Spun main

[tsirovy]

Finally decided to do some surgery on my engine today to find the knock noise. Checked all the rod bearings and they were perfect. started in on the main bearings @ the 4th main and the bearings were completed spun where the notch had broken and was allowed to spin freely. I moved on to all other main bearings to inspect and they were mostly copper also.. all five of them except the first main were copper and worn. The 1st main was perfect.

HOW could this be happening.. I have ordered new main bearings but would like some input about the reasons why this could possibly happen before installing them. My always hopeful guess this time is that when the 4th bearing spun this created a oil pressure leak and allowed the other main bearings to become too hot and wear faster but i dont know.

Any guesses?

 

[Lextreme II]

Didnt you have engine problems last year and you took the short cut or something?

 

[tsirovy]

Had engine problems last year yes. Did take a short cut yes. Once that failed I took your advice and bought a new long block with less than 50,000 miles on it and this is the engine that I have questions about. I cant believe I have two faulty engines in a row! My first LS drove like a dream!? Why would this sparkly new engine have these main bearing issues?

 

[cribbj]

Did you reuse any parts at all from the lubrication system of the old engine to the new one? Things like the oil pump, an oil cooler, oil filter, etc.?

When a motor eats its bottom end, it's considered bad practice to reuse any part of the old lubrication system in the rebuild or in the new motor, due to the likelihood of trapped metal particles coming loose and causing the same problem again.

I worked in the Caterpillar organisation for a few years, and it was forbidden for our techs to rebuild a customer's engine and reuse the oil pump or his oil cooler if the engine had thrown a rod or spun a main or rod bearing.

This was a fairly major cost difference between a Cat rebuild and a private shop rebuild, and if the customer didn't like it, he was welcome to go elsewhere. Cat simply would not warranty a bottom end rebuild that used lubrication system parts from a failed motor.

 

[tsirovy]

Good thinking cribbj

I absolutely didnt use any old parts from the original engine I used all new parts and kept it clean.:wtf:

 

[cribbj]

Is it possible you could have used too much, or the wrong type of sealant when the motor was assembled? There are horror photos all over the web showing motors that were assembled with ridiculous amounts of the wrong sealant, and the stuff got into the small oil or water passages, blocked them up and that was it. One very well done motor.

Secondly, could the failure have been thrust related? Is there anything in your drivetrain that has been changed (like a torque converter, etc.), that could have caused the engine's crankshaft thrust clearance to be lost?

Also, excessive premature wear on mains can be caused by "silent" detonation from oil burning. Did you notice the motor using a lot of oil before it failed? Say more than a quart in 200 or 300 miles?

Lastly, I would have the failed main shells analysed by a bearing expert. Perhaps something can be learned from them.

 

[JBrady]

Where did you get the longblock?

Was it a rebuild?

If so I would be very suspect on bearing clearance of the assembly.

 

[rms]

Where did you get the longblock?

Was it a rebuild?

If so I would be very suspect on bearing clearance of the assembly.

All the 1UZ's I have stripped have had OEM plain whitemetal bearings. Copper backed mains could be after-market and had clearance problem.

The fact that rod bearings are OK seems that it is not an oil supply problem.

1UZ's are very 'tight' on brg clearance.

 

[tsirovy]

cribbj- I used high temp red sealant when I reassembled the pans, I think this is okay. The thrust on the engine should be the no different I didnt change the converter,etc. Also I did not detect any oil burning at all. All good suggestions I did not consider.
jbrady- I bought this longblock out of a 1993 SC400 with <50,000 mi on the clock. Everything on the block was stock.
rms- your input is unique.. the oem whitemetal bearings you have experienced leads me to believe that my original engines bearings must not have been stock either b/c they have minor copper showing from minimal wear, moreover I also believe that the oil supply was sufficient b/c the rods bearings are perfect.

 

[JBrady]

cribbj- I used high temp red sealant when I reassembled the pans, I think this is okay. The thrust on the engine should be the no different I didnt change the converter,etc. Also I did not detect any oil burning at all. All good suggestions I did not consider.
jbrady- I bought this longblock out of a 1993 SC400 with <50,000 mi on the clock. Everything on the block was stock.
rms- your input is unique.. the oem whitemetal bearings you have experienced leads me to believe that my original engines bearings must not have been stock either b/c they have minor copper showing from minimal wear, moreover I also believe that the oil supply was sufficient b/c the rods bearings are perfect.

Confirm that the bearings are either factory or not. If not then my suspicion along with Erol would be that it was rebuilt using incorrect bearing clearance on the failed bearings.

If in fact it was rebuilt there is no way of knowing why. I am always suspicious of these low mileage engines always with 50k miles or less. I do not like rebuilds because there is no way to confirm if the work was done correctly without dissasembly and personally checking everything. I would prefer a higher mileage factory assembly.

I just re-read your second post and you state it was a longblock. Unusual to find a used non rebuilt long block. To me that would suggest it was a rebuild and not a factory assembly. Find yourself a fully assembled, never opened engine and you should be fine. These can be found for $500.

 

[tsirovy]

Another one bites

Turns out bearings are in fact factory. The engine is factory original. I will just buy a new engine again when warm weather comes. 3rds a charm.:trink26:

After close inspection I found the 4th main bearing notches broke and spun. The 3rd main bearing is just as worn if not worse. From there the 2nd main bearing is descently worn and 1st and 5th are perfect! I am convinced that the broken metal notches created the manifestation of wear.