I got my dream pickup, a 1981 720.

[banzai510(hainz)]

Muffler looks new whats wrong with it.?

[TinKanTosser]

9 hours ago, banzai510(hainz) said:

Muffler looks new whats wrong with it.?

The insides rusted out and the end that connects to the tailpipe slid out. Maybe it doesn't have any miles on it but it did have the engine blow a bunch of water steam into it, then sat for years, then ran again and got soaked, then sat for months. Worst part is it spent all that time with a broken insulator so the muffler bore the whole weight of the tailpipe. I'm currently using an old timing belt and a ziptie as an insulator because I may do something different with the exhaust in the future.

 

I found out my alternator wasn't charging because a couple plugs to the positive on the battery were corroded, cleaned every plug in sight and now it works great. I still cannot for the life of me get the left front turn signal to work, and I don't have time to go through it all, but I'm gonna check current and ground to the turn signal bulb when I can. I figure it can only be a bad socket or partially failed connection in the hazard switch. The hazards used to work and now they don't.

 

Exhaust still blows white smoke on and off, coolant level does drop but I do have a leaking old intake hose that I literally can't replace because no one sells it. It's possible the coolant is leaking out and all the smoke is from crud in the gas tank, maybe a sizable layer of water considering the fuel cap seal was broken all that time.

[banzai510(hainz)]

14 hours ago, TinKanTosser said:

I figure it can only be a bad socket

yeah clean them the contacks.

 

 

I got a Dynomax super turbo(small case size has the U shaped deflectors) for my 521 like 25 years ago and still going fine. Its a Little loud in the morning. I wish I got a more quiet muffler now that Im older.

Edited April 25 by banzai510(hainz)

[TinKanTosser]

Update: still no left front turn signal, now with low oil pressure!!

I started noticing the idiot light coming on when I'd corner hard right, which makes sense because the sender is on the right, so oil is moving away from the sender, I guess that makes sense. Then when starting up in the morning the light flickered and then stayed on one day. I'd seen that the oil senders on these motors are not very reliable and the pumps are usually robust, but I went ahead and ordered a new sender and a Hitachi pump for a KA24 as an upgrade. Today I changed just the sender intending for the light to stop coming on so I could just drive it to work for today, but the behavior is the exact same even with the new one. Being 45 years old and not run for the vast majority of that time, maybe it's not surprising the oil pump would go weak. Hoping it's not the pickup stopped up because I don't want to deal with removing the oil pan right now, that's another mini-project, another thing I'm gonna have to de-rust and paint as soon as I take it off the truck, etc etc.

 

I fuelled up this past week and when it reached the top I noticed gas pouring out onto the ground near the top of the tank. Wasted maybe a half a cup of non-ethanol gas, feels like $10 down the drain!! Turned out to be the vent hose that runs alongside the filler neck. Looked very much like a rat chewed into it and decided he didn't want what was in that tank. I'm really grateful and still astonished that the fuel system mostly just works in place without me having to drop the tank and refurb too much, just a few more hoses to change and it will be... passable.

 

My alignment is out and I got some ball joints to put on, but I figure I also need to do the front end bushings at the same time. Huge pain because I don't have any free concrete space right now to jack the truck up on and I never seem to have the tools or strength to remove front end bits properly.

 

My Weber has a manual choke and I've never had it hooked up, I'm planning to drill into the dash on the flat indentation where the dash light dimmer knob goes. The plastic seems sturdy enough; plan is to drill holes to each side of the existing one and relocate the dimmer knob to the right of it, and put the choke cable to the left. Then someday when I do my dash up with real wood trim I'll cut a piece to go in the indentation and cover the hole where the dimmer used to go.

[datzenmike]

Oil pressure sender location has nothing to do with the light coming on on right turns. If light comes on, on right turns, it's just the oil sloshing to the left and uncovering the oil pick up tube. The pump then sucks in air and the pressure drops. This is not normal and most likely cause is low oil level.  

 

Oil light still coming on with new sender could be a bare wire to the sender touching ground on right turns. 

[TinKanTosser]

7 hours ago, datzenmike said:

Oil pressure sender location has nothing to do with the light coming on on right turns. If light comes on, on right turns, it's just the oil sloshing to the left and uncovering the oil pick up tube. The pump then sucks in air and the pressure drops. This is not normal and most likely cause is low oil level.  

 

Oil light still coming on with new sender could be a bare wire to the sender touching ground on right turns. 

