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Thanks again to Guy and datzunmike for getting me onto the forum when the registration system suffered catatonia. If registration fails there is just no way to get help other than finding someone on the forum to help. Just after I got on the forum the part of what I wanted to post questions about gained a solution. But that wasn't the end. Short version, but even it is long:


Bought an 85 720 2.4 4x4, Weber 32/36, >200k miles, suspected bad head gasket, water in oil. I figured there was no point doing a compression test, if it was a bad gasket. I would not run well enough for vac check. Pulled the head and replaced the head gasket. Deck and head were straight. Ran just the same: bad. Would not tune—would either run but not start, or start but not run.


Disassembled the carb completely, no real problems found.  I DID find a half-cup shaped flow deflector sandwiched between the two carb gaskets under the primary barrel, which would have directed the primary carb bore flow mostly to cyls 3&4. I saw no reason that would do anything good and took it out.  Chastise me if you must but I don’t see why giving some cylinders more flow than others is a good thing; not usually what we try to do. Took extra care to ensure no vac leaks in carb attach.


Vac was about 14 and steady. Found small vac leak between #3&4 intake manifold.  Did a compression check, both dry and wet. Dry compression was 1:175, 2:118, 3:170, 4:170. The wet run increased 1, 3, and 4 a few pounds, and #2 to about 7# up to 125#. Concluded probably a bad #2 exh valve, and the other cyls being near equal was a good sign.


Pulled the head again, and decided to also pull both manifolds for new gaskets as the exh was as old as the leaking intake. #2 exh valve was carboned, but had a smooth face, so I hand lapped it, then thought I’d better check the intake. Intake mating face was wavy on its way to recession, not lappable, so I figured I needed a new seat. Took two weeks to find a decent machine shop, and got it back after another week two days ago with 4 new intake valves and head looking great.


So first question: bad compression in one cylinder might be due to bad valves, but could also be party due to a broken ring. With a leaky valve a wet test would not tell you much. If it isn’t a bad ring, good, if it is, the thing needs a hone and new rings, and I’d really rather not go that far. Bear in mind the last time I got this far into an engine was 1976 on a 240Z.  Getting up and down off a concrete slab for this old body isn’t what it used to be.


So Question #1 is: What’s the general opinion about whether or not to go all in for rings too, as opposed to just putting it back together now?


I need some good opinions and reasons, but very unfortunately, it isn’t that simple. Those who have pulled heads know the many steps needed. One really tiny one is pulling the lower cam half moon valve cover seal out of the head to get the cam bolt out. It was slippery. And just that quick it went boink boink right down the front cover and into the front of the oil pan. Oops, really really big oops. Just pull the pan, no problem. Not on a 4wd.


So I apparently have three choices: 1) leave the thing in there and hope it sinks to the bottom. 2) leave it there and hope the crank chews it all up and into the oil filter and all its bits go to the oil filter and nowhere else. Right. 3) Pull the engine, do the damned rings, and get the rubber moon out of the pan. And take a lot of painkiller before I try to sleep. This would be simple in a 2wd.


I have looked everywhere and there is only one bit of hope by one person to counter the long laundry list of disgusting disassembly instructions by many experienced people about pulling a 4wd engine. A data point of one is not heartening.


So the last questions:

1) What will probably happen to the oil moon if I leave it there in the front of the pan? Will it float or sink? Is there enough clearance between pan and crank that it won’t be whacked or swept by oil wave action? Or is it probable it will be picked up and ground up by either the crank or the crank cam chain sprocket?


2) Can I pull the engine by loosening but not removing all the drivetrain pieces Nissan says you must? I really am not up for disassembling everything Nissan says to. I’m hoping to remove the 4 front diff bolts and lower that a little, and remove and lower the trans crossmember and lower it a little. I don’t want to drain the diff or transfer or trans because I just got done filling those with clean fluid from TX. My hope is from the one person who wrote that he raised the engine some, lowered the trans some, unbolted the oil pan, let the pan sit there, and then pulled the engine up and out. (yeah the oil pickup would be vulnerable)


Right now the front wheels are on car ramps and there’s a gantry with hoist overhead to hoist out the engine—no head on it of course which makes it more difficult. That’s enough. All opinions appreciated. -Jim

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Buy a new valve cover gasket and replace the missing 'moon'. It's not going anywhere and it won't hurt anything.


