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1980 720 L20b California junkyard rescue


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I saved this truck from being scrapped when I worked at a junkyard about 3 years ago.  With 192,000 miles It quickly became my daily driver and so I had brake lines and suspension replaced.  It has been an AWESOME ride up until I accidentally let it overheat.  Bad radiator cap let my coolant evaporate and somehow I didn't catch it.  Shortly after refilling the coolant and replacing the cap, it started to drive pretty rough.  I have confirmed a blown head gasket with my mechanic.  So here I am.  This is a 1980 with an L20b and from what I have been researching, they are as hard to find as they are worth keeping alive.  Before I dump time and money into this truck, can anyone give some advice on options.  The only place with a rebuilt L20b I can find is California Datsun, which I have seen some mixed reviews about...  As far as rebuilding mine, there are not a whole lot of rebuild kit options out there.  I've used this site as an amazing resource over the last 3 years and minor issues I've had and figured I'd start documenting.


I tried adding the image to this post without success so here is the imgur link https://imgur.com/a/910WtB7


Work done so far

I have replaced the carb with a Weber since it was giving me trouble.  Of course keeping all original air cleaner and carb to clean up and maybe put back on one day.  I just plugged all the vacuum lines I could find and it ran SO much better.  Other than some backfiring when it was cold...

LOTS of backfiring blew up the muffler (very loud) so I replaced the exhaust up to the block.  Still backfires sometimes but much quieter.  Tuned the carb better.

Suspension replaced

Brake lines replaced

Found some proper sized wheels since it had mismatched over sized wheels on it

New fuel pump

New Starter

Replaced valve cover gasket

Replaced wiper fluid bottle and pump/lines

Found some original seats from a datsun RV that were in great shaped and matched the interior so I bolted them in





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That is a nice looking truck, I like the scoops, but I would have pointed them backwards, but that is me, what are they off of?


How bad did it overheat?

I would likely would just replace the headgasket myself and see if that fixed it, it's not that hard to do if you have done it before, if you have never done it before just ask, one or more of us will describe step by step how to do it, it can be done in less than a day if the head is not warped, don't just start pulling stuff apart, you need to use/make a keeper to keep the timing chain tensioner in place once you are ready.

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Thanks!  it came with the scoops and there are actually vents in the hood.  


It overheated twice... both times were for not very long.  As soon as it started to get into the red, I pulled over and let it cool down (first time it started to smoke and bubble up from the overflow bottle and I immediately pulled over).  I drove it for a while afterwards and it had no problems, then maybe 2 weeks later is started to get really rough during driving.  Still drives everywhere, always starts and goes.  Great truck.  I know it's old, so I drive it pretty mellow, not often on the highway.


We're quarantined here, so I was thinking I could work on it in my driveway.  I have access to a lot of tools.  I have taken engines apart, but never replaced a head gasket.  It leaks some oil, so I'd probably do the oil pan gasket as well?  Step by step instructions would be great.  Timing chain is the main concern I have.  I'm pretty handy and suddenly have a looot of time on my hands. 


It's at my mechanics, maybe 5 miles away.  If it has coolant and just gave it an oil change last week, how risky is it to drive back to my house?  

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I cannot advise on if you can drive it home or not, if it were mine I would likely have a couple gallons of water with me and drive it home, but that is me.

Have you seen the timing chain tensioner holder, here is a fancy one.



I just made mine out of these plastic strips, I have also used a 1"X2" wood stick when I could not find the ones above, and I cut it to fit on my band saw, the photo above gives you a good idea what you need.



Here is one made out of wood, normally mine go down in there almost all the way to where that piece sticks out(see first photo) and it fits snugly.



You do not want this happening.



Get it home and turn the engine to TDC, the rotor should point to the number 1 plug wire on the distributor cap, then get everything off the head(intake/exhaust), then remove the valve cover, put the wedge in, then with an impact loosen the cam bolt from the timing chain gear, leave it hand tight, make sure the crank is still on TDC, if not turn it back to TDC, then make sure the wedge is tight, mark a link and the cam gear so you can put it back on the same place) and then remove the cam gear, now loosen all the head bolts and remove them, I tend to loosen them from the ends towards the middle(sort of backwards of the torque sequence), then lift off the head.