Thank you for the tip about the wire, I had already inspected it from the sender to the harness but it turns out it comes out of the harness and into a plug just a few inches away, and in that location the wire had worn through from friction with the battery tray. Even with the bare wire isolated the light still goes on and off, but I'm not completely without oil pressure so I'll let it go for now. It could be worn through somewhere under the dash. I'm planning on putting a mechanical oil gauge in the console where the 4x4 had its gauges.

[TinKanTosser]

I took home a free kitten a couple months ago and today I mounted it on the bonnet. Now I have a Jagsun.

 

My right corner light that doesn't work has bent contacts and just needs them bent back out with a pin for it to grab the bulb properly, it almost makes contact off and on, maybe tomorrow I'll get to that. I painted my 620 bumper with bedliner today and will install it and run a tag light to it tomorrow.

 

The single most annoying thing I'm dealing with now is I bought a new bushing and pin set for my shifter before I had it running and misplaced it in my garage, now I'm ready to install it and can't find it LOL

[TinKanTosser]

Today I installed the new oil pump. Bad news on several points...

 

1. The oil was low. The dipstick reads horribly wrong. With one gallon in the pan, the stick reads over twice as high as the full mark, and when the stick is at the full mark it's low enough for the oil light to come on. I measured what came out of the pan and it was just over 1.5 quarts 😬

 

2. The "white" smoke is oil. I may be colorblind but I have never seen blue smoke. After I drove the truck for long enough and apparently ran the oil low enough, it mostly stopped smoking, which seemed like a good thing. Now with one gallon of oil in the pan it smokes horribly, constantly, just like before.

 

I take it to mean that the previous owner revived it, saw it smoking, thought it was a blown head gasket, changed the head gasket and made it MUCH WORSE, at which point it changed hands to me. Given that the truck is so low-mileage, could a ring just be stuck?

 

It's seeming like I need to find a running Z24 to drop in because I don't have time to do a full bottom end rebuild after how long the head gasket took me.

 

Edit: To be clear, I have another engine with leaky valve seals, and I wanted to avoid dealing with that again at all costs so I had the valve seals changed on my Z22. Given that it smokes as much after that as it had before, this likely has to be ring leakage.

Edited May 7 by TinKanTosser

[NC85ST]

Does it smoke when you’re on the gas or when you let off the gas? When you’re on the gas, rings, off the gas, valves.

[TinKanTosser]

1 hour ago, NC85ST said:

Does it smoke when you’re on the gas or when you let off the gas? When you’re on the gas, rings, off the gas, valves.

On the gas primarily. It will smoke at idle and then die down, and when I rev it up it shoots out another cloud but will also continue for a bit after. Before I plugged my EGR threads in the exhaust it would fill the cabin with smoke from the shifter opening, only when I was accelerating through the gears.

 

Severe oil deposits on the cylinders explain why it's been dieselling when shut off.

 

I dumped in a quart of Marvel Mystery Oil while in town just to see what would happen. Heard diesel and transmission fluid have been used to unstick rings too. My dad suggested pulling the plug wires to one cylinder at a time to see which one it stops smoking on, if it's just one.

 

Anyone with a 720 Z22 dipstick, can you show me where the cap/stopper for the dipstick is supposed to go? Mine slides up and down the stick and someone tried to tape it, but the tape didn't hold and the cap slipped up so the stick went down low in the pan. I've adjusted it down to the part where the slight crook in the handle is, but if anyone can show me where it definitely should be I'll glue it in place so this won't happen again.

[datzenmike]

Severe oil burning is white, you can't see through. It's more evaporated oil from heat, like steam from water. Regular light oil burning is blue. If using that much oil you may have a hole in a piston or broken rings. Do a compression test.  

[TinKanTosser]

Compression is still good, now consistent since I've done the head gasket:

170, 172, 170, 172.

All plugs are damp with oil, some spots have a cracked hazy film:

[datzenmike]

Drive it. They are self cleaning but may foul on the way home. Take for a romp and check them. If dirty at home you may be running slightly rich.

[TinKanTosser]

Good to hear. I haven't had any fouling problems at all, the twin spark helps ensure combustion enough for the plugs to get clean again.

I hate myself for running it so low of oil for a few days. I'm not sure if it's knocking, it is a noisy engine. The compression rings probably aren't as good as the compression test suggests, considering oil in the cylinders brings up compression and I have lots of it. I watched one cylinder hang at 150 psi for a while, until presumably the oil pressure built back up and it jumped to 170. Still 150 all the way across wouldn't be too bad. Just hope I haven't ruined my bearings.

