Replacing the Rear Seal on the U-20

The R&R of a 1969 2000 was the basis of this "How To". However, it should work for most other roadsters too. Where I think of it, I will mention any obvious deviations for the 1600.

Gaskets Needed (for a 2000)

Qty Nissan Part #

1    Oil Pan** 15066-78200
2    Rear seal 12279-58000
2    Side seal 12289-14600
2    Lower tensioner gasket 13079-32200
1    Oil pump 15066-78200
1    Timing cover (Left) 13521-25500
1    Timing cover (Right) 13520-25500
1    Water pump gasket 21074-20100
1    Cylinder head front cover(*) 11047-25500


* This gasket may not be available by itself.

**Tom Walter prefers the cardboard competition oil pan gasket. It is less likely to stick to the engine and come off in pieces!

Please check all these numbers with your Nissan parts person. Or better yet, buy it from your favorite Roadster specialist!


Now keeping in mind the disclaimers at the bottom let's move on... Expect to send about 16-20 hours doing the following steps...


1. Do you have a bad rear seal?

You have oil on the ground and it appears to be dripping out of the little rectangular hole between the engine and the transmission. BUT: this is the lowest place on your engine. The leak could be coming from almost anywhere else (rear corner of your cylinder head, cam cover, oil filter, oil pressure hose, distributor oil hose, oil pan etc.). Spend the time looking for other sources of the leak. I can't imagine anything more frustrating then to spend 20 hours R&R the engine to find out that you only needed to tighten a nut.


2. Raise the front of the car

Block the rear wheels securely. Jack up the front of the car and use a safe mechanism to keep the front part of the car off the ground (and you!)


3. Remove Oil Pan

Drain the oil. Remove the oil pan. You will need a 10mm socket (3/8 or 1/4 drive is best). Loosen all the nuts evenly with your socket wrench. Put them in a baggy and label them.

After all the nuts are out, grab the oil pan and pull it away from the bottom of the engine. At least 50% of the time, the oil pan is stuck to the engine block and you will have to be "creative" in getting it loose. (Tom suggests that you leave four bolts loosely in place, two on each side, and whack the oil pan with a rubber mallet. Sounds like good advice!) After you get the oil pan loose, gently move it around so that the oil pump is disengaged from the well in the bottom of the oil pan. The oil pump is on the passenger side, approximately 3/4 of the way towards the rear of the engine. The combination of the oil pump and the front cross member of the chassis, makes removing the pan a tricky chore.

Once you remove the oil pan, put it in a garbage bag (clean) to prevent dirt from getting into the pan.


4. Remove oil pump

The position of the oil pump makes its difficult to get to the rear bearing cap, so remove it! It is held on by two nuts which on my car take a 11mm and a 12mm wrench. The 11mm nut goes on the side of the oil pump with the least clearance.

After you have removed both nuts, you should be able to gently pull the oil pump out of the engine block. Put it in a freezer size bag along with its nuts. Don't forget to remove the gasket that was between the oil pump and the engine blocks.

5. Remove rear bearing cap

At the back of the engine, is the rear bearing cap. It is held on by two large bolts. Loosen both bolts a little at a time. They are torqued to 65+ pounds so be prepared for a little grunting.

Once you got the bolts out, you can remove the rear bearing cap. It is in the engine block very tightly, so you will need a puller or some other mechanism to pry the rear cap out. The Nissan manual shows the use of a special tool that you can make. Alternatively, you can screw a bolt into the hole in the end the cap (it is the same size and thread as the engine - transmission mounting bolts). *DON"T OVER TIGHTEN THE BOLT INTO THE REAR BEARING CAP* With the bolt in the bearing cap, you can then put a piece of 2x4 across the bottom of the engine and pry against the bolt using the block of wood. I put a washer on the bolt so that I have a larger surface to pry against.

6. Examine rear bearings

If the bad seal is in the bottom bearing cap, then your job is simple. Just replace the seals (main seal and two rubber side seals) according to the instructions below and you are done! (Well, you still have to back put on the rear bearing cap and oil pan.) A failed seal will be usually easy to identify because part of it will be missing or chewed up. If the seal is whole in the bottom bearing cap, look up at the engine block with a good light. You will probably not see the stem of the rope seal on one of the sides of the bearing. With my rear seal, I could see a 1" gap in the block where the seal had been worn away.