Found these timing chain guide pieces in a KA engine oil pan,been there for years. Had new guides on it.





What was the compression on #2 after you had the valves done and the head back on? Did you re-test to see if this fixed the compression???????

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Thanks for that Mike, that's a relief, and thanks again for getting me on the forum. Ratsun has been the best source of info. I haven't put the head back on yet because without some feedback I didn't want to go through reassembly and then have to take it all apart again. I grew up on a farm where I learned that if I didn't fix things right the first time I'd be the guy trying to fix it again later when its 20 below. The valve cover gasket is new--had only been on a couple days, and I have another new moon plug. I'd love to get this thing fixed to unplug my shop. Will update when its back together.--J

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You stated the truck had about 200,000 miles on it.  It could have a bad ring,  there are 2 ways to tell, 1 tear it down mike cylinders and if cylinders are in spec hone  clean pistons and re ring pistons and re assemble.  2 roll the dice and install head and see how it comes out.

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Thanks Charlie. Yeah I understand three good ring sets don't guarantee a 4th, and that a bad valve adding carbon to the cylinder could have helped enable ring failure in #2, which the other cylinders didn't have. That's why I put the engine's total miles in the description. There's also the oft-said, that if you seal up what was a leaky top end, you increase the pressure on the bottom end, ie the other combustion sealing parts of the cylinder. I put rings in my Z at under 150k because then i thought that was a lot of miles. Heh heh, that was true of the cars I had previous to the Z. If this was 2wd I'd pull the engine and ring it, but the extra work extracting this one is a big inhibition and I think I'll chance it. I drive slow now and am easy on everything, for mpg and to avoid wear. My daily Metro is at 203k with a valve I hand lapped in at 162k, but I think it is heading for rings in the next 10 or 20k. If this engine does go downhill the next repair edition will be to go through the whole engine.

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I understand the work involved in pulling the engine from the 4 wheel drive.  I have an 86 720 king cab 2 wheel drive that has over 400 thousand miles on it.  When this engine finally goes I will swap a V6 VG or VQ engine and automatic trans in.

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  • 2 weeks later...

Ok I just now posted what I thought was a big step fwd, but it wasn't, so I deleted it. That's good for you: it was long. The problem has advanced a lot since my last post but all that has happened isn't worth mentioning yet. What I thought was a valve/piston interference is not so, but the problem does seem to be that the missing half moon seal is jammed somewhere and not allowing the crank to move, or at least not with the force I'm willing to put on it. If the jam happens to be under a crank counterweight (or lowest part of the rotating crank assembly), as I just now realize it might be because the crank is stuck right at #1 BDC, then forcing the crank to rotate might not hurt anything. But if it is in a place where it could do some damage, like somewhere around the long distributor drive shaft, where forcing the crank to move might bend the shaft as the two gears try to mesh and suck the moon in, then I don't want to be forcing crank rotation. I'd really like to know exactly how much clearance distance there is between the crank at #1 BDC in the shallow front end of an 85 4x4 2.4 oil pan, or an oil screen or baffle if there is one there (Edit: especially clearance between the most forward counterweight and any stationary structure around its arc). I've never seen the inside of one of these pans. I have found a couple Google images. Will update when I know more.

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I honestly feel if this is a keeper that your time would be best spent pulling the engine, completely tear down the engine inspect and mic all surfaces and hone or bore if needed.  New rod and crank bearings new oils pump.


Have the block hot tanked and be sure they brush the the oil and water galleys.  Have block check for cracks not always visible.  If block checks out proceed with machine work and build. 


Was the head gone through?  How is the camshaft lobes? 


If you do all of this above please splurge and buy a new oil pump.


By doing it this way you know what you have.

