1990 LeSabre LM3 Vibrating Crankshaft - Thoughts on my plan? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 04-30-2016, 05:32 PM   #1
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Default 1990 LeSabre LM3 Vibrating Crankshaft - Thoughts on my plan?

I've got what I think is an interesting problem...well, actually 2 problems, but I believe them to be directly related. I have a 1990 LeSabre that has an intermittent knock at idle and during initial acceleration, as well as an oil leak from the front crank seal. The car has 107,000 miles, and has been well maintained--never driven hard.

First the noise: The knocking noise is most prevalent at idle, and right at initial throttle acceleration. Once the rpm'* raise, the noise settles waaaaay down. It will not knock 100% of the time, but it'* frequent. In trying to identify the source, I removed the serpentine belt and started the engine. The knock became louder. This eliminated the harmonic balancer as the culprit, but would seem to indicate the noise coming from the crankcase. While running the car and looking closely at the harmonic balancer, I can see the slightest of side to side movement---which for lack of a better description would appear to look like it is vibrating slightly. The same is true for the harmonic balancer center bolt as well. The movement isn't much, but you can definitely see it. I also took a prybar and pried gently on the balancer to see if I could get any side to side movement out of the crank manually, and I could not.

Secondly, the oil leak: I have an oil leak that is getting onto the balancer and slinging oil all over the front of the engine, leaving me with a nice mess. The area directly inside the back of and under the balancer seemed to be wettest, and I could see a track of oil coming from the face of the timing chain cover. Believing it was the seal, I replaced the old one with a new GM seal. The job was easy, the cleanup was not.

Now, after taking the car out last night, I came out later to find my leak was still with me, and I had a new stain in the driveway. Hooray. So this morning, determined to find the source of the leak, I brought the car into the garage, re-cleaned the engine, top and bottom, put the car on stands, started the car and got underneath to watch---Lo and behold, I found the oil seeping from the bottom of the front seal again. I watched it appear from the direction of the block and head out towards the balancer.

I believe the movement of the crank and the leak at the front seal are directly related. I would be hard to seal a crank that shimmys or vibrates side to side. So at this point, my plan is to pull the engine and install a new crank kit and new connecting rod bearings.

Having said all of this, does anyone have any advice or insider information they could give that would help this job go as smoothly as possible. It appears pretty straightforward to me. Oh yeah, and being a 1990, I will need to identify the crank casting on mine before ordering the kit---apparently, GM used 2 different cranks in 1990.

Thanks for reading!

Dave
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Old 04-30-2016, 08:39 PM   #2
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I have noticed a similar movement in my harmonic balancer and bolt in my Park Avenue and my dad'* former Bonneville (1990 SSE). Both ran (or are running) fine without issue.
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Old 04-30-2016, 11:55 PM   #3
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Are you sure there is not separation from the harmonic balancer?
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Old 05-01-2016, 07:26 AM   #4
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Are you sure there is not separation from the harmonic balancer?
Absolutely. I had it removed to replace the front seal and inspected it on the bench. The balancer looks like new, and is bonded tightly on both sides. I also performed the balancer "run" test to be 100% sure. When I removed the serpentine belt and ran the engine, the knocking noise actually got louder not quieter.
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Old 05-01-2016, 07:35 AM   #5
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I forgot to mention, when I inspected the balancer I noticed it has a 2013 date code on it, which would explain why it looks new.
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Old 05-01-2016, 10:22 AM   #6
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Did you notice a groove in the shaft of the balancer, where it mates with the seal?

You do realize all the work involved in replacing a crankshaft on this?
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Old 05-01-2016, 10:57 AM   #7
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Did you notice a groove in the shaft of the balancer, where it mates with the seal?

You do realize all the work involved in replacing a crankshaft on this?
No groove, That was one of the first things I looked for when I popped it off. I would have sleeved it if it did.

As for the work? Sure, it'* pretty easy once you get the engine on the stand and roll it belly side up. I won't consider ordering any parts until I know exactly what the source of the noise is, and what needs replacing. I'd like to believe it'* a main bearing since the noise gets louder with the belt and all tension on the crank removed...but I won't know for sure until I get inside to see what'* what.

It'* on the agenda for this week.
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Old 05-01-2016, 03:05 PM   #8
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Well, then, good luck....
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Old 05-01-2016, 03:27 PM   #9
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Thanks.

Oh, I also forgot to mention another important piece of the puzzle...the engine is quiet and knock free when stone cold. There is a slight knock on startup that immediately goes away as soon as oil is moving through the system, then the engine quiets right down. The detectable knocking (as described in my first post) begins once the engine has warmed. Again, leading me to believe I have the early stages of a bearing issue. Mains or rods? Both?? I'll soon find out.

If there'* any interest, I'll keep this thread updated with findings, pics, etc...

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Old 05-01-2016, 06:49 PM   #10
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Sure, some pics would be great....
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