In the past I have zip tied the cam gear to the chain but as I recall it was a big hassle getting the head off, so after the head was off I would zip tie the cam gear onto the chain in the correct position until I was ready to install the head, now I just mark them with a punch or marker and call it good as I know if I screw up(felt mark gets rubbed off) I can get it right without any marks as long as it is at TDC.

You absolutely do not want that tensioner to pop out of its hole, it will require removing the front of the engine, do the oil pan gasket last if your going to change that.

After you check the head with a straight edge and it is flat just put it back together the reverse of how you took it apart, head bolts, cam gear, ect.


This was the short version, when you get around to doing this I am pretty sure there will be lots of folks willing to help being we have been asked to stay home.

You need a head gasket kit, head gasket, intake/exhaust gasket, valve cover gasket, clean all the head bolts and if you have the proper tap clean the block threads also.




Edited by wayno
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16 hours ago, ]2eDeYe said:




How does a truck this nice show up at a junkyard to be scrapped.... nice save....


No need for a new motor, L series are pretty resilient motors and easy to rebuild..... 


Should be able to find a rebuild kit no problem.... felpro for sure make one.... 



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The louvers in the hood are to let heat out so flip them around. The '81-'81 had louvers on the middle sides of the hood. Scoops are a good idea to keep rain out.


Geez why would anyone want to scrap this truck??? Maybe the mileage.


Do you have emissions testing? That Weber won't pass. Find and rebuild the stock carburetor and have it ready and find out where all the hoses go. There should be an emissions sticker on underside the hood. Wouldn't hurt to have a 1980 Nissan factory service manual (FSM) if keeping it. Get the Nissan one not the Haynes or others, they cover all years and don't really cover enough for your specific year. Try e-Bay. They pay for themselves the first time you use it.

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Wow this is amazing.  Thanks!  I'm pretty excited to have the time to do this over the next couple weeks.  I will do my best to document everything.  


I can definitely make that timing wedge at work, so that's perfect, thank you for the pictures wayno.


As for the find of the truck, it's actually a funny story.  Like I said, I worked at a local junkyard and we were always full on cars, sending truckloads to get scrapped and keeping the ones worth stripping down.  This guy came in who was just tired of dealing with all the problems it was having.  Turns out, that means he had fixed a lot of problems for me 😅.   He tried to donate it to a local radio station and they didn't want it.  My boss gave him $100 for the truck and offered it to me for $200 (more like gave it to me).  A new battery and fuel pump got it driving right away.  I took it home and started working on it in my driveway, when my across the street neighbor comes over.  He was the guy that dropped it off!  It had been parked on the next street over and I never noticed it...  It was a little awkward, but he was really nice about it and gave me the Hayne's manual with info on things he had done to it.  Also, told me he paid $2,000 for it the year before.   I took that info as an excuse to spend some money on it and turned it into a daily driver with the suspension, brakes and tires/wheels.  I feel a responsibility to keep these things alive, it really would have been put on a truck to get smashed that week if I didn't want it.  It does have a clean title somehow, but the VIN on the dash and doorplate do not match... So there is some story to uncover.  Once it gets in my driveway I'll get more pictures up.


I'd love to get it back to stock, they Weber was a quick fix to see how it runs.  I have gotten it smogged... twice...  😉Junkyard connections...  But my end goal is to get it as original as I can.  Once the engine is dialed, I will work on the carb.


Nissan Manual.  Great advice, I will look that up now.  Flip the scoops around?  Interesting, never thought about that.  I'll take a look at it.  I've always wondered why it had them.  Doesn't seem stock, but the hood definitely is made for them.


I'm ordering gaskets now, probably work on it over the weekend.


Thank you to everyone!