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Honestly Charlie this was a cheap truck that has 200k miles, unknown maintenance, and has been popped slightly in the driver's side so the door doesn't close as it should. I got it for my son but I don't think he wants it. Above all, it is much more complex to work on than a 2wd truck which is the opposite of what I want. I like 4wd but they can't walk on water. Best thing about this is having the low side of the transfer case so you can go really slow. I have a lot of miles including 18 wheelers and autocross (not with a semi:-) and can drive most places in 2wd that most people think they need 4wd to get to. Falling into a ditch when it's slippery is one thing, but I'd bet that more than half of all accident participants are innocent, meaning that if conditions are bad you're best to stay off the road because of other bad drivers, not yourself...unless it's so bad everyone is home, in which case its safer :-) I also am very easy on my vehicles....they wear out slower. So I'm not inclined to do what you suggest, which BTW I agree is the prudent approach. I like the general truck, and engine, and Nissans, but right now I just want it running to unplug my shop. I wanted something smaller and simpler than my 68 GMC, but this 720 is not simpler. I want to sell the GMC; its simple but bigger than I want, and it has only a little more than half of the 720's miles. I also have a spare engine and trans for it. Maybe all it needs is power steering to make it more pleasant to drive.  A Nissan answer is probably 2wd, and I have a 720 2wd diesel I haven't started working on yet. I have watched the oil pressure the little I've run this one and recall its12-15 at idle and 40-50 at say 3000. Head has 4 new int valves, touched up exhaust faces, new valve seals, same guides, and is straight. We'll see. Gotta fix it and run it first.

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It can't get to the crank throws from the timing cover, but it can get chewed up in the sprocket or bounce around and slip down into the oil pan just in front of the front crank bearing cap, whole or in pieces. It is urethane or what passes for oil resistant rubber these days. Someone here took an old engine apart and found the remains of a wooden wedge used to block the tensioner in place.

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I'm making this post out of a sense of reporting duty, with the risk it may harm my pristine integrity...........


I had mused on the possible "urethane" composition of the little half moon, and having put in urethane suspension bushings I knew that urethane is oft chosen because of its resistance to pressure and fragmenting. Using a hammer or other blunt instrument to break up a chunk of rubber or urethane questions the choice of tool. Never the less having flipped the rockers over yesterday to allow the crank and cam to rotate while preventing any cam valve movement, I went out this AM to have a showdown with the hidden impediment and grind it up with resolve using my longest 1/2 breaker bar to overcome any resistance. There was none. Over it went, smooth as silk, over and over with nary a hint of pause. It was a gigantic letdown combined with shock. So I did the next step, stuck my finger in #1 spark hole, and turned it again. No compression. No compression on #2, 3 or 4 either.


This is not fair. With new valves sprung closed and pistons going up and down this is impossible. I had begun to wonder if the shop gremlins has switched their usual game of hiding my tools to a cooperative gang-up on my truck, but this kind of impossibility seems more like a wrinkle in the time space continuum.


Possible causes: 1) 4 bent valves, very unlikely; 2) bad head gasket installation, very unlikely; 3) alien intervention, increasingly likely; 4) I'm departing sanity. The only rational response to this is a maniacal cackle echoing through the woods. I think there was one of those.


3:19: Three hours and a beach walk later: There is a #5: Extreme mental density. You probably figured it out already. All razzing accepted with humility.

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It is urethane or what passes for oil resistant rubber these days.

Urethane comes in many forms of softness but anyway I worded it this way because I couldn't remember the actual material and hoped someone would correct me. It's probably Neoprene or Silicon base material. It's got to be soft enough to crush in order to seal as a valve cover gasket.



Well is the cam timed properly? TDC should see both valves on #1 closed. Are they? Cam only has to be off about two teeth 18 degrees to have a valve not closed at TDC.

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>(the half moon) It's got to be soft enough to crush in order to seal as a valve cover gasket.


The new one I put in was a tad taller and hard enough and resisted crushing enough that I had a small oil leak around it and wished I had put back in the old one rather than a new one. That is, before I dropped it down the hole.


>Well is the cam timed properly? TDC should see both valves on #1 closed. Are they? Cam only has to be off about two teeth 18 degrees to have a valve not closed at TDC.


Yes it was heartening that both #1 valves were closed at TDC, and timing was off/advanced just 1 tooth from my estimate when the crank was at BDC. Easy change to make when I took off the rockers again to flip them over, and by then I was ready for all this to be over..........


