'84 720 4WD pre-buy checks

[ttyR2]

I'm looking at a 1984 (12/84) 720 4WD standard cab MT that has been parked for a long time. Tags expired back in 2010. Jumped off my 4Runner, it turns over ok and doesn't emit any bad sounds (thrown rod, etc). When I ran a compression test, the front two cylinders both blew about 10PSI or so (no joke), and the backs both blew 150PSI or so. I had all four exhaust plugs out while cranking. When I tested the front cylinder, I heard air being forcibly pushed out of what I believe is the second plug hole. This all tells me that it has a blown head gasket but could just a head gasket cause *that* low of a compression test? Likewise, the radiator is empty. The dipstick didn't show anything really bad, but I know oil floats on water so there could be a bunch of water in the bottom of the pan.

 

I had a 1985.5 720 2WD back in the early 90's but no Nissan's since.

 

The guy is asking $500 and won't budge. Body appears to be in really good shape. I'm in NE Oregon and it's pretty dry here, so things don't rot away as fast as other places.

 

Any reason *not* to jump on this deal? Unfortunately I can't verify the drivetrain obviously.

 

I have a well equipped machine shop at home so fixing most anything won't be an issue, but I'm not familiar with these trucks yet.

[datzenmike]

Gasket could be blown between 1 and 2 and will push the compression back and forth into the empty cylinder. Between cylinders doesn't necessarily mean through a water hole. Water can't get into the oil except past the rings as steam and if run that way for any time the oil would be milky. Left ten years wet the cylinders will rust. If it turned over alright it's probably ok. You could loosen the oil drain bung and see if water drips out.

 

$500 is not a bad price plus a gasket and time to change it out. Would you be doing this yourself? The last one I did came to $20 for the gasket. This assumes there isn't other reasons the owner abandoned it. Changing the HG is just wrench turning, nothing complicated, however you must be aware that the timing chain has a tensioner than MUST be secured from falling out before you start to remove the head. Failure to secure it will add several more hours of work and some more gaskets to retrieve it and put it back in.

 

As to the cooling, electrical, suspension and braking systems and the drive train.. they are all an unknown. Brakes left for 10 years isn't good. I guess it comes down to risk management.

[Stoffregen Motorsports]

$500 for a mostly complete vehicle is a good price. If it has been sititng more than ten years, expect to replace every single rubber part in the fuel system, the brake system and the cooling system. This includes water pump, fuel pump, brake and clutch cylinders, etc.

 

All in, with all new hoses and cleaned out hard lines, flushed block and radiator, you'll probably have $1000 in parts to get it back on the road.

 

That is assuming things like the trans, diffs and motor are usable.

[NC85ST]

If you want a project, that doesn’t sound like a bad one.

[ttyR2]

The mechanical work isn't an issue, just making sure I know what I'm looking at for a project. I'll be doing all the work myself. Unbelievably, the brakes seem good as does the clutch system, but yeah...I'm expecting rotten hoses. I pulled the valve cover while checking the engine out and spun it over. All the valves moved as they should, and there was a touch of valve lash on all rocker arms when I checked, so none of the valves are being held open.

 

I like keeping things OEM (OEM is more rare, most vintage vehicles are cut up and modified these days), but would be looking at a Weber 32/36 retro just for driveability. I remember the stock carb on my 85 720 years ago was a real pain.

 

Hope to pick it up this week. Thanks for the input guys! I'll have other questions, I'm sure. I do have the book How to Keep Your Nissan/Datsun alive. I knew I hung onto that book all these years for a reason.

Edited December 10, 2023 by ttyR2

[datzenmike]

Have a look at the CV boots on the front axles. They are NLA.

[ttyR2]

I see comments about periodically re-torquing the head bolts on the Z24 engine. Would installing an ARP stud kit with nuts fix that permanently? Is it because of weak stock fasteners, or threads in the block? I noticed two of the exhaust manifold bolts on the rear manifold flange are missing.

 

Headgaskets...which is best? OEM or Felpro?

