GM 3800 Crank Sensor Replacement

Joined
Sep 27, 2015
Messages
4,308
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USA
Cutting to the question here: Is the crank bolt really not reusable? GM says not to reuse it but it seems hard to find a new one and the intention here is most likely to get the car running and sell it so I'm not big on spending a lot of time or money.

Longer story: My friend's 2006 Buick Lucerne with 3800 V6 engine cranks but won't start. I think I have the proper diagnosis of crank sensor since the electronics all have power, but there is no spark; the OBDII live data shows zero rpm while cranking. (No codes found). One of the channels of the crank sensor has the 3 pulses between 0 and 6.4 volts per revolution but I couldn't get any activity on the other one (the yellow wire), always at 6.4 volts. There is continuity from the ICM to the sensor on the yellow wire and no short to ground.

So I bought a new sensor and rented the harmonic balancer puller and will start the replacement in the next day or two. (if you're looking for the question go back up to the top).
 
Joined
Nov 20, 2006
Messages
28,668
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MA, Mittelfranken.de
The problem isn't reusing the bolt it is getting the old one off. GM puts some orange snot under the bolt head making it tighter than a bulls A hole in a hurricane and a PITA to get off, this one can make a Honda J35 feel finger tight if it has never been removed. I would replace the bolt, it is liable to be pretty banged up once you get it off.
The starter trick may be your best/only bet if it really stuck. Look this up before doing it, I am not advocating it but it works.
 
Joined
Jul 10, 2011
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667
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Martinsburg West Virginia
I have actually made this happen by heating up just the bolt with a heat gun and using a wireless impact on it. Trying not to heat up the balancer too much. Before the heat, no movement, after the heat it backed out slow and then came right out. Whatever they put on there holds pretty well.
 
Joined
Nov 15, 2019
Messages
160
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MA
Application of penetrating lube, then waiting couple days, then heat using propane torch, then using the HF Earthquake impact wrench got mine off. Without the heat, the bolt was not budging. The loc-tite stuff they used on the bolt must soften up with the heat.
 

mk378

Thread starter
Joined
Sep 27, 2015
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USA
The job is done, the car runs again! I started by simply hitting the bolt with my 500ft-lb CH impact, it did move a little from the first pull of the trigger, so staying on it for a few seconds it came out. Didn't find any compound under the bolt, it was covered in motor oil which I guess is to be expected since it is inside the oil seal.

Next I found the puller holes in the balancer don't match any of the bolts in the puller kit; I guessed correctly they are M6-1.0. These bolts need to be about 70 mm long to fit the typical "duck foot" puller. They only turn in about 3 turns before hitting the back of the tone rings, so don't overtighten or the rings will get mangled.

Balancer off, now remove plastic cover ( it snaps on in 3 places) and R&R sensor. Replace balancer, tighten bolt to 110 ft-lb + 76 degrees, more or less. Replace serpentine belt and turn key.

Thanks to everyone for the advice.
 
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