This is a rough draft, I made it to help folks find the right car, hope it helps
You can download software I made, for 97/98 240sx, to generate an estimate of it's value:
http://www.megafileupload.com/91o0/240sxestimation.zip
It was written from the perspective of a poor college student who desires a reliable daily driver that will maintain its value in the long-term, and also provide a solid foundation for a future project
Unofficial 240sx diagnosis for purchase flowchart
For all Original Parts
240sx Chassis, generally 1997-1998 USA
Body:
-Garage kept status (Good dashboard, unfaded interior, should also have original paint and no unacceptable rust)
Original paint
-Car sat in the sun, paint is original but faded (still a very good thing, because wherever you see original paint, you can bet there has been no body work and thus no accidents.)
-Car sat in the sun, but was repainted (paint job should be a few years old and holding up well. Beware of anything freshly painted)
-Paint job is a few years old but does not seem to be holding up well. Also, paint job was done around the same time the car switched owners. (bad sign. Car might have been wrecked, fixed, painted, sold.
Original engine
-Are you sure ?
All vin tags in place
Missing vintags in order of importance: (Hood, front support, trunk , fenders, doors, bumpers)
Leaking anything besides oil (Transmission, differential; power steering does not count they all should leaking PS or you will be suspicious)
-Frame rails are good (you can live with it )
-Frame rails are excellent (better than you would hope for or expect DESIRED)
-Frame rails are mint (nearly perfect, no malicious jacking no dents RARE)
Doesn’t leak water into the sides of the trunk (good sign it was never hit in the rear, lights not removed)
-Basically Accident free
-Accident free
Engine and underhood:
All original clips and wiring no modifications
missing some clips that hold down the air intake tube AND more than 100,000 miles
Oil looks clean after an oil change.
-Under valvecover fairly clean (oil is not super bright and clear but there is no oil sludge buildup visible)
-Under valvecover extra clean (no sludge, camshafts clean, no black oil sitting on top of the cam caps)
-No oil leaks (a little from the valvecover is ok)
-No obvious obnoxious silicone protruding from anything (no repairs, original parts)
Original bumper hardware, nothing missing
*Original headlight hardware, original headlight “cut-off” and proper alignment of lights
Engine has:
Under 150,000 miles (2-3 more years of service)
Under 120,000 miles (4-5 more years of service)
Under 75,000 miles (6-7 more years)
Under 50,000 miles (7+ years of service left)
An OEM KA24DE engine should go at least 150,000 miles or more (sometimes 180,000+) without needing any major repair. You should expect to replace it around 180,000-220,000 miles, but some can go even farther.
Minor repairs include: valvecover gasket, water pump/thermo, radiator & hoses, vacuum lines, clutch fan, a/c gas refill)
Chassis has:
200,000-220,000 miles (look for replaced suspension components, check the inner tie rods and shocks)
150,000-200,000 miles (shocks, also check the differential if there is oil in it, and what does it look like)
100,000-150,000 miles: (TC-rods are bad between 60k-120k)
Under 100,000 miles: mostly original suspension parts. Tie rod ends could be halfway shot by 40K.
Under 50,000 miles: very unlikely. Rare.
For all chassis, you would like the inner tie rods to be original and unbent.
Interior
Original carpet is nearly mint (drivers side is almost like new, RARE)
Original carpet in excellent condition (drivers side especially is in good condition with no holes)
Original carpet in good condition (drivers side has a tear from use but overall carpet is nice
Original floormats clean (somewhat rare)
Original uncracked dash (valuable and rare)
Uncracked but somebody changed the dash (original one may have sat in the sun, or the airbag went off)
All visible electronic components (such as relays and wiring under the dash clearly visible) is OEM/clean
Dash is cracked from the sun or any other reason
Cluster is original and works (carfax verified)
Door locks work
Windows work
Windows seal up nearly completely (drive at 80mph and check for rustling) rare
What generally doesn’t matter:
Interior: Switches, buttons, plastic panels, center console, radio, plastic trim, door panels, speakers, seats, carpet (most of these things are available and affordable)
Exterior: everything matters
Original “Mud Flaps” (flimsy plastic panels around the tires) are intact and all plastic clips are in place (describe) rare
Drivetrain inspection points assuming original parts, check for maintenance of:
steering rack condition (describe)
power steering lines (describe)
sway bar, control arms, all end link rubbers, check for accident / curb contact (describe)
dirt and filth under the hood? Condition of chassis underhood paint including hood and insulation? (describe)
signs of pressure washing or strong solvent use under the hood to remove filth? (describe)
State of “everything else”:
Items such as driveshaft, engine mounts, most brackets, should hold up until you would normally replace them anyways such as during an engine swap. Most OEM 240sx components last as long as the engine. The catalytic converter may be ruined inside due to age and often needs to be replaced.
