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Pretty in primer. A ‘69 521.

Slow Loris

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Hi, here’s my evolving story on a 1969 521 I just got. Seeking any and all comments, input, and advice.


We pulled this truck out of the backyard between two also non-running 620s. Previous owner was clearly a lover of Datsuns, but became physically unable to work on them.  He tucked them away in the dry climate of far Northern California for some lucky chump like me to come across. RIP P.O. he left Datsun collection to his kin, I purchased this one from them.


Number plate indicated a J13.


Frame is solid, body has tons of dents but no scary rust that I can find. A couple of globs of bondo. Well-coated in primer at some point (baby blue underneath, one door cream, one fender red, interior sprayed black). Lots of little modifications—this truck was well-loved and according to seller was a real daily driver for decades. Aftermarket gauges (who knows what’s going on with wiring), bucket seats, steering wheel, annoyingly short shifter, radio, smog stuff, etc done by p.o. Seller said they recollected it needed a new water pump—maybe, couldn’t remember exactly but there was a reason p.o. put it away.


Truck would crank but not start upon inspection for purchase. I offered up the cash then before the seller tried anything else to keep the price from going up further. Seemingly, this turned out to be because of clogged fuel filters/lines. After trailering truck home, dropped the gas tank and cleaned it per advice found here. Flushed lines and replaced hoses. Filled up the float chamber with gas and…it started! (Oh I did do all fluid changes before starting). Idling rough, so much more work to be done there.


So there are a few question marks with this truck. In looking at photos and diagrams, I didn’t recognize the exhaust manifold in my truck as belonging to a J13. Also the spark plug wire set I got was comically short for what my engine needed, but wasn’t sure how the distributor could have moved that far. Then I finally unearthed a stamp from beneath all the oily grime that says “A87.” Info on this here forum says that means L16, L18, or maybe L20B?


Here’s a clue on the motor maybe could help someone identify—it has a dipstick towards rear in usual spot, and one towards the front. The end of front dipstick is snapped off, but presumably it can only be dipping oil. Double dipstick specific to any particular engine?


This also probably explains the new “shifter” is a whole other trans and perhaps why he needed to cut a hole in the tunnel to accommodate it. Transmission stamp says 1720-159 on top.


If anyone has thoughts on what this engine is… that would be really helpful for buying parts!


Lots on my to-do list. I was going to do the water pump given seller’s comment, but the one I bought for the J13 sure isn’t going to fit. In process of that job discovered heater core has crack and leak.


The truck needs cleaning, for one. It is currently glued together with grease and dirt. Can’t remotely access the zerks they are so caked up. Needs suspension work, all rubber degraded, truck is leaning to one side. Brakes, I’d like to convert to dual circuit master eventually. Floor pans are the rustiest part, but not full of holes. Could use new window rubber.


On the last startup, blew blue smoke out of the exhaust. Just changed the spark plugs and they do not look good. Black and oily and build up. The plugs seemed very loose in my under informed opinion. Have not started it since that discovery.


So blue smoke, oil all over the engine bay, oily spark plugs…is this a valve cover gasket, valve stem seal replacement situation at minimum? Other means of diagnosing the oil burning issue?


Alright so about me—I’m new to wrenching on cars and I’ve got a lot to learn. Please feel free to give me advice fit for novices, I won’t be offended. I’m not dense, but yeah I’ve never done this before. I’m not afraid of labor-intensive jobs. I AM afraid of spending a bunch of cash, so I’d prefer to do things cheaply. I’m pretty handy.


Anyway thanks for reading. More to come, of course. So cool to see all the advice and enthusiasm in the group!














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It's an import engine. Leave the front dipstick alone unless it is leaking. It's been deleted.


L18s did use A 87 letter/number heads. The L18 was only used in the '73 610 and in both the '74 710 and 620 so not a lot of them around.


Oily blue smoke?


Make sure the oil isn't over filled.


Most likely the rings are worn out. Run a compression test on a warm engine and record the numbers. Generally all readings should be within 10% of the highest. What you want to see are almost all the same compression for all 4 cylinders and preferably above 130. Give 3 or 4 squirts of oil into any low cylinder through the spark plug hole and repeat compression test. If the number jumps up significantly the rings are worn. If no change probably one of the valves is sealing badly but a bad valve wouldn't necessarily be the cause of blue smoke.


