Broken Timing Belt Confirmed

[BamaHeel]

Is it possible that since this is no race engine (compression is 10:1) that the angle of the valve train is such that even if the piston is at its highest point and the valve is extended at its highest point they still wouldn't come into contact?

That way it could still be an interference engine and explain why no damage to the valves. Especially if the piston face is relieved in some way for valve clearance. I'm not talking a huge amount of space here just thinking of how this would be possible.

That could explain Spresso's observation and what occurred here.

 

[OregonLC]

Then it wouldn't be an interference engine, no?

 

[APKhaos]

Then it wouldn't be an interference engine, no?

Yes......or No, it wouldn't be one of those. Or something.

 

[Krazytoy]

If you can rotate the cams with the timing belt removed then it is not an interference engine. Why not just accept that fact instead of making up crazy scenarios?

 

[GDenver]

Any update on this? My timing belt broke as well, curious if it actually is an interference motor or not

 

[jgray]

I had no other damage but all data seems to point that this is an interference motor. No bent or broken valves. Maybe I was lucky!? All I know is I took the opportunity to replace everything I could think of while everything was torn down. It's been running great since putting everything back together. I just did full brake service all around and replaced a 02 sensor last weekend but drove out of state and back last weekend. All is good - just tripped 208K today... So I've put 4,000 miles on since my belt broke... She's still alive feeling good with the new makeover services!

 

[2001LC]

From all accounts I've seen in this forum it is not an interference engine.

But to be clear I've not see any thread on broken belts concerning the VVT engines.

 

[GDenver]

Mine is a 98, so I believe I should be safe.

This is great news, as I was about to pull the trigger on a used motor. Now, to pull the heads and see what condition my motor is in.

I will report back once I know more

 

[Gdubyacobb]

I had the belt shred on a 97 Nissan Pathy. I called a dealership and asked about the interference on the basis that I knew the belt had gone and didn't want to spend the money to bring it in if it was dead.

They checked and called back letting me know that it wasn't an interference engine.

Worth a call to a dealership.

 

[jgray]

There still aren't many cases of this happening. I can confirm first hand my results and posted pictures of teardown and rebuild.

The thing that still puzzles me is all factory documentation, shop repair manuals and parts descriptions we referenced during this specific to my 1999 Land Cruiser clearly state "Interference Engine" or "Interference Engine Application" in many different write ups.

Keep us updated on your progress with your 98! Wishing you good luck!

 

[GDenver]

Well it looks like the Toyota literature is wrong. Put it back together and it fired right up. Finally had a chance to have my LX torn down and here is what caused the issue:

This is with 40k on the belt. This bearing was completely F'd and so was just about every other bearing. Put a new timing belt and all associated pulleys, bearings, water pump, etc. and it fired back up no problem.

As far as I can make out, this is not an interference motor, and it certainly wasn't in my case. Looks like the myth of this being an interference motor may be busted. Happy this was fixed without head damage, but disappointed with Toyota for misleading people. I imagine many motors have been replaced due to misinformation.

 

[Muddy Bean]

I'm convinced that something else will fail before the belt itself. Water pump, pulley bearing, etc. I have 150,000 miles on my original belt now. I broke my front diff before I broke my TB.

 

[jgray]

Good news GDenver!!! Mine is still running great as well but I replaced a whole slew of stuff while everything was torn down and pulled the heads to confirm no further damage... Glad to hear you are up and running again with basically just a timing belt replacement kit...

 

[OUbobcat20]

143K on original belt here. I recently pulled the cover and the belt looks fine. No noticeable cracks on the belt or wear on the edges.

Going to wait until next April before i do the full service. I will probably be at around 147k by that time. I've got a 14 day 4500 mile road trip planned so I'll want to get it done before that.

(T Belt, Tensioner, idlers, cam seals, water pump, thermostat, serpentine belt)

 

[ClankBang]

Another data point here..

2001 Cruiser with about 210k on the clock.
I bought it with 175k and though there was some evidence the timing belt had been done there wasn't a sticker or any papers.


NAPA belt broke with unknown milage.
Truck died with my wife driving it she says she was just pulling from a light and the truck slowed to a stop.

After confirming the belt was broken I opted to just replace the belt and see what happend. I turned the cams and the crank by hand and had no interference.
I set the cams and crank to the marks and put the new belt on. It fired right up. Probably put 3k on the truck since with no issues.

I do plan on doing a proper timingbelt job soon but I wanted to spend as little $$ as possible on a potentially dead engine.

So... I spent less than $100 to get back on the road; pretty darn impressive.

 

[jgray]

^ very interesting and good news. This makes several known instances of timing belts breaking and causing no additional damage... I don't believe these are interference motors anymore. Im betting anyone that breaks a timing belt can replace it and will be fine. Mine broke at 60+ mph on the interstate and I tried starting it multiple times prior to knowing what the problem was... Another good post!

 

[ClankBang]

I know the literature says that the 4.7 is an interference engine.
I have a theory that the 4.7s built in Japan (Cruiser engines) are slightly different than the ones built in the U.S (4runner/Tundra engines)..
I have to say that after this experience my 100 feels more like a Cruiser than it did before.
I feel better knowing that it seems the engineers put the need for robustness over the want for efficiency.

 

[toddmorr]

I know the literature says that the 4.7 is an interference engine.
I have a theory that the 4.7s built in Japan (Cruiser engines) are slightly different than the ones built in the U.S (4runner/Tundra engines)..
I have to say that after this experience my 100 feels more like a Cruiser than it did before.
I feel better knowing that it seems the engineers put the need for robustness over the want for efficiency.

this is a fascinating thread. Starting to get skeptical as to whether the 4.3l V8 in the Lexus LS430, for example, is an interference engine, as has been claimed. Over on Club Lexus there are no documented cases of TB failure but lots of guys are doing their belts as they go over the 100k mark anyway. A definitive answer would calm a lot of people down on doing these repairs so early

 

[jgray]

I have also read accounts of timing belts breaking on the 4.7 Tundra and causing no other problems as well. When mine broke I scowered the web looking for other reports of similar incidents from 100 Series LC's and Tundras with the same motor... I only found a few other stories of broken belts but broken Toyota belts are extremely rare... The belt that broke on mine was a aftermarket "dayco" belt installed by a shop that did the timing maintenance for me originally (long, long time ago before I became extra picky about making sure all Toyota parts were used for maintenance). I had no idea the shop provided parts were not OEM at the time... The aftermarket "dayco" belt that broke on mine had about 70K miles on it IIRC and I definitely would never use one again...