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OlDatZMan

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No answer yet to my question so I'll rephrase: Shouldn't I be able to clearly sense compression on each cylinder when turning over the crank on this Z24 using a 1/2 ratchet even if the ratchet action isn't very fast? I know I certainly can feel compression when hand cranking my 51 Farmall Super A and it's only a 113CID 4 cylinder with 6:1 compression. I'll try just turning the crank pulley by hand which will make it easier to feel resistance. Just answered my own question: I can't turn the engine over by hand gripping the crank pulley. So I guess it does have compression and it's time to assemble a few more things to do a starter spin. Also knit together the exhaust system back together.

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On the up swing you would unless....

 

The cam is out of time with the crank... if all cylinders are zero

One or more valves are bent and can't close

Valve seat fell out and valve can't close

Hole in piston

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Not much of an update. A week ago I bolted on and torqued the supposedly fresh head with 4 new intake valves and 4 old lapped exh valves using yet another new head gasket, and the EZ LOK repaired rocker bolt hole. After getting the cam timing wrong and making a couple other mistakes I was too embarrassed to publicly admit at the time, I corrected the cam timing to the point of being able to do a compression check. Compression on the formerly good cylinders was unchanged. Compression on the formerly low #2 cylinder was low and unchanged, an unwelcomed surprise that whacked my confidence. That suggested bad #2 rings.

 

 

After a few days of mental recovery I rigged my compression tester to be able to inject air into #2, but not cobbled together as a full blown leakdown tester to check % leakage. I'm looking for location of the leak route, not the fact there is one. I fastened/ taped thin plastic wrap about 0.0005 thick over the crankcase vent, over the carb, and over the #2 exhaust port to try to show any flow out of 2 through valves or crankcase. Rotated crank so both #2 valves are closed. When injecting air with enough flow to hear flow, but not enough to force pistons to turn the crank, I can hear air flow in excess of what I would hope for a tight cylinder, but there’s no sign of flow out anywhere. Movement of plastic film may not be sensitive enough to be visible with low flow, and the carb cover admittedly cover has more leaks to reduce outflow if the intake valve is leaking. Can’t find my stethoscope (though I did find my missing Metro head I’d been looking for for two weeks), but I could not use the steth to move around to listen for air exit routes while I'm controlling airflow in at the same time. Will search more for the stethoscope but must wait til I get help to listen at probable leak locations, and then at improbable ones.

 

Edit/add: Found stethoscope, rigged to a listening tube, air flow quickly located coming from cam chain hole. (Valve cover is off.) Yeah I should have thought about other possible crankcase venting exits other than CC ports, ie breather....the vertical cam chain cavity is a big one though nt a port. Bad #2 rings.

Edited by OlDatZMan
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This sucks.  If you are going to rering #2 you might as weel hone and rering the other 3.  Oastigauge the crank mains and rod bearings while there.

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Yeah Charlie you're right. It also immediately raises the question of whether to pull the engine which is another expansion of shop area needed, and more to put back together. I was trying to convince myself that since the other cylinders are ok now I would try to do #2 only, and that it might be possible to do it while the engine is in the truck. I have little interest in rebuilding the entire engine for cost or time needed; the truck is barely worth it, it will only be a local truck for me, and since I have another PU my truck need is not that pressing. Where do you stop when the engine is out? And if the engine is out, why not just find another block? I was just about to search for whether anyone has done rings in frame or a 720 4wd to see if that is even possible. I think it is, but not easy, though easier than pulling the engine. I re-ringed my 240Z but it had no front differential, and that was a tad over 40 years ago.

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Simple question: Has anyone honed cylinders and installed new rings in a Z24 4wd 720 with the engine in the truck?

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Totally do able and worth it if only one cylinder. I haven't with a 720 but I did my '64 slant six Dodge this way. Have a care as the hone can easily hit the crank throws.

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I just did my old tired L18 about a month ago, just laid some rubber sheet across the crank, that was also long enough to curve up the sides of the main webs to reduce the likelihood of hone mud getting into the mains, or down into the rod oiling holes.

 

Learned that trick when I was a kid from an old guy that ran a mobile auto machine shop out of the back of a service truck.

He even had a cylinder boring machine that would bolt to the top of the block.

(days gone by, probably not one mobile machine shop still in existence)

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Well like I said, I have done hone and rings once before, but the difference is then it was a RWD Zcar more like Mike's slant six (great engine), but now its a 4WD. The difference is that big lump under the pan. Yes I had thought about laying some impermeable film down over the crank---saran wrap, tarp, visquine, anything to help, maybe two layers, followed by a washdown after honing. One other thing I thought of that might help someone else is to wipe down parts within reach of ricocheting cutting particles with chainsaw bar oil, or maybe K&N air filter oil, the really sticky stuff, though I don't have any KN, which might help catch and hold particles so they don't bounce where you can't see them. And I've seen mention of slitting a large hose or somesuch to put 'round the crank journal. But with the pumpkin right there the question is the amount of access. I have had jobs where I finished saying "Damn I never want to do that again". One of which was a single lower intake manifold bolt on an 88 Isuzu Trooper 2.6 that I could not see and barely reach and took two hours to get off. And to add insult Isuzu made sure that in addition to the head cooling design flaw they built into the 2.6, that there was only one count one engine which would fit the trans on that otherwise sound vehicle: the trusty 2.6. It taught me that I never wanted to have anything to do with that engine ever again. You go through those things and you say never again. Which is what I'm trying to avoid now. So far I've rationalized this as a learning experience, but at some point there's the possibility it becomes self flagellation. The Trooper tried to deal with the pan issue by making the pan a two piece with the upper section cast aluminum with the lower sump having a bolt-on flange just like the 720 pan bolts to the block. That doesn't solve the problem of the oil pickup coming but it does give a better shot at being able to reach the pickup to unbolt it. I still have the Isuz pan and it would be nice if it would just bolt up, but of course no. Though I will dig it out and see if the z24 pan could be flanged to fit the Isuzu lower pan. BTW I always like the idea of a Cressida, the same way I like the Maxima diesel, but never had one or even was close to one.

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4X4? pull the engine and do it right. The difference in doing one and doing four is only the cost of the other three ring sets.

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OK Folks I’ve thought about this a lot and it’s time to cut my losses. The truck is worth fixing but the work involved would stretch my capabilities not to mention insult my comfort at my age so I’ve posted it in Classifieds. If I was 10 or 15 years younger, or this was 2WD I’d push on, but I’m not and it isn’t. So it goes. History of the truck is in the thread above which is more info than you’d get in from a craigslist seller. Head and intake/carb are on the engine but exh manifold and exhaust needs bolted on. One cylinder is low and needs honed and rings but the other cyls are good so I don’t see any reason why it could not be driven 30 or more miles to a new home, preferably to someone who values Nissans. Sale post is in classifieds along with a list of 240/60/80Z parts plus a J15 and transmission I have had sitting in my shop too long. Truck is going to be inexpensive from prices I’ve seen. Any other questions I’ll answer from Classifieds. I’ve gotten a lot of good advice and encouragement here which puts Ratsun on a high pedestal as a Datsun/Nissan resource. I’ve learned a lot. Many thanks to you all. I’m not done with Nissan, I have a diesel 720 to start on next. If this doesn’t sell it will just drop about 6 places down my priority list. If this post or parts of it are inappropriate here please advise and I’ll edit.

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