Becca

I'm probably way off on this but when we re-rigged the race boat we learned that you shouldn't mount the engine so that the drive shaft was right in line with it. In other words you need a little bit of an angle in the connection between the two to prevent things getting hot, anyway just a hunch.

BLOWN 1100

Like GearHead said be sure and check end play that is a must.

26scarab

This may not be the cause of the failure but check every radii on the crank, we had three Eagle cranks that had to be reworked because of to large of a radius

250 sport

Looks like a bearing clearance problem, were they checked during assembly. Was the block align bored to accept the new crank? If you had a clearance problem with the bearings was it caused by a crank that was not ground true on that journal? What was the initial oil pressure? and after the failure what was it? Hope my .02 helps. good luck

Jrock

I have the same problem, a burned up thrust bearing. But, with all of the excess heat, I cranked my block. No other bearing damage, just the thrust. Mine had a eagle crank also. So it didn't starve for oil. I was told that some excessive external force was the cause. And to check the rigging.
I'm thinking of getting the inside splines cut down about 1/2" on the couple, to give me a little more clearance.
Has anybody tried this?

Elite Marine

Though that would be a cause of the thrust failure, this engine was in the boat for 2 years before the rebuild. No changes were made to the drive, coupler or flywheel.

I'm leaning toward a bad assembly or bad crank journal. It appears that that is what other seem to think.

ANy other recommendations or items to check??

Jrock

I'm hoping mines in the assembly. I've had it for a year, with no problems with the motor. Except, blowing the drives. So after two drives, I went with a Imco extreme. A month later, thats when it happen.
Everything is within specs. The input shaft, thickness on transom, and the line up.
So right now, I have a cranked block and parts that are junk.
And I'm still unsure what caused it. Keep me informed on yours. It might help me out later. Thanks

jpclear

My worst damage was with inside mains. (2,3). Lots of garbage in everything else. Had an overheat problem a few tach hrs. prior to the drop in O.P. but never thought that it had effected the lower end. Turns out, the excess heat made the main journals something short of perfectly round. Would recommend having alignment and roundness thourghly checked prior to reassembly. LOL --- Jer

FindMe

Well, I ain't Dennis Moore, but I ain't chopped liver either... lol By the looks of your photo, I have a pretty good idea as to why the bearing failed (in your case) and included some other options to check as well. The rear thrust bearing of a Chevrolet motor is not able to support the load the other bearings do, and oiling is achieved in a totally different manner than what you may think. 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 thousands of 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 support the load. A rear main seal directs oil towards the rear bearing to aid in lubrication, and to keep the pressurized oil from being pushed out past the crankshaft and oil pan... plain and simple (see below). A boat motor operates under a severe load from forces being exerted on the prop, up through the outdrive. There is undoubtable eveidence of extreme overheating of the bearing load surface and I have no doubt the incorrect rear main played a major role in this failure. I made the things I feel are most probable to your problem in bold print, and have seen failures as yours from all of them at one time or another, not saying any one single item listed is positively what created your problem. Trouble is, after the damage is done, then theory and careful process of elimination is all you have to figure it out. If none of the other bearings were damaged, then I have to say the wrong rear main seal played a major role in this failure, but some of the other things listed could be happening as well. I hope something here turns on the light and helps you determine the cause, and solve it.

Here is an explanation of bearing oiling from Clevite Bearings...
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 thousands of pounds per square inch of projected bearing area, thrust bearings can only support loads of a few hundred psi. 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 support the load. Conventional thrust bearings are made by incorporating flanges at the ends of a radial journal bearing. This provides ease in assembly and this design has been used successfully for many years. Either tear-drop or through grooves on the flange faces and wedge shaped ramps at each parting line allow oil to enter between the shaft and bearing surfaces. However, the vast majority of the bearing surfaces and all of the shaft surface is flat making it much harder to create and maintain an oil film. If you have ever taken two gauge blocks and wiped them perfectly clean and pressed them together with a twisting action you know that they will stick together. This is very much like what happens as a thrust load applied to the end of a crankshaft squeezes the oil out from between the shaft and bearing surfaces. If the load is too great, the oil film collapses
and the surfaces want to stick together, resulting in a wiping failure.

Causes of main bearing 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

Main bearing 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) n/a Excessive Torque converter pressure.

b) n/a Improper throw out bearing adjustment.

c) n/a Riding the clutch pedal.

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

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 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.

Believe it or not this is a big problem, and overlooked 99.9% of the time...
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.

An easy mod to help lubricate stressed rear thrust bearings (images below)
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.





The procedure below will align the bearing thrust faces with the crankshaft to maximize the amount of bearing area in contact for load carrying.

When assembling thrust bearings:

1.Tighten main cap bolts to approximately 10 to 15 ft.lb. to seat bearings, then loosen.

2.Tap main cap toward rear of engine with a soft faced hammer.

3.Tighten main cap bolts, finger tight.

4.Using a bar, force the crankshaft as far forward in the block as possible to align the bearing rear thrust faces.

5.While holding shaft in forward position, tighten main cap bolts to 10 to 15 ft.lbs.

6.Complete tightening main cap bolts to specifications in 2 or 3 equal steps.

Lastly, if you have a crank that is not true, you will have irregular wear on several of the other bearing halfs, some upper, some lower, some on the edges etc. Also, anything creating harmonics or vibration, like assy belts being loose, belt mis-alignment, or an out of ballance flywheel is possible. I presume the flywheel was ballanced with the rotating assembly and bob weights? Good luck my friend, my heart goes out to you... I hate this $hit.... ~smile~

Vinny P

Where does this guy dig all this stuff up? As usual, another great job from Find-Me.