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Old 12-06-2011, 05:02 PM
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Connecting Rod Help

I have a 350 that broke a crankshaft and one rods taper got a little messed up. I am budget overhauling it and like to know if I could try to fix the taper with a round file. I have not found a rod as most want to sell as a set. The last time I had a piston R&R off a rod the shop told me they had a problem putting it on but it should be ok. That piston got distorted in the process some how and made noise when I got the engine running. If I take in to have it reworked they have to take the piston off to do it. Any suggestions?

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Old 12-06-2011, 05:07 PM
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take it to a machine shop and ask them or post some pictures of the rod for us to see
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Old 12-06-2011, 05:30 PM
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I don't understand what you mean by "taper". It's a real pain to hone one rod which is what has to be done if the piston is on and even having the piston on is a pain, but for a cheapo fix I would rather do that than to remove the piston in a press. It almost always deforms the pin boss, but even that can be fixed....with a little luck.
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Old 12-06-2011, 06:48 PM
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That's what happen to me the last time and a machine shop did the work. These are X rods and I didn't want to mix them. Maybe I will go to a rebuild-er and see if they have an X- Rod and get them too put it on for me. I Am buying a crankshaft kit from Oreilly's and some rings so that will finish the shortblock. I have the valve job fresh heads with Z-28 springs. The cam bearings and freeze plugs are fine. The motor had less than 5K miles. Just a defective crankshaft, it just snapped smooth where the bearing surface connects to the counterweight.

Last edited by Chevyjeepster; 12-06-2011 at 06:50 PM. Reason: Need to
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Old 12-06-2011, 06:55 PM
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Speed bump: The beveled edge of the rod next to the bearing saddles. That's as about as good as I can explain it. It looks to be about 40-45 degrees of angle. They cut it on a lathe.
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Old 12-06-2011, 07:06 PM
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If the chamfered side of the rod where it meets the crank surface is damaged, you will need to have the rod diameter checked to make sure the big end is still round and the right size. If it measures OK, just deburr the area and youre money.
Resizing a rod with the piston on is a hassle but I have done it many times and have a fixture for holding a rod pair with the pistons installed.
Removing and installing a stock piston without tightening up the pin bore on one side is a challenge
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Old 12-06-2011, 09:04 PM
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Thanks I will have it ck.
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Old 12-07-2011, 09:31 AM
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If you're in a sharing mood, I'd like to see a picture of that fixture, if you've adapted it to fit a Sunnen hone.
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Old 12-07-2011, 04:27 PM
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Reconditioned rods can be purchased. And most any parts store has access to them.

http://www.northernautoparts.com/Pro...tModelId=25635

FYI
Al
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Old 12-07-2011, 08:04 PM
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Thanks for the info, I think I am going to use it. I touched it up with a flat file and it didn't take much. I will measure the big end to be sure it wasn't distorted. I feel good about and I think it will be fine in a stock motor that will hardly ever see over 3,500 rpm. When it's built I going to break it in on a test stand with cooling system and exhaust. If it passes than into the jeep it will go.
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Old 12-08-2011, 12:07 PM
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A picture would be great. Cracks usually start at sharp edges....
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Old 12-08-2011, 02:21 PM
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here some pictures and this was the best i could do with a $20 phone.
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Old 12-08-2011, 04:24 PM
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Quote:
Originally Posted by Chevyjeepster
I have a 350 that broke a crankshaft and one rods taper got a little messed up. I am budget overhauling it and like to know if I could try to fix the taper with a round file. I have not found a rod as most want to sell as a set. The last time I had a piston R&R off a rod the shop told me they had a problem putting it on but it should be ok. That piston got distorted in the process some how and made noise when I got the engine running. If I take in to have it reworked they have to take the piston off to do it. Any suggestions?
I certainly have concerns about this, just how old is the broken crank, whose crank is it, and how was it and how is it being used? You mention a build that caps the revs at 3500, is this typical of your use? 3500 is certainly moderate, breaking a 350 crank at those low RPMs is most unusual.

Which journal busted? A smooth fracture with a rough break at the end shows either a manufacturing defect or a failure at extreme overloading. Look very carefully to see if there are progressive "beaches" showing that this started as a surface crack that would progress to a point, then stop, then start again, this would also be either a manufacturing defect or a fatigue crack.

Does it have a damper, was the crank assembly ever balanced, has the block been checked for alignment or honed through the main saddles?

Did you follow the main cap and head bolt torque sequence and to what limit were bolts tightened? Are any bolts replaced with studs?

X rods are not anything so special that I'd try to salvage them. I'd being worrying about life long fatigue in all the rods. Not that new rods are a guarantee, but I shy away from used or rebuilt rods because no matter how pretty you make them they have been subjected to how many millions of cycles that have tried to compress them, then stretch them, and between these two extremes, bend them.

O'Reilly's for a crankshaft, really?

Pressing the pin out usually junks the piston.

Bogie
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Old 12-08-2011, 04:59 PM
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Damn! Bogie let's see. I buy engine cores from a friend that owns a 12 bay shop. Sight on seen for $60 for Chevy long blocks. This motor was out of a 69 classic truck. The customer wanted a create engine so that's what he got. They new that this motor was new but had problem so instead of tearing it down it can to me. When I got it home and took it part it was spotless inside. Heads, engine valley,oil pump,pan ect. But I seen the problem a broke crank. No spun bearings just a broke crank. I took the crank out and look at for 2 days in amazement! It broke smooth as a babies butt, I have been around the block a few times and have never seen a break like this. So with no other problem other than the one rod I think it was defective. So as cheap as I am I am buying a crank kit from Oreilly's new rings, cam & lifters valve springs and it goes back together. As far as the rpm 65 mph @ 3250 with 31"tires. Sure it could go over that from time to time but not often. My Jeep has 3:73 or 4:11
Not sure the tag on the Dana said 3:73 but I wonder?

Last edited by Chevyjeepster; 12-08-2011 at 05:01 PM. Reason: Messed up
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Old 12-08-2011, 05:17 PM
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If it were me I would clean up the chamfer with a small fine hand file and some emery cloth. Then check out of round with a mic. or take it to someone with a rod machine and have it checked. Put it back together and 99.9% of the time you will be fine.
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