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How to rebuild your motor through misdiagnosis and head scratching


supererogator

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I am now thinking about completely rebuilding the motor.  Kind of a, "Screw it, let's pull it and do it right, so we do not have to do it again soon.", mind set.  I suppose the thread name doomed me to this fate, but it will be a rewarding fate IF I pull it off.  At this point, I have replaced everything in the engine compartment, except the brake booster, dizzy, wiring, oil pump, and a few other tidbits.  Why not take it all out, clean it all up, and put it all back pretty like.  What I am afraid of, is getting in over my head.  BUT…..IF I get in over my head, I would rather do it on this than on my '65 Mustang (first car, still have it), that I want to tackle next.  SO...

I have already done the timing chain and components.  I need to do something to the crankshaft area, but not sure what.  I expect the main bearings, as that is where the signs are. I have found very affordable sets of bearings (see above), but I have also found "ring kits" for about $150.  These seem to include rings, all crank bearings, gaskets (doesn't say if it includes a new head gasket or not, but I think it should be a part of MY job.  I assume they mean the timing cover gasket kit, plus oil pan gasket).  I am going to buy an engine stand eventually anyway, a hoist I can rent easily enough, my kid has a car I can drive if I need, I even have a garage, tools and know-how-ish stuff.  It is starting to seem like just rebuilding everything that makes the car move and exists in the engine compartment is a mere kit and time/tool investment away.  Does it make sense?

I suppose my questions are:

Is it logical to rebuild this thing?  I am not asking reliably practical.  Shoot, this is the second newest vehicle I have ever owned.  Is it reasonable that if I fix this and the janky front suspension that I could get another 100k out of her plus the fun?

 

Am I really that close to a full lower end rebuild? Am I missing something that I have not tossed into the equation?

 

Any favorite sources for lower end rebuild kits or parts?  I am not looking to "ROD" this thing, but I am not averse to performance parts if they are a reasonable expenditure.

 

How do I know if I need over sized stuff (read: bearings, pistons, rings, et al.)?  Some kits even come with pistons (although I read in the archives here that they rarely need replaced).  I have not seen any measurements in my books (yes I have the factory manual), but I also have not really looked, as I just started thinking about this.

What am I missing that is going to kill me in the long game?

BTW,  I have no wife to justify this with, merely the bank account of an only parent who's kid is now driving also.  Keep advice manly, but frugal.

 

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The cylinder wall wear limits are in the FSM. If you exceed them get the block bored to an over size. Here you can go to the largest over size for about the same cost and the smallest. Find this out first before buying any kits.

 

Crank oversize bearings can only be used if the crank is damaged and needs to be ground down to make it round again.

 

A rebuild is indicated if your compression is very low or low in one or more cylinders and is not caused be poor valves. Excessive blow by and oil burning is another. If your compression is 150 across all (or better) and it's not burning oil then why bother. The crank can be rebuilt or replaced and with new bearings without rebuilding the whole thing.

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Thanks Mike.  At last test, and to the best of my memory, compression was around 125psi in each cylinder and varied by less than 10%.  I am thinking this will prevent further issue, and basically give me a "brand new motor".  For the cost difference, it seems like a "may as well" kind of thing.

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  • 1 month later...

Ok.  For those following along, I purchased a 1995 Pathfinder.  She and I already did and 800 mile round trip.  

 

I also purchased an engine stand.  I am going to take the motor out of my 720, and rebuild it.  Paint and polish, replace some parts as I go.  I am going to start with the piston and ring kit, and see what else goes belly up.  I am in no rush….well, except I want to get the motor into the garage before the last of this unexpected good weather goes away.  Any prat falls I should know about?  I plan on getting everything loose and then going and renting a hoist, for a day for the final pull and mount on the stand.  Any hints on what the books are not telling me?  For instance, the book never told me I needed to remove the oil pan or get an extra height hoist to clear the front end on my old Mustang. (Deflating the tires worked great BTW, but by about 3cm)

Also an off topic question.  I know a bunch of your folks own newer Nissan too.  Anyone have a favorite diagnostic computer for a '95 Pathy/also should work on some '90's Hardbodys, I am sure others too? I am new to this world of computers in cars.  I have found some help on NICO, but I trust a bunch of you here.  Keep in mind that I am a hobby  and need based wrencher, I am not looking to spend more than $200ish.

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According to a random Google search, the Pathfinder is OBD-I up through '95, and is OBD-II from '96 onward.  OBD-I varies from manufacturer to manufacturer to manufacturer, and OBD-II has a common access mechanism (and common functionality) across manufacturers, although the manufacturers generally _also_ have extra proprietary functionality.

 

This page seems to be pretty thorough as far as the OBD-I Nissans go:

http://www.nissanforums.com/truck-suv/84839-how-check-your-ecu-error-codes.html

 

 

As for pulling your Z24, I think my first suggestion is to have a plan on how to attach the motor to your stand.  Ideally, you want to get it centered up reasonably well so you can spin it without it flopping over with a ton of force.  I know nothing about how to actually accomplish that with the Z24, or whether it's even doable, but it's something that bit us on my Saab racecar, so it's always in the back of my mind :o)

 

Other than that, figure out if you need to disassemble your exhaust to get the exhaust manifold off the head?  If everything is seized up, that's something to figure out sooner rather than later.  I _believe_ I've heard (but could definitely be wrong) that supporting the manifold by the exhaust will lead to cracks in the manifold.  Again, I could be wrong, and have no personal experience one way or the other.

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  • 9 months later...

OK, dishonor aside, for my absence,  but I am looking for a detailed book on rebuilding the L series\s motors. My motor is on a stand in my garage, my tranny is in the back of the truck, and I need motivation. I have a 1980 720,  vac delete, weber 32/36/ new almost everything: ) coil, bat, plugs, vac lines (existing), plug wires, timing chain, alt, starter, tune-up parts, fuel pump,etc…) if you don't feel like going back through my posts/responses.

 

I found this book: http://www.lybrary.com/how-to-rebuild-your-nissan-datsun-ohc-engine-p-333144.html?gclid=CjwKEAjwluetBRD98L639p35p0QSJACC8BlKUYaz4sJtIsY8KUhFs1D8QEzqfCP1TPwFgmcycfHyjBoCBczw_wcBis that the better one? I figure I need to continue restoring my faith in my wrenching skills and walking through the rebuild with a  book would not hurt.

I own the Chilton, Haynes, Clymer and Factory books already, but more resources the better.

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I found this book: http://www.lybrary.com/how-to-rebuild-your-nissan-datsun-ohc-engine-p-333144.html?gclid=CjwKEAjwluetBRD98L639p35p0QSJACC8BlKUYaz4sJtIsY8KUhFs1D8QEzqfCP1TPwFgmcycfHyjBoCBczw_wcBis that the better one? I figure I need to continue restoring my faith in my wrenching skills and walking through the rebuild with a  book would not hurt.

 

I have this book. It's very detailed. I'd definitely recommend it. I got mine off of Half.com for 6 bux

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