I'll be removing the 3.5 liter VQ35DE engine out of my 2002 Pathfinder to assess the level of damage and either overhaul or replace it. I figured you all would like to see my progress. Questions and comments are welcome.

This engine is a victim of the infamous power valve screws ingestion. It burns oil, has a cold start knock, a knock over 4k rpm, suffers from low oil pressure, and oil analysis came back not-so-stellar. However, it still runs and the vehicle is otherwise in fairly good shape. I have done quite a bit of work to the car since purchasing it in 2015 with 174k miles (most of which is documented elsewhere on this site), and so I have a comprehensive knowledge and attachment to it. Current odometer is ~204k miles.

Two days ago I began disassembly in roughly the following order:

Had the shop evacuate a/c refrigerant
Relieved fuel pressure
Removed:
hood
battery
air cleaner assembly
acceleration and cruise cables
emissions hoses; vacuum hoses and manifold
coolant
oil
upper and lower intake plenum
disconnected hoses from a/c compressor; sealed and set them aside
radiator
belts
fan and shroud
trans fluid
harness
a/c compressor
alternator
steering pump and reservoir; zip-tied to body near battery tray
fuel rail
exhaust manifold and pre-cat assembly
oxygen sensors
crank sensor at transmission
transmission fluid tubing

I used bright green masking tape to note the location of every disconnected hose, and to flag disconnected electrical connectors. Most everything was a breeze, as I have previously removed all of the above on this car except for the fuel rail and exhaust. Except for those two, removal took about six hours. The fuel rail was challenging. The exhaust was a nightmare.

When I tried to remove the exhaust manifold, several studs stayed in the heads. I figured I wouldn't be able to remove the manifolds, so I tried to remove the cats. To get at the six bolts that connect the pre-cats to the manifolds, I would have to remove the heat shields. However, most of the heat shield bolts were so rusted, and had lost so much surface area, that a socket or wrench would not turn them. I tried prying and pushing the shields aside to get to the bolts, and after much hardship was able to access three of the bolts. Two of them snapped. At this time I did not realize there were three more bolts waiting for me, on each side! I tried disconnecting the exhaust downstream, which went nowhere. I then tried cutting up one of the heat shields with tin snips, which was excruciating in that tiny space. My body gave up around 11:00 PM, after 13 hours of work.

After some much-needed rest and homemade donuts for breakfast, I took to NICO (reddit.com/r/mechanicadvice was useless, as usual). I searched for 'cat' and was lucky to find Blindaviator's post, which made me realize that I could, in fact, remove the remaining studs from the head. A 1/4" socket did the trick, although most were stubborn. I took my time, knowing that snapping one of these was not an option. Once the studs were out, the exhaust dropped away from the block. On the driver's side, the oil dipstick had to be unfastened from the block, and moved aside. On the passenger side, removal of the large mail coolant tube made stud and manifold removal easier. The downstream bolts on both cats came loose just fine, and the assemblies came out through the bay without a problem.

Tomorrow I'll remove any remaining items from the engine that may hang up, remove the transmission-to-engine bolts, and lift the engine out of the bay

I've been trying not to think about the possibility of my '02 falling victim to the power valve screw curse. I bought mine with 172K miles on it. It now has 220K , still performs well, and burns no undue amount of oil. (less than a quart every 3K miles) Do you think it's just a matter of time until I lose a screw to this infamous, self-destructive issue or is it possible this curse will pass over my Pathfinder? The cost for a bottle of thread-locker, new intake gaskets, and wrench time would be less painful now just to be sure it doesn't happen than to kick myself later for all the added expense if it does happen before I do some work to prevent it. Do you know if there are some stats on manufacture dates where this power valve screw issue is typically a problem or is the consensus that it's more of a random occurrence?

Mdmellott, you saw my post above. I'd rather remove the plenum and see for myself whether the screws are loose. If they are, put loctite red on them and screw them back in. If they're tight as a drum, put everything back and leave it alone, you'll be fine. The issue was that some of the screws did not have thread lock applied at the factory.

You made some awesome progress, I like how your putting bolts/nuts back in place as your removing them.

What some people might not realize is that automotive oil filters have a spring loaded bypass valve inside so that under high flow / clogged up filter material oil situations, oil can still flow. (Better to have unfiltered oil than no oil).

So as your engine has been munching on those hardened steel screws, bigger than microscopic particles of your cylinder walls/rings/pistons are getting pumped around you engine.

I personally love tear downs because it’s a free activity, but actually replacing everything that was damaged by mileage and foreign particles will be costly.