7. Can I use the "Chinese finger trap on a cable trick" to replace the upper seal?

NO! I tried it and the clearances are two close. All I did was to get a big bump on my head when the cable and the seal separated.

I did talk to someone that had claimed to have been successful using the "Chinese finger trap on a cable" tool. However, it took him 2 days and 2 finger traps before he succeeded. He also had the car on a lift that allowed him to put his full weight on the cable. In my home shop, I can only lift the car up several inches. So I never was able to put my full weight on the cable.

8. Use Crawford's checklist on engine removal to get the engine out of the car

(Anybody have the URL handy for the ftp site?)

I would only add/change four things:

a. Completely remove the oil line that goes from the engine block to the distributor. It is in a vulnerable spot and can easily get caught on the battery clamp down bracket.

b. Leave the oil pan off (unless you have a dirty car). Without the oil pan and pump, you have gained 3-4" of additional clearance that makes it easier to remove the engine. I would replace the oil pan if I felt that there was any chance that dirt would get into the engine.

c. Completely remove the vacuum line between the distributor and carbs. It also can get crushed or torn as you pull the engine.

d. Loosen the bolt on the front pulley. You will need to have the car in gear and the radiator out to get to this nut. You can wait until later when the engine is swinging on the cherry picker and you have a locking mechanism on the flywheel, but that seems dangerous to me. That bolt is tightened down to 144.6 ft-lbs! I would prefer not to tempt fate by putting that type of pressure on the engine pulling hooks... If you have an impact wrench, you can probably wait until later. However, I have always wondered about the advisability of using an impact wrench on something as sensitive as the crankshaft Tom Walter feels that it is fine to loosen the bolt with an impact wrench but you need to torque by hand.

After the engine is out and swinging on the cherry picker, do the following:


9. Remove the starter

Its on the driver's side and connected by two bolts. Put the starter and bolts in a baggy for later reuse.


10. Separate the engine from the transmission

You have to do this with the engine and transmission dangling from the cherry picker. This is not the most stable setup and so you should be especially careful!

Loosen the bolts: I believe that there are 6: two on top, two most of the way down the side of the engine, and 2 sets of nuts and bolts that connects the rear engine plate to the transmission. (Re-installation Note... The Datsun Service manual for the 2000 gives a torque value for these bolts of 19.52-26.75 ft-lbs for the large bolts and 3.62-4.34 ft-lbs for the small bolts. I have no idea whether these torques apply to 1600's too.)

Once you got the bolts out, the fun begins. You will definitely need two people for this job. The transmission and engine always stick together. There really is no good place to pry them apart. Tom Walter recommends that you set the motor and transmission down onto some 4x4 blocks of wood on the floor and separate it there where you can get some leverage without worrying that you will topple over the Cherrypicker. (sounds like good advice!) It should be much easier to separate the gear box while both are resting on the floor. There is a piece of the transmission that sticks up higher then the engine block (and so it is not a bearing or seal surface). So you can slip a pry bar between the engine and the transmission at this point and get some leverage to start the separation. NOTE: This point exists on the 5-speed transmission, it might not exist on the 4-speed! If you left the oil pan off, you may want to consider re-installing it before putting the engine and transmission on the ground to keep the dirt off.


11. Remove the clutch

Depending on how long your rear seal has been leaking, you might be now looking at a very big mess...

Remove the clutch pressure plate (I believe that there are 6 bolts). Loosen the bolts evenly to avoid distorting the pressure plate. When you have all of the bolts but one removed, prepare yourself to catch the pressure plate and the clutch disk. The pressure plate is a lot heavier then it looks and could surprise you if you are not ready. (Re-installation Note: The Datsun Service manual says that these bolts are torqued to 18.1 - 25.3 ft-lbs. I have no idea whether this is the same torque value for 1600's or earlier engines. Tom Walter suggests that the bolts are SNUG just when the lock washers flatten out. To much torque, and the snap.)

