Exhaust manifold cracks and egr hole fun

[Foxhound]

Welp, I had to take off the manifold to figure out how to plug the egr tube hole after massacring the tube nut. I have that King Midas touch, but instead of gold things turn to shit. The datsun gods--all hail--blessed me though with nice loose bolts and nuts to the head and flange, suspiciously loose actually. Maybe it was the occasional pre-liquid wrenching the past 8 months since I've bought the truck in foresight of my inevitable dumbassery. There was also that 250$ first vehicle I got in Maine who's rust traumatized me for life and I now use liquid wrench on rusting bolts like holy water on the poltergeist. Either way I was overjoyed to have taken it off with such ease knowing what possible tom-foolery lay ahead for the egr hole.

 

After taking it off and cleaning up the mating surfaces I noticed a couple hairline cracks in manifold, about 2 inches or so long on opposite sides of the manifold. Theyre not near any bolt holes or mating surfaces luckily and pretty hard to spot. I'd like to salvage this manifold if possible. Whatever happens it's going back on the truck anyway. I'm already this far in, might as well get some xp and level up my fuck around and find out skill set. I could just buy a new manifold, but where's the fun in that. I couldn't look myself in the mirror if I did. Might as well buy a fancy suit, start working in one of them fancy skyscrapers, and pay someone else to bang my lover because I'm too busy drinking fancy champagne with fancy hookers.

 

For the EGR hole I've started to drill it with a 3/4" bit which should be about the perfect size to not cut into the manifold threads if it stays centered, which it has because of the smaller diameter hole from the tube. My hope was that the old threads would kind of peel up a bit as I drilled but nope, only a little at the top. Maybe a reverse direction bit would have been better but my biking-distance-homedepot isn't going to have that and I was eager to start. Boy was it slow drilling though with lots of oil. I think I have it about deep enough to where it needs to be and I'll have to wait for a 24mm tap to get here to continue my dumbassery.

 

I wanted to take out the air injection nut/tubes as well. I'd already cut them and folded them a while ago becuase I don't even have a cat, I have a dog *cough* EPA bots *cough*, and they were just in the way a lot of the time. They are proving to be just as difficult to break free. Wish I had one of them fancy induction heaters, but we all know the slippery slopes of fanciness. I'm not gonna risk using any wrench of sorts more than what I already have and just buy a 24mm socket. God I hate buying single sockets.

 

For the cracks...hmm. My monkey brain tells me I should eat a banana. Then maybe drill small holes at the ends of the cracks to try and prevent them from spreading and carve a little valley with a dremel for some high heat jb weld, though I have my doubts about any jb weld at those temperatures. My other thought is just smear some rtv red in there and paint over it. They're so thin it's hard to gauge whether I should even worry about them but I'd like to take care of it while I can. I'm painting it with proper heat resistant ceramic yada-yada either way. I don't have a welder nor the skills to weld cast iron which I've heard is notoriously difficult. What I really don't want, and the reason I started all this, is extra sounds preventing me from hearing the engine and actual issues that might need attention. Definitely could use some suggestions on this.

 

Another questionable thing I noticed after I got the manifold off was an obvious color difference of soot on cylinder 2s exhaust hole. Its much lighter than the other 3, gray even. Any ideas as to what could cause this? Coolant burning? Too lean mixture? Valve issues?

 

 

 

 

 

 

[NC85ST]

I hate to tell you this, but Z24 exhaust manifold’s are known for cracking. 

[datzenmike]

 

Cylinder two is running cleaner than the other. Can't be a mixture problem as all cylinders draw from the same source. Black is carbon possibly from a miss fire or oil from worn rings and/or valve guide seals. You could check a few things...

 

1/ Plugs are BPR5ES for the exhaust side and BPR6ES for the intake, gaped to 0.032". Always use NGK and NOT from Amazon... too many counterfeit out there. Timing set to 5⁰ BTDC. Visually inspect the rotor, cap and the wires, if they look bad... they are.

 

2/ A compression check might show a low cylinder. Gives a relative wear indication. Good compression 170 and above, worn below 150, tired below 130. All cylinders must be within 15% of each other. Consistent compression is best even on a worn engine. The Z24 is known for blowing head gaskets so look for two adjacent cylinders that are low.

 

3/ Check and set the valve lash on a hot engine. 0.012" for all.

[Seven Two Oh No]

I repaired a crack in my manifold with JB Weld but it didn't last long, probably because differential expansion/contraction between the metal and JB Weld eventually separates them. A manifold for a 1986-1989 D21 (https://www.napaonline.com/en/p/NOE6002391) will supposedly bolt on - haven't replaced mine yet but planning on it soon. I've read you can weld/braze the cracks but need special skills to deal with cast iron

 

Edit - remembered that I used the JB Weld High Heat putty but still only got a year (maybe) out of the repair, despite thorough surface prep, etc. Manifold is just too hot for patching like that, as Mike mentions below

[datzenmike]

JB is two part epoxy plastic with fine metal suspended in it. Exhaust manifold is too hot for it.