Except the 2nd from aft pass side rocker bolt pulled out the alum head's threads, not even on the final torquing round, at less than Nissan's torque number. So as I wrote someone recently, things are never so bad they can't get worse.


First thought after I got done swearing was Helicoil, which I've never used, but those and its competitors Pioneer and Time-Sert are around $100 for the insert and very special insert tool and left hand tap. And a GM repair site talking about rocker bolt thread repair said they had had too many Helicoils fail and have gone to Time-Sert which isn't the coil spring kind of thing a Heli Coil is, instead it's an internally and externally threaded bushing. Looking farther, E-Z LOK is the latter type and cheap because you don't need special tools, only the insert. So does anyone have direct experience with several of these thread fix brands especially E-Z Lok?.....and if so, would you pull the head off to be able to put it on a drill press for drilling oversize, or would you leave the head on and use a hand drill. I am sounding more placid than I am.


Links I found:


(I'm guessing and not certain that the bolt in question is an M12-1.77, that's just what I looked for)







Pioneer (no details)


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I have used Helicoils for ov er 30 years and not 1 failure.  Used for head bolts, rocker stud bolts. intake manifold bolts/studs, and water neck bolts.


There is another product that you actually stake the threadsert in with tiny spikes.


If there is not enough material then the Helicoil will fail every time.

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The helicoils are good if you don't have to remove the bolt again... I believe that's when they start failing....


Personally I like the time-sert or ezlock... I think another name is keensert, those have the little spikes... once installed it will not back out.


The only problem with the time-set style is you need a new bigger hole, so measure that there is enough material to install the insert...

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Thanks Charlie and Crash. For the present I'm pushing on to see whether I'm headed for a reasonable repair time and cost, or down a rabbit hole. It's nice to see there are more choices than Heli. For any insert option I would need to remove the rocker bolt hole cam bearing locate bushing which would delete the locating benefit Nissan thought it needed. Is that acceptable? I don't see an easy or even reasonable way to install an insert and retain the locate bush.


There's not much room on the top of the cam block mount tower. Drilling out for a threaded insert reduces the material needed to anchor an insert.

Concern about insert purchase took me here (a Helicoil pdf):


There the relevant term is "residual wall thickness", the amount of material remaining after the original bolt bore is drilled out to the spec'd insert OD, found on pages 13, 17, and 18.

For Heli: residual wall thickness = 0.375 x OD of insert

M8-1.25 Helicoil OD is 9.62mm or 0.3787”

Residual wall thickness for M8 Heli is 0.375 x 0.3787 =  0.142”

0.142” x 2 (walls) = 0.284”

Total residual wall thickness of 0.284” plus M8 Heli OD of 0.3787” = 0.407"

The locate bush is not centered on the cam block mount tower.

My measured distance between aft oil feed bore and fwd cam block tower edge is 0.626”, which is sufficient.

My measured minimum distance is between the locate bush OD and cam mount tower is 0.090”

Therefore the residual wall thickness (at least for Helicoil) is less than stated minimum in the bore arc closest to the cam.


I'd prefer EZ Lok for cost and simplicity but EZ LOK’s web site is a hassle--lots of scrolling and numerous pages without finding a residual wall thickness for their insert. EZ could learn something from the pdf above. But there is a distributor about 10 miles from me.


This repair would be much be less time and hassle if done with the head on the block where it is now, rather than pulling off the head and then supporting it precisely on a 10" dia drill press table. What are your opinions about drilling with a hand drill with head installed vs pulling the head off and eating the time for that and another head gasket to drill out for the insert? The bolt is long so the drill angle would have to be fairly exact.

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If it was me I would pull the head and use a drill press, or step up the drills slowly by hand, but I wouldn't want the chips in my engine either way you drill it..


2nd if it's the bolt I'm thinking it is, ( had to look up some pics of the head) I would probably use the helicoil, just because it doesn't look like enough material for the inserts...


My last thought are there any threads left in the hole? Could you possibly tap deeper and use a long stud instead?

