Though we're not sure about the failure, attached is the rear main bearing form my 15 Hour engine. It appears that the thrust surface is most warn indicating a crankshaft thrust problem. What are the typical causes of this type of failure? I want to check everything to avoid this in the future.

Some info on the engine:

Reworked 7.4L with a Procharger, Roller cam, roller lifters, roller rockers, Eagle forged crank, JE Pistons, Dart Heads. Stock
Bravo 1 drive.

Appeared to be a very good rebuild until the bearing went out.

Any ideas?

Thank You,

Kirk

I Had had a problem on a truck engine eating up thrust bearings,it was caused by the stock torque converter ballooning under load and causing thust bearing failure that led to excessive crank end play.I have heard that some Eagle Cranks had a Radius that was too large causing the rod bearings to bind.Maybe your mains have a similar situation Check your crank with a new bearing half and see if there is clearance in the radius.There are some sharp Guys on this board and I am sure someone has seen this before. PS what prop are you running at what rpm/mph?

Good Luck
Rob

We're checking the coupler and the drive shaft length etc... Something caused this and if we eliminate the external parts, it has to be something internally.

I'm running a 29P Mirage Plus, haven't had it opened up to WOT. My speedo only goes to 80 and it was buried aroung 4,500 RPM.

I have since bought a 100 MPH speedo. When I get the engine back in I'll post my numbers to see if I'm doing everything correctly, ie prop pitch, gear ratio, etc...

Thanks for your post. I'm hoping Mr. Dennis Moore will chime in here!!!! I didn't see pictures like that in his book though!!!

What was the end play in the thrust when the motor was assembled? It is hard to tell from the picture, but are you sure the failure is end play or thrust related and not just an oiling problem with the main bearing?

Is the copper of the bearing loose???
It doesnt look like end play failure- it looks more like improper clearance or lack of proper oil preasure to the bearing. That bearing had to get real hot to do that.

I tend to agree along with Tinkerboaters thoughts, adding possible partial blockage of oil passage to this rear main bearing.
Looking at the photo, it appears there is still a small line of bearing surface remaining on the left, bottom side, by the parting line of the bearing shell. If this is true, the last bearing journal surface could be ground on a taper. Its also possible the bearing cap was installed with foriegn material under that corner of bearing cap.
Is crankshaft straight? Was bearing cap tight (torqued) when engine was disassembled ?
Why is there so much contamination on the bearing cap mating surfaces ?
If bearing cap was not properly torqued during assembly, imagine how that cap will walk around with the oil pump mounted on it.
Do you have the "as built"bearing clearances ?

Hope this helps, David.

Is the seal the right one? I know yellow is for right hand,all merc drives are left hand engines.Was their oil in the bilge?

Did you check the engine alignment ? I had the same problem

and it was caused by the motor droping on one side and

throwing the motor out of alignment

when your motor is out of alignment and you trim the drive it

puts pressure on the coupler-flywheel-crank

We are checking the alignment of the bearing bore this week. We will also check out the crank.

Six Leg, you are correct, the engine builder did install the wrong seal. He claims that he has been installing the yellow seal in hundreds of engines. He didn't know that they were for reverse rotation. (scary huh?) He also claims that that couldn't be the cause of the failure. I agree it may not have cause the failure, however with the flutes in the seal facing the wrong way, the seal acted like a pump if the inner seal was torn.

I don't know that we'll ever figure this out, but I'd like to see everyones input so that I can check everything. I don't want to do this again in another 15 hours!!!!

The thrust side that is worn is the rear side. This shows that the crank is being pushed/pulled forward. The oil comes to the bearing at the center of the journal. If you had an oil problem it would be with the entire bearing, I think.

On a passenger/truck engine this type of problem is usually caused by the torque convertor not being installed correctly when assembled. The convertor isn't seated completly on the front of the transmission and pushes against the flex plate and wears the thrust out.

Since you don't have a torque convertor, but you do have a flywheel and drive plate, I would look at that area. Something is pushing the crank forward when it is bolted up.

I don't see where the wrong seal will cause it. It will cause a leak, but that's about all. There is no suction there it is more of a scraping to push the oil back away from the seal.

I have seen, now only once where the timing chain was installed wrong, 5.7 Chevy, and when the harmonic balancer was installed it pulled the crank forward. Doing the same damage to the main thrust also. But, that was only once and is alittle out there.

Did the builder check the end play when the engine was assembled??? Or did he just assume he had it.

Good luck, just my $.02