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The 1980 Datsun 720 with the hood with the louvers did not have a dash with the VIN number on it, that was a 1981+ thing, the 1980 still had a VIN plate under the hood on the passenger side where the 1981+ info tags are.

I expect your dash came from a later model 720, and that is why your numbers don't match.

Edited by wayno
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Just an update, I have received the gasket kit from fel-pro and had the truck towed back to my driveway.  I just solved the issue on my other vehicle which makes this project way less stressful and I'm going to try and take my time with it.  I'll do my best to document everything as I go.Pw4qac5.jpg

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  • 2 months later...

OK, finally got around to surgery.  Put it at TDC.  Started unbolting and unhosing.  Everything came off fine so far.  The timing wedge I purchased looks a bit small, makes me nervous, might want some advice on that.  When the Weber was removed, the intake manifold looked perfect underneath.  I was surprised how clean it was.  Then I drained the coolant (after I had loosened most everything, which was probably not a good idea) and after draining I now have a small puddle of coolant in the intake.  Did I screw up something worse than just a little puddle of coolant?






Notice how far down the wedge is?  That's enough to hold that chain in place?




Here's under the valve cover




The last part keeping me from easily sliding these manifolds off ( I think) is this metal hose, with a very rusted nut.  Do I have to get this off?  I'm worried it will just break if I try.  



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I won't be able to tell you if that metal pipe/nut needs to come off to remove the head. But, spray that nut down with PB Blaster where the threaded area is, and where the pipe goes into the nut.  Do this several times over the next two, three, or four days. If possible use a flare wrench on it. A flare wrench (correct name?) will be like a closed end wrench with an opening in one side just big enough for the pipe to fit over, unlike an open end wrench that is C shaped. This will have more of the wrench surface in contact with the nut than an open end wrench. Once you have a wrench put just enough force counter clockwise on the wrench/nut to crack it loose (1/32 inch?). Then reverse the direction of rotation about the same distance. Then go back the same way you started. Rock the nut back and forth, increasing the turn just a little bit each time. Occasionally spray the nut with penetrant. Continue this movement until all the rust is broken free/ the nut is removed.


I'm not sure if I got the words right, but working the nut carefully to breaking the nut free from the rust that is very likely in the threads is very important to not breaking anything. May God be your guide in this endeavor.



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Not really a wedge, more of something to block the tensioner (on the left) from pushing out and ending up like this...




Once out you can't un ring this bell.



Why not take the head off with both manifolds on it? Not much to unbolt, nothing to break, nothing to leak.

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  • 2 weeks later...

I'm having trouble getting pictures up right now, but it's the head with rounded exhaust ports.  So W58 I believe?  I'll double check when I'm back at the house.


Any advice on where to find a new head?  California Datsun has rebuilds for $600 and $75 shipping.  There's some gambly options with the current one, but I think replacing it makes some sense.

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I don't believe a high compression closed chamber head would have been sent here back in '80. This head is likely from an import engine. No way this would have passed emissions back in the day. Also has red RTV on the intake/exhaust gasket. Yeah I guess replacement.


I would have it TIG welded and milled. But that's me and only because it is a closed chamber and worth saving. I found a closed chamber W58 once .

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12 hours ago, datzenmike said:

I don't believe a high compression closed chamber head would have been sent here back in '80. This head is likely from an import engine. No way this would have passed emissions back in the day. Also has red RTV on the intake/exhaust gasket. Yeah I guess replacement.


I would have it TIG welded and milled. But that's me and only because it is a closed chamber and worth saving. I found a closed chamber W58 once .

Rebuilt engines and parts from California Datsun is throwing money away.  Research how many company name changes California Datsuns has.

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On 6/23/2020 at 8:19 PM, california720 said:

If it's worth saving, I'll see if I can get it welded.  Nothing to lose on that.


Any advice on getting the carb rebuilt?  I'd like to get it back to stock.

Whatever you do, hang onto it or pass it along to another Datsun freak. They aren't making new heads anymore...


I'd have it welded.

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