OK 400 block,scat 3.75 stroke rotating assembly. This is a street car so just drove it to some shows and it started a rear mail seal after 300 miles did not think nothing to much easy fix right....wrong dropped the pan and found metal checked some and seen the thrust bearing,I assembled the motor but checked everything during assembly even crank end play. Took it to the machine shop let him tear it apart found that crankshaft had been pushing forward.Check converter clearance and thickness check out fine.
Now I find out if the cooler does not have enough flow it can push the crank forward has anyone seen this on a 727 I know TH400 will do this, Got a Hughes 3000 converter and a Coan reverse manual valve body thanks for any input. Thanks Randy

Bump, I am interested as well. I just saw my balancer moving around in my 360 from a wiped thrust. I had drag week starting the next weekend so I swapped in a a parts store crank and bearings lol. It's got about 900 miles on it in the last few days and.......I haven't looked at the balancer while it's running haha.

My converter has good spacing and moves freely before bolting it up also. My cooler is a b&m stacked plate with -6 hoses, radius bend fittings etc.

I myself have never heard of this BUT if the cooler
doesnt flow for crap then the back pressure backs up
but I didnt think that would be in the conv... I basically
buy coolers that have equal or larger lines than the
5/16" of the trans... my 518 trans has 3/8 lines from
the factory and the cooler has 1" tubes but necks down
to just under 1/2" so the 3/8" hose(short pieces)
just works on.... plus I enlarge the trans fittings
some by drilling the ID out a bit... just for a bit
more flow

I'm going to check the cooler line pressure when the motor is back in I'm running 5/16 and a fin style cooler with -8 adapted down to -6, we can clearly see the crank has rubbed the back side of the mains thats how bad it pushed forward. I did some reading and the cooler pressure should be 5 to 30 PSI.

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.

Alignment:

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 ft.lb. 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.

Loading:

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 parts have 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 correct it 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.

Thanks for that write up the info on the cooler restriction is very helpful that's what I've been looking for and really believe that is my problem now just have to do some test1

A torque converter is a hydraulic pump and it is ALWAYS trying to push itself out of the transmission. That said, if the trans is pumping more fluid in the converter than it can exhaust it WILL eat the thrust in a short amount of time

Monte

Rossler makes a cooler line bleed off . Takes the pressure down to 65 lbs .

I'm also chewing up thrust bearings . 3 times in 15 passes . I'm chasing my tail . I had a new pump in my trans , last set of bearings I had the bleed off in and still same results
Had my crank thrust repaired but nothing there either . I did the parting line chamfer and still ate it .My concern is the repair to the thrust was not done properly .Hopefully I figure something out before winter hits .

Had the same thing happen to the LA in my Dart after ~10k miles. Was setting the timing and thought I saw the balancer moving but told myself I was going crazy...

Haven't found the cause yet, but am pretty convinced the trans pressure is the culprit.

We had a converter at one time that was pushing on the crank so hard, it broke two rods before we found out the problem. It would eat the thrust, then take up the rod side clearance and toss one out. Broke number 7 rod and tossed it out the same hole twice.

We decided at that point to have our motor machined for a roller thrust bearing like the turbo guys run.........problem solved.

Monte

Went by the machine shop and you can see where the crank had scuffed #1,2,4 cap and the front side of the bearing was not touched so something is pushing forward for sure.

Check the converter to see if it's "Balloning".

Get a different vert for sure IMO

Have had the same issue, went form .004 to .015 in less then 200 miles, engine out 4 times this year, two converters flexplate, oiling mod to bearing. Nothing fixed it. This time I'm changing the trans, lines and cooler. Might as well upgrade so I can spray the house down.

"Inadequate electrical grounds have been known to exacerbate thrust surface wear. Excessive current in the vehicle drive train can damage the thrust surface"

This happened in a friends car, he installed the battery in the trunk and did not run a ground wire to the block.