Yeah, threading the bolts back into place is essential. I look forward to seeing just how good or bad the inside looks.

This morning I removed the trans fluid-to-radiator hard lines, then got to work on the trans-to-engine bolts.

I used an u-joint adapter and several extensions to reach the most difficult ones. Im doing all the work from underneath.

I removed the front driveshaft to make it easier to reach the driver's side bolts. With it and the cats out of the way, I can reach my hands all the way around the transmission while laying on my back. Having two hands up there helps to secure a socket and extension into place before attaching the other extensions and a breaker bar.

Today went well. I removed the trans-to-engine bolts, but left one in hand-tight just in case, the only one facing the engine bay on the passenger side. While working on these bolts I realized there were a couple of transmission vent hoses attached to a hard line at the rear of the engine. I disconnected them and labeled one.

I realized it would probably be better to remove the engine without having to pull the torque converter with it, so I removed the starter and removed the torque converter bolts through the starter access. I turned the crankshaft with one wrench, while another wrench worked the bolts. I had to put pressure on both at the same time, in opposite directions, to break them loose.

I was then ready to loosen the top engine mount nut, as well as the mount bracket bolts, and hooked up the chain for the hoist. I bolted one end of the chain into a bracket that is attached to the very rear of the driver's side head, normally just below the throttle body (I think). The other end I bolted to the front of the passenger head, where the power steering pump bracket is normally located. I took the slack out of the chain, removed that hand-tight bolt through the engine bay, jacked up the trans a touch, asked my wife to come in the garage for backup, and started lifting.

It turned out that I had missed a trans-to-engine bolt on the driver's side. When lifting the engine I noticed that one side of the engine was separating from the trans but not the other. This bolt was accessible from the engine bay, so I dropped the engine back onto the mounts, dropped the trans, unscrewed the bolt, and started over.

When pulling the engine on my Forester a few years back, the engine would not separate from the transmission. I drove carpentry wedges between them to pry them apart. However, I had replaced the transmission on this vehicle a few years back, so the two were not stuck together.

Every few pumps I inspected both sides of the bay to see if anything was hanging up. The crankshaft position sensor that is normally located under the transmission hung up on the motor mount. I also found one last hose I failed to disconnect: the front differential vent hose.

As I was using a crane-type hoist, the engine naturally came toward the front of the vehicle as I pumped it upward. A few items caught the a/c condenser as it came forward, but I was able to maneuver the engine above the body. My wife, who was watching all this unfold from the driver's seat, put the car into neutral on my signal, and I pushed it out of the garage.

I realized, when I wheeled my engine stand next to the hoist, that I did not have the proper bolts that were both long enough to fit through the engine stand tubes, yet thick enough to fit in the top trans-to-engine bolt threads. I scoured the accessories: alternator, compressor, starter, and came up with nothing. Looking around the engine itself, however, I realized that the large fan pulley bolts at the front of the engine were the perfect size. I used two of these for the top two arms. The bottom two arms were held in place by bolts taken from said accessories. I briefly wished for a load leveler, as the engine was at an awkward angle, and kept spinning away. But after some time I got the hang of the stand.

I mounted the engine, cleaned up the residual coolant that had spilled during hoisting, put my tools away, washed my hands, changed my clothes, and joined my family for dinner.

I'm a little jealous, but also not. Good on you! Make sure you replace the engine mounts. It's amazing what a difference new ones make. You'll think you dropped in a brand new engine.

Good move putting the bolts back in as you take them out. It makes life so much easier to not have to mix 'n' match 'n' guess

Thanks man, I know what you mean.

I was wondering about the engine mounts, and had already decided against new ones. I tried prying them with a large screwdriver and they didn't give, so I figured it wasn't worth it. Maybe I'll give them a second thought...

Anyways, I'm back with an update, as the pre-machinist work is complete. Rather than slow things down here, I have lots of cool photos for you all to check out in my imgur post.

Long story short, I didn't get the cylinder damage I expected. Instead, I have three destroyed piston crowns. The portions of the cylinder heads that mate with those pistons are all chewed up, and it remains to be seen whether they can be salvaged with machine work. Because the damage is so extensive, I doubt it.



The main bearings are pretty bad.



The connecting rod bearings are downright terrible.



However, all of the bearings were in place in one piece, and the crank or rod caps don't look too bad. The cylinders, connecting rods, and piston skirts show normal wear. I wouldn't be surprised, however, if the cylinders needed to be bored due to cupping. The crankshaft does not appear to be scored, but I'll let the machinist be the final judge. The camshafts are OK, although the cam seats in the head are scored. Finally, I am a little concerned about the state of the upper oil pan. It is all cracked inside, with some of the cracks rising up in sharp ridges.

