Best source for Z24 heads...

[720inTX]

My 1984 Z24 is leaking oil above and below the rear of the exhaust manifold, as well as  overheating. Although I can't see a crack, I am expecting a cracked head when I pull it off. Where have any of you found the best price and quality for a replacement? I have found heads at Advance Auto or OReillys for $600-$700, and one at Auto Zone for $460. I am a little suspicious of the cheap one. I would like to make this repair once and not have to repeat it for at least several more years. Of course, I would like to save a few bucks if possible. Is there a respectable option in the middle? Thanks.

[datzenmike]

 

 

1/ Over heating? Immediately change the thermostat. Cheap and easy to do and if not the problem you now have a new one. Spin the fan with your finger. It should firmly resist turning and stop as soon as you let go. If it spins easily the clutch fan may need replacing. If still over heating the head gasket is likely blown. If changing the head gasket find out how to block the timing chain tensioner so it doesn't fall out when the cam sprocket is removed. IMPORTANT it will save you 4-6 hrs. of unnecessary extra work.

 

2/ My advice for the oil leak is to change the valve cover gasket but check 1/ above first as the head may have to come off first. Use a thin  smear of RTC on the little half moon plugs on the front and rear. You don't need it on the gasket itself. Spray down the head and valve cover gasket mating surfaces first with carburetor spray de-greaser. This is way cheaper than a new head.

 

Oil can also come from the block vent tube that comes up out of the block under the back pair of exhaust pipes and around the back of the head to the intake to the PCV valve..

[frankendat]

Aliexpress and Alibaba sell Nissan Z24 heads for a little less. As far as quality, it is likely they come from the same factory as the Autozone heads. BUT,  read all the fine print, pay with something that has a hard limit or multi step verification and even with that, you pays your money and you takes your chances.

 

You realize that even the most top shelf pristine head will not be "plug and play". The symptoms you describe could be a great number of things. DatzunMike provided a few optimistic options. I'm not optimistic and would wonder what warped or weakened with the overheating.

 

For not much more than the head prices you quoted, have your head checked and decked and reassemble with good quality parts that will compliment your future intentions. Alibaba sells bare heads for under $100 (watch out for shipping it can range from "Free"  to over $300) and don't take a deal for more than you can afford to lose. 

[datzenmike]

7 minutes ago, frankendat said:

Aliexpress and Alibaba sell Nissan Z24 heads for a little less. As far as quality, it is likely they come from the same factory as the Autozone heads. BUT,  read all the fine print, pay with something that has a hard limit or multi step verification and even with that, you pays your money and you takes your chances.

 

You realize that even the most top shelf pristine head will not be "plug and play". The symptoms you describe could be a great number of things. DatzunMike provided a few optimistic options. I'm not optimistic and would wonder what warped or weakened with the overheating.

 

For not much more than the head prices you quoted, have your head checked and decked and reassemble with good quality parts that will compliment your future intentions. Alibaba sells bare heads for under $100 (watch out for shipping it can range from "Free"  to over $300) and don't take a deal for more than you can afford to lose. 

 

While the Z24 has a long history of blowing head gaskets it's not the head that causes this. It's the inability of the bolts to retain their clamping pressure on the head gasket. The head does not warp, it's something to do with the block, possibly the metallurgy or the amount of threads the head bolts screw into? The preventative is to re-torque the head bolts once a year.

 

A $30 head gasket is way cheaper that a $30 head gasket PLUS a new head you probably don't need.

 

 

[frankendat]

3 minutes ago, datzenmike said:

 

While the Z24 has a long history of blowing head gaskets it's not the head that causes this. It's the inability of the bolts to retain their clamping pressure on the head gasket. The head does not warp, it's something to do with the block, possibly the metallurgy or the amount of threads the head bolts screw into? The preventative is to re-torque the head bolts once a year.

 

A $30 head gasket is way cheaper that a $30 head gasket PLUS a new head you probably don't need.

 

 

The OP is losing oil, didn't mention water, or the light brown oil water gunk. I like your headgasket first approach, for me the cheap/easy fix is only the first of many. Maybe his luck is better.

[datzenmike]

My aim is to eliminate everything but the costly head.

 

Have never seen or heard of oil leaking from the head gasket. Valve cover is the most likely cause.

 

Over heating could very well be the head gasket but there are many many other causes. If you are loosing coolant... very likely HG.

