The engine is blown: bebuild or replace.
Anyone offering to "repair" your crankshaft is a scammer. Do not ever deal with them again. The only situation where a crankshaft can be repaired (in situ especially) is if there is a timing sensor on the end of the crank that has become dislodged, damaged, misaligned or otherwise prevents the engine computer from being able to pick up appropriate information. Bearings should not be replaced unless rebuilding the entire engine and a twisted or otherwise damaged crankshaft is JUNK and should be replaced. Therefore, repairing the crank is actually replacing it which REQUIRES an engine rebuild. The journal bearings on the crank need to be properly matched and possibly machined (the crank) to fit correctly without knocking and leading to a speedy demise of your newly built powerplant. Buy a new crankshaft, a rebuild kit and a video.You can rebuild an engine with the right tools (most of which you can borrow or rent) and some friends to help get the engine in and out. This is the most difficult part and with a little attention and patience, (and the friends) it can be done in a weekend not including any machining (which is generally not necessary when REPLACING the parts that are damaged.) Just replacing the engine is a job anyone can do with a hoist and ratchets, screwdrivers and friends.
Additionally, if you had an early vintage, extremely rare dusenberg or flathead V8 that was IRREPLACEABLE you might consider having a talented machine shop try to fix it, but on a '90s Nissan it simply is not worth it.
The simple and really only answer I can give you is to find the leak and repair it.
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1997 Nissan Altima with the Automatic Transmission - has 4 lug nuts per wheel
It is 1.0 mm to 1.1 mm or 0.039" to 0.043" You can check in the manual for Nissan 1997 Altima
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On a 1997 Nissan Altima the water pump should be mounted on the front of the engine. It is right at the thermostat housing.
In a 1997 Nissan Altima, the transmission dipstick is located next to the motor. The dipstick has a red handle to pull out.
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Under hood, center, front engine area, mounted on front lower driver side of engine
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on the oil pan
you go to a Machanic.
With reservoir 8-1/4 qt (US) == == Again Refer to to the Nissan Altima 1997 Manual
Under the passengers seat.
2 front and rear
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The EGR valve in a 1997 Nissan Altima is located at the top of the motor in a position near the firewall. The EGR valve is held in place by a vacuum line and 2 nuts.