A few months back I replaced the timing chain tensioners because of a cold start noise. I found that the left tensioner had collapsed. Well, when I opened up the timing case this time, I once again found that the left secondary chain was a little slack. I figured it might be due to low oil pressure, until I looked inside the new tensioner and found slivers of what looks like aluminum. Most likely it is bearing material, but could it be the oil pan?

After I pulled the engine out of the bay, I realized that leaving the bolts in the block would not work, as in my experience machinists like to take them all out. So I created a nut and bolt catalog consisting of marked ziplock bags. I thought I would need to separate and label cam and crank caps, but fortunately they were all stamped. I did make a sketch, however, of how the camshaft caps sat in the heads, as in this case the stamps did not provide quite enough info.

All in all, it took me 24 labor hours to remove the engine, then 18 to get down to the crank, and another 12 to pull the valves out of the heads and clean everything up.

After removing the upper oil pan, I phoned a neighbor friend and asked to borrow a few sockets. The crankshaft cap bolts required a Torx E-14. The piston caps and cylinder oil jets required a twelve-point 10mm socket; a six point just wouldn't do. Additionally, a Torx E-8 allowed me to remove intake studs from the heads. In fact, this was the Torx socket that I could have used on the exhaust studs, had they not been excessively rusted.

I have been wanting to do this for a long time. I am dreading, however, what the machinist might say and how much it might cost me. Stay tuned.

Wow, lots of work. It is a very complicated engine, more than any I've been into, and I've been in a lot. Not pretty inside either, sad to say. I'm normally a fix it, not replace it kind of guy, but in this case I'd be thinking seriously about just trying to find a low mileage replacement engine.

Then again, there's nothing like the smell of a rebuilt engine firing up for the first time. And the satisfaction that comes with it.

Yeah, you've pretty much summed up my gut-wrenching feeling about it. However, I'm not making any decisions until I hear what the machinist has to say.

I dropped off the engine parts at the machinist, and at first glance the guy wasn't too worried about the damage to the heads. He said that although it won't look perfect, they will be able to smooth it out and that the heads are usable. Whew! If correct, that should save me about $800.

He also said that the crankshaft looked really good and that they should be able to buff out some light scoring. He said "these newer engines" typically typically take out the bearings, not the shaft. I showed him the bearings, and he said that upper rod bearing damage is likely due to oil starvation, which is typical in engines that burn oil. I also told him about cold start noise possibly due to chain slap, and he confirmed that low oil pressure to the chain tensioner may cause this. My engine did burn oil and suffered from low oil pressure. In regards to replacing pistons, I asked whether the use OEM or aftermarket, and he said they very rarely use OEM.

He seemed disappointed that I removed all the valves and springs, but I told him that I wasn't too worried about them, as upon inspection the valves moved very smoothly in the guides, and that the car had very good vacuum before disassembly. He had me drop off the valve parts anyways. I should get a report and a quote sometime this week.

I made an inventory of hoses, gaskets, sealants, and parts I will replace, and thus far am out nearly $600 with shipping. Ouch. However, I don't mind replacing hard-to-reach parts while the engine is out of the vehicle. The plan is to replace all of the hoses behind and under the engine, any hose clamps that have not been replaced, all of the gaskets that I have not replaced in the past five years, both thermostats, and replace the head gaskets with OEM. I measured the crank cap and head bolt diameters, and neither have stretched even halfway to the point of needing replacement, so I am going to put those back in.

Mind sharing your list?
I am considering doing a full refresh of my engine when I pull it out of the donor. It would annoy me greatly to have a oil leak show up month after putting the engine in.

I don't mind, I would be happy to. I am still ordering things, so I'll post the complete list once I make sure I have all the right items and put everything together.

Storytime!

In my experience this is a very tough part of the project. On the one hand, having access to every corner of the engine is a great opportunity to replace things. On the other hand, it is a twenty-year-old vehicle, so you don't want to put too much money into it. To me the whole point of repairing the engine (repairing anything, really) is to get more life out of it and thus save money that would otherwise be spent on a new(er) car and higher insurance rates.

When making these decisions, you have to be able to judge which parts should be replaced and which can be re-used. If replacing them, you need to have a sense of whether OEM is imperative or aftermarket is acceptable. It seems to me that this knowledge can only be based on experience, which is why it's good to start small and build up to a project of this size.