At this point you need to decide whether you need a new clutch disk or whether you can re-use your old ones. If the clutch was slipping, get a new clutch disk. If it wasn't, look very suspicious at the clutch disk and think serious about replacing it anyway... If your oil leak was only minimal and was relatively recent, you may be able to use brake cleaner on your pressure plate. (This may be a classic case of being "penny wise and pound foolish..." I would probably replace the clutch plate unless it was very new!)


12. Put the engine on TDC

As you turn the engine over clockwise, it is the last of the four marks on the pulley. Make sure that the rotor in the distributor is pointing towards the sparkplug wire for cylinder #1 (the forward cylinder). If not, you need to rotate the engine one more complete turn.

13. Remove the front pulley

Hopefully you followed my earlier advice and loosened this bolt while the engine was in the car... If not, you need to put a flywheel lock on (I have one that was originally designed for a VW bug and it seems to work). And then put 144.6+ ft-lbs on that bolt. Be careful you don't break off the hooks on which you are holding the engine!!! Again, you may be able to use an impact wrench here, but I am worried about the impact (sorry for the pun) on the crankshaft.

Remove the pulley with an appropriate puller. There are two threaded holes in the pulley that you should use to grab it. You can then push against the pulley bolt to loosen the pulley. The Datsun Service Manual shows a special tool to do this. I have used a standard pulley puller and grabbed the outside of the pulley. This is a BAD idea because the outer part of the pulley is a separate piece of metal from the center piece with the keyway. The two sections are held together with a band of rubber! By using my method you might accidentally separate the pulley halves or at least knock them out of alignment. Consequently, I recommend that you figure out some pulling mechanism that allows you to work on just the center piece of the pulley.

Be careful not to move the engine off TDC as you remove the pulley. If the crank moves, rotate it counterclockwise a 1/4 of a turn past TDC and then bring it back to TDC.

14. Remove the flywheel

If you have not already done so, put a flywheel lock on. Remove the 12 allen head cap screws that holds the flywheel to the crankshaft. These are metric allen heads (ALL 67.5 and later are METRIC. '67 2000 is metric), don't use a SAE allen head! They are close in size, but you will regret this later... These allen heads are torqued to 57.8 ft-lbs and should be loctited in. I would also recommend getting replacements for these allen head screws. One of these allen heads broke when I tried to remove it, so I don't trust them for re-use!

The original allen heads are NLA. I would check with your favorite Roadster specialist on aftermarket replacements. These allen heads have a very important bevel. I ended up getting some grade 8 at a *very good hardware store* that seemed to be the right size. However, recently there has been some discussion on the maillist that Grade 5 would be a better selection given the type of application.
1600's use a different mechanism for attaching the flywheel to the crank. I have no opinion on loosening/tightening/torqueing the bolts that hold the flywheel to the crank.

15. Secure the engine on an engine stand!

After you have put the engine on the engine stand, breathe a sigh of relief. The most dangerous part is over.


16. Remove the water pump

You can't miss it. It is held in three places. On my engine, there are 8mm and a 10 mm studs and a 8mm bolt. The 8mm bolt and studs takes a 12mm wrench. I believe that the 10mm uses a 14mm (?) wrench. As you loosen the water pump, be careful, there is probably some coolant left in the water pump that will make a mess.

17. Remove the water pump studs

If your water pump is held by studs, you probably should try to remove them. Otherwise, your range of movement is restricted when you try to remove the timing cover. Put two nuts on the each stud, tighten them against each other, and try turning the lower nut counterclockwise. Be careful, these studs could break. The rear of the studs stick into the coolant cavity and so they could be rusted in! Obvious it would be better to live with restricted movement of the front timing cover as you remove it then to break these studs! Tom Walter recommends that you confirm the condition of these stud. He has see quite a few ALMOST rusted out completely from the back side!

Remember when you re-install these studs (or bolts) that you use a sealant on their ends to seal out the coolant. Here Tom Walter recommends PTF (??)compound, common to plumbing. It will keep coolant from seeping past the threads. Locktite applied to CLEAN bolts and threads does the same thing.


18. Remove the front timing cover

If you have mounted the alternator on the passenger side, you will need to loosen alternator to get off the timing cover. If you have a 1600, you might have to remove the alternator completely.