 

My 620 bumper did not fit, the pitch of the railing that bolts to the bumper interferes with the taillight area of my 720. Sadly I'll need to use the punier 720 bumper from my dad's truck.

[TinKanTosser]

My brakes fell apart!!! Previous owner left it without any cotter keys in the pins. I was hearing an occasional loud rattle or knock and didn't know where it was coming from, and my first suspicion was the middle U joint on the driveshaft that has the rubber worn away. Then after the most lovely crunchy metallic noises I've ever heard when driving home one night, the brakes started making rotor wear noises.

 

Got the wheel off today and found the pads down to nothing, and at least one pin missing with no cotter keys at all. Luckily I'd already bought new rotors and pads from RockAuto anticipating this, but I wasn't anticipating it this quick. I'm hoping the parts store will have the pins and other hardware I need to put it back together.

 

I'm also struggling because I need to clean and grease my wheel bearings since I had to take the hub off, and I can't get the inner grease seal off to remove the inner bearing. I also don't have new ones so I'm hoping not to damage it. Parts stores around me have nothing for this truck.

[datzenmike]

Not a good idea to reuse old seals. The inner seal should just pry off with a large screwdriver, bearing just falls out minus the outer race so don't drop this. I used lots of paper towels and scooped the old grease out and replaced it. If the grease is totally contaminated with water, better power wash and thoroughly dry the hub.   

[TinKanTosser]

Took this long to get my new brake pins and wheel seals, got it all done and grease packed nicely. The new Bosch ceramic pads are smooth and quiet.

 

When I bought brake hoses I had to get Sunsong brand for the two "inner" hoses under the hood (which serve no sensible purpose), I got Raybestos for the driver's side caliper hose, and had to get Dorman for the passenger side, which is a weird and rare part because it has the proportioning block built onto it. The new Raybestos hose turned out to be stamped Sunsong when I opened it up. The Dorman hose turned out to be stamped June 1992. I get anxious seeing how rare parts are now for this truck. When the old stock is depleted I'll have to be retrofitting brakes from later Nissans, but even D21's are old now... Makes me glad I got a Triumph TR7, unlimited parts supply for that!

 

Next up is a valve adjustment, they're loud. Still burning oil too, but I made a long trip out to Sam's Club to buy a couple cases of Rotella diesel oil today and it was a pleasant drive. I'm not losing a completely unsustainable amount of oil so I'll just keep driving it.

 

Also, checked my gas mileage for the first time today, which is annoying when you don't have a trip odometer, but I got 25MPG. But non-ethanol gas costs $4.79 now so I'm not exactly winning.

Edited May 21 by TinKanTosser

[TinKanTosser]

I believe my oil burning issue is not the rings nor valves, but the PCV. The biggest concentration of smoke comes when I've idled for a while and then punch it, like the vacuum of the closed throttle plate is pulling a bunch of oil up into the suction hose, then revving it gives it positive crankcase pressure that pushes the oil into the manifold.

 

I drove on the interstate at a steady 80 MPH for a total of an hour (the faster this thing goes, the smoother it gets!!) and burned less than 1/4th of a quart, no smoke visible until I stop and then rev up. That consumption doubles or triples in city driving with stopping and going, and the smoke is frequent and pronounced.

 

This makes sense considering the PCV suction hose connects to the lower crankcase, near the oil pan on this old Z motor. A lot more oil seems to make its way up the hose. But the only thing NOT original about my PCV setup is that the passive hose connected to the valve cover does not have the filter that would go in the air cleaner, since I'm using a Weber air cleaner. When I put my finger over this upper hose at idle I feel a steady suck then blow each stroke, with more suction than blowing. Perhaps that filter is needed to restrict the upper hose, and prevent the lower crankcase -> manifold hose from pulling so much air in.

 

With the upper hose restricted somewhat as it was from the factory, the lower hose would hit a limit in the volume of air it could pull through the crankcase at idle. Just my theory. In the attached picture, the #2 filter is the one I'm talking about. It's like a piece of cotton or steel wool jammed into a pocket inside the housing. Maybe I could achieve something similar by stretching a thick piece of cloth over the hose nipple on my Weber air cleaner.