[Thomas Perkins]

What does your spark plugs look like?Many things can cause you to blow a head gasket.I never had a head gasket to blow because of bolts needing retighten.I had one blow cause the cat came apart and blocked my exhaust,it blew between cylinder 3 and 4 and the the exhaust plugs there were getting toasted,and it was making a noise there.When the head gasket was sent out to a machine shop for warpness and pressure tested for cracks and valves adjusted,It was put back on and started and noise was still there.He found the cat came apart and was blocking the air flow,causing it to back up in the engine.The cat was removed and now I don't have a cat.When I bought my truck in 94,it did not have a cat.My muffler went bad,took to shop for a new one,they said they could not work on it without a cat,the law here,so my dumb ass had them put one on it and 11 years later,it came apart and blew my head gasket.Ripley's Believe it or not.Also if your engine is leaking oil on the back side,then your head gasket is leaking there.Sounds like your head gasket is leaking.Do like Mike says,put a new thermostat,new oil and filter,new spark plugs,new distributor cap and rotor,new coils.New coolant.New valve cover gasket,put black silicone around half moons,and in  screw holes,torq to 2.2 lbs,also get rid of them Nissan  phillip head valve cover screws and use hex bolts,hard to torq with them phillip screws,I got rid of mine long ago,bad Nissan idea.This is what I do when my head blows. While you have the valve cover off,Paint it.I did mine.

Edited April 18, 2023 by Thomas Perkins

[datzenmike]

I don't believe that a bad cat blows head gaskets. I mean why would it? If the exhaust can't get out eventually it just won't run and before that it wouldn't idle.  What I do believe is that Z24s do blow head gaskets and those who have had them blow didn't have a cat or there was nothing wrong with their cat if they had one. 

[720inTX]

Thanks everyone so far.

 

I have previously changed the valve cover gasket, hoping that's where the oil was coming out. It didn't stop the leak. The spark plugs were dark with carbon- not sure how old. I bought this truck several months ago, and have been repairing 40 years of jerry rigging done by previous owners. So I have new plugs, new wires, and a new valve cover gasket.

 

I am taking datzenmike's advice, starting small. I bought a thermostat, gasket and new upper hose. I was shipped the wrong parts from Autozone, now waiting for the right ones. I also ordered a top end gasket kit and head bolts. When those get here, I will pull the head and put on new gaskets. Hopefully that gets me running well. 

 

I am also looking for a good power steering pump. Mine sounds like a slaughterhouse under the hood. I find rebuild kits for these often- anyone have opinions on rebuilding vs. buying rebuilt? Thanks, guys.

[Thomas Perkins]

On 4/18/2023 at 7:46 PM, datzenmike said:

I don't believe that a bad cat blows head gaskets. I mean why would it? If the exhaust can't get out eventually it just won't run and before that it wouldn't idle.  What I do believe is that Z24s do blow head gaskets and those who have had them blow didn't have a cat or there was nothing wrong with their cat if they had one. 

Wrong again Mike..

[Thomas Perkins]

If your exhaust gets clogged up,then it will back up in your engine and the head gasket will blow,Mine did,just because it never happened to you Mike,does not mean it can't happen to my 720.Be opened minded about stuff.It will run.It will put pressure back n the engine and the head gasket will give.It was not completely clogged up,but enough to blow the gasket.On one side of the cat looked good,other side,the inside was broken apart,he showed it to me and I also got a new pipe leading from the exhaust manifold.Remember my temperature gauge when out on my dash,you kept saying bad thermostat,and it was a bad temperature gauge.I knew it wasn't the thermostat.I had my 720 for 29 years and never had a problem with the thermostat.You seen that the wire on the temp. gauge was fried.No one here said it was the gauge when trouble shooting ,why the gauge was reading low,A thermostat won't do that.Even the water pump I replaced was good.I even replaced the sender and sensor.All the stuff I replaced was free cause of life time warranty.

[powderfinger]

Just because you had a cat that was broken apart on the inside when your head gasket blew doesn't mean the cat caused the head gasket to blow.

[bottomwatcher]

13 hours ago, 720inTX said:

Thanks everyone so far.

 

I have previously changed the valve cover gasket, hoping that's where the oil was coming out. It didn't stop the leak. The spark plugs were dark with carbon- not sure how old. I bought this truck several months ago, and have been repairing 40 years of jerry rigging done by previous owners. So I have new plugs, new wires, and a new valve cover gasket.

 

I am taking datzenmike's advice, starting small. I bought a thermostat, gasket and new upper hose. I was shipped the wrong parts from Autozone, now waiting for the right ones. I also ordered a top end gasket kit and head bolts. When those get here, I will pull the head and put on new gaskets. Hopefully that gets me running well. 

 

I am also looking for a good power steering pump. Mine sounds like a slaughterhouse under the hood. I find rebuild kits for these often- anyone have opinions on rebuilding vs. buying rebuilt? Thanks, guys.

Make sure you are familiar with the chain blocking procedures before pulling the head. Power steering pump is usually just installing a new seal and bearing.

[datzenmike]

11 hours ago, Thomas Perkins said:

Wrong again Mike..

