Spun bearing... What are typical reasons?

[Groovy911SC]

I am in the process of tearing down my 911 SC 3.0. I have copper colored glitter in my oil filter and a few chunks of metal in my oil pump sump screen. I am assuming the engine spun a bearing. The distributor gear is still intact. I have not removed the cam housing yet so I don't have proof that a spun bearing is my problem. It is my guess. My question is... what causes a bearing to spin loose? I've been told that this problem is not typical for 911 3.0 engines.

[Steve@Rennsport]

Indeed, spun bearings are certainly NOT typical for any 911 engine.

Its usually caused by:

1) Incorrect bearing to crank clearances

2) Insufficient oil pressure

Excessive wear and a poor choice of oil adds to the problem.

[Wayne 962]

Steve beat me to it. I concur with the low oil pressure statement, which can be caused by excessive clearances. As clearances wear (and the engine gets older), you want to try to run not so thin of an oil - it will cause leaks and will also not "fill" the clearances as well. Running thicker oil will help low oil pressure problems.

For reasons like this (and the dried-out seal problem), I don't recommend running synthetic in older engines...

-Wayne

[HarryD]

Originally posted by Wayne at Pelican Parts
Steve beat me to it. I concur with the low oil pressure statement, which can be caused by excessive clearances. As clearances wear (and the engine gets older), you want to try to run not so thin of an oil - it will cause leaks and will also not "fill" the clearances as well. Running thicker oil will help low oil pressure problems.

For reasons like this (and the dried-out seal problem), I don't recommend running synthetic in older engines...

-Wayne

Wayne, just because I seem to be "thinking impaired" today...

As an engine ages (wears), you are saying it is prudent to go to a heavier weight oil to improve pressure and have more "stuff" to allow the worn pump to move the correct amount of oil.

[Groovy911SC]

Steve, Wayne, thanks for your responses. I do appreciate the information. Next question... Since all that copper colored glitter does not look too healthy for any engine, I will purchase new "on the engine" and "fender mounted" oil coolers and associated plumbing. What should I do about the oil pump? I would think cleaning is too risky. What would you guys do... upgrade to a carerra oil pump?

[Steve@Rennsport]

I always disassemble and inpect the oil pump internals. Its a matter of experience on whether its damaged but bearing materials rarely damage those hardened steel gears. The oil pump housing is what suffers.

I would certainly replace your oil pump only if the internals are scratched and/or scored. The SC and Carrera pumps are now the same.

All oil lines and tank are THOROUGHLY cleaned and scrubbed and oil coolers get ultrasonically cleaned.

[Wayne 962]

Originally posted by HarryD
Wayne, just because I seem to be "thinking impaired" today...

As an engine ages (wears), you are saying it is prudent to go to a heavier weight oil to improve pressure and have more "stuff" to allow the worn pump to move the correct amount of oil.

Not entirely. The thin oils will tend to run quicker, run thinner, and in general give lower oil pressure on older engines. As your clearances wear, your pressure will drop. Sort of like a water hose where you block the flow with your thumb (high pressure). As the opening (clearances) get bigger (as you remove your thumb), the pressure drops. Having very slick, very thin oil at this junction is less advantageous than thicker oil. Just one of the reasons I don't recommend synthetic on old engines (newly rebuilt ones are fine for use with synthetic).

-Wayne

[aigel]

One more reason for a spun bearing (rod that is) is overrevving the engine. The rod bolts will stretch just a bit, allowing the nut to work itself loose. Then, after time, the bearing will have a chance to turn with the crank instead of with the rod. This can happen a long time after the engine saw the over-rev. It isn't as likely on a 3.0 as it is on a 3.2. I'd assume on an older stock 3.0 the piston would have chased the exhaust valve down before the rod bolts stretch.

To add to Wayne's thoughts: A thicker oil will also provide a complete film in a bearing clearance that was enlarged from wear. If there is too large a clearance for too thin of an oil, the film will not be continuous and you will run without sufficient lubrication. For your garden variety american V8 you can get high volume oil pumps that help this condition also.

