1999 4.7L Engine (Crankshaft/Rod Bearings) Replacement - North American Grand Cherokee Association
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Old 09-16-2008, 11:03 AM   #1
tedallen
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Default 1999 4.7L Engine (Crankshaft/Rod Bearings) Replacement

My son drove his 4.7L GC with a coolant leak and I believe it overheated to the point of damaging one or more rod bearings and/or the crankshaft. When I got to the vehicle there was still coolant in the reservoir, but after allowing it to cool down, the level was extremely low in the radiator and the coolant in the reservoir was not drawn back into the system.

After topping off the radiator, I attempted to start the vehicle and it shook horribly once it started and sounded to me as if something in the bottom end of the engine was at fault.

What I am wondering is if it is possible and reasonable to attempt to replace the crankshaft and rod bearings from underneath without pulling the engine?

I don't have the faciliities to pull the engine, but I could get the vehicle elevated enough to drop the components necessary to access the crankshaft if this is an option.

I noticed that Autozone lists a Hi Tech Cranshaft Kit (Remanufactured) which contains the crankshaft, thrust washers, and bearings for $396.99 (excluding core charge).

A rebuilt 4.7L engine ranges anywhere from $2300 to $4000 based on what I have found and finding a used one at a salvage yard is proving quite difficult and still runs $1500 or more. With $900 - $1500 labor to replace the engine, I would end up with the entire value of the vehicle practically in the repair.

If anyone has had a similar situation and had experience replacing these components w/o pulling the engine, I would appreciate any input and guidance.
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Old 09-16-2008, 03:32 PM   #2
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I haven't done this in a 4.7, but it can be done. You should be aware also that other top end parts (like camshaft bearings) could have been damaged if the crank was hot enough to be damaged.

You should be able to just drain the oil, pull the pan, remove the bearing caps, remove the rod caps, remove the crank, and replace... while you are inspecting the crank and bearings, look at the cylinder walls with a flashlight. You can push the piston up in. I place rubber hose ends on the rod threads when doing this so I don't scratch cylinder walls.

When doing this, it is VERY IMPORTANT to put all of your bearing caps in the same orientation (location and facing the exact same way) as they were originally. You must also torque the rod and crank caps on to spec. I would hate for you to do all that work and not fix the entire problem. The engine needs closer inspection (top and bottom) before making a decision on what to do next. Pull the coil tops and remove the valve covers to inspect the cams.
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Old 09-18-2008, 07:03 PM   #3
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Default 4.7

Just to add my 2 cents.If you spun a rod bearing that rod should be replaced as you won't get the proper bearing crush when tightening it. The tip about the cam journals in the head is something you need to watch.Once the journals are scored bad the head is wasted. Very expensive to have the journals welded and align bored.
Is the oil a milky gray?
As Iroc said there needs to be a closer inspection to determine the failure and then go from there.
You will still need to pull the engine or slide the tranny back to get torque converter pilot out of the crank IMHO. Oil pump is driven off the front of the crank too.
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Old 09-18-2008, 07:12 PM   #4
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The 4.7 has a main bearing bed plate, so may be more involved than just pulling the oil pan to remove the crank.
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Old 09-18-2008, 10:01 PM   #5
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Good input, I haven't done this on the 4.7 before. Any more details...?
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Old 09-19-2008, 09:51 AM   #6
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You can download a free service manual for your jeep grand cherokee from the internet. This takes about 10 minutes if you have a high speed connection and is in pdf format. Search 1999 jeep grand cherokee service manual download, as I don't have the exact int. address.The manual I downloaded looks like it is the real deal.
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Old 09-19-2008, 12:08 PM   #7
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Oops forgot about the bedplate.
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Old 09-19-2008, 03:51 PM   #8
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Spooky, you know to much to only have 4 posts...where have you been, lurking in the shadows? Great to have someone aboard with more info.
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Old 07-27-2012, 11:44 AM   #9
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Smile 4.7L PowerTech Crank Replacement

In spite of what you may read elsewhere, the crank can be replaced without pulling the engine. Usually the culprit is the number 8 rod which is furthest from the oil pump. The bed plate can be removed from below. Engine mounts are bolted to both the bed plate and the engine block. Remove the two lower bolts that connect to the bed plate and wedge the motor mount outward to clear the bed plate. You will need to remove the cam chains before the crank can be removed. The silly Germans forgot to put wrench flats on the overhead camshafts, so removing the chains is cumbersome. Replacing the chains is even more cumbersome, and you will have to carefully rotate the engine a few degrees to get the right side chain sprocket back on.
Once the chains are removed, put long bolts on the tranny and pull it back a couple of inches. Unbolt the bed plate, but leave a couple bedplate bolts on and loose. Pop the bed plate loose by prying in the manual specified locations only. Once the bed plate is loose, just remove the loose bolts and the bed plate will come right out from under the car. the eight rods will hold the crank in position. Support the crank with luggage straps at the front and rear. Remove the rod caps, carefully keeping them in the proper order when stored. Lower the crank by loosening the luggage straps. Unless you pulled the tranny way way back, you will have to remove the flywheel before you can get the crankshaft assembly completely out.
Now the real issue. Usually the number 8 rod is the culprit. If the bearing has spun, you will have to replace that rod because it too will have been worn. Super serendipity, the number 8 piston is the only one of the bunch that can be removed from the bottom ! Use a razor blade to scrape carbon deposits from the bottom area of the cylinder wall where rings did not keep it clean. It should then come straight out. When the piston is out, inspect the top of the piston and peek up the cylinder to inspect the valves for possible damaging contact when the rod was loose.
Press your new rod onto the original piston and ring assembly, paying close attention to the front/rear orientation of piston and rod. You can put the piston/rod assembly back in from the bottom using just your fingers to compress the individual piston rings, since there is a slight taper at the bottom of the cylinder (not so if putting it in from the top, where there is no taper).
Push all the rods up high, then get your new crank nearly located. Attach the flywheel and torque the bolts. Then use your luggage straps to carefully pull the crank up into position. Be very careful not to ding the crank on any of the rods hanging down. Once the crank is in position, reach up and pull the rods down onto/near the crank. Place the new bearings into the rods and attach the rod caps in order. Torque later

Now, put the bed plate, main bearings, and thrust bearings back in place using the recommended anaerobic sealer. Torque the bed plate bolts. Now, the rod bolts are TTY (torque to yield) which the manual insists must be replaced ($8+ each) after each use. I just re-use them and torque to 55 ft-lbs (just at yield), and so far no problems. Once all the rods are all torqued, you just need to replace the pan gasket(quite re-usable), oil pump, pan, support bracket, tranny, timing chains, front plate, etc, and you are done. A big job, but actually less than an engine swap, and only about $350.
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Old 07-27-2012, 06:12 PM   #10
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Rebuilt the 4.7 in my 2000 a couple of years ago. #7 and #8 rod bearing were bad, also broke the ring landing on 8 and scored the cylinder. I can tell you from my experience, There's no way I was going to do this work with the engine in the vehicle. I guess if you just want to slap a crank in it and call it good you may save some time and money. Top to bottom rebuild on my 4.7 with machining, cost me about the same as a used 4.7 - $2600 - but it's essentially new. If you're having reservations about pulling the motor, I'd re-think about replacing he crank - it's no joy with this engine.

Just my 2c.
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