Requesting Opinions: Repair or Replace 4.3L Engine?
#31
Instructor
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.
The position of the vvt system the op's scenario is irrelevant. It only controls cam timing with respect to the crank position. Valve lift is still the same and is what causes interference. When the belt breaks the cams stop immediately due to valve spring pressure. The crank continues to spin because it has much more inertia and the only things slowing it down are friction, which is minimal, compression, but only in the cylinders that have all 4 valves closed, and mechanical force from the valve stems it's bending or breaking. The only way there is no carnage is if none of the valve were at, or close to, full lift. In a V8, this is almost impossible.
#32
Driver School Candidate
Thread Starter
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.
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.
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.
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.
The position of the vvt system the op's scenario is irrelevant. It only controls cam timing with respect to the crank position. Valve lift is still the same and is what causes interference. When the belt breaks the cams stop immediately due to valve spring pressure. The crank continues to spin because it has much more inertia and the only things slowing it down are friction, which is minimal, compression, but only in the cylinders that have all 4 valves closed, and mechanical force from the valve stems it's bending or breaking. The only way there is no carnage is if none of the valve were at, or close to, full lift. In a V8, this is almost impossible.
#33
Lexus Fanatic
Exactly as I understand it too (though my understanding is, admittedly, minimal), I think what we are saying (or at least what I have been trying to say is) because of VVTi they were able to built an interference motor but not have any interference when running (assuming everything is working as designed).
I did follow your prior advice on this and used a wrench to rotate them. I didn't notice any interference. Although there was one spot on the left set of cams that seemed like there was interference. There was definitely a little more resistance for a few degrees of rotation, but when I held it there and moved the crank back and forth it didn't make a difference. I (maybe incorrectly?) concluded that the extra resistance wasn't from interference. That said, it doesn't mean things weren't pushed/smashed out of the way prior to me turning things manually.
Unfortunately at this point the damage (or not) of the engine is not conclusive. At least in my mind.
#34
Driver School Candidate
Thread Starter
Could be but it was only at one specific point in the rotation and only for a few degrees. There is so much cam spring pressure that it caught me off guard, I now see why they say to rotate the extra 50* so they don't rotate on their own when removing a belt. Might be that too??? I don't really know because I'm just not familiar with the setup.
Agreed.
Agreed.
Last edited by ItHappens; 08-12-21 at 07:29 PM.
#37
Driver School Candidate
Thread Starter
Very interesting topic, ItHappens any updates?
#39
Driver School Candidate
Thread Starter
Sorry about the late response and updates. As recommended here, I ended up swapping the engine, and have a couple of updates regarding that process. With a rack, it was a very simple process just to unbolt it from the trans at the bellhousing and pull it up through the top instead of doing the whole trans/engine through the bottom process as mentioned in the service manual. I would highly recommend this method as it will save hours of labor over removing everything under the car.
As for those who said the 3UZ-FE is an interference engine and physical damage was guaranteed after the timing belt broke, they were 100% correct! I wasn't able to see it with the smaller (and much cheaper) borescope I had that fit into the spark plug hole. However, once the engine was out, and I removed the heads (yes, I know I could have removed the heads with the engine in the car, but I needed to remove the engine to address the cracked oil pump housing), the damage to two cylinders was plain as day. The reason why I was able to rotate the crank without any interference was because everything had already been pushed (slammed is probably a better description) out of the way.
As for the replacement engine, I bought it from a local junkyard for $750. The most difficult part of the swap was messing with the various wiring harness connectors. Due to their age (in both the original and the replacement) they had become very brittle and easily broke under the very slightest amount of pressure. I ended up ordering a handful of them from the Lexus dealer as I didn't want to risk them separating under vibration while the car was underway. The carfax report showed regular services done at a local dealership, and one service, not that long ago, included replacing the starter. Thus, I didn't replace it, but I did replace the timing belt, water pump, timing idlers, tensioner, and rear main seal.
The end result is that my wife has her car back, and is a happy camper again. Thankfully, it runs just as well as it did prior to the catastrophe, and hopefully we are done with fluke timing belt issues for the rest of the life of the vehicle.
As for those who said the 3UZ-FE is an interference engine and physical damage was guaranteed after the timing belt broke, they were 100% correct! I wasn't able to see it with the smaller (and much cheaper) borescope I had that fit into the spark plug hole. However, once the engine was out, and I removed the heads (yes, I know I could have removed the heads with the engine in the car, but I needed to remove the engine to address the cracked oil pump housing), the damage to two cylinders was plain as day. The reason why I was able to rotate the crank without any interference was because everything had already been pushed (slammed is probably a better description) out of the way.
As for the replacement engine, I bought it from a local junkyard for $750. The most difficult part of the swap was messing with the various wiring harness connectors. Due to their age (in both the original and the replacement) they had become very brittle and easily broke under the very slightest amount of pressure. I ended up ordering a handful of them from the Lexus dealer as I didn't want to risk them separating under vibration while the car was underway. The carfax report showed regular services done at a local dealership, and one service, not that long ago, included replacing the starter. Thus, I didn't replace it, but I did replace the timing belt, water pump, timing idlers, tensioner, and rear main seal.
The end result is that my wife has her car back, and is a happy camper again. Thankfully, it runs just as well as it did prior to the catastrophe, and hopefully we are done with fluke timing belt issues for the rest of the life of the vehicle.
The following 2 users liked this post by ItHappens:
LatinLS430 (01-04-22),
LexRex (12-31-21)
Thread
Thread Starter
Forum
Replies
Last Post
andyman32
LS - 1st and 2nd Gen (1990-2000)
7
03-17-13 07:58 AM