Edited December 10, 2023 by ttyR2

[Thomas Perkins]

Also check and make sure the cat is not broken apart and clogging the air flow.Delete it if you can.Felpro is good.It has been on mine since 2009.I have never re torqued my bolts.Got 104,000 miles on them Felpros.That is when I had the new Jasper engine installed.Something caused your head gasket to blow.Check your head for warpness.Also adjust the valves.Jack sent my head to the machine shop.I can't do it.Pressure tested it too.Yes get a Weber with a idle cut off solenoid.I use all my vacuum  lines and had a new egr valve put on.Had this zRedline Weber since 2016.I had A North American Weber on it before.

Edited December 10, 2023 by Thomas Perkins

[datzenmike]

2 hours ago, ttyR2 said:

I see comments about periodically re-torquing the head bolts on the Z24 engine. Would installing an ARP stud kit with nuts fix that permanently? Is it because of weak stock fasteners, or threads in the block? I noticed two of the exhaust manifold bolts on the rear manifold flange are missing.

 

Headgaskets...which is best? OEM or Felpro?

 

The blown head gasket seems to be solely on the Z24 and not the Z22/20. There is a difference between the Z24 an the Z22/20 and that is that the Z24 block is taller by 2cm or 3/4" and the height difference is at the top of the block. The Z22/20 bolts are the same part number. The Z24 are different number, but not clear what the difference is. The FSM says to tighten in a pattern to 22 ft lbs, then again to 58 ft lbs. Then loosen fully and repeat the two tightening sequences and when done tighten them all 90⁰ more. This sounds more like a TTY (torque to yield) to me. Anyone know what a Z22 FSM says about tightening the head bolts?  

 

What happens is the clamping force lessens over 100k miles and the gasket de-laminates.  The preventative seems to be to tighten the bolts every tune up or once a year to keep the gasket tightly compressed.  

 

No guarantee that the ARP will cure this. What are they about $100? and in 100k they blow anyway, or they may not, but it's certainly easy enough and cheap enough to just re-torque them.  

 

Ive used FelPro before. The Z24 only has 8.2 compression.

[ttyR2]

No smog checks in my area yet...so yeah. any emissions gear may come up...err...missing.

 

I'll post more pix when I pick the truck up. Paint is waaaaaay down the road, but saw pix of the metallic bronze/copper paint with red/orange 4X4 decals...think that's what I'll go with. But I'm getting waaaaaay ahead of myself.

[620slodat]

In Oregon the smog check is only the metro Portland area and Medford. Medford is probably because that area is bad for smog because all the smudge pots in the pear orchards around there. I lived in Grants Pass in the early 70's and that was the smog problem then.

 

Don 

[None_zero]

I'd just like to add here that oil strictly speaking does not float on water since it's a denser heavier liquid than water in reality water floats on oil. The phenomenon of oil floating on water occurs when there is more water than the weight of the oil can displace. I may be wrong about this because I'm going off half remembered tests and then filling in the rest of the science with things I think I know about stuff, however I wouldn't bet on me being wrong. I thought I was wrong once... but I was mistaken.

Edited December 14, 2023 by None_zero

[datzenmike]

Water is one gram per cc. Oil is .700-.900 gram per cc so it will float on water. Ive drained oil pans on engines left outside for the winter and..... water comes out first.

[None_zero]

Well I did say I could be wrong about this however I have seen water float on oil so maybe I just it backwards and water needs to be in the minority to swap positions 

[datzenmike]

Specific gravity is what determines if one liquid will float on another. Water is 1 gram per cubic centimeter. (it's how a gram is defined) Petroleum products are less than 1gr/cc so they float.

 

 

[None_zero]

I've seen water sit on top of oil with my own eyes 

[datzenmike]

I can't know what you saw but ask 10 people if you pour oil on water what happens and they'll all say the oil floats.

[Thomas Perkins]

Oil floats on top of water due to differences in density. Density is the measure of mass per unit volume. Oil is less dense than water, so it floats. This is because the force of gravity pulling down on the oil is less than the force of gravity pulling down on the water. The principle at work here is known as buoyancy. Objects with greater density than the fluid they are in will sink, while those with lower densityYes,oil will float.