Broken timing belt

I have an 01 tundra with the 4.7L V8 and I was sitting in front of my house idling, the truck shuddered and died. I tried a handful of times to start it and after some research, figured out my timing belt broke... Is there any chance that since I was only at an idle that I didn't cause any damage to my engine?

 

Yes, there is a chance that you didn't damage the engine since you have the non VVTI engine. Some have gotten lucky in your shoes.

 

You can always borescope the cylinders to check for damage by pulling the plugs, but yes, your risk is low for damage.

 

Better at idle than 70 on the highway. Do not attempt to start and replace belt.

 

It's not a great situation but you've got a fighting chance since you were at idle and thus low momentum. We've seen it plenty of times.

DO NOT buy any brand belt other than OEM or Aisin kit (which will be Mitsuboshi brand, not Mitsubishi but Mitsuboshi). Don't buy it on scAmazon/fleaBay or any other shady online market.

Were you not aware the belt is supposed to be changed every 9yrs/90k miles, if you're using OEM equipment? (or half that, if using aftermarket)

 

Tagged: interested in the result.

I was so fearful of this very thing happening, I parked the truck the day I bought it and let it sit all winter. I then had it rollbacked to a stealership that promised to push it into the shop for the belt change.

(Along with a ton of other maintenance).

Good luck, prayers said for you already.

 

This is really useful, My last big job was on a Subaru that blew its timing belt (totally destroyed the valves, but that is normal for subarus) and I replaced with a AISIN kit....but I saw the belt was what I thought, Mitsubishi spelled wrong, which made me worry I got scammed as I didn't know they didn't make their own belts.

As far as I can tell from years on this forum and facebook, the OP has about a 75% chance of not having damaged your valves. Our engines are interference engines, but apparently just barely interference engines and have a lot better luck than say, a subaru.

 

Yep, @BubbaW rightly called me out on my fearmongering on it a couple years ago, and I'm glad he did.

Ever since, I've been making a point of saying "low interference engine" instead of simply "interference". In a proper interference engine, belt snap at any speed will brick the engine. At low RPM, with heavily reduced rotational momentum, belt snap on he 2UZ will, clearly, not always cause internal damage. But we have plenty of documented cases of people snapping belts while going 30mph+ up to highway speeds, and completely bricking their 2UZ.

I'm curious what the line in the sand is. We've had quite a few people who snapped theirs at idle slap a new belt on and the engine still ran. No clue if there was actual damage, but it ran.

 

I don't think the speed is the factors.Your pistons and your valves are the 'immovable object and the unstoppable force' at any speed.

My theory is just that when the belt brakes, most of the time the cams snap into a position where all the valves are out of the way before they get clipped by the pistons.

I will also note.....worst case, is that you need a valve job. Which is not great.....but is a thing that is done on engines all the time.

 

Speaking purely from a basic physics standpoint, if your engine is at 2,000RPM, the kinetic energy it's carrying is going to be substantially more than if it were idling at 700RPM. That kinetic energy, when the belt snaps, at 2000RPM, the crank is going to continue throwing (thanks to the kinetic energy) for substantially longer than it would at 700RPM. You may clear a half a cam rotation at 700RPM, you're liable to complete two or three full rotations with the kinetic energy held at 2000RPM, and that full rotation is where I'd personally expect the damage to happen.

It's also possible I'm overthinking it, or my logic is flawed. IDK. I just know, counting back over the couple dozen timing belts we've had snap here, there's some fuzzy area above 1k RPM that nearly every case I can think of someone having a belt snap, the engine survived. But without fail at highway speeds/RPM, engine is toast. I think it's due to the kinetic energy of the crank and pistons forcing them to cycle while the cams aren't moving any longer.