causes a spun bearing?

patragz22

Registered User
what causes a spun bearing? and is there anything to do to avoid this in the future?? I now know what I am doing this winter.:(
 
Assembly clearances in the motor are critical. If you just "assemble" the motor without carefully verifying clearances it is very possible to have under .001" clearance which is an absolute no-no on a performance engine like ours. Bearing clearances should be .002 minimum on a performance build.

The other thing that will cause a spun bearing is excessive detonation. Too much boost and too much timing will combine to hammer out the bearings.

Finally, very often on an SC motor if it has been running rich (which seems to be a common problem for many SC owners) your oil will be thinned out with fuel and will lose it's lubricating ability. If you ever experience this situation and/or ever smell gas in your oil, change it immediately.
 
>what causes a spun bearing?

This is the final stage of bearing failure that can occur when metal meets metal with little/no lubrication.

Causes include:
  • oil starvation (check engine for proper level, oil leaks, check clearances, make sure dipstick is calibrated correctly...don't overfill)
  • oil breakdown (lack of proper maintenance)
  • oil contamination (internal coolant leak and/or dirt)
  • failed oil filter, oil pump...oil pressure 'relief' valve hung open, etc.

If the engine was torn down before, and there are issues now with rod/main bearings, there is a good chance most problems can be traced back to mis-assembly.

Note that if upper rod bearings in an otherwise low mileage engine look fatigued, they may have been subjected to detonation.

Suggest that all journals, bearings and bearing lands be inspected accordingly before reassembly.
 
Last edited:
I want to thank you guys for shedding some light on this issue, the motor was a rebuilt by a local mechanic. I am not blaming him but the engine is overdriven 25% and did have an strong odor of gas. The engine will be pulled and sit until I have some money. Funny thing is I just put synthetic oil in it.
 
I had an automotive machinist press in the wrist pins for my engine, while he was prepping the block and crank. He put the circlips for the 94-95 (floating) wrist pins on my 89-93 (non floating) pistons. They came with the engine kit he ordered, and must not have known any better (Which is funny considering his specialty is circle track engines). They limited the connecting rods ability to center itself on the crankshaft journal. This cocked the connecting rod just enough to spin the bearing in less than 1000 miles. The engine spun over fine when assembling it, just not good enough at 5000 rpms. When I tore the engine down, it had one spun bearing, and two others show a ton of wear. The same piston that spun the bearing galled the wrist pin to the point that I couldn't move it. The other pistons were in varying degrees of the same situation. I had to have the pistons honed out when having everything machined again. I also made sure the circlips were thrown in the trash this time.
 
wow, did the engine builder gave you a warranty? my situation sucks because I just got laid off. the car will sit for a while now.
 
When I tore the engine down, it had one spun bearing, and two others show a ton of wear. The same piston that spun the bearing galled the wrist pin to the point that I couldn't move it. The other pistons were in varying degrees of the same situation. I had to have the pistons honed out when having everything machined again.
ALL pistons should be at least lightly honed before assembly. It is very typical for Sealed Power pistons to be too tight as manufactured. Just one more reason it pays to have someone build your SC engine who is familiar with the motors.
 
I have my old engine sitting in the garage, bone stock. it has 70,000 miles on it. To save the cost of rebuilding, I will swap the cam and heads over. Is that a good idea or not??
 
No warranty. It's unfortunate that it happened, but to try and prove that it was his fault, I suspect, would be a waste of time. He will always say it's someone elses fault. Regardless, I had to put it together again. This time, I knew the critical aspects of the assembly, and was able to control the process. After 1000 miles, everything is still running great.
 
that's great, you did it yourself, my thing is I can take it apart but reassemble is my downside, but sometimes have no choice.
 
Back
Top