[NC85ST]

Sounds like valves. Let it engine brake down a long hill, you may see some smoke, but then punch it at the bottom and see smoke, valves. Vacuum pulls the oil down by the valve seals and then when you punch it, you see it come out the tailpipe.

[datzenmike]

There is a baffle in the block to prevent oil droplets getting up the PCV hose. If the engine has extreme blow by, that volume of air will push oil spray out the valve cover breather and into the carburetor. Air filter and the top of the carburetor inside will be wet with oil. 

 

Do a compression test on a hot engine and record the readings. Put a couple of tablespoons of engine oil in each cylinder one at a time and retest and record the results. If the compression jumped up then the rings are worn.

[banzai510(hainz)]

at idle if alot of stinky oily smoke come out(ezer to find at night with a flashlight youll see it ooze out from the hood . its the rings are shot out over pressure the case. when you rev up it sucks back in usually.

[TinKanTosser]

On 5/28/2026 at 3:01 PM, datzenmike said:

There is a baffle in the block to prevent oil droplets getting up the PCV hose. If the engine has extreme blow by, that volume of air will push oil spray out the valve cover breather and into the carburetor. Air filter and the top of the carburetor inside will be wet with oil. 

 

Do a compression test on a hot engine and record the readings. Put a couple of tablespoons of engine oil in each cylinder one at a time and retest and record the results. If the compression jumped up then the rings are worn.

There's no oil coming up through the valve cover PCV line at all, every time I pull off the air cleaner lid it's clean. When I pull the oil cap off while it's running it absolutely sprays me with oil droplets, coats everything under the hood, but like I said it's got more manifold suction than blowby pressure, and evidently when I'm driving it hard the blowby still isn't forcing oil up the valve cover hose.

 

Rather than spend any time trying to diagnose, since I'm gonna drive the heck out of it anyway, I remembered I have a catch can I never really used before, so I'm trying to figure out how to mount it on here, and if blowby is pushing oil up the PCV suction hose then I can just catch it all and dump it back in. I get the impression this antiquated PCV design with the suction hose down on the block has caused a lot of worn-but-still-good engines to smoke like a freight train.

 

I wonder if the mid-80s Mazda pickups had this same design? Because my dad had one that fit the description of mine, where it ran perfectly but would fill the pasture with smoke.

[datzenmike]

Pull the hose off the valve cover and drive it. Any change in smoke? less?? Now try pulling the PCV valve hose off and drive it. Does the smoke decrease, or the same. If either decreases it may be assumed that oil was going up the hose. Then you could try a catch can but I find them a waste of time. What are you going to do with any captured oil? Recycle?? throw in the environment? might as well just keep burning it.

 

My guess is not much will change and the rings and valve guides/seals are just worn. 

[TinKanTosser]

On 5/30/2026 at 7:52 AM, datzenmike said:

Then you could try a catch can but I find them a waste of time. What are you going to do with any captured oil? Recycle?? throw in the environment? might as well just keep burning it.

The idea is to dump it back in. I'm losing a quart of oil every couple days, it's not feasible to keep dumping in good new oil and I don't want to put poor quality oil in it.

But you were right, the PCV turned out not to be the main issue. When I pulled the suction hose off it was soaking wet with oil, but when driven that way it smoked about two times as bad. So while the PCV is sucking oil from the bottom, it's not the singular cause of the smoke. And it seems like the PCV is helping the ring seal just enough to mitigate some of the smoke.

 

I don't have time to have it down for full rebuild right now especially not on a truck that's leaking rainwater in through the doors, windshield and floor (I keep finding new leaks) but it did dawn on me yesterday that I have all the donors I'd need to build an LZ23. I have a bad-condition Z24 from my dad's truck, and presumably an L20B in a king cab 620. I know our older 620 has been sitting out with the valve cover off for 30 years though, so if the L20B has been too then it's a no-go I guess. Unless I could get a new cam for the head.

 

I don't have the area or equipment to pull the Z24, especially not with it out in the woods, but if I could do it and get the parts together I could build the LZ23 on a stand at my own pace, then drop it into the truck when it's ready. Seems like a good idea considering I have a low mileage gearbox and diff; a new motor would solve everything but the rust.

[datzenmike]

An L20B and a Z24? You can't make an LZ23 out of those two.  For that you need a Z22 or L20B block bored to 89mm, a Z22 crankshaft, Z22 or L20B rods and KA24E pistons.

 

If you fit the L20B head on the Z24 block you would have an LZ24 with 9.47 compression.