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What did you do with your GMT400 today...or yesterday....

MrMarty51 said:
Well that could have been mighty disasterful. 😖😩
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Yes, we got lucky or it failed as designed. Truck started running poorly and throwing a bunch of codes, include TDCO. He sent me videos showing the IP gear not turning when he turned the engine at the crank bolt. The timing chain would but not the gear in front of it. I knew then we had sheared the key or something worse. He pulled the water pump and found the loosened and bent bolt which explained the cause. Now those bolts are in with blue loctite and torqued to 33 ft/lbs.

Everything in front is back on. Tomorrow we have the lower/upper intakes to install, connect coolant hoses and refill it, then start it and time it.
 
dbrannon79 said:
Are these "interference" engines where something like this happens or worse and the valves can kiss the pistons?
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I don’t know. It happened in the driveway. Engine was still running fine, but he shut it down. He then went to change the IP and that’s when he discovered the upper gear would not move to allow him to remove the bolts holding the gear to the IP. I then instructed him to pull the water pump and timing cover and wait until I got down there. Cleared the deck of other things and went over to help him today.
 
just searching online the only thing I can find is this. but I think all of the GM books tell us the same thing. iirc all of the smaller SBC engines weren't considered interference ehgines. I have been wrong before though.

1654384751755.png
 
dbrannon79 said:
just searching online the only thing I can find is this. but I think all of the GM books tell us the same thing. iirc all of the smaller SBC engines weren't considered interference ehgines. I have been wrong before though.

View attachment 75157
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Relax. We've turned the engine over by hand and there is no loss of compression.
 
Big T said:
I don’t know. It happened in the driveway. Engine was still running fine, but he shut it down. He then went to change the IP and that’s when he discovered the upper gear would not move to allow him to remove the bolts holding the gear to the IP. I then instructed him to pull the water pump and timing cover and wait until I got down there. Cleared the deck of other things and went over to help him today.
Click to expand...

Thinking it through, I think I have the specific timeline and the final issue. Son had never set TDCO and it threw codes. He had dumped the cable for laptop hosting the OBD I software into the box with my GM Tech 2 and that ended going up with me to MT. Unable to time it, he thought the IP a was the problem and pulled it to put in the AC Delco IP. He was using the starter to move the IP gear to position the bolts for removal through the oil fill. Gets the bolts out, removes the IP and tries to install the AC Delco IP. In doing so, pushes the IP gear foward where it locks up on the loosened water pump bolt, shearing the key. Both IP and the timing gears never moved after that.
Engine never ran after the timing gear key sheared, so it is unlikely for there to be damage from a valve hitting a piston. Pretty sure this captures the sequence of events.
 
Final thought on this, the timing chain sprocket on the cam never stopped, as that portion of the key holding it to the cam did not break. Thus the valve train was always moving in synch with the crank, thus it was not possible for the valves to impact and damage the pistons.Timing gear and IP gear stopped moving, thus the no start.
 
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