Spun Bearing ARRGGHHH

[sundog]

I have recently had a noise in the engine, light knocking at 4000 rpm. I have taken a look in my oil filter to see if there is a problem, and loe and behold, Copper in the oil filter. This has happened before, 20K miles ago, and it was a spun rod bearing. The engine was professionally rebuilt, $13K, and it seems like the same problem is back.

I bought the car with 120K miles on it, with a $20K rebuild on the engine at 110K miles. The car now has 160K miles on it. Does anybody have any idea what would cause the repeated spun bearing?

This time, I think that I will rebuild it.

[dtw]

What kind of engine, and who did the last rebuild.

[sundog]

Sorry for the lack of details,

1991 C2 Tiptronic. 3.6 Litre engine. Last rebuild done at T&D performance in Campbell CA. Replaced oil pump, Crankshaft with used one, old one was "bent".

[Steve@Rennsport]

If the whole oiling system; tank, lines, cooler, was not removed and thoroughly cleaned when the engine was "rebuilt", this will keep happening. Oil coolers and tanks must be ultrasonically cleaned.

I must confess,.......after 30+ years, I've never seen a bent crankshaft unless it had been dropped on the floor.

Typically, people do not always resize the rods and thats a major cause of rod bearing failures.

[asphaltgambler]

"If the whole oiling system; tank, lines, cooler, was not removed and thoroughly cleaned when the engine was "rebuilt", this will keep happening. Oil coolers and tanks must be ultrasonically cleaned"

Steves right, this is the most common problem that I've witnessed

[911SCfanatic]

Where can you send the tank and cooler to be cleaned? How much should it cost?

[asphaltgambler]

Look for machine shops that deal with aircraft engines / machining. They will have a sonic cleaner for the oil coolers.

You can use a pressurized flush gun (like the kind for a/c work) to flush all the oil lines out on the car.

[ChrisBennet]

Originally posted by 911SCfanatic
Where can you send the tank and cooler to be cleaned? How much should it cost?

Pacific Oil Cooler Service. http://www.oilcoolers.com/
Last one I had done was $115 ($85 cleaning, $15 repair, rest shipping).
-Chris

[beepbeep]

your bearing is probably not spun, but I would dissasemble engine as soon as possible. Bearing shell is probably wafer-thin and further driving could result in spun bearing and damaged crankshaft. If you are lucky, new set of bearing and clean opil cooler could do the trick.

Speaking about crankshafts, they do not bend. They can break in half though if you drop it on the floor Spun bearing will result in severe damage/scratches on bearing surfaces.

[sundog]

I was told by the rebuilder that the crank was bent by .005, and that it needed to be straightened or replaced. I chose replacement. I still have it in my office, and the surfaces do not look bad. Is there a serial number on the crank, that I could trace?

I'm starting to think that I got taken to the proverbial cleaners with the last rebuild. That's why I'm going to do it myself this time.

[camgrinder]

A bent crankshaft can be easily straightened. Typical cost is under $50 to magnaflux inspect and straighten. Call CCR 650-342-0568, Armando can usually do it while you wait if you make an appt.
If the crank journal is out of round .005" then it needs to be ground to the next undersize and nitrided.

[beepbeep]

That's news to me. So cast crank can actually bend? I tought they are fragile but very hard to bend...?

Do they bend when they overheat and go into plastic deformation mode?

[350HP930]

A spun bearing can cause a crank to bend. The shop where I used to work would always grind the spun bearing journal first since the crank will often become distorted again after the galled surface layer is removed.

[asphaltgambler]

If you have a 3.2 I'll buy your bent crank. PM'd you

[JohnJL]

A $20K engine rebuild????? Did you have your case gold plated?

[sundog]

The $20K rebuild was an insurance rebuild by the previous owner. Basically a "new" engine, clearly not done correctly though.

[JohnJL]

Mate, you should get 2 quality stock rebuilds for that! But that does beg the question, what happened to the car that insurance would rebuild the engine? Was there rear impact damage?

[Elombard]

I might consider a good used motor for 5 or 6K??

[sundog]

I was told by the sales person that there was sugar in the gas tank, and the insurance company paid for a complete rebuild. No collision damage, as the car has a clean carfax.

[350HP930]

The sales person was probably full of $hit. They usually are.