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Old 06-19-2017, 03:33 PM   #1 (permalink)
RatsMC
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Confirming Broken Timing Chain?

Deciding what to do with my truck right now.

I am fairly certain that I have a broken timing chain and thus a broken motor. It was making noise at the front. After a brief un on the freeway, it got really loud as I slowed to take the exit. Then, It just stopped dead instantly. Turning the key, the starter makes a screeching noise and doesn't really sound like it is turning the motor.

So, before I do anything, it would be nice to know if this motor is in fact hosed. I have pulled the water pump off but I can't get a clear view of the TC. Do I have to pull the HB and remove the cover to tell if the chain is broken?

Is there any other way to confirm? With a gasser I can just check the distributor. If I turn the motor over manually, the IP drive gear shouldn't rotate if the chain is broken correct?

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Old 06-19-2017, 05:46 PM   #2 (permalink)
1967KaiserM715
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Correct, broken chain means injection pump won't turn-it could be the key broke or something else-but chances are a lot of valves hit pistons and there are some bent push rods, so at that point it's moot what actually broke.


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Old 06-19-2017, 07:46 PM   #3 (permalink)
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Well, it appears that the TC is fine but something else is very, very wrong.




You can see in the first video that the motor is barely moving when the starter cranks but in the second on, you can see that the flexplate and Torque Convertor are spinning.





Broken Crank? When I rotate the motor by hand it feels normal and has good compression. The flexplate doesn't appear broken.
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82 GMC K1500 6.2l

Banks Sidewinder Turbo
TH400 Transmission
Rebuilt 10 Bolt 3.42 Diffs
NP208
Electric Lift Pump relocated to the frame
Manual Glow Plug Set up
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Old 06-19-2017, 08:24 PM   #4 (permalink)
1967KaiserM715
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Confirming Broken Timing Chain?

Pull the front pulley, use a large socket on the front crank bolt, and slowly rotate(may help to remove glow plugs) and watch the flex plate-if it doesn't move with the front half, you need to remove the torque converter and make sure all the bolts are installed. If they are, then a broken crank is likely

Should say, it isn't necasary to drop tranny, just need to push it back.


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Old 06-19-2017, 08:47 PM   #5 (permalink)
RatsMC
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So, I found that it is the Flexplate. It is shredded right around the crank. Just didn't look carefully enough the first time.

I have two threads going, this one and one for the noise I was getting before this failure. The questions I still have are why would the flexplate failing cause the motor to instantaneously stop? And what was the noise I was getting before the flexplate broke?
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82 GMC K1500 6.2l

Banks Sidewinder Turbo
TH400 Transmission
Rebuilt 10 Bolt 3.42 Diffs
NP208
Electric Lift Pump relocated to the frame
Manual Glow Plug Set up
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Old 06-19-2017, 09:04 PM   #6 (permalink)
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Quote:
Originally Posted by RatsMC View Post
So, I found that it is the Flexplate.
I was just going to suggest that. The video clearly shows it doing the wobble dance.


Wonder why it stopped dead?

Last edited by DieselPro; 06-19-2017 at 09:05 PM.
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Old 06-19-2017, 09:21 PM   #7 (permalink)
1967KaiserM715
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Could still be a broken crank-excess vibrations resonating along the crank causes it to crack-think of the flex plate like a second harmonic balancer.

Now, you'll still need to try and determine if the front and rear of the crank move with each other or if there is a lag between the front and rear indicating a separated/broken crank.

And maybe luck has it-the flex plate broke while driving, jammed up against the crank momentarily and stalled the engine...possible, but it would take quite a bit to stall the motor, so...further investigating is required.

In your other thread, I believe you said the harmonic and pulley checked out good?


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Old 06-19-2017, 09:35 PM   #8 (permalink)
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The front of the motor looks good and normal HB is in decent shape and everything moves as it should.

My plan as of right now, is

- Order the flexplate
- Pull the transmission back or out.
- Check the rotation of the rear of the crank when I rotate the front.
- Replace the Timing chain since I have a new one sitting here
- Replace the HB since I will have it off to do the timing chain.
- Install the Flexplate and fire it up
- If that is successful, bolt up the transmission.
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jerry

82 GMC K1500 6.2l

Banks Sidewinder Turbo
TH400 Transmission
Rebuilt 10 Bolt 3.42 Diffs
NP208
Electric Lift Pump relocated to the frame
Manual Glow Plug Set up
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Old 06-19-2017, 09:53 PM   #9 (permalink)
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Might be wise to pull the transmission front pump and inspect. Does not take a lot to damage the pump. Maybe others can chime in on the pump or start a new thread on transmission.
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Old 06-19-2017, 10:05 PM   #10 (permalink)
RatsMC
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Hmm...if there is a transmission problem, I am just going to do a manual transmission swap. I hate this TH400. But I would like to hear anyone's thoughts on possible damage to this one.

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jerry

82 GMC K1500 6.2l

Banks Sidewinder Turbo
TH400 Transmission
Rebuilt 10 Bolt 3.42 Diffs
NP208
Electric Lift Pump relocated to the frame
Manual Glow Plug Set up
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