Datsun Roadster engine build

Recently, my wife was going through an old external hard drive and she came across a little write-up I did years ago documenting a high performance engine build for my old Datsun Roadster. It was fun to read it again and I though it would be worth posting here. Below is a photo of the car before it was sold off to purchase my first Porsche. More on that later!

1970 Datsun Roadster engine build

The Datsun 1600 roadster offers a great deal of fun, with it’s classic styling, nimble handling, and responsive motor. Considering its relatively modest pricing and good reliability (at least for a 40 year old sports car), it makes a great candidate for modifying and improving. Though my 1970 1600 has always been entertaining to drive, it’s good handling and braking have always begged for more power. There are numerous ways to get power out of these early Datsuns, and everything from American V6 and V8 engines to modern Nissan motors have been tried with varying degrees of success.  Other possibilities include using the U20 over-head cam two liter from the Datsun 2000 roadster, which offers a claimed 135 hp in stock form, or using the internals (crankshaft, rods, and pistons) from the U20 to build a stroker motor out of the 1600’s R-16 overhead valve motor. This last option had intrigued me since I first heard about it years ago, and since I really like the 1600’s raspy character and old school technology, I thought it would be a good choice when it came time to put the roadster on steroids. 

            The first order of business was to get my hands on a U20 donor engine, which proved easy enough thanks to a friend with a race-prepped 2000 roadster.  A $100 later, I had a complete block with all the internals I needed and a partly disassembled head.  When the time finally came to start building the stroker, I have to admit I had to do some soul searching about whether or not I should just rebuild the U20 and use that, or go with the stroker build.  A little research on the prices of U20 parts (very expensive, especially if you want OEM) sold me on the R16 stroker.  So it was finally time to dig in.

            Pulling the motor, along with the transmission went smoothly, and once I had the engine mounted on an engine stand, I was amazed how accessible everything was.  Not to mention most of the work could be done without stress on the back, which if you’ve done much car work, you know that’s a rare luxury.  Disassembling the engine revealed a fairly healthy bottom end, with good rings and bearings.  The original domed pistons were looking a little worse for wear, with pock marks and chipping in evidence across their surfaces.  No matter, since they’d be replaced anyway.

            One of the benefits of working with the R16 is that there is a variation of the motor, called the H20, that is commonly used in Nissan forklifts.  The configuration is the same as the R16, with the exception of the crank and rods, allowing for a 2 liter displacement.  In fact, some people have built their stroker motors using the H20 crank and rods, and some people are actually running the H20 in it’s original form.  Because of it’s common industrial application, engine parts are readily available, fairly cheap, and for the most part can be used in the R16, stroked or not.  As a result, I was able to buy an entire engine build kit from Swift Forklifts, including .040 overbore pistons, rings, bearings, oil pump, complete gasket set, valves, valve springs, and guides for about $350.  Compare this to buying just the pistons for an R16 or U20 for $300-400, and you can see I was money ahead by going with the forklift parts.  There are some things to know to successfully use the forklift parts in a stroker, but I’ll outline them as I explain the build.

            With the parts delivered to the door (it was pretty exciting to go through that box of parts), it was time to building the stroker.  The first thing to deal with was the crank.  It looked in decent shape when I pulled it from the donor motor, so I just took it down to the local machine shop to have the rod and main bearing journals turned down .010.  Routine enough, but the tricky part about using a U20 crank in an R16 block is that the nose of the crank is an inch too long, meaning that when the crank bolt is tightened on, it won’t compress on the R16 crank pulley.  Most people have the extra inch removed from the nose of the crank, but I could not find a local machine shop to tackle the job.  So I decided to go with a unique option I had heard about that used a collar or spacer to make up the difference.  In talking to the machinist who relocated the crank keys for me (a necessary job, regardless of how you deal with crank nose), he felt that spacer idea should work fine.  So the next question was, what would I use for the spacer?  The U20 uses a harmonic balancer, which is why the crank is longer, and since I had the ratty old harmonic balancer that came with donor motor, I decided to machine out the collar.  This took quite a bit of work, but I eventually got it out and cleaned up.  Since it was made to go on the end of the crank anyway, I had the benefit of the slots for the crank keys.  With a little machining to the length, I got it fit on very nicely.      