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I haven't measured the hole depth yet (I will now) but know the bolt went into the threads quite a ways, 6 or 8 turns. The OEM bolt is also long, 3". Finding a longer one would be harder than going to the local hardware store.


Keeping the alignment bush means a new bush with an ID larger than the insert OD, meaning an even bigger hole and less material remaining for the insert. Also means finding a bigger bush and drilling the lower cam bearing block to match. One might possibly find a bush about the dia of the insert, chamfer the inside of one end, slice it down to a ring maybe 1/16" tall, chamfer the outside bottom of the OEM locate bush, and cut down its length so the internal and external chamfers f the two bush's engaged like a compression fitting. That's a lot of ifs, and grinding down a bush into a ring doesn't sound safe or fun. I don't have a reasonable solution yet.


Just about anything is repairable, but there comes a time when someone not consumed by the repair just says "get another head'. Not there yet but the thought is closer than it used to be.

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Forum slow today. Condolences to admins trying to troubleshoot. This reply didn't take, trying again:


RE using a longer bolt to reach remaining good threads in head:

Hole depth in head: 1 3/8" (maybe not threaded to the bottom)

Minus 1.4" locate bush stickout = 1 1/8" max hole depth

Bolt length: 3" from cap face

Upper cam bearing block height to cap screw surface: 2.250"

3" - 2.250 = 3/4" bolt threads max available, also meaning all hole threads at max bolt depth are failed

1 3/8 hole depth + 2.250 upper cam block = 3 5/8" max depth for new bolt (if hole threaded to bottom)

1 1/8" max hole depth - 3/4" OEM bolt engagement = 3/8" untouched threads at bottom of hole if the hole was threaded all the way to the bottom

IF hole threaded all the way to the bottom, 3/8" might be enough for steel threads, but I don't think aluminum. And I doubt the hole is threaded to the bottom. Doesn't look very promising.

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7-11-18, last three days:

EZ LOK threaded insert installed to repair pulled threads on the intake side at the center rocker mount boss with the oil port. Head back on with new gasket and cam sprocket back on. Crank turns easily, no obstructions.

@ crank mark TDC, #1 and #4 pistons at TDC

line on cam boss just to right of rocker post casting line

#1 valve lobes at 4:00 & 8:00

distributor rotor at ~ 7:00 from driver’s fender, ie pointing to #1 intake plug distributor wire

No compression on #1 either with finger in the hole or spark plug snugged--haven't checked other cylinders and don't see the need to if #1 doesn't work.

Crank pulley and distributor have not been removed since it last ran, reasonably well with one cylinder at 118 for compression

 If I r

otate the crank to where distributor rotor is pointed at 9 and 4 the crank pulley, crank TDC mark is about 45 degrees BTDC


I don’t see how the chain could have jumped at all, certainly not 45 degrees. Chain is US made, probably replaced (before I got the truck) when the last head gasket went on and the head was milled flat, I think less than 40k mile ago.


Distributor timing is a different issue than cam timing and compression. Distributor could have been previously pulled and put back in wrong but I should still have compression turning the crank, and the truck DID run reasonably well before I pulled the head.

I've marked out the valve durations on a paper degree wheel and turned the crank while referencing the wheel and all seems correct. How can I not have compression?
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That's the mistake I made last week. I left out some things this post; didn't want it to be too long. Rockers but 4 only the #1 valve lash is set.


Edit/add: I can't say that I have zero compression. I'm turning it over with a 1/2" ratchet on the crank which admittedly is not fast, but there doesn't seem to be much resistance, even thinking about a 5hp mower motor. I set the valves on the other 3 cylinders just now so all 4 should be talking to me especially since before all this recent work I had over 170 on a compression test (6 revolutions using the starter) on 1, 2, and 4. I haven't spun it with the starter yet but I guess that's the next try, but wanted to get some good news before I started reassembling all the things that came off changing the head gasket. Intake manifold is on but not exhaust. Cam sprocket bolt is snug but not torqued in case I needed to pull it again to change the valve timing which doesn't seem likely now.

Edited by OlDatZMan
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You cannot put an L or Z series distributor back in wrong, impossible. The drive spindle that turns the oil pump and the distributor would have to be taken out and turned and put back in wrong.






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