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KDW_80-720

'80 720 L20B

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Looks fine. Have never heard of a chain or sprocket failure or wearing out. This is why the KA use a single chain... the L and Z series were over engineered with a double row chain and never wore out. The L16/18 have two adjustments for wear or stretching, (each 40 or about the length of the etch mark on the cam thrust plate) the L20B is set on the middle one so one adjustment, but you could always go negative to the #1adjustment hole and move the cam sprocket ahead one tooth or 90 vs. 2 X40. No one can be bothered to check they just replace.

 

Chain guides and the tensioner shoe are another story. They are neoprene? coated and will wear out. Chains? pretty much never.

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From the 2 pics the cam lobes look ok, even fairly clean inside. Makes me curious if the head was recently done & it was the PO attempt to put things back together that created the issues. So if the cam gear teeth are still flat across the tips and not sharp & pointy, there is some good news in that.

 

Pull the spark plugs out & assuming you can turn the engine by hand (with a ratchet) then crank it until #1 is at TDC - verify this with both valves being closed & check by inserting a probe into the cylinder - confirm TDC on the piston by turning the engine FWD and REV enough for that verification. Got TDC with valves closed, check that the external timing mark on the crank confirms 0 degrees. Does the cam chain timing mark agree with the index? If so then you're doing great! If things aren't in agreement, you have more work to do but things will be better than before.

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Maybe he just changed the oil regularly. Could happen...

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Yep. Did that one. 
 

Got head off, not sure what I’m looking for on this one. 

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Water passages look plugged.

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Yup those are definitely plugged! And is that a hole in the piston??

 

hole in piston.jpeg

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Does look a little dark.

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9 hours ago, EDM620 said:

Yup those are definitely plugged! And is that a hole in the piston??

 

hole in piston.jpeg


I got the pistons out. It looks like al 4 of them have a not. My engine builder friend came by last night and checked everything out. My bearings all look good(going to change anyway), crankshaft and overall the block. I can’t get the bearing cap at the rear and of the engine out though, it looks like there might be a little trick to getting them out. 
 

Is there a quick simple little bore on the block I can do to get just a little more out of engine?

 

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What's plugging those water passages???? Looks like someone went crazy with some kind of rad stop leak and plugged everything up. NEVER use that stuff. Thoroughly power wash that crap out of the block and head. Better check out the rad and clean it too and back flush the heater core too. Someone did this... expect the worst.

 

The cylinders should be measures for taper, ovaling and wear. Above a certain amount the clock should be over bored and new over bore pistons and rings installed... you then have a new engine. You can opt for a quick 'hone and ring' to squeeze some more miles out of it. If you do, use cheaper cast iron rings for a quicker break in. Because the cylinders won't be perfectly round  from boring, chrome rings can often wear out before they can seat. If you do go over sixe that go with chrome molly rings.

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Oh I’m going full rebuild at this point. I’m already there so I might as well do it. It’s a project so I have some time to get stuff done. 
 

there’s some major wearing in the cylinder walls and some gaps, so we’re thinking about what to build with it now

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2 hours ago, KDW_80-720 said:

Oh I’m going full rebuild at this point. I’m already there so I might as well do it

Excellent - will spare you headaches of sorting out some problems...

If you're able to measure the current cylinder wear accurately you'll know what the minimum over-bore you'll need to do. Get your new pistons & ring sets then take them with the block to the machine shop for boring - they'll ensure the bores are matched to the pistons.

 

Any idea of how many miles/km are on the truck? Nissan used high-grade steel in the blocks so wears well.

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2 hours ago, datzenmike said:

Better check out the rad and clean it too and back flush the heater core too.

As datzenmike says, with the passages that plugged, expect to find more of the same throughout your cooling passages. If the PO put that stop-leak into the rad, it was probably leaking so taking it to a local rad shop for a flush - or plan on a replacement there too.

 

Thought: pandemic lockdown excluded, but if you have a local school that has auto shop, some of those tasks you could get done by students & cheap labour rates...

 

The machine shop will hot-tank/degrease the block but you should pressure wash the head unless you're also going to do a full-on rebuild of it too, the aluminum head is prone to warping at hot-tank temperatures resulting in additional machining costs. Pressure washing saves you from that (cam boring too). Talk to them about their hot-tank option, as a head resurfacing will probably be needed plus crank-boring. I spared myself those extras by choosing just the degreasing - noting my passages didn't look like yours - and my block didn't need a head resurfacing/crank align bore.

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Odometer says 120k. Head gasket looked brand new, so I think they did the head thinking it would solve problems, then realized it was another good chunk to finish it.

 

I'm thinking of going with something Mike said on another thread about swapping to a Z22 crank w/ KA24E pistons and pretty much use all the same parts from L20B.

 

Just gotta find the pistons and crank.

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Boring from 85 to 89mm is rather ambitious on an L20B. It's a scary amount but do-able. You need a Z22 crank anyway so get an entire Z22 and bore that block from 87mm to 98mm.