My strategy in this case is to focus on replacing the hard-to-reach items that would also have a severe impact on the vehicle if they broke. Coolant hoses are a good example. Mine don't look great and I don't know whether they have ever been replaced.

When it comes to molded hoses, I don't dare cut corners anymore, it's OEM all the way. I made the mistake of ordering aftermarket heater hoses for this vehicle a couple of months ago and sent them right back; they were the wrong size. Besides OEM being top quality, the fact that they are molded means they don't get in the way of anything else in a very tight space. I am replacing the hoses coming out of the oil cooler, because they pass under the engine in an impossible space. Those heater hoses I never replaced? They're up top; they can wait.

Another part that I am unwilling to cheap out on is the head gasket. I want to sleep well knowing I have no chance of coolant and oil mixing, destroying the bearings, due to the failure of an inferior part.

In my experience, most aftermarket parts are indeed inferior, but sometimes this can be used to your advantage. Do you really need to spend big bucks on top quality for a part that is easy-to-reach and has a low impact on the vehicle's function if it fails? I don't think so, which is why I ordered the white label intake gaskets for a dollar. Further, I believe that some aftermarket parts have the same function as OEM, but don't look quite as nice or are inconvenient in some way.

Again, this is such a tough part of the project, because tough decisions need to be made. Am I willing to spend $150 on OEM valve stem seals? (Six bucks a piece for OEM, really?!) Admittedly, this is a hard-to-reach part, but if they leak I'll try my hand at the "compressed air in the cylinder" trick. Here is a good example of a part I would prefer to have OEM, but won't spend the money on. I believe that OEM retailers jack up the prices on these items because they are hard to reach, and "as long as we've got the darn thing apart" allows for a 300% (or more) markup. In this case I went with upper-middle aftermarket.

At this point I ask myself: With so many brands to choose from, and not being able to physically inspect them, how can I determine the difference in non-OEM quality? I'll answer this by sharing some research I've done in regards to bottom-end parts.

The machinist's verdict was that I needed to replace pistons, bearings, and rings. The shop said they usually went with either XYZ or ABC brand. According to them, the two were the same. Looking at the XYZ line on Rockauto, I realized that these were the cheapest available parts. Experience tells me that you get what you pay for, so I asked the shop whether they thought I should go with OEM. "We hardly ever put in OEM," they said.

My neighbor told me that "it's a slap in the face to get machine work done and purchase your parts elsewhere." Fair enough, I should support my local machinist, especially if I want them to give my engine the attention it deserves. And what about the fact that they hardly ever put in OEM? Aren't these folks pros? Would they still be in business if they promoted trashy parts? Although I felt pressured to accept what they recommended, my gut was nagging at me otherwise.

I wake up in the middle of one night, think about this, and start browsing a few forums looking for advice. Well, I wanted to see what people thought of XYZ brand, and among the discussion I found a nugget of wisdom. Someone pointed out that these parts only had a 3-month warranty and that, in their experience, parts they have purchased with that level of warranty have fallen apart. No part with a one-year warranty, this person said, ever failed on them.

Of course! A manufacturer will offer a warranty commensurate with the statistical likelihood that their parts will fail. I immediately went back to Rockauto and confirmed that XYZ brand had a 3-month warranty. What was even more interesting was that all of the other non-OEM parts had a one-year warranty, leading me to believe they were all roughly the same good quality.

I called the shop that morning and told them that I didn't want XYZ brand, but that any part with a 1-year warranty would be fine. They seemed annoyed, but accepted my polite request, and called back a few hours later. Would you believe that they then recommended ABC brand, which they said carries a one-year warranty? This line was not carried by Rockauto, but I was able to confirm this with the distributor and a third party. Win-win: the shop gets to choose their distributor of choice, and set their price on parts. I receive parts of an acceptable quality, and save myself the embarrassment of slapping them in the face.

So how come the shop said the two were the same? It is entirely possible that when the machine shop gets parts from XYZ, they compare them to the ones from ABC, and that the parts look identical. However, it is also possible that the ABC distributor has additional quality control methods in place, allowing them to offer a better warranty.

In short, without being able to physically inspect myriad parts, or when one is unsure how to determine quality, a good starting point is to use price in conjunction with the warranty fine print to compare the quality of parts.

I tested out my newfound insight on some wiper nozzles. OEM was $40 each with a two-year warranty. Aftermarket was $3.50 a piece with a one-year warranty. Installation is simple, failure is unlikely to cause a severe problem. Which would you choose?

