98 5.9L bearing problem

The 5.9L motor in my 98 2500 quad cab has developed a lower end knock. It's most noticeable on start for a few seconds but it's always there just much quieter. This truck has about 100K on it. My thought is a
rod bearing but I guess it could be a main bearing.
Other than this the motor runs strong. We pull a 5000 pound trailer about 200 miles every weekend for several months. We're looking to possibly be pulling for longer distances next year.
Are there any reasons to not putting rod and/or main bearings in? Or is a short block the only way to go?
Thanks for any suggestions.
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The change in sound you are describing sounds like a main bearing. The problem is that if a bearing has failed, the chances are pretty good that the crank journal that the bearing supports or rides on is also damaged which will require removal of the crank for machining. While this can be done with the engine in the vehicle in many cases, it really defines PITA to do it. If it was a main bearing, you also have to check the block for damage from this as well and if it is, out it comes. If you intend to keep the truck for a while and with the work load you put on it I would suggest going with a short block and with about 100K on it, you might think about going with a long block instead and get the new (rebuilt heads) and valve train as well.
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So how much would a long block cost ?
TBone wrote:

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that
be
PITA to

keep
suggest
about
valve
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Hardly. Mains make very little noise when failed. In fact, an engine with a failed main could run for quite some time, depending on how much oil pressure is lost due to the failure. Particularly in the 360, where the mains are 2.800" diameter, the crank is stiff enough to keep any flex to a minimum.
Fact is, it could be any bearing on the crank, but is much more likely to be the rods than the mains.

Otherwise, seems like you are hitting the mark.
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"Max Dodge" wrote:

flex
likely
I agree that mains rarely make noise themselves and "might" cause a little vibration rumble in the engine if the get real loose along with bad oil pressure. But indirectly they do cause noise form other sources because when main gets worn, they can cause rods to go because of lack of oil pressure to rods so in a way worn mains do cause noise.
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"SnoMan" wrote: > [quote:04fbefa096="Max Dodge"]> The change in sound you are > describing sounds like a main bearing. > > Hardly. Mains make very little noise when failed. In fact, an > engine with a > failed main could run for quite some time, depending on how > much oil > pressure is lost due to the failure. Particularly in the 360, > where the > mains are 2.800" diameter, the crank is stiff enough to keep > any flex to a > minimum. > > Fact is, it could be any bearing on the crank, but is much > more likely to be > the rods than the mains. > > [/quote:04fbefa096] > > I agree that mains rarely make noise themselves and "might" > cause a little vibration rumble in the engine if the get real > loose along with bad oil pressure. But indirectly they do > cause noise form other sources because when main gets worn, > they can cause rods to go because of lack of oil pressure to > rods so in a way worn mains do cause noise.
If the engine is running fine otherwise and not using much oil, I would just put new bearing in there and be done with it myself.
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I guess the concept of mic'ing the journal to see if its still round is too complicated?
"just slap another bearing in it" never works out the way you think it should.
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"Max Dodge" wrote:

it
It is too much trouble if the knock just started and the bearing is not burnt. If the journal is still smooth and nothing is burnt, it will not be out of round enough to worry about it if at all. If it is pounding all the time, (which it is not)it is a different matter but it is not by this post. You tend to try to make thing more complicated than they need to be at times.
BTW I have seen some pretty bad jouranls do fine for a long time in new bearings that boost oil film pressure.
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So let me get this straight, you are STARING at the journal, with the bearing removed, and its "too much trouble" to pull open the drawer in the box with the 2-3 outside mic in it, and spin the barrel out, and back in again to check the journal twice?

Bullshit. For lack of 60 seconds worth of verification, you just spent $250 that might be ok, or might be a waste in 7-10 days.

60 seconds with a decent mic is complicated?

Yup, and I've seen some jounals that looked fine go to absolute shit within hours. All because someone didn't have the mic, and/or 60 seconds.
Your mechanical expertise is lacking.
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Assume this is the gas V8?
If you have a knocking from the engine, it could be a rod, but also could be wristpin related, or piston slap. You'll need to diagnose the actual problem first. However, if its rod bearing related, simply putting in another set of bearings isn't the best idea until checking to see:
1) what caused the problem, (lack of oiling due to clogged passageway?) 2) if the crank journal meets acceptable specs (isn't out of round or worn down) 3) that the rod meets specs (isn't out of round, bolts intact) 4) no other problems due to metal floating in the oil. 5) oil pump is performing to spec
Given the possibilities, it may be quicker and easier (once a definite diagnosis is made) to go with a short block.
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"Max Dodge" wrote:

Not likely a wrist pin or piston slap will last more than a few seconds because it take a while for the piston to heat up and swell.
Sounds like rods but mains may be worn too because rods get oil via main journals thru cross drilling and whne mains get worn, the rods get less oil pressure and more wear. You can replace the mains and rods in the truck as long as you can get the crankcase pan off of the engine and I would not replace rods without the mains either because the problem may have started there.
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Unless of course the piston is worn enough. But that never happens, right?

While true, mains rarely make noise when worn.

Of course, if the bearings are worn, and a proper hydrodynamic wedge was not formed, the OP is back to where Tbone put him in taking the engine out.
Bottom line, this is better done outside the confines of the engine compartment, no matter what the problem turns out to be.
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Thanks for all the suggestions. Now any recommendations on where to look for a good quality short/long block? Or companies to stay away from?
Thanks again.
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Thanks for all the suggestions. Now any recommendations on where to look for a good quality short/long block? Or companies to stay away from?
Thanks again.
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