Rust anywhere? Describe
What often rusts that is not a big deal: exhaust parts and brackets close to the heat of the exhaust. Original Brake master cylinder often rusts. Subframe may develop a very slight surface rust that should appear minimal and slight, especially around the output shafts of the differential. Many bolts and nuts under the hood will develop a slight rust as well. Sunroofs in many 240sx have rust also.
You should restore a protective coat to anything that appears to be actively rusting away. WD-40 is a temporary fix but a permanent solution should be found. If it is a bolt, replace the bolt. If it is a washer or bracket, replace that. The subframe and differential can be changed easily as well.
Trunk area:
Check the corners of the trunk for water. Check under the spare tire for water.
Water In the trunk is often due to leaking rear lights, which often indicates that they have been removed at some point. Sometimes for paint, but other times for accident repair.
Look carefully at the seam glues, they are the best indicator for repairs. Clean factory glues all the way around is desirable.
Look at the insides of the body panels (quarter panels) for accidents and body work. A quarter panel is very difficult to replace and as such many accidents require body work in that area as opposed to replacement of whole quarter panels. Often the factory will make small seemingly pointless spot welds on the inside near the center, this is normal. (include picture)
Check the rear light wiring and make sure all of the clips and loom is intact. The 240sx rear light wiring should not ever be removed and it should survive just fine for 20+ years. Any signs that someone has tampered with the wiring indicate that there was a reason to remove or re-wire the rear lights which may have to do with an accident. Painting the vehicle should not require removal of that wiring.
Remember, we can change the seats, dash(debatable), carpet, door panels, plastic trim, transmission, engine, engine wiring harness, differential, rear subframe, outer tie rods, steering rack bushings, Tension control rods, hubs, windshield, hood, trunk, spoiler, exhaust, most plastic clips, (add more) EASILY.
What we cannot change easily or cheaply (would not want to have to change):
Inner tie rods (preferable), Lower Control arms, headlights, body panels, core support, steering rack (debatable), frame rails, any under car damage and dents, firewall, under dash components, mounting supports/locations for headlights, original bumpers and bumper hardware (debatable), steering shaft, A/C related hardware (besides lines off the compressor), rust or accident damage,
If any of that is damaged or ruined chances are the car is permanently ruined (with respect to original-ness , daily driver status, or high dollar minimal modification builds *clarify). Once its been wrecked or hit, yes bodywork can be done, but rarely will anything line up the way it used to, and even if it does, there is no way to truly hide body work from a professional eye unless its all done exactly like the factory does it- Which is possible, but very expensive and rare, which is not likely for a 240sx as the cost of a repair like that would often be more than the car is worth.
4-lug / Base (will be lighter and faster in the long run) personal preference
5-lug / SE (heavier, spoiler, options) personal preference
How to approach the 5-lug conversion on a 4-lug 240sx:
Many people are selling “5-lug conversions” that cost around $200-$500, but NOT all conversions are equal. You do not want the spindle/bearing from 240sx here in the USA for your conversion due to mileage concerns and brake size. The ideal 5-lug for the front comes from a Japanese S14/S15 Silvia because it will often have low miles and large brakes and the cost is similar to the high mileage tiny brake conversions you find here in the USA.
As to the rear, when the time comes to upgrade the engine, a great option is use an S15 sr20det and get the complete subframe from the Japanese S15 silvia to get the 5-lug, low mileage wheel bearings/axles/control arms, and low ratio differential for the six speed transmission. You also get fresh subframe bushings usually.
The idea is to use low mileage OEM components to push the 240sx chassis to 350,000+ miles reliably.
Keep in mind:
Even if the car is already 5-lug, you will usually still desire to change the spindles/brakes/subframe anyways due to mileage related wear and tear.
