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L18 Engine: 1. How to determine if the motor has been rebuilt. 2. what L16 parts are interchangeable


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1. I am going to look at an L18 engine block with crank and pistons this week. What stamps or markings do I need to investigate to determine whether the L18 motor is stock or has been rebuilt with new pistons or rings? I read somewhere if the motor has been rebuilt that the machinist shop who did the work would stamp the cylinder with 0.02 or 0.04. 


2. Is there a complied list of interchangeable L16 and L18 parts? 


Any guidance would be greatly appreciated




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None of the machine shops I have ever used for L motors have stamped anything on the block or crank.


The L18 is different in almost every way from an L16, but most exterior pieces will interchange including the front cover and everything inside it, the cylinder head, manifolds, etc.


I would have a look at the rod and main bearings (if accessible) to see if the crank has been ground and yes, measure the bores too. I'd rather have stock crank journals and stock bore, but if there are no scratches or cracks (or rust),  and they aren't ground/bored to their max, who cares?


Look for cracks around the middle cylinder head bolts. These are notorious crack spots, and may be hard to detect without a little sandpaper. Ideally it would not be cracked, but even those can be fixed.

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1/. You don't mention a head so just measure the bore. A stock bore is never exactly 85mm and can range between 84.985mm to 85.035mm. The top of the cylinder where the rings don't wear will still be accurate. Twenty or 0.20" is close to 0.5mm and 0.040" over is about 1mm. I imagine you are going to rebuild this block????? Finding pistons, oversize or not, will be difficult. Better see what's out there before buying this engine.


2/ Parts? Only difference between the L16 and L18 is the bore, the crankshafts rods and pistons. L16/18 crankshafts and rods will interchange.

L18 crankshaft and rods fitted with L16 pistons in the L16 block would make it a 1,687cc engine.

L16 crankshaft and rods fitted with L18 pistons in the L18 block would make it a 1,672cc engine.


L16/18 rod and main bearings are the same.


You could over bore the L16 block 2mm to 85mm and fit the L18 crank/rods/pistons and make it an 1,769cc or basically into an L18 displacement.


The L16 comes with 210 a letter head. L18s were usually open chamber A87. All L 4 heads interchange but the 210 has small ports and valves but on an L18 the compressing would increase to 9.38. Any L20B head will have better breathing than the A87 head and keep the stock compression but on an L16 would drop it from 8.5 to 7.2.


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On the L16/18, from center line of crankshaft to the top of the block is 207.85mm, so stroke/rod/piston must fit within this limit. Too long, the piston hits the head, and to short the compression will suffer.


L18 crank throw is stroke 78/2= 39mm

L16 rod........................................ 133mm only 2.8mm longer than the L18 rod

All l series pistons are.................38.1mm

..................................................... 171.1mm leaving 36.75mm above the piston making a massive combustion chamber and almost no compression


If you can find a set of early Z20S (also 85mm bore) pistons with a pin height of 35.56mm + L16 rod 133mm and 39mm stroke = 207.56 IT FITS!!! No compression increase but rods are 2.8mm longer 

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I’m going Thursday to inspect the block first before buying any pistons. But your probably right about ordering then a reply email to your order that the pistons are no longer available. I’ll update if I move forward on the L18

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Hainz on here always complains that it's hard to fine L18 pistons. Could be that there were very few L18 ever produced '73 for the 610 and '74 for the 710 and 620..... that's it. Not much of a market. L20B pistons will work but unless the head is shaved will drop the compression because the dish in the top is larger.

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After doing L18 research, parts availability and no history of the block, I ended up passing on the L18 and took a gamble on a L20B. It looks like everything is in decent shape for a 40 year old block, however I have not had chance to crack the head and timing chain cover. The previous owner purchased a package deal of engines and parts and the the only history he had on the L20B was the head was rebuilt. Can tell the a head rebuild by the cam shaft shims and the ports have been polished.  Half of me is tempted to clean up the block, head replace the necessary parts from the L16 and get the 510 back on the road after 2 years in the garage. the other half ->  the motor is out,  a great time to deep dive into the motor, document what has been done and what needs to be done to get the motor in tip top shape.










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Loose the fram filter.... unless you're going to paint the block. That's all they are any good for. Head looks clean!


You'll like the L20B compared to the L16. Lots more bottom and mid range torque and almost 20 more hp. I put one in my 521 back in the late '70s. Was impressed with passing and not having to down shift. You will need an L20B flywheel. If you get a car one you L16 clutch will fit it otherwise truck ones are larger 

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@datzenmikeFRAM LMAO 🤣 I saw the FRAM oil filter when I picked up the motor and just laughed. The previous owner gave me a 6 bolt 225mm flywheel- Truck flywheel.

Needs resurfacing though. And will need to order a new 225 mm Clutch kit.

Will my current L16 collar work? 



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The Jason Grey FAQ lists several feasible L-series franken-engine combos, as well as stock specs for pistons, rods and cranks, etc.



FWIW, per the Honsowetz book "How to Modify Datsun OHC Engines", the '73 240Z and '74 260Z (2 seater) 225 mm clutch covers have the same diaphragm height as the stock 510 clutch, so you could use your stock 510 TO bearing sleeve with that clutch kit on your L20B flywheel. Looks like it has the same clamping force as the 620/720 PU clutches. 


Edited by Tedman
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N1601 and 23001 are for the 200mm L16 in the 510




As you can see above there are differences in the L + B length between the N1601 (510) and the N1600


 For 225mm applications....



I found that 30501-1C104/1C100 is late '90s truck, Pathfinder and Xterra VG30


If you have '79 clutch get N1600 collar. 

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