Remove each bolt that holds the front timing cover and carefully record their position. I usually draw a picture of the front timing cover, numbered each bolt on the picture, and put masking tape on each bolt and write the corresponding number on the tape (in pen, pencil doesn't stand up to oil/grease). Tom prefers to take a hunk of cardboard, make a sketch of the front cover. Now poke holes into it, using an old bic pen. As you remove each bolt poke it into the cardboard. Sounds like a better idea!

If you have a 1600, skip the next paragraph and gently remove the timing cover.

If you have a 2000, remove the two 6 mm bolts that connect the top of the cylinder head to the timing cover. Tom Walter notes that these bolts were originally studs! Hopefully somebody has already replace those studs or you will have to pull the head to remove the timing cover!

Carefully use a razor blade to separate the timing cover from the cylinder head gasket. Try to separate the gasket from the timing cover. This minimizes the likelihood of damage to the gasket. Gently rock the timing cover off the front of the engine block.

Remove and store the oil slinger that is on the nose of the crankshaft.

19. Mark the position of the timing chains

At this point, you are staring at the timing chains. On the 2000, there are two chains, but fortunately you only need to remove the outer one that connects the crankshaft to the jackshaft. On a 1600, there is only one chain and it connects the camshaft to the crankshaft.

There should be two timing marks that align on the two gears. These marks are typically punch marks on one of the teeth of the gears. These marks should be opposite each other (I know this is true on a 2000, I believe this is also true on a 1600). If not, it is possible that one of your gears is miss marked. On my jackshaft pulley, the timing mark is not on a tooth, it is in the valley between teeth. Obviously, this pulley must have been made near the end of the life of the manufacturing jig to allow such a variance. In any case, since you want these pulleys to align up in exactly the same position when you reinstall them, mark the two teeth that are opposite each other that are also on an imaginary line that connects the center of the jackshaft with the center of the crankshaft. Hopefully, you will be able to use the original timing marks...


20. Remove the lower chain tensioner

If you have a 1600, you only have a single tensioner that is mounted directly to the engine block. Note the position of the pressure pad and just remove the tensioner. Be careful not to allow the spring in the tensioner to shoot the pressure pad across the room...

If you have a 2000, the lower chain tensioner sits on a block that raises it to the correct level for the outer chain. There are also an oiler hole that starts in the block, that goes through the spacer, and then into the tensioner itself. There are also gaskets between the engine and the offset block and the offset block and the tensioner. These gaskets have little round holes in them to allow the oil to get through. Draw pictures on how this tensioner goes. I did and I still found myself looking at outlines on the block to get a clue on how the tensioner is re-installed!


21. Remove the timing chains

Remove the bolt that holds the larger gear to the jackshaft. Now simultaneously pull both the large jackshaft gear and the smaller gear on the crankshaft. If you are lucky, the gears will start moving together and eventually the jackshaft gear will come off. You can then leave the crankshaft gear where it is. If you are unlucky, you will have to use some type of a puller to get the gears starting to move. I only had to do this once on a gear that I was going to throw away. You will want to be careful how you pull the gear to avoid damage to them. Pull both gears simultaneously.


22. Turn the engine over on the stand

Since you have left most of the parts on the engine, it is *very* heavy. So be careful as you turn it over.


23. Loosen rods

Since you have set the engine at TDC, pistons #1 and #4 should be all the way down the cylinders (they are at the top of their stroke). Pistons #2 and #3 are at the bottom of their stroke and so their rod bolts are easily accessed. But it is also very important to remember that Pistons #2 and #3 are in a dangerous position. There are valves open down there! Consequently, its very important that you be extra careful as you loosen these rods. Tom reminds me that 3 inch sections of rubber hose (fuel line is good!) over the rod bolts will protect the crankshaft from getting scratched!

Start by loosening the rod nuts for pistons #2 and #3. NOTE: On a 2000 (and probably all other roadster engines), these nuts are SAE not metric! Don't use a metric socket because you will round the nuts!!! After you have almost removed the nuts for pistons #2 and #3, carefully tap the top of the nuts to separate the halves of the rod. Make sure that you are holding the portion of the rod that connects to the piston so that the piston doesn't suddenly drop and hit that valve! (Probably couldn't happen anyway unless you were in desperate need of a ring job...). After you have loosen both rods, push them carefully down into their cylinders until they do not go any further (remember those valves!).

