure available. The pressure gauge must be "teed" in so as to allow the cooler circuit to flow. Normal cooler line pressure will range from 50 psi to 80 psi , under a load in drive.

    Causes for excessive torque converter pressure:

    There are two main causes for excessive torque converter pressure: restrictions in the cooler circuit and modifications or malfunctions that result in high line pressure. One step for combating restrictions in the cooler circuit is to run larger cooler lines. Another, is to install any additional cooler in parallel as opposed to in series. This will increase cooler flow considerably. An additional benefit to running the cooler in parallel is that it reduces the risk of over cooling the oil in the winter time—especially in areas where it snows. The in-parallel cooler may freeze up under very cold conditions, however, the cooler tank in the radiator will still flow freely. Modifications that can result in higher than normal converter pressure include using an overly-heavy pressure regulator spring, or excessive cross-drilling into the cooler charge circuit. Control problems such as a missing vacuum line or stuck modulator valve can also cause high pressure.

    What will help thrust bearings survive? When a problem application is encountered, every effort should be made to find the cause of distress and correctit before completing repairs, or you risk a repeat failure.

    A simple modification to the upper thrust bearing may be beneficial in some engines. Install the upper thrust bearing in the block to determine which thrust face is toward the rear of the engine. Using a small, fine tooth, flat file, increase the amount of chamfer to approximately .040" (1 mm) on the inside diameter edge of the bearing parting line. Carefully file at the centrally located oil groove and stroke the file at an angle toward the rear thrust face only, as shown in the illustration below. It is very important not to contact the bearing surface with the end of the file. The resulting enlarged ID chamfer will allow pressurized engine oil from the pre-existing groove to reach the loaded thrust face. This additional source of oiling will reach the loaded thrust face without passing through the bearing clearance first (direct oiling). Since there may be a load against the rear thrust face, oil flow should be restricted by that load and there should not be a noticeable loss of oil pressure. This modification is not a guaranteed "cure-all". However, the modification should help if all other conditions, such as surface finish, alignment, cleanliness and loading are within required limits.

    Other External Problems. Aside from the items already mentioned, there is another external problem that should be considered. Inadequate electrical grounds have been known to exacerbate thrust surface wear. Excessive current in the vehicle drive train can damage the thrust surface. It affects the thrust bearing as though the thrust surface on the crankshaft is not finished properly finished (too rough). Excessive voltage in the drive train can be checked very easily. With the negative lead of a DVOM connected to the negative post of the vehicle battery and the positive lead on the transmission, there should be no more than .01 volts registering on the meter while the starter is turning over the engine. For an accurate test, the starter must operate for a minimum of four seconds without the engine starting. It is suggested to disable the ignition system before attempting this test. If the voltage reading observed is found to be excessive, add and/or replace negative ground straps from the engine to the vehicle frame and transmission to frame until the observed voltage is .01 volts or less. Note: Some systems may show a reading of .03volts momentarily but yet not exhibit a problem. For added assurance, it is a good idea to enhance the drive train grounding with larger battery cables or additional ground straps.

    A special thank you goes out to Dennis Madden of ATRA, Dave Hagen of AERA, Ed Anderson of ASA, Roy Berndt of PERA and John Havel of AE Clevite for their contributions to this article.

    The AERA Technical Committee

    March 1998 - TB 1465R
    Last edited: Oct 5, 2017
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