Engine 1993 Freshly Buily 347 Seized?

tkollmeyer3

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Mar 13, 2018
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I have a newly built 347 i just installed into my 1993 mustang, new cam (b303), lots of other things thrown in as well, got everything in line, got it running for about 10 minutes, idling a little rough while it was cold which the old 5.0 i took out did as well so i figured maybe just an IAC issue, it sounded great but stalled in my driveway a couple times while idling but would fire up again just fine. One time it died and we just left it off for the night, then the next day i started it again, ran for a few seconds, sounded healthy but died (i normally have to hold the rpm a little higher until its warm, figured thats all it was that killed it). I went to refire it and just heard a single loud clank at the turn of the key, thought it was a starter issue so i got a new high torque mini starter installed, battery fully charged, etc. Went to start it again, same clank. When i checked, the engines not turning over by hand at all, and the clank was the starter slapping against the flywheel. This is really concerning because the engine had oil pressure, stayed at a good temperature, and was just rebuilt before it went in the car. I pulled all 8 spark plugs and loosened all the rocker arms pretty good to see if it was a valve clearance issue or if it would turn with less compression in the cylinders, but still no luck. No warning signs, no noises while running, nothing. Ran beautifully and then died and wont spin. Any suggestions? we kept the motor covered so i cant imagine anything got inside the engine, is there anything i could try or check out? ive been told to put the car in 5th gear and push it but havent had anyone to help me try that yet. any help is greatly appreciated
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
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Try rotating it backwards with the plugs pulled, just a little, if it does turn then rotate it the other way, don't force it, let us know
 

tkollmeyer3

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Mar 13, 2018
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Try rotating it backwards with the plugs pulled, just a little, if it does turn then rotate it the other way, don't force it, let us know

tried rotating counterclockwise with plugs pulled as well, doesnt want to turn easily in either direction, trying with just a ratchet, i could put a cheater pipe over it but didnt want to break anything or make anything worse
 

tkollmeyer3

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Mar 13, 2018
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I'm gonna climb out on a limb, your likely gonna pull that thing, make sure the transmission is not causing it to bind up.
how would the transmission cause it to bind up? i mean you can move clutch freely and shift through all 5 and reverse without issue (while off of course). could something potentially be wedged between flywheel and bellhousing? no dont know what i would learn from pulling it again, i might find something but like what could be going on inside that would require me to pull?
 

Hoytster

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how would the transmission cause it to bind up? i mean you can move clutch freely and shift through all 5 and reverse without issue (while off of course). could something potentially be wedged between flywheel and bellhousing? no dont know what i would learn from pulling it again, i might find something but like what could be going on inside that would require me to pull?
Well, if you already ruled out the valvetrain and any external accesories as being to cause of the drag on the motor, then you are probably going to have to pull the engine to tear it down and find where the problem lies. There is some stuff that you can pull and check in the vehicle, but since this is a new rebuild, id double check everytjing external and then pull the motor to check it.

Who rebuilt the motor for you and do you have the rebuild specs?
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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polk county florida
Without knowing anything about your car/build, it's a guessing game. Miss matched bell housing and/or transmissions or clutch. Cam, crank or rod bearing also could be too tight, wrong bearing tolerance, improper assembly method, poor oil pressure on startup, your likely gonna be pulling the engine,
 
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hotpony

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I am building a 347 right now and something I've been finding is that most 347 cranks can't take an OEM pilot bearing because they don't seat all the way and the input shaft of the trans puts forward pressure on the crank, causing the thrust bearing to go bad in a matter of minutes.
 

Rick 71

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Mar 11, 2019
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I have a newly built 347 i just installed into my 1993 mustang, new cam (b303), lots of other things thrown in as well, got everything in line, got it running for about 10 minutes, idling a little rough while it was cold which the old 5.0 i took out did as well so i figured maybe just an IAC issue, it sounded great but stalled in my driveway a couple times while idling but would fire up again just fine. One time it died and we just left it off for the night, then the next day i started it again, ran for a few seconds, sounded healthy but died (i normally have to hold the rpm a little higher until its warm, figured thats all it was that killed it). I went to refire it and just heard a single loud clank at the turn of the key, thought it was a starter issue so i got a new high torque mini starter installed, battery fully charged, etc. Went to start it again, same clank. When i checked, the engines not turning over by hand at all, and the clank was the starter slapping against the flywheel. This is really concerning because the engine had oil pressure, stayed at a good temperature, and was just rebuilt before it went in the car. I pulled all 8 spark plugs and loosened all the rocker arms pretty good to see if it was a valve clearance issue or if it would turn with less compression in the cylinders, but still no luck. No warning signs, no noises while running, nothing. Ran beautifully and then died and wont spin. Any suggestions? we kept the motor covered so i cant imagine anything got inside the engine, is there anything i could try or check out? ive been told to put the car in 5th gear and push it but havent had anyone to help me try that yet. any help is greatly appreciated
look at poly locks to rocker arm clearance.
 

Rick 71

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Mar 11, 2019
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look at poly lock clearance. bottoms hit rockers at top of stroke. cost me 13,000 $ ( 3 rebuilds) wont see unless it rolls over.
 
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