Galco

Its interesting that it's unclear if these are interference engines or not. One would think it would be common knowledge among Lexus/Toyota service techs and a conversation with a shop foreman at the Lexus dealer would answer this is short order.

If going this alone, seems to me the logical thing to do is identify the damage one step at a time to confirm if you do indeed need to do an engine swap. At only ~72K miles, I would try to save this one, first. I like the borescope idea through the spark plug openings and have a good look at piston tops and cylinder walls to see if there is any obvious collision damage with valves. If obvious and significant damage, move on to the engine swap. If the pistons and cylinder walls looks good, I would do the work to replace the timing belt and in doing so you will have to move the cams to get the engine in time anyway. Someone here or a proper service manual should be able to identify which position the crank should be first to not interfere with the valves so you can set the timing of the cams.

If the cams spin smoothly it suggests valves are in good shape and you have gotten over the next hurdle. Time the engine with a new belt, tensioners and oil pump as needed and give the crank a manual spin gently to assess if there is any interference with valves. If there is interference then pull the heads for inspection and potential rebuilding.

I could be very wrong here as I've never done this level of work but the above would take time but I have to assume its far less work and significantly less $$$ than an engine swap.

Just my 2 cents. Please keep us posted on your progress.

toddmorr

wow, the belt just randomly broke??? never heard of that. Was it original belt, or replaced with other brand??

bradland

All 400 and 430 engines between 1998-2006 are VVTi (interference) design.

ItHappens

First off, a big thank you to everyone taking the time to reply. I very much appreciate your opinions and insight!

Your making a lot of sense to me! It's not so much the purchase I'm worried about, it's my time as I plan to do all the work. Thus, I'm trying to decide if I should spend the time to replace the oil pump, throw on a new belt, then do a compression (or better yet leakdown test), or just jump right into buying, and preparing, a replacement engine. I already have the full Aisin timing belt kit, and will put that in whatever gets installed. If the oil pump didn't need replacing, it would be a no-brainer. I would slap a belt on and go straight to a leakdown test. However, the damaged oil pump housing is a complete game changer.

One would think! If you are into frustrating challenges, give it a shot; I have and got different responses from different service techs. Although they all agree that it's an interference motor (on paper), some then add something like 'well, at least that's what we have been taught, but hasn't been my experience when timing belts broke'.

Agreed that the 72k miles definitely makes it tempting to put effort into it. From what I'm seeing 72k is nothing for these engines.

I'm no so much worried about the block or bottom end, I think the problem will be found in the upper end (heads/valvetrain).

My experience with scopes has been that ones that fit easily into a spark plug hole and are short enough to then maneuver to get a detailed look at the valves are very few and super expensive. I have two scopes, the head of one is about 15mm so that's out. The head of the other will fit into the hole, but the rigid part is so long that it's not flexible enough to get it where it would need to be for a detailed look. I'm very open to bore scope suggestions from anyone who has successfully pulled this off.

I understand where you are going with this, and appreciate the input, but swapping out the oil pump is a big deal, and also requires the engine be removed from the vehicle.

Ummm.... not so sure! It's true that IF there ends up being no valve damage (which many others are certain is the case), then yes. Otherwise, cheaper and less work to do a swap since the engine has to come out anyway.


There is a reason my username is what it is, lol. My whole life I have heard the likes of "Wow, that never happens," "I have never heard of that," "Never seen such a thing," etc. etc. etc.

Yes, belt is stamped Toyota. I don't see any of the original timing lines on it, but can read the Toyota. I showed it to a service tech at the local dealer (who didn't believe that something didn't cease, causing the break) and he verified it's a factory belt.

Yep, that's what I've been told by countless people, then a whole other group claims real life experience has shown that it's not always an interference engine. Both sides are VERY adamant about their position. For what it's worth, I'm in your camp, BUT don't have real world experience with these particular motors (or any overhead cam engines).

bradland

The only trouble with this statement is the simple fact that UZ timing belts basically NEVER fail. Yes, of course there are exceptions but finding a tech that's seen it happen multiple times is unlkely.

bradland

Actually, the engine doesn't have to be removed as long as it's securely supported from above.
911LE did a great thread on this a few years back- https://www.clublexus.com/forums/ls-...e-removal.html

ItHappens

Now this I easily believe! I'm a fan of timing chains, but I do believe that timing belts are most often replaced prior to breaking, and also that 72k miles on one is a very low amount and should be outside of the risk region. Could be an age thing too, but the rest of the belt is fantastic, not even close to disintegrating (and was clearly pulled apart with extreme (read: not normal) force).