To a lesser degree worn valve seals can cause oil consumption but worn valve guides even more so. If the rings are worn likely the valve seals are too.


L16/18 use the same bearings, valve seals and gaskets if rebuilding. The L18 rings are unique to the L18. 

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Ok thanks for that info, will keep those model years in mind. I am not sure how to describe oily smoke or not. It was pretty thick smoke and did not smell good.


Here’s the results of compression test:


Engine didn’t run for terribly long before doing compression test because of smoke cloud enveloping neighborhood I was causing made me a little nervous. 

1- 90 psi

2- 90 (this spark plug hole burped smoke when removed after warm up)

3- 95

4- 115


Did the oil squirt and then:


1- 95

2- 100

3- 120

4- 130


Then I put the plugs back in and idled for a while and the smoke mostly went away after fiddling with the choke (seems it was running in a very rich setting). Still a little smoke from the exhaust but nothing remotely like previous—I was able to see and breathe. I am a little hesitant to idle for too long because of potential water pump not functioning and no clue if water temp sender works either. 

So compression test (on not too hot engine) says bad piston rings but then choke adjustment drastically improved the symptom that concerned me in the first place. Where am I at now?







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Sounds like the rings loosened up and are mostly sealing. You might even find it tests a lot better now. Cyl 1 could be an issue, but if it drives ok, just enjoy it as is for now. I have a tired L18 in my car, but it's fun and reliable enough for what I need atm.



Edited by slowlearner
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Well that’s obviously the opinion I was hoping someone would have…glad to hear it!


The long idle I did AFTER the compression test where the smoke cleared up was by far the longest it has been run in 9 years, so maybe the rings just need a little heat and a little lubrication? 


Once I get the new water pump in whenever it comes in I’ll try the test again on a hotter, more frequently run engine.


Would there be any point to pursuing replacement valve seals or stem guides simply given that the engine has sat for so long? Or is that trouble not worth seeking out until necessary?





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See if the build date is on the driver's door jam. If the build date is July '69 or after then it's a '70 model year truck. You definitely have an L series engine and that's a lot of work to replace a J13 in a '69.


Cylinders 3 and 4 really jumped when oil was sealing the rings. Compression down near 100 is not good. Get running and check the choke does shut off, check the valve lash. Does it over heat? Does it use coolant?  Drive it a few miles and retest. Some compression may come back but don't hold your breath.

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Alright I won’t get my hopes up. Piston ring replacement sounds like a…serious learning experience. Can’t wait. If I am to do the rings, this is like, totally doable and worthwhile on this motor or not necessarily? The parts don’t look too expensive but I have never attempted such a job so no clue the wormhole it might mean. 


Well there’s no info placard on the door but according to Car No. interpretation guide I found elsewhere in the forum, the number places it between Oct. ‘68-June ‘69.

From what I briefly learned about the previous owner from his kids is that he was just the right type of individual to go through the trouble of this engine swap. Why? I dunno. But I think this was his favorite of all his Datsuns. Maybe it was his first. 

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The J13 was probably played out and an L18 is just 40% larger displacement for the win. L18s were around 83 hp, J13 in the 60s?


Assuming it wasn't over heated and the rings broke and buggered the pistons and scored the bores a quick and dirty hone and ring job will get you going. If the pistons are bad stop right there. I don''t think L18 pistons are available. Find out before ordering parts.


Head and oil pan gasket, ring set*, rod and main bearings. If you lift the head off with the two manifolds on you won't need a manifold gasket and there is no chance of busting a manifold bolt off in the head. Optionally you could/should replace the rear crankshaft seal as it's only got at with the engine out. The valve seals can be easily done head on or off later, but as the head is coming off, do them now.


*rings.... get cheaper cast iron rings. Chrome molly rings are for perfectly over bored cylinders with perfect hone. Yours will be worn, tapered and/or oval and perfect for the softer rings to quickly bed in.


Bearings... get anything you want, they will be better than the ones in there. 


Gaskets are also sold as a rebuild kit having every gasket and seal used in the engine but cheaper to buy only what you need head/pan crank seal, valve seals. 



Best advice here... do NOT take the camshaft sprocket off until you know how to properly block the timing chain tensioner from falling out when the chain goes slack. Saves you 4-6 hours of extra work fixing this problem.

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I think the pistons will govern if you should rebuild it. If they are damaged I don't think they can be replaced. L20B pistons are the same size but they have larger combustion chambers and this would drop the compression into the mid 7s.


