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realsquash 04-19-2004 10:23 AM

Broken 400 SBC flexplate with a 350 block...
I have a dilemma here. I have this old chevy truck that I bought and it has a TON of redneck crap that I'm basically reversing. The truck had a knocking sound and I figured it was the flexplate. Well it was indeed cracked, so I removed it. It looks like a 400 flexplate to me because it has a counterweight. I've attached a picture of it.

I know the engine has been rebuilt, and the casting number (3970010) says it's either a 327 or a 350. I'm concerened/hopeful that this is actually a 383 (400 crank in a 350 block), so I need to figure that out so I can get the right flexplate on it!

I've heard there are externally visible differences on a 400 harmonic damper? Any ideas? Help me figure out what the hey this thing is!


DoubleVision 04-19-2004 10:56 AM

if it`s a 383, then on the harmonic balancer there will be a counter weight cut out, in other words it won`t be completely round all the way around the outer circumference, but that don`t mean it`s a 383, since all balancers interchange, it would go on a 350 but would be out of balance with bearing damage resulting. one way to be sure is to check the rear mounting flange of the crank, if there`s a dowel pin in the flange, it`s a 400 shaft.

Jmark 04-19-2004 10:58 AM

You indeed do have a 400 flywheel in that pic. The 350 balancer will be smooth all the way around, inside and outside surfaces.
The 400 balancer will have a big recess in one area, that is the "light" side of the balancer.


jimfulco 04-19-2004 10:18 PM

What is the shape of the rear flange of the 400 crank. The imprint on the flexplate might be a clue.

coldknock 04-20-2004 09:25 AM

There aren't any differences visible from the outside. Drop the pan and have a look at the cranks casting number. It's possible that a 400 damper and flexplate were used on a 350. It'd shake like he-double toothpicks when it ran. I mean it would vibrate so bad that you'd know something was very, very wrong. It would take about 5-10 min. of running to kill the bearings and the oil pressure would drop quickly.


realsquash 04-20-2004 11:23 AM

It appears that it has the correct harmonic balancer for a 350. I know from driving the truck at about 40 mph was a real event, tons of vibes. The rear driveshaft was completely shot, I'm suprised it survived the trip home, but I suspect that was where the vibrations came from. The engine sounds great and had good power, so I don't think the bearings have toasted... Of course none of the gauges are hooked up either so who knows if it even has oil pressure.

I know for a fact this truck was driven quite a bit, I even rode around in it before I owned it. I'm pretty sure it's a 350 with the wrong flexplate now.

Thanks for everyone's input, it's greatly appreciated.


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