Yes, yes, makes absolute sense. I wasn't trying to state that any one tech had seen it multiple times (maybe someone has, though I agree it's doubtful). I only meant that each one, in the non-interference (in real life) group, claimed to have some sort of knowledge about, or experience with, a timing belt breaking that didn't damage any valves. The other camp had the opposite knowledge/experience. The groups are split about 60/40 for damage/no damage respectively. My writing wasn't very clear, and I should have said 'when a timing belt broke' instead of 'when timing belts broke'. Thankfully, I wasn't quoting, I was paraphrasing and meant it as a collective statement (which wasn't clear).

AWESOME write up! Not sure how I missed it because I did an oil pump replacement search (or at least thought I had, lol). Thank you for pointing it out, and thanks to 911LE for creating it! In addition to the write-up, I also really enjoyed the pics of the disassembled pump as I was able to see what the inside looks like where our pump cracked.

911LE came up with a very cool way to cheat and not have to remove the engine; however, it still appears as though his method will consume an awfully large amount of time. Furthermore, unless the vehicle is also on a lift, all the work will need to be done from under the car with minimal amount of clearance. I'm a very large guy and not comfortable spending hours working on my back without room to maneuver. If access to a lift is available (such as in my case), personally, I would rather just pull the engine. I have done it on a few vehicles so it's not all that much of a daunting task anymore, and it doesn't take me all that long. Makes me wonder if 911LE had a lift available to him, and, if so, if he still chose to do all the work from underneath so close to the ground. Of course, when I pull the engine, something will need to go back, hence my original question.

P.S. I tried to message someone but can't find the option to do so. Am I just confused (probably the case, lol) or am I too new here?

LeX2K

I don't believe in guessing, so won't speculate on the odds. This is very simple, put the crank in a position so half the pistons are at TDC, easiest way is use the mark on the crank pulley/lower timing cover. Then rotate the exhaust cams, then intake cams. Check for any resistance/valve collision. If that succeeds rotate the crank 180 degrees and do the same thing again. If you get no resistance either the valves are smashed or this is a non-interference engine.

I'm confused about this talk about the crank being rotated 720° that's two rotations. Two rotations is the same as one rotation except you did it twice.

BTW VVTi has nothing to do with interference or not as far as the camshafts and phasers go. There is no variable lift so it doesn't matter if VVTi is active when the belt breaks. I'm told VVTi engines from Lexus are automatically interfere but if true this is due to mechanical design of the heads and pistons nothing to do with cam phasers.

911LE

720 degrees is 2 crank rotations but only 1 rotation for all the cams. They run at half of crank speed.

ItHappens

LeX2K: Thanks again for all the replies!
Just to clarify... The quote of mine you posted was in reference to your prior statement that, since I can rotate my crankshaft w/o any interference, I took it you thought that there are no bent valves (and you might be right), I wasn't asking you to guess (although I wouldn't mind you doing so).

Umm... It might not be so simple, but then again you might very well be onto something. However, since this is a V8 so there won't be any way to get half the pistons at TDC for any given crankshaft position. Two cylinders will be at TDC every 90 degrees (one finishing the compression stroke and one finishing the exhaust stroke). Your method (using unsynchronized cams) would require checking it at 0*, 90*, 180*, and 270*, which is fine. However, as for rotating the intake and exhaust cams separately, that would require I pull the valve covers and do something to unlock the cams (not sure what synchronizes each cam to the other). That's a lot of extra labor that could just be put into pulling the engine. Furthermore, as I see it, if I drill all the way down to the cams, I might as well just remove them to reset all the valves and do a leakdown or compression test. I could be wrong here, but that makes the most sense to me (unless resynchronizing the cams is a total nightmare).

I believe where that was going was that when the cams and crank are in sync it takes two full revolutions of the crankshaft to have each, of the eight cylinders, cycle through all the strokes (again, due to a cylinder firing every 90 degrees, 8*90=270). Since my belt is broken, and the crank and cams can be rotated independently, there isn't any reason for more than one rotation for any given cam(s) position (except to repeat a test more than once).
EDIT: Just posted this and then saw 911LE's response while I was typing. He said it in a more clear manner and with a lot less words.

