GM Crankshaft & Harmonic Balancer Advice

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Jan 20, 2023
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2003 Buick Century 100 k original owner was my granny.

So had a mechanic redo the oil pan and timing cover gaskets and throw on a new motor mount. (Also new brakes, oil, pump, thermostat, temp sensor, new harmonic balancer.)

Upon pulling the harmonic balancer off he broke the bolt off inside the crank shaft, drilled it out and put a new bolt, got it crooked......now makes awful noise. Then he got the virus and can't honor the repair. He's a friend and a shade tree so i have no recourse to force anything.

Haven't driven it much.....took to a shop I've been dealing with since my old mechanic is no longer an option.

New shop found my mysterious overheating issue to be a blown headgasket.

He wants to do some welding on the crankshaft and rethread the crankshaft. Says he has a 90% success rate doing that. I'm opting to have him re do the headgasket. $2 grand for head gasket $400 for harmonic balancer/crankshaft jiob.

My question is: Should i go with the mechanics plan to weld and retap the harmonic balancer/crankshaft or should i just pay the $3400 or so to have him just put in a new crankshaft and basically rebuild the engine?

He says the engine runs surprisingly good for 100k. And i agree. I've been meticulous on maintenance and always used best parts available.
 
20 years old and 100k. It’s rolling the dice no matter which level of repair you choose. If you have $3400 available maybe research what’s out there you can buy as a replacement and then sell the Buick for whatever it brings. That $3400 repair would likely end up around $4000 before completion.
 
Arg, I've long had a horrible fear of breaking off the HB bolt.

If you're at all thinking of repairing the engine (rather than replacing it), I wouldn't drive the car. The off-balance HB can kill the engine fairly quickly.
 
Arg, I've long had a horrible fear of breaking off the HB bolt.

If you're at all thinking of repairing the engine (rather than replacing it), I wouldn't drive the car. The off-balance HB can kill the engine fairly quickly.
No it's at the shop waiting to get started on. I would like to keep the engine as i just slapped a bunch of new parts on it.
I'm just wondering if its better to gamble on the retapped crankshaft or just have him redo the whole thing since he's going down to the headgasket anyways.
 
Yes. Just did buncha work to it too
I've run two GM 3100 engines in my families fleet to well beyond 250K, and it WASN'T engine problems that sent them to the boneyard; both of them ran fine when "other drivers" totaled them out. If the rest of the car is in good shape, I'd certainly go with Trav's advice, a low mile used engine.
 
No it's at the shop waiting to get started on. I would like to keep the engine as i just slapped a bunch of new parts on it.
I'm just wondering if its better to gamble on the retapped crankshaft or just have him redo the whole thing since he's going down to the headgasket anyways.
I hope your tech can give you good advice.
 
Being upside down financially on an older vehicle doesn't seem to be a consideration with many BITOGERS self included. The only crankshaft repair I would do would be to set the crank in a lathe and drill and tap accurately.
 
Upon pulling the harmonic balancer off he broke the bolt off inside the crank shaft, drilled it out and put a new bolt, got it crooked......now makes awful noise.
I'm trying picture this in my head. There is just one big bolt holding the balancer on, right? Maybe an M20 with a 30 mm socket?
1) How is it possible to break that off?
2) If he drilled it out and got the new bolt crooked, how is it making awful noise. Is the balancer scraping on something?
3) Can't you remove that bolt, retap the hole and start over, carefully installing a new bolt?
 
You can get another engine for much less. You can buy another 3100, upgrade to the 3400 or the newer 3500/3900 high value engines, and of course the 3800 (though it is 90 degrees rather than 60), but it came on the Regal, both NA and supercharged.

There are so many better options than the job you want to do
 
If the balancer was left loose and it was wallering around on the crank both are junk now. If you really like the car spring for a rebuilt engine. Be aware that the cost to fix this car outweighs the value.
Ah wasn't left loose and ran a bunch. Before other mechanic got sick he did the work broke the bolt and put it in crooked and used a wrong sized bolt. Yes i am aware but it's cheaper than a new car....in California so yeah prices are sky high here.
 
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