ItHappens

New here and was looking for a 3UZ-FE forum since the 4.3 was used in so many vehicles, in different generations, and my question pertains specifically to the engine and not the car it's in.

Anyway, here is what happened... long story short, I was driving my wife's car when it just quit and wouldn't restart for anything. Towed it home, read the codes, and found cam and crank signal/circuit errors. I hooked my scope up to the left cam sensor (since it's so easy to get to), turned it over, and nothing but a flat line.

End result is the timing belt broke with only approximately 72k miles on it. Naturally, I assumed something seized, but not the case! Everything in the belt path is good. Idlers are smooth, tensioner is fine, water pump spins smooth as silk.

If this isn't disaster enough, there's more! It appears as though, a chunk of the teeth from the part of the belt that was being stretched (and ultimately failed), fell down and got jammed between the belt and the left side idler (the fixed position one, not the one with the tensioner). The extreme tension caused so much force to be side loaded against the idler that it cracked its mount -which happens to be the oil pump housing. Ugh!!

So the questions I would like expert opinions on are:
1) If the timing belt breaks while the 4.3L engine is running at cruising RPMs, will piston-valve contact occur (bending the open valves)? Personally, I can't see how it wouldn't, but I'm not familiar with this motor and have been receiving differing opinions (and, as is often the case, both sides are certain they are right). Even here, in these forums, I have seen both sides argued. I'm not trying to revive a debate, but instead am interested in hearing from people where this has happened to them and what their actual real life experience has been.

2) Since I'm going to need to swap out the oil pump before I can reinstall new timing components on the current engine, should I just buy a low mileage 3UZ-FE and install it instead of wasting my time with the current one (which is low mileage and was running flawlessly -was being the key word)?

LeX2K

First thing is verify if there was any valve to piston contact, of so look for a replacement engine. If not and assuming nothing else got damaged I'd replace the oil pump.

I kinda gave up on interference vs. not I've never seen anyone actually verify. Quite certain it is interference but again can't be sure.

Striker223

It's dead. You are best served just finding another engine entirely but it would be worth it IMO to at least take the cams off and test compression. You may have the 1/10000 engine that didn't kill hard parts and if so the long block is useful still.

Issue is when you say cruising RPM that usually implies that VVT is active and the valves were very much chasing pistons up and down when timing sync was lost. It's very likely totally dead.

Only the non-VVT 1UZ engines can break a belt and live

ItHappens

Makes sense, but doesn't this require a ton of time that could just go into a swap? I know my way around big cubic inch pushrod engines but have no clue as to what's involved here with its four overhead cams.

By "totally dead" I assume you mean various valves are totally dead, or are you thinking other engine components are dead as well (other than the obvious oil pump housing)?

Ok, but what's involved with 'taking the cams off'? Is this something that requires just a small amount of time under the valve covers? Also, how about putting them back in at a later, how much time is involved there?


Another question is can I drop the transmission out the bottom (looks rather simple), then pull the motor from the top and not have to mess with all the suspension and such. It looks like it wouldn't be that difficult, but the repair manual says engine and trans combo out the bottom.

LeX2K

If you have to remove the heads that's a whole can of worms both in time and money. I'd be tempted to slap a timing belt on see if the engine runs.

I've pulled the engine topside in an LS400 it was easy didn't see the need to drop everything out the bottom. .....pulled engine/trans as one unit.

ItHappens

Absolutely agree on not wasting the time to remove the heads. Not sure about removing the cams though. Can they be removed (and reinstalled) quickly and easily?

I can't put a belt on it and run it (as you suggested) because of the broken tensioner mount for the timing belt. Trust me, if I could I would put a new timing belt in it and then do a compression test. However, if there's not a ton of time involved with removing the cams then the valves could close (well, if they are okay that is) and I could do a leakdown test.

Thanks for the info about pulling the 1UZ-FE topside! Seems to make more sense to me to go this route.

LeX2K

I wouldn't say easily, everything on top of the engine has to be removed. Much easier to get a borescope for your phone. Another thing you can do is verify is the engine is interference or not, slowly rotate the cams/crank see if you get valve collision. Remove the spark plugs first so compression is not a thing.

If valves never hit the pistons the crank should rotate easily no matter where the cams happen to be.

ItHappens

All the plugs are removed and the crank rotates as smooth as can be, but any damage would have been caused when the belt broke, so who knows what was already pushed out of the way.

As for rotating the cams, I'm a bit worried about doing so, won't that just introduce more potential for valve damage (or additional valve damage)?

Striker223

It depends on what you define as easy, since you are used to big cube pushrod cars I would liken this effort wise to swaping lifters. I can and have done it in my home garage in less than 3 hours and in that sense it's not hard for ME to do but the same thing could take days for others. Head removal is then 10 extra minutes.......

For the 3UZ to remove cams it's about 2-4 hours once again depending on how you do it and skill level. It does require you to reapply RTV to quote a few areas and I recently had to do this job again on a replacement engine in my car since I got lazy. If you are replacing the engine and HAVE a lift, drop the engine and trans as a unit with the subframe out the bottom. You can be done in under a day easily, if you don't have a lift then yeah you would be better served to pull it out the top after separating.

https://www.clublexus.com/forums/ls-3rd-gen-2001-2006/971066-well-i-was-lazy-and-it-bit-me.html

Here.....may help clarify things. Honestly if I was directly in your position I would pull the passenger side head off and check since best case the engine is good and I can leave the block in place and worst case who cares since it all needs to come out then. In reality though it absolutely has broken valves.