It is easy to determine if oil starvation (from too thin an oil, too low a pressure etc.) was the problem if you document which bearing went or which one looks worst. If there is a general oil suppy problem, the bearing farthest away from the source of oil is the one that goes first...

Good Luck with your teardown. Pay good attentinon and take some pics for us and let us know the results in the engine build forum!

Cheers, George

PS: One more thought. If you had debris like that, it will be mandatory that you clean the case very thorrough, especially the oil squirters!

[Wayne 962]

Right - make sure you take and post pictures of the inside - you can learn as more from a failed engine than a torn-down tired one...

-Wayne

[350HP930]

In addition to over-revving chronic detonation can also lead to rod bearing failure.

A lot of hammering takes its toll on those bearings.

[Groovy911SC]

I have read Waynes Engine rebuild book and have taken the advice given concerning taking pictures. I have arranged the digital pictures in folders by date so I can go back and refer to a specific section. All parts are bagged and labled with part name and date. I am waiting on the tools (from pelican) to remove the cam right now. Initial tear down went quicker than I thought thanks to all the good info in the book. I will post pics when I crack the case. I supose it will be then when I learn what happened. Thanks to everyone for their ideas and support!

[Groovy911SC]

Here are two fuzzy pics of what you do not want to see in your oil filter. After my incident, I changed my oil and looked closely at what came out, even strained it.... I did not see anything telling until I removed the sump screen. It looked a bit dirty so I thought I would wash it some gas. That is when I saw the debris in the bucket - what a sickening feeling... That is when someone on here suggested I carefully open the oil filter...UUuuugh

[aigel]

Groovy:

Those shavings probably fill oil leaks very nicely.

But seriously, that is a gearheads's nightmare, especially on an engine that is so expensive in parts to rebuild right. Not to beat this thread along, but I was wondering what the symptoms were that got you on this? Do you actually have a knock?

Good Luck!

George

[Groovy911SC]

Hey George,
I was running the car in a DE when I heard a slight grinding noise when accelerating. I immediately coasted into the pit area and only fired it up again after it cooled to verify something was wrong. It sounded terrible - like small ball-bearings rattling around in the engine. No prounounced knock. Afterwards, I did leak down tests on all cylinders which came back normal for my car. No bang, no knock, just a sickening noise!

[Wayne 962]

Look at this as a fun experience, and a chance to learn something new. That's what I did when my wife's BMW head gasket took a turn south...

-Wayne

[Ho Hum 74]

Groovy,

I just experienced the EXACT same thing as you did. One interesting thought which hasn't been brought up yet: if you track your car and use R-Compound tires, they can produce enough decceleration to cause oil in your tank to move forward of the pickup. Your oil pressure can drop so low that the light comes on. Then you blip your throttle to 5000 rpm and your engine is starved of oil for these few seconds. If you track your car you must mod your oil tank with a baffle.

A master engine builder (who's well respected in building race engines and mentioned in Bruce Anderson's book) told me to do this mod over upgrading the oil pump. It doesn't matter if you have the biggest pump if it has no oil to pump!

Good luck

Tristan

[joestrickland]

Who do you recommend to install the baffles (I recall hearing of some shop that is well-known for doing this upgrade)? Or is there a reasonably-priced baffled tank on the market that is recommended? In my case this would be for a 72 T with a 75 2.7L engine...

[Ho Hum 74]

Joe,

I am told that Fabcar in Indy can do it but it's $400 which is really steep. Chris Streit (who posts here all the time just did his himself and is doing mine for me). I'm sure he'll do yours if you want. Fabcar actually adds capacity to the tank.

Check here for his thread: Oil pressure drop on hard braking. My answer with Pics

[joestrickland]

Great info - thanks.

[Groovy911SC]

Yes, Great info Tristan. Sounds like inexpensive insurance to me!