# 1970 Datsun Roadster with L20B engine



## priest1710 (Apr 22, 2011)

New to Roadsters, and I am trying to purchase a 1970 Roadster with an L20B engine installed. The prior owner bought the car with the original engine and trans removed (fortunately he kept them both) and the L20B engine with five speed. I have test driven the car, on the surface it drives well. What should I be looking for with the L20B? Normally, I would not expect the L20B to fit inside a Roadster hood, so it led me to think that the engine mounts may have been modified (cut?), the transmission cradle modified, or some other metal was cut. I did not see that fortunately. Can the engine mounts be reduced somehow to bring the engine within tolerance, or is there something more sinister at play here?

Any help will be appreciated.

By the way, the seller is throwing in the original motor and transmission free with the sale. Kind of two for one. Just looking at what it may take to get it back to original shape, or is this a lost cause.

Thanks in advance,

Steve


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## SPEEDO (Jun 9, 2003)

the "L" motors(L16,L18,L20B) where pretty much interchangeable.. I doubt the mounts have been "modified" (good engines by the way)


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## priest1710 (Apr 22, 2011)

Thanks Speedo.

My only concern was the space in the 1600 chasis. Seems to work OK though.

Steve


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## smj999smj (Jan 1, 2006)

Original engine would have been a U20. I'm not sure how much differance there is in the mounting. L-series engines were pretty solid and Datsun's copy of the old Mercedes Benz engines. Problems were pretty much limited to occassional blown head gaskets and carb issues, but no more than many other Japanese aluminum head engines back in the day.


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## DatsunDave (Apr 24, 2011)

Speedo seems to be inferring that there is no issue swapping the L20 out for the L16 or L18 which is correct since their mounts are the same. However...

I am not sure if I understand him correctly or not, so apologies Speedo if I have this wrong, but it seems that you have assumed the L series came originally in this car. It did not.

And smj99smj isn't exactly correct. There were two engines available for these cars (from 67.5 - 70). The 1.6 litre is known as the R16 (not the same as an L16). The 2 litre is known as the U20. The easiest way to tell what engine came original in the car is to look at the serial number.

If it is SPL311...then the original was the R16.
If it is SRL311...then the original was the U20.

So, if the seller says he has the "original" engine and it is actually an L series then he does not actually have the original engine. 

Now your question is really about whether or not the L Series engine and transmission mounts match up with the R16 and U20 mounts (the latter two are the same). I have no clue...not much help there am I.

If the original engine isn't around anywhere then run it as is or swap in an SR and hold on for dear life!

Best check this car over very carefully. 

Pop over to 311s.org if you want roadster info


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## priest1710 (Apr 22, 2011)

Thanks guys. Fortunately, the additional engine the seller gave to me is a U20 with a matching serial on the block. I will most likely send it out to be machined thereby cleaning it up. The L20B runs good, just burns more fuel than I would like with the dual carb. Would I get better fuel endurance with the 510 carb?


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## smj999smj (Jan 1, 2006)

Maybe, but you have to remember the carburation has to match the engine. The question is have there been any mods to the L20B, ie camshaft, increased displacement, headwork?


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## DatsunDave (Apr 24, 2011)

priest1710 said:


> Thanks guys. Fortunately, the additional engine the seller gave to me is a U20 with a matching serial on the block. I will most likely send it out to be machined thereby cleaning it up. The L20B runs good, just burns more fuel than I would like with the dual carb. Would I get better fuel endurance with the 510 carb?


Start checking parts prices before you commit to the U20. NOT CHEAP. 
If it is in good shape now I would try to avoid the rebuild if you can.Definitely install a new timing set.


The single downdraft 510 carb (dellarto?) won't work on the U20 unless you build some sort of custom manifold or find one already done.

There are plenty of SU carburetor set-ups available for the U20 (stock) and the fuel economy is pretty darn good. Go to 311s.org and ask there.


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## smj999smj (Jan 1, 2006)

I think he's talking about putting the stock carb on the L20B, as it has a dual-carb setup on it now, rather than put the L20B carb on the U20 engine.


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## DatsunDave (Apr 24, 2011)

smj999smj said:


> I think he's talking about putting the stock carb on the L20B, as it has a dual-carb setup on it now, rather than put the L20B carb on the U20 engine.


Ahhhh. That makes way more sense.


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## priest1710 (Apr 22, 2011)

Thanks for the awesome advice. DatsunDave, first a correction to prove my ignorance of Fairlady stock. The additional engine outside the car is an R16, noted by the SPL311 numbers on the dash/hood plate and the engine block coincidentally marked R with the engine block serial stamped on the spur right after the R. Sadly the old R16 is a rustbucket, albeit matching. Needs an acid dip, honing, etc. Fortunately, it appears to have all of its parts. It appears to have been cut out and removed from the chasis completely intact to make room for the L20B. I will need to take it apart to see what I am working with, but as you said, $1000 at a minimum is my guess to recondition it. Worth it to me to get it back to factory specs.
SMJ is right, my intention is to place a stock 510 carb on the L20B for the time being. Right now it has the dual reservoir carb on it from the R16 engine, and although it gets good MPG, I know it can do better with the right hardware. My B210 in 1987 got 36 at a minimum before I cracked the block, and some 510s back in the day could get 40 Highway. So, one more questions since I am on a roll:
1. Would it be wise to change out the radiator to support the L20B motor? It has the dual core for the R16 on it now. I noticed it heated up pretty quick at idle today in the late afternoon temperature, which was about 75 degrees. Since it gets up to 110 out here, I am thinking it may need to accomplish this task.

Thanks again,

Steve


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