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The Green Machine Reborn - 1973 620


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I've been posting pictures on instagram for a couple months now, but I've come to realize that I like how much the community here at Ratsun helps everyone out. Moving forward I'll be documenting my build here in the hopes of gleaning some wisdom from all of you. Thanks in advance!


When I was 18 I got an 73 620 as my first real truck, and it was a jalopy. For $500 bucks I got a truck that was used to haul firewood, had 250k+ miles on it, and no back window. I loved it! I wrenched on the thing every day I had off from delivering pizzas in it. Lowered it a couple inches, unwound the torsion bars, and got some old aluminum rims from a friend's friend. I drove the living tar out of it for about 3 years, and while it never really ran great, I still loved that thing. Funny how we can become attached to something so un-beautiful. Eventually I got better jobs and needed something more reliable, and so I traded her in at a dealership. Ever since then I've always had fond memories of her, and hoped one day to get another one as a project.

 

My original 620:

avhbGiM.jpg

 

So finally, about 2 months ago I bought a 1973 Datsun 620 off of craigslist from the Denver area.

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The engine runs, after a little bit of fuel pump and carb work, but it's still a tired L16. I shortly found a donor 77 620 KC with a L20B and a 5 speed tranny in it.

I96XTnV.jpg

 

Got them both into the garage:

C0vZyHa.jpg

 

I've pulled that motor and tranny out, stripped the motor down, and am about ready to take it to the machine shop:

Qbq54z9.jpg

 

M95aBqv.jpg

 

U67 Head:

bqNxOkF.jpg

 

Along the way, I've read hundreds articles here on ratsun.net, as well as anywhere else on the net that I can find. I do have the "How To Modify Your Nissan & Datsun OHC Engine," the rebuild book, and the Haynes manual (still had the one I used 25+ years ago.) I used to race super stocks (F Body) at Altamont Speedway, a short circle track. As such I have experience with small block chevys, but not a ton with Datsuns (except for years ago.) I Ultimately want to build this as a street/project truck with some performance increases and some weekend fun.

 

Instagram link in case anyone is interested:

instagram.com/208datsun620 

 

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To fit the L20B and 5 speed into the earlier '73 you'll need the shorter front drive shaft on the 2 piece drive shaft and everything forward from the '77. This is because the later 5 speed is longer than the original 4 speed.   The good news is you have everything needed.

 

 

 

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I've been working out what kind of build I want for this L20, and still have a couple of decisions to make. I had wanted to build something like the long-rod 2.1, but sourcing z20 rods was proving to be difficult. So, with the stock rods I decided to get some 280zx flat-top pistons .020" oversize, bring my bore to 86.5mm. After some back of the napkin math, it should net me about 10.05:1 CR. I like that, 10:1 seems to be a decent streetable compression. Got those pistons coming to me so that I can bring them in when I bring the block in for machining.

 

Next comes the valvetrain, which I haven't quite settled on yet. My stock cam looks like it might be pitted, so I may have to get a new one.
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And with the higher CR it probably makes sense to get a bit more cam in it. It's a lot of added expense, the rockers/lash pads/springs in addition to the cam is a bit of coin. But if my cam is toast anyways, then it's something to look into.

 

My setup:
- Flat-top pistons (10:1)
- U67 Head
- L16 Exhaust manifold
- L20 Intake manifold
- 32/36 Weber (currently)

 

If I want more torque, or rather as much as I can get, what kind of cams should I look at? The one that initially caught my eye was a Comp Cam 252/422. I think this is close to the stock cam, but I'm going by advertised specs. I've read that high lift is better than long duration for torque, but I don't know enough about cams yet to be sure.

 

Also, if I do get a cam like this should I get some higher performance springs?

 

Any thoughts?

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Can't help you on the motor, but i wanted to say welcome.  Its really nice to see someone realize that social media has been the death of user built technical info, i.e. old forum threads.  When we help each other here that gets saved and becomes Google searchable for the future.  Social media completely loses that feature for future enthusiasts.  Long live the forum! 😁

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NICE!  

Camshafts and head work is the key to power.

Increasing lift will increase time at peak head flow which is an obvious huge benefit.  Duration will change the power band more than anything.  High duration will benefit the top end at the sacrifice of the low end and vice versa.

The 252/422 is a solid choice in my opinion.  Should wake it up a bit and not be crazy!
 

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  • 2 weeks later...

Doh! I got the wrong cam!!

 

roBpLW1.jpg

 

I obviously wasn't paying attention and picked up this nice 252/422 cam, which is for a Z series motor 😒. When I pulled it out of the box I realized that the journals were way too small. Oops!

 

So, after some sleuthing I found an Isky cam that's pretty good, although a bit more aggressive than I had wanted to go. It's a 270/475 that also required springs/retainers/lash caps that worked with it. Oh well, it'll be nice to have all those new parts to put in 😐.

 

On Monday I was able to get the L20B off to the machine shop. They're gonna check the block over and give me a call before they start boring it, so it'll probably be a week or two before I get that back. I also got the distributor out to Advanced Distributors for a rebuild/recurve, thanks distributorguy!

 

xsTZee5.jpg

 

And lastly, I pulled the engine and tranny out of the '73 so I can get the pan off of it and start working on cleanup and front suspension stuff. I really need to fix up my cherry picker or buy a new one. I just doesn't quite lift high enough, very aggravating!

 

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I think you can get by using the stock springs. What I did is use one inner aftermarket spring and a stock outer or vise versa.  take a look which looks spring slook separated more between springs. as normal street driving that set up should be enough with out over wear on the cam.

 

I would pick the 475 cam

 

 

I usually leave the eaxhaust manifold hooked up  and just push it over when pulling a motor you IO don't have to fuck with the Y pipe and gasket (breaking 40yr old rusted bolts

Edited by banzai510(hainz)
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