2010 U20 Rebuild

So since I'm building a clone I  needed a U20 Engine. The U20 came with SU's, but they did offer a 150HP performance package with larger oil pan, performance cam (B Cam) and twin Solex 44's.

I picked this engine up in Florida.  It has the correct performance parts, but it's a late model U20 with a "smog" head.  A true 67.5 2000 had a non smog head.

Head and front cover off.  This is the dual chain set up on the U20.  Chain slop can be critical on this overhead cam design.  

The main oil passage is plugged on both ends, you can also see the oil restrictor used on the bottom chain tensioner this small restrictor must be installed to pressurize the foot to puh out.

Bottom end.  Crank and Jackshaft.  The Jackshaft drives the distributor (and oil pump) and there is a lobe to actuate the manual fuel pump.

To really clean the main oil passage out, the plugs need to be pulled.  I drilled through one and knocked them out with a long rod.  

I machined two new plugs, but decided to thread the block and used a plug should it ever need to be cleaned out again

My goal is to do as much as I can on the car myself, but I used a machine shop to tank the block and install the one-piece jackshaft bearings as they are a press fit, and proper equipment is needed beyond me beating them in with a hammer. 

One final cleaning of every passage and crevise in the block.

Covered everything that needed protection and painted the block.  The correct color is an off blue/green look. Dean sells the Datsun color, but again this is not a real 67.5 so I went with red.

Rebuild kit had all soft plugs including the large brass one on the rear of the block.

Sat for a few days to dry and harden.  Ready to put it together.

The machine shop pressed in the main bearings.  

The rear bearing has three oil holes that must line up.  One is critical as it's the only passage to the head oil passage.  I verified everything was lined up.

My final cleaning was to blow out passages as well as verify nothing was blocked.

The rear main seal is a rope seal.  I soaked the seal in oil and then rolled into place with a large socket.

After compressing into place, I trimmed the ends.  Scott Sheelers Roadster book describes the cut as not too little and not too much, but just right.  The idea is to have a small section to seal with the cap.

Ready for crank.

After the rear main cap is torqued, there are two side seals that are tapped in.  Again, the piece can be trimmed as the oil pan gasket will ride on this area and any part sticking up may lead to a gasket leak.

Oil restrictor back in.

New rod bearings.  The old ones weren't horrible, but they did have wear.

Installing new rings.

Ring offset.

All pistons and caps clean and ready for install.

Covered threads to avoid scratching crank journal, A small rubber hose is probably quicker, but this is what I had available.

Rings compressed.

Simply turn crank to the cylinders lowest position and install piston.

Tapping the piston home. 

After the piston roads were torqued, I installed the jackshaft.

The Jackshaft has a retaining plate installed on the front of the block. 

This is the Evil L as described in Roaster circles.  The engineers designed a gear holder to allow the cam gear to be held when working the top, but as the chain stretches, gears wear, or oil pressure is low, the timing chain can contact the L and grind metal into the oil system. 

The obvious solution is proper care of the system and replacement of worn parts, but to avoid contact at start up due to low oil pressure the tensioner can be shimmed.  I like to just remove the L, but to retain the feature of holding the gear, I simply made it removeable holder.

To install the gears and top chain the timing marks are simply aligned.

The previous pic was the gear on the jackshaft, and this is the other end on the cam gear (marks aligned).

The lower chain assembly goes in with its two gears aligned to their chain marks.  This is considered the checking position as a verification that all chains are aligned correctly.  After the gears are turned all of the install marks are aligned and pointing at each other.

Full image of all chains installed, and marks are matched.

Installing lower chain tensioner.

Finishing up chains.  I use the bottom chain guide, but some leave this piece off.

I cut the zip tie off of the lower tensioner and here the oil slinger is going on so I can install the front cover.

Verify Top Dead Center before the chains are covered.

Front cover on with new front seal.

Harmonic balancer is dead on timing mark. 

Oil pump disassembled and cleaned.

Assembled with oil and new gaskets.

Oil pump installed.

With the oil pump in the dizzy drive needs to drop in to turn old pump and dizzy off of Jackshaft gear.  This is the correct install with the small area forward and the gear at the 11:20 position with engine at TDC.  This puts the dizzy correctly at the #1 cyl. This adapter turns slightly as it engages the gear so without correct alignment it's easy to get one tooth off and that will impact timing.

To lock that dizzy gear in I installed the dizzy tower.  This is also the oil filter mount, oil pressure sensor, and the fuel pump block off.

I cleaned up the head and to get it put on I need to install all of the top end.  I cleaned all chambers and ports.

The valve guide fit is great.  Time to seat the valves.

To install each valve, I cleaned up the head and then lapped each valve to its seat.

You can see the valve and the seat have a nice precise contact point.

Checked each port with light.

Installed new valve seals and reused cleaned springs.

Slid B Cam in the towers and bolted head to block.

Cam gear bolted to cam and lowered top tensioner into place.

Tensioner bolted in.  even though these are new parts, I shimmed the upper tensioner anyway as a way to keep it pushed out until the oil pressure takes over.

Painted up the head and installed some external pieces.

Used some anti seize on these bolts as the thermostat area tends to corrode together.

The gaskets for the thermostat have metal staples through them to ground the sensor to the block.

Rocker arms in.  Installed and adjusted intake and exhaust to cold clearances.

Ready to get the carbs done and get this running and tuned.

These are late year Solex's and are preferred by some for their ease of jet changes and external float adjustment.  Mine are very dirty and need complete teardown and clean up.

This is old dried out varnished gas in the float bowl area.

Continue to tear down and clean, clean, and clean some more.

Block off plate with position dictated by front or rear carb.

Underside starting pump.  You can adjust position based on where you install the height of the pump pin (more or less fuel when actuated).

This is just crazy how bad dried out fuel can get.

All cleaned up and ready to assemble.

All of that crusty scale is removed and the rebuild kit had all new gaskets and diaphragms.

The new diaphragm is way more pliable then the old dried out one.

Final piece of the pump stack.

Held tension of spring in stack and installed retaining screws.

Tightened up pump.

Installed jets into their tubes and installed into carbs.

Top cover. Note I have a complete Mikuni manual that has great exploded views of where stuff goes.

New float valve installed in top cover.

Float adjuster. Note small tension spring that keeps it pushed back.

Gasket on and float installed with a simple pin that allows easy up down motion.

Once float is adjusted the lock nut can be engaged to prevent movement.

Fuel banjo fitting with filter screen in the inside.

Solex carbs complete!

To finish the engine, I bolted it to a 5 speed and installed on the test stand.

Bolted on the intake and exhaust manifolds.  I did the starter as well prior to having other items in the way.

Test stand has all components to run the engine.

Carbs installed and hooked up with fuel lines and water tube.

Completely operational engine.