Rod knocking

TERMAXCO

MEMBER
2002 BUICK LESABRE
3.8L
V6
2WD
AUTOMATIC
160,000 MILES

Rod started knocking.

Drained oil pan later and had lots of separated water in pan. Put in new oil and let run for short time and no water got back into oil.

Pulled oil pan to check crank (noticed it has been off before by someone).

Spun rod bearing: Bearing was scored thin (almost all from rod and cap outside surface) but bearing still whole and in tack and not burnt etc.

Rod and cap scored but did not 'eyeball' as oversize or warped? (Cap is exact same as good caps and bearings seemed to fit the caps the same with the same crush factor etc. Hard to tell about rod with engine in)

Crank rod journal was scored some but noticed that it miked exactly.030 less than the other crank rod journals? It doesn't seem that the softer bearing condition was severe enough to eat that much into crank that quick to an exact.030 undersize?

I'm willing to risk somewhat before pulling engine and heads:
1. Assuming I can 'backyard' polish out mild crank scores, is it okay to have only one '.030' undersized rod bearing put in or is that too unbalanced etc?
2. And if okay to do, is this at all feasible or does experience tell you that the odds are too high the crank, rod and cap are warped etc?

3. And, is it feasible the water in oil is a one time event such as maybe engine got hot but still okay cooled?
thank you

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

The water in the oil is not likely a one-time issue. When the engine was running, I suspect coolant leaked past a head gasket and got into the oil. When the engine is off and cool, it may not happen.

As far as the crank, if the scores can damage a new bearing, that is a problem. As far as removing them, you have to remove metal to do it which changes things as well.

Here is what I can offer. First, I attached a pic below (pic 1) providing all the crankshaft specifications. Compare what you have to the specs.

Second, I would check the crankshaft and bearing clearance. You will need a product called plastic gauge to perform this. However, it will let you know if there is too much clearance.

The remaining pics explain how to test. Also, if one of the bearings is oversized, that's fine (odd but fine) as long as the clearance is within spec.

I hope this helps. Please feel free to let me know if you have other questions.

Take care,

Joe

See pics below.

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Wednesday, July 28th, 2021 AT 10:23 PM

TERMAXCO

MEMBER
54 POSTS

Thanks. This helps.

I see only main bearing cap bolt torques. Would you happen to have the rod cap bolt torque handy? Thanks

So, even if engine overheated, it most likely requires a permanent burned head gasket etc. To get water in oil? Can I assume a badly leaking water pump cannot get water into oil? [ This all happened when flushing out unusually bad rust in cooling system thru engine with hose pipe which, got the water pump leaking real bad (assuming the rust had been plugging the leak?).

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Friday, July 30th, 2021 AT 9:18 AM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

The water pump really couldn't cause coolant to get into the engine oil. To answer your other question, if you overheated the engine, there is a good chance it is the head gasket. Once it's bad, normally they remain bad.

As far as the connecting rod torque, I attached that info below. Note that it is done in two steps. First, evenly torque them to 20 ft/lbs. The second step is to tighten the nut an additional 50 degrees.

I just reread your post. Similar to the rust causing the pump to leak, something may have moved allowing an internal leak.

I hope this helps you. Let me know if you have other questions.

Take care,

Joe

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Friday, July 30th, 2021 AT 8:35 PM

TERMAXCO

MEMBER
54 POSTS

Thanks again. This is good help.
'Got it' on the two stage torque and degree.
And yep, I think you hit on it - the rust (lots of it?) May have caused an internal leak. It was my only assumption that the temperature. Gauge must have not been working good due to coated rust on it so I guessed the engine must have overheated without me realizing to cause the water in oil. But actually, I never thought the engine got that hot, or overheated at all. It was a complete surprise when the rod started knocking. The water got in the oil mysteriously to cause it.
Looking like a complete tear down to find this leak you think? Can you point me to some possibilities regarding rust causing internal leaks to look for or, will it be obvious?

Thanks again.

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Saturday, July 31st, 2021 AT 6:46 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

You could do a compression test to check for a head gasket issue. However, I think you already have it torn down. If you don't, here is a link that explains how to check it.

https://www.2carpros.com/articles/how-to-test-engine-compression

Also, here is a link that helps determine head gasket issues. If you page down through it, there is a video showing how to perform the compression test.

https://www.2carpros.com/articles/head-gasket-blown-test

Let me know if this helps or if you have other questions.

Take care,

Joe