Datsun Roadster (1600) Head Gasket Replacement

Someone recently sent me an email asking about the 1600 Head Gasket Replacement Tech Tip. I didn't have one, but Allan had written this up. I've added a few comments to it, but Thanks to Allan we have another tech tip! ;-)

Have a new head gasket (I got mine at a reasonable price from Nissan--good idea to buy a spare while you're at it) and manifold gasket before you start.

[Avoid those ones that are just plain metal on one, or both, sides. Haven't seen one in ages, but they were difficult to seal]

Start with a cold engine, ideally one that has sat overnight.

Disconnect negative cable from battery. Remove the spark plugs. Disconnect the temp sender wire. Drain coolant. There should be a drain tap on the block, if you can get it to turn (usually VERY difficult). Remove all plumbing from head and manifold. If possible, you may want to remove the thermostat housing now, while you have something to torque against. Remove the air cleaner and carbs. Remove the starter. Disconnect the tail pipe from the header first, then loosen the exhaust manifold nuts/bolts, and pull the exhaust manifold away, which makes it easier to remove the intake manifold.

Remove valve cover. Loosen head bolts progressively in reverse (10-1) of the pattern for torquing them on. There is a special locking plate under the right-hand rear rocker stud nut. Remove the rocker arms. Remove the push rods (check the see that they are straight)--replace them in their same holes later.[hint: I like folding a piece of stiff paper in the form of a "W" with holes in the middle, then inserting the push rods one by one in the correct order so I do not mix them up. TW]

        |  10    6     2   3     7      |

        |                               |   ---> front of car

        |  9     5     1   4     8      |


When you remove the bolts, clean the threads, and check for corrosion. If the threads are damaged, they must be replaced. (Note that the head boltsare metric hex head, but SAE thread on the 67.5 and later engines). If you reuse a bolt, make sure it goes back into the same hole as it came from--I use an egg carton, and punch the bolts through to keep them in order. Note that the one holding the hoist hook is longer than the others. Chase out the threads.

Measure the length of each bolt as they are removed. Nine should be the same, the tenth one should be longer. It is fitted with anengine hoist bracket on the left rear of the engine (#10 above). If the engine hoist bracket is missing, you should replace it with a shorted bolt [TW]

Tap the head free by applying even taps all around the head with a SOFT mallet--no hammers.

After removing the head, check the gasket around the water jackets and the chambers--you should (if your problem was the same as mine) see where theleak was.

Now's a good time to examine the cylinder walls (Oh my god, just look at the scoring--I guess I'd better tear down the rest of the engine... ;-( )

Before cleaning the old gasket off from the top of the block, stuff cleanrags into the cylinders to keep crap out of them. I use a sharp, wideputty knife--take extra care to not score the surface.

Also find some pipe cleaners. Make a loop in the end of one, and stuffthe straight end down into the oil feed hole to keep stuff out of the oil passage. [TW]

After cleaning the top of the block, it is a good time to run a thread chaser (7/16"x14tpi on both SAE and METRIC engines) into the head bolt holes. Idea is to clean all the crud out of them. (You can also use an OLD bolt... cut a few groves into the threadswith a small triangle file, and run it down in and out of the threadedhole a few times, as it will remove the dirt.) [TW]

Be even more careful when cleaning the old gasket off the head--the soft aluminum scores very easily. When clean, check the head for flatness. i use a machinists' rule and feeler gauge. Lay the rule on edge, diagonally. Look between them, and if you can see any light (gaps), then use the feeler gauge to measure the size of the gap. (Mine was warped by .013" )

The max allowed is .0039" (0.1mm) Same for the block--check it too.

Keep the valves in place, and you can clean out the chambers on the head with a wire wheel. [wire wheel? Usually aluminum doesn't like that... I used that nasty Permatex "Carbon Remover". Use gloves, and do it out side... nasty fumes. TW]

If you want to clean off the pistons, move them to TDC, and use a sharp piece of hardwood. As I scrape, I use a vacuum to suck up the crap and keep it out of the space between piston and cylinder wall. DON'T remove the last bit of crap around the edge of the piston--leave a ring about 1/4" of carbon around the piston crown. DON'T remove the ring of carbon around thetop of the cylinder wall. (If your rings are still good, you'll want them to stay that way.)

Installation is the reverse of removal (Don't you just hate it when the manual says that?)

If the head was sent out for machining, I always like to make a trial fit WITHOUT the gasket in place. Carefully place the head on the block, and run all the bolts down FINGER TIGHT (this also makes sure the bolts are not too long). ROTATE THE ENGINE BY HAND. Everything should turn over just fine. After that, I go back and add a littlemodel clay to the top of the pistons and install the rocker andpushrods. Head bolts just snug. Rotate by hand a few times, and remove the head and inspect the clay to make sure there is enough valve to piston clearance. Ya this is pretty picky, and explains why it takes me so long to rebuild an engine. [TW].

Once the clearance has been confirmed, you are on your way.

If the gasket has been wrapped in plastic with a STICKY surfaceit is ready to install. If it was just in a box, and has a non sticky surface I like to COAT it with a light coat of "KopperKoat" gasket spray. Light mist is all you need. Helps seal thewater and oil passage. [TW]

Tighten the head bolts is three passes, using the pattern shown above. MAXIMUM HEADBOLT torque for the R16 is 50 ft-lbs. Three steps: 30 ft-lbs all around, then increase to 40 ft-lbs, then to the final 50 ft-lbs. The original manual recommended DRY bolt threads... just a little drop of oil under the bolt head is all. [TW]

Tom's recommendation: I like using a simple beam type torque wrench on headbolts, as I can feel the bolt tighten down as it turns. Those "torque to click" wrenches go out of calibration, and I hate that "snap" feeling wondering if a bolt just started to let go.

Retorque the head after 500 miles. COLD Engine, one bolt at a time.

I hope I got it all right. I'm sure others will be able to provide a critique of this.

Al Carmichael
67.5 1600
Victoria, BC