 

That head isn't the original, you can see that it has closed chambers so a W58 if round exhaust ports or an A89/219 if square. This will complicate building a big bore 2.3 because the compression will be 10.4. HOWEVER, you can unshroud around the valves all you like. There's about 4cc difference between closed and open chamber heads.

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22 minutes ago, datzenmike said:

Boring from 85 to 89mm is rather ambitious on an L20B. It's a scary amount but do-able. You need a Z22 crank anyway so get an entire Z22 and bore that block from 87mm to 98mm.

 

That head isn't the original, you can see that it has closed chambers so a W58 if round exhaust ports or an A89/219 if square. This will complicate building a big bore 2.3 because the compression will be 10.4. HOWEVER, you can unshroud around the valves all you like. There's about 4cc difference between closed and open chamber heads.

 

 

It does have the round exhaust ports.  so it's which one?  I think you said round ports twice, so I'm a little confused on that.

 

 

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Corrected..... W58 are the only heads with round exhaust ports.

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5 minutes ago, datzenmike said:

Corrected..... W58 are the only heads with round exhaust ports.


okay, thank you. I guess I’ll do some more digging on the correct build with my current parts outside of pistons. 

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That is what is called a "Peanut" head.  Mike will be posting info and pictures of the heads.

Edited by Charlie69

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I've had members swear their head was never changed and they've had it since new and it came with a closed chamber on it. I find this very unlikely. Nissan would never send random open and closed chamber heads because the higher compression would never pass emissions. The '78 and up were W58 open chamber and low emissions. If they shipped closed chamber heads in the EPA would go ape shit on them. 

 

My theory is that in the '80s when these engines might be needing a valve job it would be cheaper to buy a head from an import engine than replacing seats and grinding valves. Even worse today. Mechanics don't like to work, they don't and can't fix things, only replace old, worn broken parts with new ones.

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1 hour ago, datzenmike said:

I've had members swear their head was never changed and they've had it since new and it came with a closed chamber on it. I find this very unlikely. Nissan would never send random open and closed chamber heads because the higher compression would never pass emissions. The '78 and up were W58 open chamber and low emissions. If they shipped closed chamber heads in the EPA would go ape shit on them. 

 

My theory is that in the '80s when these engines might be needing a valve job it would be cheaper to buy a head from an import engine than replacing seats and grinding valves. Even worse today. Mechanics don't like to work, they don't and can't fix things, only replace old, worn broken parts with new ones.

True. 
 

I’m gonna pop my head in to a machine shop friend of mine and have him take a look at the head for now, I need to get ahold of that how to modify your Datsun engine to find the best mod with my current set up outside of pistons. 

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You could remove the pre-heat liners inside the head and port the openings as well.

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13 hours ago, KDW_80-720 said:

True. 
 

I’m gonna pop my head in to a machine shop friend of mine and have him take a look at the head for now, I need to get ahold of that how to modify your Datsun engine to find the best mod with my current set up outside of pistons. 

 

I've removed the exhaust liners before, the valves need to be out. They are thin soft steel. I slit lengthwise past the valve guides with chisel and twisted them out. The first took a hour to figure out the last was 15 min. There are several bumps in the port wall that support the liner away from it so it isn't cooled from contact. The exhaust then heats them to glowing and with air from the injection pump any unused gasses are burned. You can gring the bumps away. More of a post heat.

 

Bolt the intake gasket on the head and scratch the outline of the opening on the head around the port. Grind away any aluminum out to the scratch mark and smooth into the port for an inch or more. Now use gasket on the exhaust manifold. If not a scratch use spray paint and grind away any paint that shows. The ports and the exhaust manifold now match perfectly (and are larger) and without a lip. While you are there you can do the intake and intake ports as well.

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Personally I would not rebuild that block, I would find a Z22 block/crank/rods out of a 1981/82 Datsun 720 and rebuild that, a Z22 block bored out to except stock 89mm Z24 dished pistons, I put a closed chamber head on mine and Mike said it was 8.9 to 1 compression ratio.

Of course I had I believe 42mm 280 Zcar valves/hardened seats installed in my head, I had the head intakes ported to match the 1.5" Dual SU intake manifold and I run dual SUs and I left the exhaust port alone, you likely would be just fine with them liners in your exhaust ports and I think you already have 1.5" intake ports but I might be wrong, this is not a race truck so you should be fine, but you will almost have the torque of a Z24, and you will walk away from a Z24 on the freeway.

The only issue is finding a Z22 without any cracks around the water jacket, they are known for this issue.

I did have to re-curve my distributor because I run regular gas(I have a reason), other than that I have had this engine in my work truck for close to 9 years now, I have no issues hauling my trailer(electric brakes) or mass amounts of weight, at this time my truck rolls over the scales at 3900lbs empty, and it hauls ass empty, I broke my speedo needle off breaking the engine in.

Edited by wayno
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