These are some things I am thinking about. I hope you are enjoying this journey with me. More to come.

Well I would say you “JinxedYourself” by calling this thread a overhaul instead of a less tragic refresh.

Did you consider replacing the engine with a JDM or much lower mileage wrecked one?

I'm glad you asked. Yes, I did!

I looked around for used engines online, as there is not a junkyard nearby, certainly not one that would have many imports. The rebuilt short blocks were out of my price range at about $4,000. The JDM ones I simply wasn't sure about. There were a few online retailers that I considered, the entire engine costing between $1,000 to $1,500. I especially liked the ones that showed videos of the compression. And of course there was eBay, which was the cheapest option. But I chose not to go this route for a few important reasons.

Having spent so much time with this engine, I knew exactly what was wrong with it and, more importantly, what I had replaced. Even if the used engine was in OK condition, I would still be tempted to replace many of the gaskets and such, raising the price.

Although the used engine was the "cheaper" option in terms of up-front cash, what if I dropped it in and it had the same or similar issues? I would be in worse shape than I am now and feel like a chump.

Short of any disastrous mistake, performing a rebuild would virtually guarantee me an engine in good shape for years to come.

I consider the experience gained and tools purchased during such an endeavor to be an investment. If a penny saved is a penny earned, I would effectively be making money in the future, as I don't plan on giving up this hobby any time soon. This would offset any perceived savings had I purchased the used engine.

I would be giving between 30-50% of the total engine cost to eBay and UPS, and they don't really need my money. Don't get me wrong, I use these merchants all the time, and certainly appreciate what they do. But in this case, the money would be better spent in supporting my local machinist, especially if you or I want to do this in the future.

I just wanted to do it, I was ready for it, it's fun. It's not my daily driver. I had the knowledge, the money, the tools, and the time.

Writing that down makes me realize that this kind of project is not right for everyone.

I don't see any pics of the cylinder walls, what do they look like? Any damage from the screw ingestion? Any ridge to speak of?

Mike, check out my imgur post for the full line of photos. I'll add to this set as I get the engine back and start re-assembling everything as well.

I fully expected there to be cylinder damage, but to my pleasant surprise, there was none. The cylinders had 0.002" of wear, which was low enough to only warrant a hone. I could even see some of the original cross-hatch in some places.

No ridge either, the pistons came out without a problem.

One of our most awesome threads on this site!

Thanks, that's very nice to hear. I'm glad that I'm not the only one enjoying myself.

I took atraudes' advice and inspected my motor mounts more closely today, and found that the left one had quite a bit of give. I was able to unbolt the right one just fine, but of course the differential made it impossible to get a socket onto the looser one. I stripped the bolts a bit trying to turn a wrench on them and realized that I would have to drop the diff. With the help of my wife I pushed the car into garage, and started looking over my Haynes manual to come up with a plan.

I was thinking that as long as I was going to drop the diff and replace the engine mounts, I should replace the differential mounts as well. However, I could not find any aftermarket diff mounts or bushings for my vehicle. Looking over the Nissan exploded views, I realized that the mounts were only sold as an entire OEM assembly, at a fairly steep price. These would have to wait. If the car still vibrates after replacing the motor mounts, I can consider replacing the diff mounts when I do the front control arms.

My plan was to unbolt the diff from its mounts and lower it with the driveshafts attached. I started on the right side. Two of the bolts broke free with a socket attached to a breaker bar. The other two, harder to reach, required a u-joint adapter and several extensions. The left side was similar, though a bit easier with slightly better access. As I removed these fasteners, the diff began to separate from its mount without an issue. I had a jack underneath it and easily lowered it enough to slip a socket and breaker bar onto the engine mount bolts.

Here you can see the diff lowered a few inches to make enough room for a socket and breaker bar underneath the motor mount. Notice the two bolt holes just under the motor mount, that's where the diff used to be.



Had I started with the left side instead, I probably would have been able to lower the diff without touching the right side bolts. The left mount came out without a problem, and I was able to closely inspect both on the bench.

I'm glad I took atraudes' advice, as the left side mount is starting to come apart:



The right side mount is fine, so I put it in place of the left one and ordered a new mount. Since the right side mount can be installed without moving the diff, I bolted the diff back into place and will install the new one on the right side when it arrives.

I am also taking the advice of a stranger on imgur and replacing the torque converter seal. I chewed up the housing a bit in removing the old one, but it came mostly clean with some emery cloth. I think it will be fine.