Now rock the crank 90 degrees (be careful that the rod bolts for pistons #2 and #3 don't scratch their crank journals!) so that rods for pistons #1 and #4 are at about mid stroke. Now loosen their nuts and separate the bottom of the rod from the top. Again, after you have loosen them, push the rods down to the bottom of their cylinders.

BTW: Don't mix up either the rod caps or their bearings! They need to go back on the same rod. There is a number stamped on the side of the rod cap (1,2,3, or 4) that matches the corresponding number on the rod. But still be careful! Some previous owner might have lost a rod and you might have two #2 rods! I do! Make sure you know which rod cap goes with which rod! Tom points out that the number should be stamped on the cap, and the rod. Both should be visible on the same side of the rod. There is also a front and rear to these caps. Triple check!!!


24. Remove main bearings

Assuming you took my original advice and have already removed the rear bearing cap, so remove the front cap (otherwise remove the rear bearing cap first). Then alternate sides of the middle bearing removing #4 and then #2. Leave the center bearing for last. (If you have a 3 bearing motor, your job is simpler by 2 bearings!) Except for the middle bearing, you should be able to gently pull and rock each of the bearings to remove them. On the middle bearing, you will notice a bolt hole (remember that one on bearing #5?). You may need to screw a bolt into the cap and pry against a piece of wood like you did on bearing #5.

As you remove the bearings, make sure that you keep them in order and you note which side faces front (there is usually an arrow on one side that faces front). The main bearings may or may not have marks on them indicating their position. If the marks are not obvious, you should figure out a mechanism to determine which one goes where. Putting a bearing back in the wrong hole is a quick way to create a need for a engine major overhaul!

25. Remove crankshaft

You should now be able to grasp both ends of the crankshaft and lift it up. Be careful not to tilt it and jam a bearing....


26. Clean out old rear seal

Finally, you will get your first clear view of the culprit, the upper rear main seal. You will probably find it a mess. Remove the seal, clean out the slot that the seal fits into. Do the same thing with the rear bearing cap. Remove the rubber side seals that fits into slots on the rear bearing cap. You should also find some remnants of silicon seal on the side of the rear bearing cap and along the walls where the rear bearing cap meets the engine block. Clean all this silicon sealer out. Be careful that it doesn't drop into the engine!


27. Prepare new rear seal

Soak your new rear seal in oil. I soaked mine in 30wt oil for a couple hours. Maybe you could get away with soaking the seal for a shorter time period. But a couple hours worked for me. Try to minimize your handling of the seal.


28. Install rear seal in engine block

Pick up the rear seal that has been soaking in oil and carefully insert it into the rear most slot in your engine block (the crankshaft has a built in oil slinger that fits into the hole closest to the bearing). Using a large socket and hammer, carefully tap the seal into place. Now roll the edge of the seal with the socket until the edge of the seal is flat and a little higher then the bearing. After you have the rear seal install, carefully cut the seals even with the tops of the bearing surface (use a new razor blade!). Be careful not to accidentally pull up on the seals as you are cut them.

Repeat this process with the seal in the rear main bearing cap (make sure you put the seal in the right slot!)


29. Re-install crankshaft

Make sure all of the bearing surfaces (both the bearing inserts and the faces of the crankshaft) are very clean! Coat the main bearing surfaces with oil. Put extra oil on the rear main seal.

Position the rods so that they are facing straight up and not leaning to one side or the other. I used crushed paper towels stuffed into the engine block for this purpose.

Carefully pick up the crankshaft and set it down in its bearings. Place the keyway of the crankshaft so it faces directly down (relative to the engine). Be careful that the rods are aligned with their respective journals as you set the crank down. DO NOT ROTATE THE CRANKSHAFT UNTIL ALL OF THE BEARING CAPS ARE IN PLACE!


