911LE

This is incorrect. The service bolt is installed to lock the two halves of the spring loaded timing gear together so the spring pressure doesn't push the cam out of the head while the caps are removed and so it can be reinstalled. The cams are timed together with another set of timing marks on the back side of the internal cam gears.

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.

ItHappens

I already used the scope at BDC and didn't see any damage on the pistons. However, the light at the tip on that one is very dull, not sure if brighter LEDs would make a difference.

Thanks for this, it's one of the best statements yet! Exactly what I was thinking/afraid of! So... If you had to pull the engine, and had a lift available, would you drop the engine trans combo through the bottom like the factory repair manual indicates? Do you see anything wrong with dropping the trans out the bottom and pulling the motor from the top?


Whoa!! 307k on one belt, dang! We couldn't even make it to 73k! However, I was certain that something seized just like what you described. If I may ask, do you work at a dealership, or independent place?

Thanks for the advice. As I just mentioned above, I already did that and don't see any damage (caveat is that scope is very dim, but the top of piston was still viewable).


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).

Gotcha, I thought you (or someone else) mentioned rotating the intake and exhaust cams separately. My error, and glad to hear the valve covers don't need to come off. 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.

Couldn't agree with you more! This is one of the primary reasons I asked the questions in the first place.


Agreed! The VVT system allows lifts which would normally cause interference, but doesn't because the valves are constantly chasing, or running away from, the pistons. At least this my simplistic understanding. As for the crank continuing to spin due to it's momentum when the belt broke, no doubt this was absolutely the case! However, there is also the times I tried to restart it too. Less RPMs but I'm sure that the torque generated by the starter could caused valve damage too.

LeX2K

I think what's happening is having variable valve timing allowed them to design an engine with higher compression and in doing so made it an interference engine. Or maybe not higher compression but a piston shape that allows for better combustion but not over the rev range so varying the valve timing gets around this.
You were probably feeling valve spring pressure.

Unfortunately at this point the damage (or not) of the engine is not conclusive. At least in my mind.

ItHappens

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.

05ls430518

iTrader: (1)

To answer op's original question your motor is toast get a junkyard one go through it replace all the seals belts etc while you have the motor out of the car. Then enjoy the car.

Galco

Very interesting topic, ItHappens any updates?

ItHappens

Thanks for the input, I believe it to be wise advice.

Glad you find it interesting, I do too (as well as frustrating!). No updates yet, because just haven't (and won't for a few weeks yet) had time to pull the current engine out. In the mean time, I'm also looking around for donors.

Galco

Curious, what ever happened with your engine issue?

ItHappens

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.