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Old 05-27-2012, 08:57 PM   #1
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2006 LJ woes(need advice)

Back story.

Low Mileage 2006 LJ 6 speed. A few months ago, my jeep lost all coolant and got hot. It blew a head gasket and was having some blowby so I tore down the engine and replaced all six pistons.

I put the jeep back together. The engine was idling rough and It came up with a p0300 code so I replaced all spark plugs.

It still runs a bit rough when cool, but my real problem is that if the jeep idles while hot it seems to lose oil pressure.

When this happened, I pulled over and shut it down. The engine seemed very hot, however the in dash thermostat read right at 210.

Anyone have any ideas on what might be the culprit? I was thinking about the OIL pump and ODPA, but I wanted to consult the experts here..

Thanks in advance.

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Old 05-27-2012, 09:07 PM   #2
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When you changed the pistons, did you replace the rod bearings, too? If not, did you ensure you put the old bearings and rod caps back on the original rod and original cylinder? I ask this because it sounds like you may have one or more rods with excessive clearance. If you swapped them around some without verifying clearances, no telling what clearances you have.

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Old 05-27-2012, 09:49 PM   #3
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When you changed the pistons, did you replace the rod bearings, too? If not, did you ensure you put the old bearings and rod caps back on the original rod and original cylinder? I ask this because it sounds like you may have one or more rods with excessive clearance. If you swapped them around some without verifying clearances, no telling what clearances you have.
The rods may have gotten out of order when they went to be pressed onto the pistons. I reused the bearings and rod caps. could all this cause oil pressure loss? I can see the rough idle... but how would this cause the engine to lose oil pressure at idle?
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Old 05-27-2012, 11:58 PM   #4
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Rods and rod bearings are not alike. Each set must be matched with the diameter of the crank journal, the clearance adjusted to spec. Adjustments are made by actually filing the ends of the bearings so that when they meet, the resulting gap between them and the crank is within spec. Swapping them around means this critical adjustment is lost. Some bearings might now be too tight as well as others being too loose. Oil pressure is governed by three things - 1)The oil pump -2)Oil viscosity -3)The amount of restriction the pump encounters. The space between the rod bearings and crank (and main bearings, as well) make up a big percent of this restriction. If the restriction is too low (bearing gap too large), the oil pump cannot build adequate pressure, especially at low RPM. Think about a garden hose. When the nozzle is shut off or flow reduced, the pressure builds in the hose. Remove the nozzle or open it wide open and the pressure in the hose drops. Turn the faucet flow down to a trickle (idle) and hardly any pressure at all builds unless the nozzle is shut off or flow reduced.

Now whether or not this is your problem, I cannot say with all surety. However, it is a very likely cause since you did not maintain the bearing and rod positions. Sorry.
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Old 05-28-2012, 12:47 AM   #5
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Rods and rod bearings are not alike. Each set must be matched with the diameter of the crank journal, the clearance adjusted to spec. Adjustments are made by actually filing the ends of the bearings so that when they meet, the resulting gap between them and the crank is within spec. Swapping them around means this critical adjustment is lost. Some bearings might now be too tight as well as others being too loose. Oil pressure is governed by three things - 1)The oil pump -2)Oil viscosity -3)The amount of restriction the pump encounters. The space between the rod bearings and crank (and main bearings, as well) make up a big percent of this restriction. If the restriction is too low (bearing gap too large), the oil pump cannot build adequate pressure, especially at low RPM. Think about a garden hose. When the nozzle is shut off or flow reduced, the pressure builds in the hose. Remove the nozzle or open it wide open and the pressure in the hose drops. Turn the faucet flow down to a trickle (idle) and hardly any pressure at all builds unless the nozzle is shut off or flow reduced.

Now whether or not this is your problem, I cannot say with all surety. However, it is a very likely cause since you did not maintain the bearing and rod positions. Sorry.
So is it worth trying to pull the oil pan off and fit new bearings onto the jeep?

I don't think there is any way of determining the original position of the rods at this point.

If I have to pull the pistons again, i'd probably just get new rods pressed on the pistons. I'm seriously considering a short block instead..

Thanks for your help.
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Old 05-28-2012, 08:31 AM   #6
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A short block would most likely fix all your woes, but an expensive endeavor. Yes, you could just pull the pan and install new rod bearins with the rods/pistons in the current cylinders. Just do it right. Get some Plasti-gauge and measure your clearances and adjust as necessary.

Another little pesky question...when you replaced the pistons (and rings, I assume) did you hone the cylinders to remove the glaze? If not, the rings will not seat and you'll have an oil burner. So, if you did not hone, a short block might be your best bet.
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Old 05-28-2012, 08:36 AM   #7
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A good machine shop can alignbore the rods/caps and assemble it for you. Might be cheaper than a new short block or new rods. I have read that the antifreeze destroys rod bearings and cam bearings if it gets into the oil. Which may have happened with the bad head gasket.
Sorry to read about your misfortune. I know its frustrating to spend a lot of time and money and not get the results your were expecting.
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Old 05-28-2012, 10:39 AM   #8
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A short block would most likely fix all your woes, but an expensive endeavor. Yes, you could just pull the pan and install new rod bearins with the rods/pistons in the current cylinders. Just do it right. Get some Plasti-gauge and measure your clearances and adjust as necessary.

Another little pesky question...when you replaced the pistons (and rings, I assume) did you hone the cylinders to remove the glaze? If not, the rings will not seat and you'll have an oil burner. So, if you did not hone, a short block might be your best bet.

Thanks for the advice.

I used a ball hone to hone the cylinders. I haven't seen any white smoke. I also pulled the tube from the pcv valve and didn't feel any blowby. Can I assume that the rings are set?

I don't get the oil pressure loss (according to the guage) until I've driven the jeep for a bit and it gets hot. Does this sound consistent with my rod bearings having incorrect tolerances?
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Old 05-28-2012, 10:46 AM   #9
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A good machine shop can alignbore the rods/caps and assemble it for you. Might be cheaper than a new short block or new rods. I have read that the antifreeze destroys rod bearings and cam bearings if it gets into the oil. Which may have happened with the bad head gasket.
Sorry to read about your misfortune. I know its frustrating to spend a lot of time and money and not get the results your were expecting.

There was no antifreeze in the engine. This whole thing started with a bad pet c0ck on the radiator. I lost all coolant. the engine got hot and blew a head gasket.

I haven't turned many wrenches in my life.... I have learned so much from this. I wouldn't want to repeat it, but this is a great learning opportunity.
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Old 09-22-2012, 06:45 PM   #10
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When you reinstalled the Rings on the pistons did you align the Ring gaps? This is a common mistake that will cause engine oil consumsion. The gaps on the rings should be 180 degrees out from each other.

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