Unofficial 240sx diagnosis for purchase flowchart
For swaps, 240sx Chassis
Attention to details during the swap:
Wiring first. It was done somewhere, look at it. Can you find it? Is there a lump in the harness at one of the ends? Heatshrink was used, right? Does it look professional?
Intercooler plumbing. Was it custom or a kit, if so what kit? What brand is the intercooler?
Most kits do not fit perfect, but some are surprising. Any custom work should be obvious and adds value if it is done right. A name brand intercooler adds value as well.
“The Hole for the cold pipe” where is it? How was it cut? Is it protected with rubber and against rust? Is it symmetrical?
Is the battery still in the stock location? Battery relocations are usually not a good sign, completely un-necessary and often done poorly. If it has been relocated, can it be moved back?
Are any ugly holes cut? Look carefully at the firewall, and in the trunk area for “custom” holes.
Is the factory wiring harness grommet intact and complete? If anything was run through the firewall, it should be done in a manner that allows for an easy 100% reversible removal.
Check the air filter. Is it name brand? Is there is a clean mounting bracket? Is the filter being kept in a proper position by something (even napkins work and absorb vibration- the point is does the air filter flop around and vibrate on the chassis or is it stationary and secure and straight somewhere)
You want the original clutch fan, you want it clean and there is no oil or grease on the fan or the front of the engine. You want a clean fan shroud with a small space cut out for the a/c dryer. Check for relocated dryers and if so, the quality of the relocation (how are the lines bent?)
If the radiator is an aluminum unit, name brands add value. OEM Is desirable but not necessary. Electric fans are ok if they are controlled by a non-invasive high quality controller with redundant fusing and multiple relays (one for each fan).
check the engine for knock off parts. Knock off bypass valve, oil pan, intake manifold, remove value from the engine. OEM parts are preferable for stock engines. OEM T-28 turbochargers are desirable and add value if the compressor wheel appears to be in great condition (looks great and little shaft play)
Original T-25 turbochargers in great condition are rare, and should be left at 7psi to preserve their life.
Is the bypass recirculated? If not, an HKS ssqv authentic bypass should be used on the hot-pipe of most stock engines to provide adjustment-free operation that is
acceptable but not optimal. An optimal bypass will be open during idle, recirculated well after the maf, allowing the compressor wheel to freely spin.
Check the oil color, look under the valve cover for black oil sitting on the cam caps. Check the cam lobes for scratches. Watch that oil comes out of every orifice that it should. Low mileage sr20det engines have very clean oil, even after 2000-3000 miles of operation. Every 25,000 miles a little black oil will accumulate on the camshaft caps and could be cleaned when you change the valvecover gasket to reset the “service interval”.
Look for oil leaking at the front main, and for oil dripping out of the transmission bellhousing. While the front main is fairly easy to change if you have experience and tools, the rear main is not as easy.
Is the ECU properly mounted? A properly mounted ECU is rare, and a sign that whoever did the swap is probably taking the time to do it right (pride in ownership)
Is the Igniter properly mounted (if applicable)? Same thing here, it isn’t necessary but it indicates that somebody is paying more attention to detail and adds potential value to the entire swap.
Is the clutch damper intact? And if not, how was it removed? Often if it is removed, somebody will bend the line in an ugly fashion, this is undesirable and removes value. You would like to see the damper installed and un-touched, because it gives you the clean factory lines to work with, and the option to remove it yourself in a clean fashion at a later date.
Is the transmission to exhaust hanger installed? This critical piece is absolutely necessary; all four 12mm bolts should be installed with the tension pulled away from the rear (keeping the turbocharger from any strain due to the exhaust system). Seeing this intact is just like seeing the ECU properly mounted; it means whoever did the swap knew better than to leave it off.
Does the car have Z32 rears? If so, follow the E-brake cable carefully to see how it was run/mounted (is it safe?) You don’t want a car with no e-brake, or half of an e-brake.
Look at the power steering hardlines behind the crossmember to see if they are bent up. When you install an engine into a 240sx it is common for these lines to get bent up. This is another indicator about the quality of the install, and helps to decide if this is the right car or not; If you see a floating ecu, a zip-tied igniter, a flopping around air filter, questionable wiring, bent PS lines, a missing trans-exhaust mount, the swap was done cheaply/poorly and I would walk away.