30. Install main bearings #1-#4

Pick up the bearing cap for #3. Make sure its bearing surface is clean and carefully set it into position (remember to make sure that the arrow is pointing towards the front of the engine!). Push the bearing down and start its bolts. Tighten them finger tight. Move the crankshaft back and forth (but DO NOT ROTATE IT) to center the bearing. Now do the same with the rest of the bearings in the following order: #2, #4, and #1. Leave bearing #5 off for the time being. Don't tighten the bolts any more then finger tight!

31. Install rods

Without moving the crankshaft, install the rod caps on their respective rods. Rods #1 and #4 will be hard to reach because they are at the peak of their upstroke. Carefully, put the nuts on the rod bolts. Don't drop the nuts! Not only will they be hard to find but you could also scratch a cylinder! Tighten each rod until the rod cap just touches the base of the rod. Do this evenly or you'll jam the rod cap on the bolts.

32. Torque the main bearings

Torque the main bearings starting with # 3 and then proceeding to #2, #4, and #1. Pry the crankshaft back and forth to align the bearings before you torque each bearing. The Datsun Service Manual indicates that the mains are to be torqued to 65.1 ft-lbs.


33. Install the rear main bearing cap

Put a small bead of silicon seal (I use ultra gray) in the corner of the engine block from the rear of the engine to the slot where the rear seal is placed. Place some silicon seal at the bottom of the slots in the side of the main bearing cap. Place a very small dab of silicon seal on the four ends of the rear seal.

Align the main bearing cap with the engine block and carefully tap it down using the wooden handle of a hammer. Tap the bearing cap evenly until you can thread its bolts several turns into the engine block. Now, tighten each of the bolts evenly until the rear main bearing cap is pulled all the way down. Torque the rear cap to 65.1 ft-lbs.


34. Install the rear side seals

Find the rear side seals. They are rubber rectangular objects that have ridges on two sides. Figure out which of the two sides with ridges has a wire. The side with the wire will go towards the rear bearing cap. Coat the side seals with silicon sealer (again I uses ultra-gray). Lightly tap them into the rear main cap. These seals go all the way down. They will easily go in all but a 1/4 inch. To seat the seals fully, you will have to force out the silicon sealer you put in the side of the rear main bearing cap.


35. Torque the rod bolts

Now go back and torque each of the rod bolts in turn. The Datsun Service Manual indicates that this torque (again for a 2000) should be 65.1 ft-lbs. Don't forget any!


36. Reinstall timing chains

Turn the engine right side up and get your timing chains. If you are lucky, you will be able to align the marks on the timing gears and gently push on the gears and chains on both the crankshaft and the jackshaft. When you are done, your timing marks should align as they did when you took the chains off. You may have to jiggle the crankshaft a little to get things lined up. It is also possible that the upper tensioner has moved the camshaft a little when you took the lower chains off. If so, take off the valve cover and make sure that the arrow on the top of the cam tower #1 points exactly to the center of the hole in the camshaft gear.

On a 2000, the jackshaft bolt is torqued to 32.5 - 36.2 ft-lbs.


37. Reinstall the oil slinger on the crankshaft

The "dish" should point out.


38. Install/Wait on oil pan and oil pump

At this point you can reinstall your oil pump and oil pan or wait until its in the car. Waiting until its in the car gives you greater clearance. If you are working alone, this could be very useful. Installing both now means that you have sealed the engine from collecting dust that could harm your engine.


When you install the oil pump, make sure that you align the slot in the top of the oil pump with the end of the distributor drive gear shaft. Don't try to force it! When you are aligned, the oil pump can be push right up to the bottom of the engine block without any effort. Don't forget to put that new gasket on between the oil pump and the engine block!


39. Now starting at step# 18, perform the steps in reverse order.



Although I believe this document to be correct, IT IS PROBABLY INCORRECT IN SOME RESPECTS. PLEASE USE YOUR OWN EXPERIENCE AND INTUITION. DON'T RELY ON MY INSTRUCTIONS 100%! So far my record is 2 good seals out of 3. However, it is probably an accident that the first seal was good and the 2nd seal certainly failed (1/2 inch gap in the seal when I pulled the rear bearing cap!). At this point, I still consider the success of the third seal a fortunate occurrence and I wouldn't want to bet on my success on a fourth one!

If you have any suggestions for improvements, please send me an email.
Mark Hatch.

©1999, Mark Hatch