            With the crank ready to go in, I turned my attention to the connecting rods.  It’s necessary to use the U20 rods along with the crank, and I spent some time lightening them by grinding off the casting marks along the length of beam and removing some material around the big end of the rod.  Final balancing using a digital scale and a little polishing, and the rods were ready for the end bushings to be pressed in and the new rod bearings to be installed.  The pistons proved to be a little more challenging, since the conventional way would be to use U20 flattop pistons.  These were out of the budget for this build, so I decided to use the H20 pistons that came with my forklift engine kit.  The problem is, these pistons are dished, which increases the volume of the combustion chamber, resulting in a decreased compression ratio.  To help compensate for this, I had the block milled .040 to bring the tops of the pistons flush with the deck.  With some primitive cc’ing methods using a plexiglass plate and a large syringe, I was able to determine my CR to be about 9.5:1, which is better than stock but certainly on the modest side for a performance motor.  The only work I did to the pistons was to polish the tops, the thinking being that if polished combustion chambers in the head help with combustion and reduce carbon build-up, it might help on the pistons as well.

             I spent quite a bit of time working on the R16 aluminum head, balancing and polishing the combustion chambers and porting the intake and exhaust ports.  The intakes were left a little rough to promote good mixture, but the exhaust ports were polished after porting.  Though I really wanted to fit larger exhaust valves, I finally gave up on researching the options.  Unlike so many British car suppliers for MG and Triumph, I just couldn’t find anyone who sold larger valves for the Datsun roadsters.  So it was stock sized valves, but at least they were the new items from the H20 engine kit.  I had read a few times about the R16 head suffering from valve float at high RPM, so I wanted to increase the valve spring rate.  Again, heavy duty aftermarket valve springs are not readily available.  After considering various options, I finally went with the new H20 outer springs (same rate the R16) and the U20 inner springs from the donor motor (higher rate than the R16).  Though the spring difference was slight, at maybe only 10-15% stiffer than stock, I felt that it could only help.  Final assembly saw the head bolted onto the block ARP head studs.

            The H20 kit came with a new oil pump, but I soon discovered it can’t be used in the R16 block because of different mounting styles.  Fortunately, the oil pump from the donor U20 was in good shape and features a higher volume than the R16 pump.  

            The American Cam reground M13 camshaft was purchased from Dean Apostle at Datsun Parts and features a 276 degree duration and .440 lift.  My decision to go with this cam was based on information I had gleaned from other stroker owners on the invaluable 311s.org roadster forum.  A new clutch disc and heavier duty U20 pressure plate hooks the new stroker up to the original 1600 4 speed transmission.  Though some people will use the 5 speed tranny from the 2000 model, it just wasn’t in the budget this time around.

            Carbs need to be addressed when building a stroker for the 1600, as the dual SU style Hitachis don’t flow enough fuel for the added displacement.  There are numerous options, including using modified R16 carbs, U20 carbs, Solexes, Webers, etc, or even fuel injection.  I my case, I went with a unique Weber carb conversion that was designed for the Triumph TR6.  The kit includes two MCHH-45 single throat side draft carbs, linkage, and adaptor plates to fit them to a standard SU style intake manifold.  After porting the intake runners to match the inside diameter of the carbs, the pretty Webers bolted right onto the R16 manifold.  

            Final details of the build included a recurving of the stock distributor to earlier pre-smog specs and the installation of a Pertronix ignition.  The recurve kit was hard to find, since many roadster owners will now instead upgrade to a modified late-model Nissan electronic distributor, supposedly far superior, but alas again out of the budget for now.  I did finally source the recurve kit from Rallye Enterprises, and after wading through their “really scary instructions”, which is literally how they’re titled, I got the dizzy back in the car. 

            As the build went along, there was a lot of effort put into refurbishing and repainting or polishing parts, since I like clean engines.  When it came time to paint the block, I was tempted to go with the factory datsun engine color, available from vaious vendors, but it’s a funky shade of blue and it’s expensive at about $18 a can.  Plus, based on experience, I’ve never been that happy with the way engine paint ages, as it often loses it’s luster and brightness over time.  Taking a hint from a popular classic car magazine, I just went with standard enamel spray paint in True Blue, and sprayed multiple coats on the block and a few other key parts.  The result looks great and so far it has held up very well.  

            So, the big question is, how did it work out?  I think the stroker is a real improvement over the stock R16.  The most notable feature is it’s increased torque, offering a strong pull from even as low as 1800 RPM.  The cam is well matched for the motor, and you can really feel it “come on cam” at about 3500 RPM.  With aggressive driving where you shift into that powerband, the car really scoots.  Now, it’s easy to break lose the rear tires from a stop, and when driving close the limit in a curve, the inside rear tire will spin on full throttle.  A limited slip would be helpful to get the car to hook up a bit more, but that will wait for a while.  Overall, the characteristics that I loved so much about the Datsun 1600 have been perfectly augmented, giving the car an eager powerplant to match it’s handling and braking.