If you recall, I chewed up the heat shield and broke a few bolts trying to get my catalytic converter apart from the exhaust manifold. When I dropped off the engine at the machine shop, I also stopped by the muffler place to see if they could get everything apart. They were able to remove the shield, but the broken bolts wouldn't come out, so I spent fifty bucks on a used manifold from a seller on eBay.

Just a few more days until it's time to pick up the engine from the machine shop!

Big project, I looked at some of your other projrcts on imgur. You are definitely a hands on type person!

I zoomed thru pretty fast, so I may have missed it, but are you replacing the oil pump? Metal particles going thru it may have done some internal damage and that may be partially responsible for low oil pressure.

Otherwise, looks good!

Yes, thank you. I'm thinking that the low pressure was primarily caused by the awful state of the bearings, as I took the time to inspect the oil pump and it looks really good; nice and clean, no damage. The tolerances are tight, everything within spec, so I'll be reusing it. The book says to fill it with petroleum jelly in order to prime it, and I'm wondering how to do that correctly.

Speaking of measuring clearances, I'll take a moment now to show off my pride and joy of this project, something I have been wanting to pick up for a while, a Mitutoyo digital caliper.





It can measure inside or outside distances, and has a tare button to quickly calculate differences. Total cost was $110. It wasn't quite accurate enough to measure, say, the insides of the cylinders or the crankshaft, but has gotten me close enough to realize that I probably had a taper issue, and proved indispensable for measurements such as oil pump clearances and bolt diameters.

Nothing like a big project to warrant a new toy, eh?

Finally, I'll fill you all in on results from the machine shop, as we have settled on some things.

They wanted to hone the cylinders and recommended new pistons, bearings, and rings. I agreed, but wondered whether the block should be bored, as I thought it had some taper and out of round when measuring it at home. When asked about the taper, they said it was 0.002". This made me concerned, as the limit is 0.0006". I asked whether they meant taper or wear; the wear limit is wider at 0.008". The front desk said it was the wear, but when asked about the taper they said they would call me back that day. They didn't. I called again the following day and spoke to a machinist, who confirmed 0.002" was the taper, but was not familiar with its limit, only the piston-to-block clearance. I sent them the FSM, and they agreed the block should be bored.

They are still waiting on parts, and have not yet bored the block, but I picked up the finished heads. They were able to grind out most of the damage, and milled the heads for good measure. Here is the result.



The shop commented about the poor state of the valves and seats. Their washing machine didn't get inside the valve passages at all really, so I spent the good part of the weekend scrubbing that. My go-to for this kind of thing is Seafoam, a toothbrush, a wire brush, some pipe cleaning cloth, and paper towels. I can get even the most stubborn oil and carbon relatively clean this way, without having to grind the valves. Here is a dirty and clean exhaust valve.



I noticed that I had put some scratches in the head's mirror finish after wiping it with just a paper towel, and became concerned about all that scrubbing and cleaning affecting its cleanliness. However, I didn't want to clean the valve passages before the machine work, as I didn't know whether the heads were even salveageable at that point. I tried to be very careful, and made sure to meticulously clean the mating surface with brake cleaner and a microfiber cloth after the scrubbing was finished.

After cleaning the passageways and scrubbing the valves, I lapped the valves in their seats. Here you can see the difference between unlapped (left) and lapped seats (right). Note how the lapped seat has a uniform, dull gray finish, whereas the unlapped seat is shiny, glazed, and scored.



A cheap lapping tool from an auto parts store worked just fine in this case. The trick is to apply enough pressure to stick the tool onto the valve, but not so much that the valve doesn't spin. Intake valves that have smooth faces are easy. Exhaust valves with rough deposits on the face are a little more difficult. If the plunger doesn't adhere to the valve, press down on the tool with one hand and spin your wrist, while with your other hand apply a little bit of pressure to the valve stem on the other side of the head. This relieves some of the downward pressure, and helps the valve spin.

I have to admit that I made a mistake at this point. I was working on the left head, but forgot that "left" is from the viewpoint of the driver, and accidentally cleaned the valves from the right head and lapped them in the left head. I plan on correcting this by cleaning up the valves that go in the left head and lapping everything once again in its proper place. Hopefully this doesn't mess with my valve clearance too much, as it will be costly to replace all of those lifters and delay my project at least another week.

Cleaning the valves has been pretty tedious, but ultimately satisfying.

