Spun bearings

Car has been running great. Shut it off one night, would not start next morning. After trying usual things with no success it was determined that engine was ceased. Upon pulling the pan discovered the bearings were spun and crank ruined. I was a mechanic for many years and also my current repair man have never heard of anything like this happening before. Oil is changed regularly and was clean now except for shaving. Any ideas why this would happen so quickly without any previous problems?

A spun insert is not uncommon but usually there is some indication of a problem before the crank seizes. There is usually some noise from the rod knocking, as in Rod Knox, especially when the throttle is punched and released. Even a minor quick acceleration will usually cause an unmistakable knock when the throttle is released. But, regardless of that, a spun insert will definitely trash a crankshaft and require pulling the engine to repair it or possibly just replace the engine with a salvaged part. The 3.8L Buick engine has an excellent reputation and such a failure in a well maintained and adult driven car is unusual.

+1 for @RodKnox. Check the drain back holes in the cylinder heads. The last case of spun bearings that I saw was in my son’s 350 equipped truck. He punched it in order to pass a line of cars on the interstate. Shortly after…the knocking started. The subsequent teardown showed that the drain back holes in both heads were almost completely blocked. The oil poured out of both valve covers when they were removed. No oil…no lubrication.

There was never any knocking or other noise to indicate a problem.

This may be far out, but perhaps an injector leaked gasoline into a cylinder above a piston, or a head gasket or intake manifold gasket failed and coolant leaked into the cylinder. Raw gasoline and coolant is not compressible. When you tried to start the engine, the engine seized and in attempting to crank the engine, the bearing on the rod under the piston was spun. This would explain why the car was running when you shut it off.


How did you know OP has a Buick 3.8 ?

I don’t see that anywhere

Right…Make, model, mileage, as always, would be helpful…

My buddy had a 96 F-150 with a zillion miles on it with the 4.6 and did the same thing ( overnight ) he said engine did about a half to 3/4 of a revolution, then he heard a noise and engine locked up. Turns out a head gasket leak filled up a cylinder that must of been on the beginning of the compression stroke, seems the starter / engine had enough momentum to damage the lower end trying to compress the coolant…

We found this out by removing the spark plugs and coolant came out of the plug hole when we found the offending cylinder. We did manage to get it to start but the knocking on the lower end was loud so it went to the graveyard as the condition of the truck was not worth getting a used replacement engine from a junk yard and not knowing what you would be getting plus the labor to remove and install.

Things like this can happen but rare but they can happen.

I’ve seen a few trashed engines due to spun bearings. It’s caused by excessive wear of the bearing and/or crankshaft journals and may not knock at all.
Odds are the overlay on the remaining bearings is gone and if the crank journals are miked you would probably find they’re under spec by a fair amount.

It gets loose enough and what happens is that the drag of cold engine oil on startup will force one shell over or under another.

For another example, a friend of mine who used to race cars on the dirt track (briefly I might add) thought an engine would rev faster if the crankshaft was turned .010 and STD. bearings were used. He was correct about revving. Unfortunately, he never made more than a couple of laps before spinning bearings and blowing up everything he had spent all week doing.

@db4690…You need to ask @RodKnox that question. He stated that right before my comment.

Apparently my one track mind got overloaded, @db4690.


Stop shortchanging yourself!

Let me have the crystal ball when you’re done with it!

Me and my crystal ball are getting murky @db4690. If I can find that worn out relic I’ll ship it parcel post and maybe you can do some buffing. The last update on it was 2005 or so.

But Re that spun bearing. If the engine refused to crank and the cause was determined to be stacked inserts on a galled out crankshaft it is certain that the galling and wiped out bearing occurred prior to the engine’s final shut down. And the clearance to allow allow bearing inserts to stack is considerable. Considerable enough to be quite noisy it seems.

Is the oil clean and normal looking? GM 3.8s are known for intake manifold gaskets leaking coolant into the oil, which will destroy bearings pretty quickly.

Guys, it has NOT been established that OP’s car has the 3.8 V6

Let’s not get ahead of ourselves

What kind of car is it @old mechanic?