I don't know what there is, or what there isn't with these particular VVTi engines, so I'm FAR from the expert with this one! However, even without variable lift, the computer should be able to change the valve event timing (openings & closings), and would make sure (by adjusting said timing) that no particular valve would ever be open far enough to come into contact with a piston. As soon as the timing belt broke, all that went out the window because the computer was no longer in control and whatever valves were (near fully) open stayed that way the next time the corresponding cylinder's piston approached TDC. If the valves aren't chasing the pistons (or pistons chasing valves, depending on which stroke it's on) then one could easily design a non-interference motor.

ItHappens

Exactly! Of course, one also needs a functioning timing belt for the cams to rotate at half speed (or any speed, lol)!

911LE

Put your scope in one of the cylinders that is at the bottom of it's travel. You don't need to be able to see the valves because if they touched the pistons (which I can guarantee they did) you will see the marks on the tops of the pistons. Look at all the pistons (firing order 1-8-4-3-6-5-7-2 to make it easier). Not all will have made contact but at least one has. I've pulled the heads off of my car and I would much rather replace the engine than do that again. The only difficult part of engine replacement would be getting all the wiring unhooked as some connectors are difficult to get to.

Striker223

Was gonna quote this post as well to show you can do the pump sans removal, on the new engine if you go that route I HIGHLY recommend removing and resealing the upper and lower pans with new FIPG before placing it in the car. The oil pumps do not normally wear out on these engines so I would say always use an original Toyota one since it's probably one of the best quality wise by a long shot.

I have personally seen one failed belt on a customer car who went 307k on one belt, car was at 550k and that killed the engine. It was a OE belt but the real cause of failure was an original idler seizing.

Lastly if you have a bore scope that does fit into a spark plug hole you can check if damage occurred actually. Since the crank is allowing you to turn it you simply need to set each cylinder to BDC and then insert the scope and look down onto the piston for contact marks. They will be bright spots in the otherwise uniform carbon layer on the top of the piston....if you see that or gouges it's dead.

Striker223

Bingo! The last section you typed is exactly why VVT state matters, you can easily have an interference engine that never has an problem as long as the valve events stay away from the time the piston is somewhere in the valves path. If you had a theoretical infinite VVT engine (not so theoretical......some are very close to this) that can use the cam phasers to phase the cam say, 180* forward as the piston is coming up you will hit valves. If the system is working properly the valves will chase and run away from the piston as it moves up and down to maximize intake charge size and maximize cylinder purge on the exhaust stroke.

If it's not then you could actually have a valve collision event WITHOUT a timing chain/belt failure but usually there are hard mechanical limiters inside the actual cam phasers to prevent exactly this unless your car says BMW on it. Google VANOS failures for reading entertainment.

You finally also do not want to remove the cams separately, they have an area to insert a screw to lock them together to avoid the potential hell of resyncing them. I have never done it on a Toyota UZ/MZ engine or any of their engine that have only one phaser for both cams (non-independent exhaust/intake VVT) since if it's anything like VAG group cars cams getting them back into proper sync will be interesting to say the least and require serious care and actual precision if not outright proprietary jigs like on VW cars.

LeX2K

I was over simplifying, probably shouldn't have. But I think putting the crank at zero and 180 is enough to determine if the valves are damaged.
That's what I was getting at, no timing belt means rotating the crank once is enough.
The computer does exactly this, call it cam phase or relative position. But the reason VVTi doesn't make any difference if the belt breaks is the crank is going to rotate out of phase (randomly basically) in relation to the cams so whatever position the oil control valves had the cams in doesn't matter.

On having to remove the valve covers no you don't have to do this, rotate the cam sprockets you don't have to rotate the cams individually, which you can't anyway they are geared together in the cylinder head.

Here's the problem with buying a replacement engine, that's the devil you don't know. It might be great, it might be bad. With your engine you know the condition before the belt broke, so if you can repair your engine you know it will be good to go. I've been burned by putting in a supposedly good engine it had bearing knock as soon as I started it. The 3UZ is quite robust but still, used engine is a box of chocolates.

edit - for context watch some of this 3UZ timing belt vid. You can easily put a ratchet on the crank and cams and rotate them independently see what happens. Nothing to lose.