Great write up.
I have overhauled and refreshed a few engines over the years and I am puzzled by the taper spec. Most bore wear is taper, and you commented no ridge. I have used ridge dogger pistons and or rings with .006 wear with no issues, one a 3.4 liter Jaguar. ( in my youth)
I always used a bunny turd hone on the American V8s and these had noticable bore wear. so I would not agree with reboring the block. my 2003 pathy used a quart per 1000 to 1500 miles from 24,000 miles to 168,000 depending on speed. so pistons rings and wear do not seems to have been an issue for you.

Good luck, miss my 2003 !

ianh wrote: ↑

Thu May 14, 2020 12:06 pm

Great write up.
I have overhauled and refreshed a few engines over the years and I am puzzled by the taper spec. Most bore wear is taper, and you commented no ridge. I have used ridge dogger pistons and or rings with .006 wear with no issues, one a 3.4 liter Jaguar. ( in my youth)
I always used a bunny turd hone on the American V8s and these had noticable bore wear. so I would not agree with reboring the block. my 2003 pathy used a quart per 1000 to 1500 miles from 24,000 miles to 168,000 depending on speed. so pistons rings and wear do not seems to have been an issue for you.

Good luck, miss my 2003 !

You have a point. Wear is always taper, it's the rings that cause wear, not the piston skirt. Well, rings, heat and pressure. I too have put together many an engine with significant wear, enough to have to ream the ridge to get pistons out, but they were always fine afterwards. However, every manual I think I've ever seen makes a big deal about taper. I mean crazy low tolerances for taper, but not so much for bore. Sounds like OP already has, but I agree, no need to bore it.

On the other hand, if he needs new pistons anyway, you might as well start out with perfect. ( I come from the BMW world where pistons are stupid expensive, I don't know if Nissan are similar in that regard)

I would worry how good the rebore job is. many years ago I was in a shop that rebuilt Toyota engines. They had a celia with 175k, block and bores looked good. I asked about wear, they said its always low with the low tension rings, courtesy of the EPA regs, and if bore was damaged they threw the block and used snother used one. The liner in Aluminum blocks is much harder wearing plus those rings compared to cast iron blocks. As I said I wouldnt bore it unless it was really screwed up.

I appreciate your inputs. It seems that the machinist agrees with ianh, as the condition of the block did not bother him. However, seeing as how this is my first rebuild, I am unsure, careful, and sensitive.

Some time ago I remember reading about how cylinder wear occurs in an egg shape, the center being more worn than the top or the bottom, and that this egg-shaped wear (if not straightened by boring) is the number one cause of premature failure in new rings. I don't know whether it is true or not, but it has stuck with me. Anyways, I believe I can't go wrong by following specifications, so when I found out about the taper being out of spec, I decided to have the cylinders bored 0.020" over. What's done is done.

Although the machinist was fine with me opting out of a valve job, he recommended that I check my valve clearances. After cleaning the intake and exhaust passageways, lapping the valves, and installing the springs, I set out to do exactly that.

This was a fun and interesting part of the project. I put the lifters and cams in place, torqued the cam caps to spec, and wedged feeler gauges between the bottom of the camshaft and top of the lifter. This could only be done on the cams that were facing up and not putting pressure on the lifters, so only two valves could be measured at one time. The cam then had to be rotated a third of a turn to measure the next set of valves. Just rotate the cam until you feel pressure build, and keep rotating until that pressure is relieved. When the pressure is relieved, look for the set of lifters that are not being pressed down upon.

The specs for the exhaust valve clearance is 11-15 thousandths, for the intake valves it is 10-13. I measured the exhaust valves on my left head first, and to my surprise only one valve was out of spec, slightly tight at 0.010" (or ten thousandths). However, when I measured the intake valves, to my dismay four out of six were out of spec! Would I have to order slightly shorter lifters? At $25 per lifter the prospect made me uneasy. But I recalled reading in my Haynes manual that you can often times move lifters and/or shims around to get things in spec. I examined the lifters closely and was pleased to find the size printed on the underside of each lifter. The numbers were very faint, and the lifter had to be held at just the right angle under a lamp in order to be seen. After examining each one, I was delighted to find that many of them were different sizes, giving me the opportunity to move them around.

On the exhaust side I had 820R, three 822Rs, 824R, and 826R. On the intake side I had 808U, 812U, 816U, 818U, and two 820Us. I assume that this is the distance between the outside top part of the lifter (which makes contact with the cam) and the bottom of the nipple on the inside of the lifter (which makes contact with the top of the valve stem). When I look up Nissan lifters available for sale, I see them listed from T=7.88 to T=8.36. I am not sure what unit of measure this is - maybe you can help me figure it out.