Striker223

If the crank rotated smoothly the valves are dead. Otherwise the crank will tap into them around 100 degrees in each direction

LeX2K

Valves are not that fragile, rotate the cams carefully but be mindful of valve spring loading on the lobes which will make the cams want to rotate suddenly.
All the valves have been bent perfectly out of the way so they don't touch anymore? Not saying that isn't the case but in my experience bent valves prevented the the crank from doing a full rotation unless you put a lot of force into it.

Also it depends where the cams happen to be in their rotation.

Striker223

More so smashed into/past the head chamber roof......To my knowledge there is no possible way to set the cams with all valves retracted at once across all cylinders on a V8 unless you have a valvetronic type system.

You can also I guess try and walk the engine though it's firing order manually by rotating the cams 1/2 as much as the crank in small steps one shaft (left cam, right cam, crank) at a time and observe if the valves on each cylinder BOTH come up and down to the same places for intake and exhaust. If all 32 somehow all act the same then you may not a have total loss. If at any point even one of them doesn't line up with it's same side neighboring valve (so any of the 8 pairs of intakes, or 8 of the exhausts) especially when the valve is on the flat (non actuating section) of a lobe pair (one of the two right next to each other is slightly lower than the other) then you have at least one dead valve and a failed head most likely from the seat being pounded as well.

This all assumes you can somehow rotate the crank a full 720* and I seriously doubt it's possible as it stands. Usually as you said above the valves get bent to block movement at least partially and in this case if the cams are not synced with the crank there should be NO way possible for the 720* to occur without bind. Even a non-damaged engine can't do 720* without the cams connected via chain or belt doing their corresponding 360* unless you move them each manually in small steps like I described above.

Now if you have a true non-interference engine sure, turn it as much as you want. Not so much on these or really any modern engine outside of some seriously strung along domestic I-6s and V8s and the occasional 4cyl. Anything modern for the sake of better specific power and BSFC will have valves that chase after and run away from the pistons.

You lose sync stuff dies HARD. Even older stuff when you optimize it loses the ability to survive a sync error, my original 5.9 magnum could survive no problem. In current trim the pistons and valves have .03 inch moving clearance at 30* over nominal operating temp......if the chain goes the valves will die now. The 3UZ was designed from the outset to be far far far more effective of an engine than a 5.9/360 was and by default is setup with overlap in the event of a sync failure. The very first pattern non-VVTI 1UZ is the ONLY one that can survive since it doesn't have very optimal valve mechanics for the engines relative size.

ItHappens

Ok, now this is helpful to me, thanks for the analogy and the time estimate. Exactly what I was looking for, and I certainly don't consider it worth spending 2 to 4 hours of my time since the engine needs to come out anyway due to the damaged oil pump housing.

I do have a lift, but would need to get it there (it's sitting in my home garage, sans lift, at the moment). After a very quick GLANCE it looked to me like I could easily drop the trans (basically exhaust and a brace first, trans next) out the bottom, then yank the engine out the top and not have to deal with all the suspension and realignment headaches. Does this make sense?

Well this SUX. Sorry to hear about the extra trouble.

Out of curiosity, why the passenger side? Does this have something to do with timing, or just because there is less crap above the valve cover? The only problem with your statement is that no matter what, I still can't "leave the block in place" because of the oil pump housing damage.

Ok, well now we are getting to the meat & potatoes (as my dad often said). So I can rotate the crank (smoothly and easily) as much as I want (360*, 720*, 1080*, 1440*...) without any issues or interference. Again, I haven't rotated the cams yet, they are exactly in the same position they were when the belt broke and the car died while on the highway.

ItHappens

Fascinating, well this is the opposite point of the above. I can indeed do full rotations (without any force), but the cams are in some random fixed position and not moving at half the speed of the crank. So to clarify, in your opinion, odds are there is nothing wrong, correct?


Agreed, but I think we were talking about pulling the cams out, that should reset/close all the (correctly operating) valves, no?

Completely agree, and thought of doing it, but didn't want to waste the time since the crank spins without interference now when it's not in sync with either cam!

Yep, I totally get what you are saying, but if the belt/chain is disconnected then 360 degrees of crankshaft rotation equals 720 degrees, (and 1080, and 1440,...) it's all the same since none of the valves are opening/closing.

This is exactly how I pictured it when I asked the question. Just weird to me that so many people have different beliefs as to the outcome. I guess it might be possible to have the cams in exactly the right positions that the whole thing could become non-interference somewhere in synchronized rotation (for mere fractions of time while running). However, my simple mind doesn't see it happening, and certainly not with the luck I had with the belt breaking at only 72k and said belt taking out an oil pump housing? I mean really?!? Has a timing belt ever cracked an oil pump housing on these engines? If so, I haven't seen, heard, or read, of it happening previously!

jainla

UZ engines are not that expensive; I see used ones on Ebay for under $1500. The market for them is not that great because they are generally reliable and outlast the car. JDM cars usually get parted out around 10-15 years of age because of the taxes being more than the value of the car (this incentivizes people to replace cars more frequently than the US) and the engines come over here. If you're going to pull the whole engine out a swap is probably going to be the easiest as opposed to tearing down and rebuilding; but again it depends what your time is worth.

While I think the UZ engine is one of the best V8s ever made if the TB went I'd probably just go the replacement route. It's a lot of money and sad to see an engine go but in the end I'd rather have a good unit than one that's questionable. Have the block polished and made into a coffee table!