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1999 C2500 Vortec 5.7 Rod Knock

Posted by vortecbill (My Page) on
Mon, Sep 28, 09 at 22:29

Great info here, except the flaming.
I have a '99 C2500 with the 5.7 vortec and this is what the story is. I had an intake manifold gasket go out and it put water in the oil. The truck sat for 4 months and I forgot to drain the oil and flush the oil system, " I know not good " I finally replaced the gaskets. I then had an injector issue ( missing on one cylinder ) replaced it with an updated spider. However before replacing the spider I was trying to go on the cheap and put injector cleaner in the tank and ran about 50 miles with no improvement. I hate to admit this, but I revved the engine pretty high ( from what I read on this post, I probably over revved the engine. I immediately had a what sounds like a rod knock. The knock get quiter under load and noiser when you let off the throttle while driving. I think it is a rod knock. I'm planning on dropping the pan, removing the rod rearings one at a time and installing STANDARD BEARINGS, and using plasti gauge to see what the clearance is and replacing the bearings according to what I read. Do you think that is a viable option and what is the std rod bearing clearance on this engine.

Thanks Brad

Follow-Up Postings:

RE: 1999 C2500 Vortec 5.7 Rod Knock

Now we have some information to work from. Case history isn't always so critical, but in this case it genuinely is. If we were playing chess, this would compare to a discovered check. When you removed the intake manifold, that allowed the already stressed engine block to relax. Then when you torqued the manifold back down, especially if you didn't use the correct torque sequence, and the very specific torque settings, you pulled the line bore out of spec which causes wear in the main bearings, and it then starves a(the) rod bearing(s).

As pro's we have debated the actual cause of the bearing failures after an intake issue for a few years running. Engineers are certain that it is our fault blaming us for failing to torque the intake correctly, and twisting the block. However I suspect the block distorts and contributes to the gasket failure in the first place, and the replacement simply finishes it off. Of course the coolant in the oil does very little to help the situation.

To repair this correctly, it needs to be pulled, stripped down and the block, heads, connecting rods, crankshaft all sent out to the machine shop. The block should be line bored (camshaft and crankshaft) and possibly decked. The connecting rods should be re-sized so that the bearings "crush" properly when installed. The heads resurfaced, the valves and seats machined. Then hone the cylinders, fit new rings to the pistons, inspect the camshaft, and see if it is still serviceable. If not the cam and lifters also need replaced. Add a timing chain and a new oil pump and of course, you have completely rebuilt the engine all because it "lost a rod bearing".

If here in the shop I attempted to do a bearing slap, and it failed (which there is a 70% or better chance that it will fail) I would then be expected to make it right, and the rebuild is what would be required. The problem is the block has stressed, and now relaxed back into a different shape than it was when it was first built. This causes the crankshaft to be bent when it turns like a drill bit that is being pushed on too hard. Of course the reason the crankshaft is getting bent is because the main bearings don't line up anymore, unfortunately it's not something you can see by eye, and if you pulled the engine and did a crank and bearing kit, without having the line bore corrected you would likely end up with a broken crankshaft somewhere down the road.

Now will slapping a set of bearings buy you some time? It's possible, in fact the problems that some engines tolerate instead of them self destructing over is pretty amazing. That simple fact is why people attempt bearing slaps, and occasionally get away with doing so. At the same time when the bearing slaps fail, as this one might, without extensive experience all someone could try to do is attempt to guess if the work wasn't done right.

RE: 1999 C2500 Vortec 5.7 Rod Knock

Thanks for all the info. I did torque the intake manifold to the correct torque in the recommended sequence. The only miles the engine received was the 50 miles trying to clear the injector. One issue that I didn't mention was obvously when you lose the water the engine heats up. I was fortunate in a way before the engine "cooked" oil was drawn into the intake system and stalled the engine. I suppose that part was a good thing, LOL. Again thanks for the info. I think I'm gonna gamble on the rod bearings, a 1999 truck really isn't worth the cost of a complete overhaul. So let's see what happens.

I'm an old guy and I remember the days in a 37 chevy when we pulled the inserts an put shim stock behind the insert and reinstalled the bearing, LOL. Can you believe that action. What can I say, we were poor kids doing the best we could. It worked for a while too, hehehe.

Thanks again.

RE: 1999 C2500 Vortec 5.7 Rod Knock

Oh, I have another question.I noticed a pair of wires ( pink and White ) with a connector on the end hanging from the harness at the left front corner near the engine control module. ( left front fender well ) Is this a test lead for the fuel pump or something or do I have a connector that should be plugged into something, LOL.

Thanks again

RE: 1999 C2500 Vortec 5.7 Rod Knock

Shim stock? :) Sure. How about melting lead into the cap and rod and filing it out to size? Or taking a lawn mower engine connecting rod, grinding the cap, and then re-fitting it to the crank all by hand. I learned how to use crocus cloth to cut a high spot down on a crankshaft, and then fit .002 bearings back to the rod, again by hand. (I've been doing this a long time too)

RE: 1999 C2500 Vortec 5.7 Rod Knock

Hehehe, too funny.....So you probably had a hollow ground triangular bearing scraper too. I used that to scrape the babbit and blue in the bearings on a Model A. ROFL.

Ahhh, those were the days.

Do you have any idea about this question?

Oh, I have another question.I noticed a pair of wires ( pink and White ) with a connector on the end hanging from the harness at the left front corner near the engine control module. ( left front fender well ) Is this a test lead for the fuel pump or something or do I have a connector that should be plugged into something, LOL.


RE: 1999 C2500 Vortec 5.7 Rod Knock

A two wire connector at the left rear of the engine with one pink and one white wire?

You easily have just described the small harness that runs from the ignition module to the coil. The pink wire being the one that brings system voltage to the module from the coil, and the white one is the "tach" lead or negative side of the coil that the module uses to drive the coil. Of course if your car is running, then the connector I am envisioning is plugged in, and the one you are looking at simply has two similarly colored wires.

RE: 1999 C2500 Vortec 5.7 Rod Knock

My step-dad passed away 2 weeks ago and now mom's Tahoe is knocking. It started 2 days ago with a rattle when you first start it and has gone to a steady knock even after it warms up. It quiets down when in gear and I tried some motor honey with no results. Its a 4wd and I told her I would have to pull the motor and take the crank to a machine shop to be ground and get matching bearings. Do you know what would make it start knocking all of a sudden and does this sound like the right thing to do. I could really use some help since we do not have the money right now to put it in the shop.

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