 

The '88-'89 4x4 D21 is an exact part number match. The 2wd may still work.

[Foxhound]

 

I was able to get a sharpened flat head behind the old threads and then slowly them pry them out. Then to appease the datsun gods I placed the 24mm bolt in a clamp along with the tap and spun it in with some silcone oil. Seemed to have done the trick. Praise be datsun.

 

Now onto the air injection bolts. Hopefully I don't have to drill them out as well.

 

I'm gonna rock with the old exhaust until I can afford a nice header. It'll do for now.

 

 

[Foxhound]

6 hours ago, datzenmike said:

 

Cylinder two is running cleaner than the other. Can't be a mixture problem as all cylinders draw from the same source. Black is carbon possibly from a miss fire or oil from worn rings and/or valve guide seals. You could check a few things...

 

1/ Plugs are BPR5ES for the exhaust side and BPR6ES for the intake, gaped to 0.032". Always use NGK and NOT from Amazon... too many counterfeit out there. Timing set to 5⁰ BTDC. Visually inspect the rotor, cap and the wires, if they look bad... they are.

 

2/ A compression check might show a low cylinder. Gives a relative wear indication. Good compression 170 and above, worn below 150, tired below 130. All cylinders must be within 15% of each other. Consistent compression is best even on a worn engine. The Z24 is known for blowing head gaskets so look for two adjacent cylinders that are low.

 

3/ Check and set the valve lash on a hot engine. 0.012" for all.

 

Just got all new plugs and wires. Plugs from rockauto. Unfortunately they don't have the wires anymore so I had to go with amazon. I did get NGK coils from rockauto as well, but was disappointed to learn they are made in China. My timing is set to 5° right now and I just put on a new weber. I have to rejet. Jets are on the way. Valve lash has been adjusted recently too. I do need to check my compression again, its been a while, but on a cold engine they were all 170ish last summer. I don't have a leak down tester tho. Couldn't it be mixture problem if a valve isn't closing properly? Could these issues be old issues and have just left their mark or are they more likely recent.

 

 

[banzai510(hainz)]

If you have 170 then I say the valve is closing

 

the stock coil might be better

[datzenmike]

Coils don't wear out.. they either work or they don't. NGK is fine if the resistance of the primary is about 1 ohm. Better check. Factory coils (0.75-1.0 ohm) are best and matched to the electronic ignition. If you have a points coil it will run too hot. It its 3 ohn you spark will be reduced.

[Foxhound]

57 minutes ago, datzenmike said:

Coils don't wear out.. they either work or they don't. NGK is fine if the resistance of the primary is about 1 ohm. Better check. Factory coils (0.75-1.0 ohm) are best and matched to the electronic ignition. If you have a points coil it will run too hot. It its 3 ohn you spark will be reduced.

 

I understand. I got new ones because the old were out of spec with the nissan manual. The new ones are also at about 1.7 ohms. I try...but to my own demise 🤣

[datzenmike]

 BTW what were the old ones measuring? Has to be disconnected to measure properly.

[Foxhound]

47 minutes ago, datzenmike said:

 BTW what were the old ones measuring? Has to be disconnected to measure properly.

 

10.5k secondary and 1.3 primary on one, and 11k and 1.6 on the other. I used two multimeters to make sure. My manual states between 1.04-1.27 for primary and for secondary I can find two different values. One on the diagnosing page saying between 7300-11000 and one on the specs page for the coil in a z24 saying 8400-12600. I'm dealing with 6 previous owners so I doubted they were stock to begin with and figured I'd just freshen up everything on the ignition side of things to help tune a new weber and have some fun extra coils to play with for the sake of science. But alas, NGK coils are 1.6-1.7 on primary. They still seem to function fine. They don't say I need an exteral resistor on the coil, but in the picture online it did say it on the coil.

[datzenmike]

They will work but I would try for around one ohm.

[Foxhound]

20 minutes ago, datzenmike said:

They will work but I would try for around one ohm.

Would installing a resistor before the coil achieve this or does the resistance specifically need to be in the primary coil itself? I'm all for opening up one of the extra coils and tinkering for the sake of science if need be. Shortening the length of coil in the wire should lower the resistance eh? I'm out of my mind.

[datzenmike]

Adding a resistor will add resistance and this would reduce current through the coil and reduce output.

 

 The lower the primary coil resistance is the more current flows through the coil and the stronger the magnetic field produced. When the distributor shuts off the power through the coil the collapsing magnetic field generates a high voltage response in the secondary windings.