Otherwise parts would add up to under $200?

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Alright—truck sat the whole week lonely and untouched. But now I’ve sorted my water pump situation and given the engine a good long warm up. Performed the compression test again and got pretty dramatically different numbers:


1- 120

2- 115

3- 120

4- 125


I did not do another round with the oil squirted on top…because those numbers sure looked good compared to last time!


No smoke except a little in the engine bay perhaps from my grease coating on every surface heating up at temp and burning off?


I haven’t gone for a drive to see how it feels because I’m utterly and completely devoid of brakes. I’ll check the valve clearance and timing and some carb adjustment and do brakes and then see how it goes. 




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Here’s the truck. See? Pretty in primer.

Grille out for water pump replacement. I do have one. What I need is outermost chrome bezel at each end (   )


Ok some updates:


Got a big show of smoke on startup after sitting all week, but then it went away after a good 2 mins of idle. Still some smoke from somewhere in engine bay.


 I adjusted the valve clearances. Then I did my best to set timing. Had some issues with that. Mark on the pulley led me to initially run out of advance so I looked at cams and reassessed TDC via cam position and peeking in the plug hole. Here’s what the rotor was doing when the cams were doing what I’m calling TDC (which matches up pretty dang well with spark plug 1 wire position) I think I did this right?




Painted a new mark on the pulley and set timing off that, but my mark is a little thick so it might not be super accurate. Ended up retarding timing a little. 


Anyway, timing set, valve clearance set—engine not sounding “smooth” at all. I know that’s super descriptive but something is amiss still. Almost like a misfire maybe but it runs good for a second and then it gives a little hiccup and then it’s back to being good and then the hiccup. 


I did replace plugs, wires, rotor, cap. The plugs already look pretty sooty. I did not replace points because the screws that hold that apparatus are stripped but I did lightly scrape the points though they looked pretty clean to me. Did not replace coil.


One disclaimer—my timing light doesn’t have an rpm counter so I could be way off. I’ll try to use this strobe tachometer app when it’s dark out to figure out idle rpm.


Also I can see in my carb that there is gasket material hanging out where it shouldn’t be so that thing needs some attention/cleaning, but since I dunno my rpm I didn’t really screw with idle / mixture screws or anything. Engine does sound better at higher rpm. But there are literal cobwebs hanging out around the carb (it’s the stock one)


I guess my question is—what do I do next to get this engine running better?


Carb attention?

Figure out idle rpm?

Replace spark plugs again?

Dial in timing more accurately?


All of the above, you dummy?

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Whew so removing 521 rear drums how come no one told me how fun that is??


Plenty of tips out there but I think what did it for me was patience and penetrating oil. I know two of those words don’t usually go together in a sentence but this time it was worth the wait. Like 3 hours of wiggling, tapping, and spinning followed by 24 hours of letting kroll oil sit. And then another 3 hours of wiggling. Also I was aided by po having chipped a huge chunk out of the drum so I had a spot to shove a pickle fork in for the wiggling.


Also parking brake cable way seized at least on the one side I’ve attempted so far. Hooked a come along up to the free end that attaches to the Y and ratcheted it tiiiiight and nothing. No movement. So…? Not sure what to do with that if I can’t even get the damn thing out.



Also, what the hell happened in the brakes? What is this greasy fur-like substance? I’ve heard of people training rats to drink up their Datsun’s oil leaks, but it looks like this one got stuck inside the drum and blew up. (No I have not actually heard of that so calm down rat lovers). 


Anyway fun times. Hoping to find some brake return springs cause I broke one and they seem in short supply.

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I would clean up the brakes.

old wheel cylinders will weep and brake dust gets wet.

also the outer seal can leak diff oil on the shoes also.


I drill jacking screw holes on the drums in case you need it ezer to pull off later.


you can dial the star brake adjuster on the bottom and clean it up and get the adjuster so it loose as possible then pry one side (the bottom loose then you can get the springs out ezer.  I assembly them with the springs on and do the reverse going back in. I try not to use a visegrip and stretch the springs so i dont go blind otr bust my hand.


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Hmm yeah I was wondering about the outer seal. Will cross that bridge at some point. Wheel cylinders feeling pretty rough will def just replace those altogether.


Thanks for the tips! Assembling with spring on definitely the way to go. Though my adjusters are not budging. The fronts were fine, but these rear adjusters are stuuuuck. 

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