96 Knocking. Rod, rod bearing or piston???

[swiesner]

My 96 blazer 4X4 with 262/4.4L has 77,000 miles on it and starting knocking really bad today. Oil pressure good. I had intake manifold gasket replaced about 2 months ago because it was leaking anitfreeze(Dexcool) Been running fine until today. I took it to shop but mechanic was out. Service guy said it sounded like a bad rod or rod bearing. Definately coming from inside the engine. (not a rocker arm or valve) My question is,,,,if it is a rod bearing, can that be fixed/replaced by simply removing the oil pan and working on rod bearing on the crank from under side of engine? If it's a bad rod, can that work be done too by removing the oil pan or does the whole engine need to be pulled out? They can't get to my car to check it out for a couple of days. If the news is bad, which it probably will be, and they need to pull the engine and go in and replace rod bearing, rod and whatever else, am I better off (cost wise) to just buy a rebuilt engine, have them fix the engine that is in it or buy a used but not rebuilt engine??

[Brian R.]

Welcome to the AF!

Rod bearings can be replaced from underneath as you suggested. If you run the engine with a bad bearing, you are probably running with low oil pressure and will quickly add to your repair bill.

If the rod is trashed because of a cap coming loose or something of that nature, then you must pull the head and bring the piston/rod pair out from the top to replace the rod. The engine does not need to be removed, only the head and oil pan have to come off.

Many times, there is additional damage done and there is more than just a bad rod. In that case, you have to take it on a case by case basis. If the crank has to be removed or replaced because of damage done by a bad rod cap, then that is the point at which a rebuilt engine becomes cost-effective.

If the only thing wrong is a rod, I would think it would be cost-effective to simply replace the rod unless you suspect there are other things wrong with the engine that will cost you money soon.

Others may have more informed opinions.

[Jeremy Fitch]

I just went through the same thing with my 96. My intake blew about 6 months ago and then last month it started knocking really bad, I never lost oil pressure either. Mine turned out to be a main bearing and a rod bearing, I also needed a new crank. I ended up having the entire engine rebuilt, including all machine work, new piston, rings, oil pump, and timing chain, all bearings and gaskets. I had it done at a shop that does just engine rebuilding and it cost me 1908.00 including tax. The problem with the bearings going is that usually when one goes it is best to replace all the bearings because of all the metal shavings that goes into the oil. I can honestly say though that after I got mine back it runs better than it ever has and is so smooth and quiet now. But honestly no one is going to be able to tell what is wrong without pulling the engine and having a look at it.


Also if you do decide to go with a reman engine check out http://www.citymotorsupply.com , they have some of the best prices that I found along with a good warrenty.

[herkyhawki]

Pull the engine.

[Rick Norwood]

I would not recommend replacing the bad rod bearing only from underneath by pulling the pan. There is a good chance that there is damage to the crank, as well as to other rod and main bearings. Jeremy is right about the contaminated oil.

Your garage should be able to offer you options like buying a new Long Block, or a used engine, or just rebuilding your existing engine. But you'll be better off in the long run letting them pull the engine and doing a complete job as opposed to trying to peace-meal a quick repair.