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Old 04-23-2008, 01:54 PM
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New Crank won't spin

I puting a new crank and pistons in a 92, 4.3 chevy. The bearing came with the crank , the pistons are in right and there is oil on them and in the bore , The crank will turn ok without the pistons install. But right now there are only 3 pistons in and the nuts are only hand tight and you can not spin the crank at all. There nothing hiting anyplace
My spec for the crank is 2.227 OD and the Rods are with the new bearing 2.248 ID .
what am I not seeing?

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Old 04-23-2008, 02:02 PM
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I would say that there is something going on with the chamfer on the rods, if you look at the rods there should be a chamfer on the big end on one side (this side should be towards the counterweights) then no chamfer on the other. If you have bushed rods just remove the rods from the pistons and flip them over. If you have pressed rods then make sure that the piston is not rotated 180 degrees in the bore (valve reliefs should be up) if the pistons are right and the chamfer is on the wrong side and you have pressed pins then you might as well throw them in the garbage and start over.
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Old 04-23-2008, 02:17 PM
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Do you have the right cap on the right rod?
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Old 04-23-2008, 02:23 PM
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Because this is a 6 rod throw engiene, each piston has its own rod journal. Because of this, there is not chamfer issue. BUT, the rods have an off-set built into them.

With the notches on the piston to the front of the engine, the bearing tangs should be away from the camshaft toward the outside of the engine.

Also, make sure you have not mixed up the rod caps or have them on bass- ackwards.

tom
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Old 04-23-2008, 02:29 PM
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tight 4.3

Did you change the pistons? If not .did you clean the ring groves before installing the new rings?
You didn't say what you've changed except the crank, do we need more info?
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Old 04-23-2008, 02:30 PM
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Well, you learn something new every day. I just assumed a V-6 would have 3 throws instead of 4 but this has 6 that is interesting.
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Old 04-23-2008, 02:34 PM
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Quote:
Originally Posted by gatliff
I puting a new crank and pistons in a 92, 4.3 chevy. The bearing came with the crank , the pistons are in right and there is oil on them and in the bore , The crank will turn ok without the pistons install. But right now there are only 3 pistons in and the nuts are only hand tight and you can not spin the crank at all. There nothing hiting anyplace
My spec for the crank is 2.227 OD and the Rods are with the new bearing 2.248 ID .
what am I not seeing?
This is not making any sense. The standard rod bearing journal size for the 4.3 V6 is 2.250". If you are measuring the rod journals at 2.227" (you did measure them, didn't you?), then they are 0.023" undersize. You are saying the bearings in the rods with the rod caps torqued to spec measure out to 2.248", which would be standard. With 2.248" bearings on a 2.227" rod journal, the big end of the rod should rattle around on the crankpin. I'll ask you the same question: What am I not seeing?
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Old 04-23-2008, 02:51 PM
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I'll ask the stupidest questions thus far.......

Are you trying to spin the motor with a wrench? Or by hand?

Do you have the correct rings for the pistons your using? ( I remember something about 2 different ring sizes for the 4.3s)

whats the thrust clearance on the rod journals?
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Old 04-23-2008, 03:22 PM
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Quote:
Originally Posted by techinspector1
This is not making any sense. The standard rod bearing journal size for the 4.3 V6 is 2.250". If you are measuring the rod journals at 2.227" (you did measure them, didn't you?), then they are 0.023" undersize. You are saying the bearings in the rods with the rod caps torqued to spec measure out to 2.248", which would be standard. With 2.248" bearings on a 2.227" rod journal, the big end of the rod should rattle around on the crankpin. I'll ask you the same question: What am I not seeing?
We'll get him straight on the piston orientation, then we'll get him on track the the undersize thing.




tom
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Old 04-24-2008, 06:04 AM
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Thanks guys the pistons were press on by a auto machine shop and it look as if the shop put some of the piston on the rod incorrect. the piston look the same no matter what way they face any reson they won't work as long as the rod is faceing the right way
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Old 04-24-2008, 09:07 AM
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Theres a Light and heavy side of the piston......Ballance will be off.

Might work but is it worth galling a piston and ruining a piston and rings?

Take them back to the shop that pressed them on and have them do em over.
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Old 04-24-2008, 12:51 PM
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It is not a light and heavy side on the piston. It is pin bore offset for major and minor thrust faces.
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Old 04-24-2008, 01:06 PM
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Light/Heavy is the term we used at MAHLE to describe the offset.
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Old 04-24-2008, 02:10 PM
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Quote:
Originally Posted by Holder350
Light/Heavy is the term we used at MAHLE to describe the offset.
Has nothing to do with engine balance.

tom
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Old 04-24-2008, 02:12 PM
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What brand of pistons are they?

tom
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