By this point I had already written out the clearance for each valve. After finding out the size of each lifter, I transferred these numbers to each valve on my chart, giving me a quick view of my options. Here I'll show you my process of figuring out how to move the lifters around.

In the image below, on the seventh line from the top, you can see the following:

2IF, 2IR, 4IF, 4IR, 6IF, 6IR

This is my way of remember which valve I am working with. The first is the Front Intake valve on cylinder number 2, the second is the Rear Intake valve on cylinder number 2, and so on. To the right, in another column, you can see the size of the lifter in each position.

Just above that, on line four, you can see the following:

new: 10, 10, 9, 8, 9, 10.

By the time I wrote this out, I had already moved some lifters around; these were my new clearance readings: 10 thousandths (in spec), 10 thousandths (in spec), 9 thousandths (out of spec), 8 thousandths (out of spec), 9 thousandths (out of spec), 10 thousandths (in spec).

Finally, at the top, you can see that I chose to swap lifters 2IF with 6IF, and lifters 4IR with 6IR.

Below that, you can see I repeated the process three times. Each subsequent swap had resulted in fewer valves in spec than the first, so the lifters were returned to their original place, the attempt was "X'ed out, and the process was started over. After my first swap I had three valves out of spec. Three unsuccessful swaps later I still had three valves out of spec. On my fourth try I discovered a swap that reduced that number to two. Finally, the fifth swap resulted in just one valve deeply out of spec, and completed the process.



At this point I have three options:

1. I can order a new lifter.
2. I can take the valve that is deeply out of spec back to the machinist and have him grind it down 5 or 6 thou.
3. I can wait and see what the clearances look like on the other head, as more opportunities for lifter swaps may arise.

If you have been following along, you may remember my warranty theory - that warranty length can be used to determine quality. I put this into action when ordering a motor mount, and chose the cheapest mount with a one-year warranty. What happened? The mount arrived with damaged threads. I immediately sent it back and ordered the most expensive aftermarket mount, also with a one-year warranty. So much for that.

All of the engine parts are back at the house. Most of the new parts have arrived. The heads are finally clean. I feel like I have made it over the hump, like the project is less frightening and intimidating, more fun and exciting again. I look forward to laying the crank in the new bearings and playing with the plastigauge. I hope you all are still enjoying this and following along.

I appreciate all you have posted on this. You asked about the markings on the lifters, like 822R, 812U, etc. Those are thickness measurements, in millimeters, as you suspected. For instance, the 822R is the Nissan part number described as T=8.22, but I can't figure out what the R or the U means. The FSM indicates this marking and states it can be one or the other and I saw no distinction in the part numbers to purchase for a specific size lifter. (e.g. 822R same as 822U same as T=8.22mm) Lifters with shims would have been easier and cheaper to deal with but those were pre-August 2001 builds only. Once again, I appreciate all your postings with pics.

Thanks. I appreciate you and this great community.

Are you thinking about checking your power valve screws? Removing the plenum is quite easy. Once you learn how it goes it makes other things, such as replacing spark plugs, so much easier. The Haynes manual shows how to do it step-by-step.

Mike W. wrote: ↑

Thu May 14, 2020 4:31 pm

ianh wrote: ↑

Thu May 14, 2020 12:06 pm

Great write up.
I have overhauled and refreshed a few engines over the years and I am puzzled by the taper spec. Most bore wear is taper, and you commented no ridge. I have used ridge dogger pistons and or rings with .006 wear with no issues, one a 3.4 liter Jaguar. ( in my youth)
I always used a bunny turd hone on the American V8s and these had noticable bore wear. so I would not agree with reboring the block. my 2003 pathy used a quart per 1000 to 1500 miles from 24,000 miles to 168,000 depending on speed. so pistons rings and wear do not seems to have been an issue for you.

Good luck, miss my 2003 !

You have a point. Wear is always taper, it's the rings that cause wear, not the piston skirt. Well, rings, heat and pressure. I too have put together many an engine with significant wear, enough to have to ream the ridge to get pistons out, but they were always fine afterwards. However, every manual I think I've ever seen makes a big deal about taper. I mean crazy low tolerances for taper, but not so much for bore. Sounds like OP already has, but I agree, no need to bore it.

On the other hand, if he needs new pistons anyway, you might as well start out with perfect. ( I come from the BMW world where pistons are stupid expensive, I don't know if Nissan are similar in that regard)

Well I had a thought, I think the taper spec is for new or rebored cylinders, not used. Its the only way the specs make sense. When used, the wear spec of 6 thou is in line with all my experience since I was 17 on my first rebuild.