L20 motor dissasembly method

[Curt]

Ok cool, I was thinking along those lines.

[Charlie69]

If it is rebuilt it should be clean.

[datzenmike]

The cam is most likely a U20 "C" cam. There were A, B and C cams. I think the C is the one you want. I don't have specs though.

 

The brackets you are missing are block stiffeners. Most people remove them over time to save weight or just ditch them because they don't think they need them. I wouldn't worry about them.

 

They were also made in aluminum. I have at least one set still.

 

Will, a member here, removed his front seat and carried an L20B cross country to New Yawk..

[Stoffregen Motorsports]

If it is rebuilt it should be clean.

Clean? How about dripping with assembly lube and oil?

 

That's the way most machine shops are.

[Stoffregen Motorsports]

They were also made in aluminum. I have at least one set still.

 

Will, a member here, removed his front seat and carried an L20B cross country to New Yawk..

I brought a spare motor with me on a trip to San Diego once. My L20B burned so much oil that I just knew it was going to fail on the trip. It didn't.

[Curt]

I would like to replace the block stiffeners at some point. I'm not sure the older 5 speed trans has receiver holes for the bolts anyway. The trans from the 80 720 has them though.

 

Yea, I was trying to keep the dog hair and other misc crap out of the assembly lube to keep both the vehicle and the block "clean". I've got some unused drop cloth plastic left over from painting. That should work.

[Curt]

Update: Got the bottom end back. I also scored this sweet ass casting from a member on here! Thought you might like a pic.

[datzenmike]

I brought a spare motor with me on a trip to San Diego once. My L20B burned so much oil that I just knew it was going to fail on the trip.

Just like a Datsun owner.

 

 

It didn't.

Just like an L series engine.

[Curt]

It's gonna be time soon to rebuild the head for this project. The w-58 that was on the l20b is closed chamber. The A-87 I have is open chamber. Should I go ahead and rebuild the a87 or rebuild the closed chamber w58? the A87 was running but has a lot of miles. The w58 was rusty but has much less miles on it and is round port with liners instead of square. The valves appear to be the same size in both heads.

 

Edit. Does anyone know offhand the size and thread pitch of the headbolts? I need to get a thread cleaner.

[Curt]

Help! Does anyone know a part number for the motor mount bushings for an 1974 620 with an L-18? I got some off rock auto and they are clearly not the correct parts.

[datsunaholic]

Unfortunately the 73-74 rubber mounts somehow got screwed up in the master parts list for everything (not just rockauto). It's wrong in every catalog, including Nissan which shows it as obsolete, and superceded by the wrong part.  I have not been able to find actual '73-74 620 motor mounts for almost 2 decades, since the part number got crossed up with  (i think) a 610 mount which is nowhere close to being correct.

 

What I ended up having to do was get the 75-79 metal brackets and use the '75-79 type rubber isolators, though they don't fit exactly right they work better that the worn out mounts.

[Curt]

Ahh, ok thanks. I went and looked at the pics for the later mounts for the l20b equipped 620 and they looked closer. Thanks for the help, that is the route I'll go. So I should try and source some l20b 620 engine brackets then as well? Did you try the L-18 brackets? 

[datsunaholic]

If I recall there was a height and bolt position difference between the brackets, but in all honesty I have an L20B in my '74 anyway.  The height difference may have been due to the flattened and warped worn out old insulators.

[Doctor510]

Head bolts M10 x 1.5

[Doctor510]

Motor mounts, are they the ones that have 2 studs on the same side? If so I have a couple.

[Curt]

These are the mounts in there. These are the mounts I need to find. They look a lot like the l20b mounts.

 

 

these are the mounts I received. 

 

These are the engine brackets that I have from the L-18. 

[Doctor510]

My last set of 510 mounts from Rock Auto were the correct ones for the truck and not the 510.  As I remember, the truck mounts that the locating "pin" on the frame side, the 510 ones are on the steel mount that goes to the block

[Curt]

Yes, the pin is on the frame side. I'll look into the 510 mounts.

Edited, Just realized the locating pin is on the block side. I ordered up a set of both the 510 mounts and later L20b mounts.

[Curt]

Anyone know the size and thread pitch for the egr tube ends on the l-18?  I'm looking to plug up the hole on the exhaust manifold side. I'm planning to make a block off plate for the intake side with a tap to keep the pcv system operational. 

[datzenmike]

Cut the tube off 1/2" and pound it over and weld closed. It'll probably be a metric pipe thread.

[Curt]

I'll take the tube into some places and figure it out. I can't weld unfortunately and I've got the tube out already. I'm going to have the manifold cerakoted so I wanted a smooth look. I read a thread here about other plugs on later exhaust manifolds that were m24 x 1.5.

[Curt]

None of the motor mounts I tried fit. Tried the 72 510 mounts and no go. The location pin doesn't clear the bracket. I did get the later l20b mounts but I'll need new engine brackets to use them. 

 

Another question. Will the head location rings that install in the block hang up when I torque things down since the head and block were milled? Very minimal mill on both, Block was .006 head was minimal too but didn't ask the machinist.

[Curt]

Is this going to matter? the liner in the head gasket is slightly in the bore in 2 locations in two cylinders.

and the second.

They are just about parallel with the bore further down, but they cover the angled grind at the top. 

[Doctor510]

Look like you got an early gasket.  You need a MINIMUM of 0.020" gasket bore more than the cylinder bore. If you use this one, you'll blow a head gasket in a heart beat.  Your pictures show 3.3154", that's 84.211mm.  What's going on here, the stock bore on an L20B is 85mm, gasket fire ring bore should be at least 85.5mm.  Something is WAY off.

 

The "locating rings" are a non-issue unless your head/block combo of milling exceeds 0.040".  Be sure to check the cylinder head thickness, stock is 4.250"

 

To plug the EGR tubing fitting, take it out, tape the tube hole and plug it with the proper bolt size if you don't want to weld it.

 

Check your parts twice before you use them.

[Curt]

I'm not sure about the measurements on the piston tops either, now that you point it out. The pistons were supposedly l20b pistons .75 over. They have .75 stamped on the tops. I never measured them myself though, just took the word of the seller. My only guess is the head gasket is for an l-16? maybe it's just a bunk gasket? All the other cylinders the gasket has much more room around it.