 

12v through a 1 ohm coil resistance will cause 12 amps of current to flow

12v through a 1.7 ohm coil resistance will cause only 7.05 amps of current to flow. Just over 70% less current.

 

The 1.7 ohm coil will still fire the plugs, I just like getting all out of the coil that I can.

 

 

[Foxhound]

6 minutes ago, datzenmike said:

Adding a resistor will add resistance and this would reduce current through the coil and reduce output.

 

 

 

Dur. I knew that. Dont know why my thoughts went the opposite way. That's a pretty decent difference in amperage. Thanks for spitting your knowledge.

[Thomas Perkins]

Hi, I am on my 3rd Exhaust Manifold,The second one I bought from Nissan when they still had them,it was 212 bucks and a 10 dollar plug came with it.This was way before the internet came out.Jack put the 3rd one on it a few years ago.The Nissan ones cracked and got pin holes in it.I've had my 85 720 4x4 for 30 years now,I am on my second pipe that connects to the exhaust manifold,it is not a Nissan part.My cat is taken off.I still use my Egr,which is my second Nissan one.Also use all my vacuum lines with the Weber.I also have a Jasper engine with 109,000 miles on it.The intake manifold is the original one.I change my coils every two years cause I have a lifetime warranty on them.Free forever.Same with the distributor cap and rotor.Just checked them and they look new still.Dont waste your time trying to fix the exhaust manifold.Time for a new one.I use NGk Iriduim spark plugs,they are way better and last a long time.The engine is burning real clean.

Edited February 28 by Thomas Perkins

[Foxhound]

1 hour ago, Thomas Perkins said:

 

Since its not crucial to the function of the engine I'm just gonna use it to get by for now. I've heard mixed reviews about using headers which was the direction I wanted to go in the future, but I'm kind of on the fence about it with all the issues I've heard about them as well as price. Still have a lot of research to do in that area. As long as it isn't terribly loud I don't mind that it's cracked. We'll see I guess.

[Foxhound]

Last update for anyone who might find themselves in this predicament. I do not recommend going through all this trouble unless your into self-flagelation or you can't afford a new exhaust. I do things the difficult way as a means to atone for my sins. I ended up having to drill and tap all 3 holes. The tap is on amazon for a little over 10$ (M24-1.5). Bolts as well, same size, 20$. Drill bit I used was 3/4 inch (25 goddam mother****** piece of **** dollars at homedepot). A reverse direction bit would probably work better. I had to hammer and pick the old thread remainings out with a sharpened flathead. Quite a pain in the ass and sketchy but do able with patience.

Painted the exhaust and put a bandaid on the crack because it will hold up just as good as any exhaust crack repair puddy/cement/etc. No I didn't paint the mating surface, just looks like that in the pic. Cleaned em up reaaal nice tho.

Threw some rtv copper in the bolt holes and on the bolts because why not.

Used rtv copper on the all 3 gaskets. It's my exhaust party and I'll use rtv if I want to. I don't have to worry about a cat or oxygen sensors, so nice. Painted the flange and some of the exhaust while I was at it. Torqued exhaust manifold nuts/bolts to 12ft-lbs, then 15. Had to torque them 3 times. Used an X pattern. Let rtv sit for half hour before tightening. Torqued flange bolts to 20ft-lbs, then 27. Had to use every ratchet extension I had and did the two end bolts from under the driver side. Middle bolt can be done from tire well. Said F the heat shields for now. Can't wait to here her pur tomorrow. Over and out.

[datzenmike]

lol with all that orange RTV I thought that was an old SBC engine. Good to 500F. Exhaust temperatures can reach  400-500F on average but spike to double. The ones directly touching the head won't but the pipe plugs may. Threads will seal them.

[Foxhound]

My idea was to try and lessen any vibrations that might make those hairline cracks travel more. And for the plugs, the threads weren't perfect. Let this be a test as to the durability of rtv ultra copper. I knew youd come criticizing like a moth to a flame! Please no fires datsun gods. In the name of the of the dat, the sun, and the holy coast, japan

[datzenmike]

I can't resist comparing orange RTV use with old chevy owners. For a reason... the parts are not close fitting and need it. But on a Datsun L series a dab at the junction of the oil pan gasket/block/timing cover, at the top junction of the head,/block/timing cover and the rear main bearing cap/block/oil pan junction is all that's needed. That's about it. All other mating surfaces use gaskets and to put RTV on a gasket is like putting two seat belts on.

 

Critical? only pointing out the limitations of RTV vs. something that probably exceeds those limitations. I've used an IR gun on my exhaust and it was 350-400F at idle. Surely much higher when working.

 

 

[Foxhound]

I'm just playing. I do appreciate your input.