 

11 hours ago, Thomas Perkins said:

If your exhaust gets clogged up,then it will back up in your engine and the head gasket will blow,Mine did,just because it never happened to you Mike,does not mean it can't happen to my 720.Be opened minded about stuff.It will run.It will put pressure back n the engine and the head gasket will give.It was not completely clogged up,but enough to blow the gasket.On one side of the cat looked good,other side,the inside was broken apart,he showed it to me and I also got a new pipe leading from the exhaust manifold.Remember my temperature gauge when out on my dash,you kept saying bad thermostat,and it was a bad temperature gauge.I knew it wasn't the thermostat.I had my 720 for 29 years and never had a problem with the thermostat.You seen that the wire on the temp. gauge was fried.No one here said it was the gauge when trouble shooting ,why the gauge was reading low,A thermostat won't do that.Even the water pump I replaced was good.I even replaced the sender and sensor.All the stuff I replaced was free cause of life time warranty.

 

Hey I understand that experience is often all we can go on.

[720_Jeff]

I seem to recall reading about a Nissan issued TSB on the 720 around head gaskets blowing and one suggest mitigation was to retighten the head bolts?

[datzenmike]

I found the same thing but have never seen it since. This must be 2005? Now all I see are my posts on this.

 

Engine must be cold. Loosen only one bolt at a time and re-tighten to 60 ft lbs. Only then go to the next bolt. With only one bolt loosened at a time you can do in any sequence you like.

[NC85ST]

Clogged cat causing a blown head gasket is ridiculous. I saw years ago what happens when you have a clogged cat. It was on a Dodge D50, Mitsubishi engine. The cat in the exhaust manifold got clogged and it would hardly run, backfired through the carburetor. Cleared the cat and it ran great. No blown head gasket. Unnecessarily replaced the timing set, which isn’t easy, second guessed numerous times about having it right, then tried the clearing the cat and it ran. 

[datzenmike]

If the exhaust is restricted more exhaust will remain in the cylinder. This is like having the EGR valve not sealing because of deposits. There is no EGR at idle because the engine will not idle. Exhaust is inert, all the oxygen is burned up into carbon dioxide so all it does is take up space. Every bit of exhaust left in the combustion chamber is just displacing fuel and air and power drops off. The amount of restriction determines how much power is lost. How will gasket blow if making even less power.

 

If the exhaust is plugged solid this just happens sooner. Won't idle and won't start.

[720_Jeff]

I think, recall Perkins saying that is what the mechanic told him.  I absolutely believe, his mechanic probably told him just that.  

 

In my line of work, tons of guys doing the job for decades, but somehow they still don't understand the fundamentals.  I suspect the mechanic has been on the job for quite some time, but still might not know the fundamentals 😞

Maybe a wiz at twisting a wrench, but diagnostics is a whole different game.

[datzenmike]

I've seen mechanics tell owners really retarded things to explain what happened. Sometimes just to basically shut them up. Who wants a mechanic who says "I don't know what caused this"?

 

The best thing is to know as much or more than your mechanic. That's not too hard when the mechanic wasn't even borne when your truck was made. What's a mechanic's rate now a days? $75-$100 an hour??? Why would you pay a mechanic to learn to rebuild your carburetor and he gets to keep that knowledge! Carburetors were basically discontinued in '82 on cars and mid '80 on trucks. Most mechanics have never even seen a carburetor so YOU know at least as much as he does. Do the work yourself and learn something. Knowing is the best way to not get ripped off. You should know what's wrong and if you haven't the time to fix it you tell the mechanic what you want done. 

[720_Jeff]

20 minutes ago, datzenmike said:

I've seen mechanics tell owners really retarded things to explain what happened. Sometimes just to basically shut them up. Who wants a mechanic who says "I don't know what caused this"?

 

The best thing is to know as much or more than your mechanic. That's not too hard when the mechanic wasn't even borne when your truck was made. What's a mechanic's rate now a days? $75-$100 an hour??? Why would you pay a mechanic to learn to rebuild your carburetor and he gets to keep that knowledge! Carburetors were basically discontinued in '82 on cars and mid '80 on trucks. Most mechanics have never even seen a carburetor so YOU know at least as much as he does. Do the work yourself and learn something. Knowing is the best way to not get ripped off. You should know what's wrong and if you haven't the time to fix it you tell the mechanic what you want done. 

 

All great points.  Some of us have more money than time, others have more time than money.  Probably not too much on these trucks that are beyond the typical guy that is fairly handy.

 

Knowledge is super important, without some knowledge, you really face being ripped off.

 

Edited April 25, 2023 by 720_Jeff

[Ooph!]

On 4/20/2023 at 4:36 PM, 720inTX said:

 

I am taking datzenmike's advice, starting small. I bought a thermostat, gasket and new upper hose. I was shipped the wrong parts from Autozone, now waiting for the right ones. I also ordered a top end gasket kit and head bolts. When those get here, I will pull the head and put on new gaskets. Hopefully that gets me running well. 

 

 

 

When or if you remove the head take it to a local machine shop, they can pressure test the head and check for cracks and if its good they can check the other parts and regrind etc as required.