Does timing belt jump cause engine damage?

Does timing belt jump cause engine damage?

I reviewed the posting in this forum. I am new to this forum. I like to have your insights on this issue.

My TOYOTA Camry 1999 (Less than 90K miles) was driving OK. I do check under the hood on and off, I did not do that check for awhile. Last week my car started OK. Within two(2) minute driving RPM started decreasing and lost power. The car engine cut-off. It crank the engine as I turned ignition, but it did not start. I towed the car home. I towed the car to auto service shop. I trusted this mechanic. He did some critical work for me on other cars in the past. Other mechanics make me run around on situation and suggested motor replacement on my previous cars. This mechanic addressed the issue and put my car on the road without changing the engine.

My mechanic is telling that my timing belt was jumped and hit water pump. He did leak test and find leakage in middle 2 cylinders. He wanted to replace the motor.

He performed the leak down test using Cylinder Leak-Down Tester as shown in

He removed upper timing cover, front passenger wheel and rotated the camshaft manually to do leak down test .

The mechanic performed the lead down test in my presence. Here are the readings from leakage Gauge.

Outer two Cylinders 0 - 10 % (Close to Green)

Inner two Cylinders 100 - 80 % (Red)

As he proposed for engine replacement in situation, because he said the inner two cylinders have bent valves. I am in dilemma to see him as scam artist.

I did not drive on high speed and drove 2 minutes from starting. My car has non-interference engine, so it had timing belt instead of timing chain. I am not sure bent valves story adds up with non-interference engine.

Does this situation cause such engine damage?

Do we able to do leak down test properly with camshaft timing being out?

I learned that when the timing belt breaks, the camshaft will always have the valves open on one or two cylinders. A competent mechanic can identify this before even opening the hood by the sound of the engine cranking. This will show up on a leak-down test as valve damage, when the valves are simply being held open by the cam because they’re out of sync with the pistons.

Did you face such situation? How did you resolve it?

Is the leak down test right diagnostic on this situation?

Thanks for your insights.

Bent valves can be replaced much cheaper than replacing the engine. If properly used the leak down test is decisive.

I don’t know the specifics of your engine, but it is theoretically possible for a “non-interference” engine to have the valves interfere with each other and cause damage, even if the pistons do not hit the valves.

But since your belt only jumped but did not break, I would be hesitant to undertake a major engine repair/replacement on the basis of one diagnosis.

If it were my car I’d put the timing belt back on correctly and see if it runs right. If it does, no repair needed. If it doesn’t you should get misfire codes in the cylinders with damaged valves to confirm the diagnosis. But don’t run it long like that because it will damage the catalytic converter.

I have never seen a Camry engine bend valves, but that doesn’t mean it can’t happen. But the fact is that your mechanic could have spent less time on the car by throwing a timing belt on and seeing if it starts and runs for a few seconds. That will give you far more info than the testing he is doing.

Here’s something to consider . . .

While the valves may not have collided with the pistons, it’s possible that there was valve to valve interference

If that were to happen, that would lead to bent or broken valves, which would lead to your 80% leakage

If you want to be sure about the diagnosis, you could have him pull the head, or perhaps use a borescope to verify the valves which are not seating

As far as another motor, a rebuilt motor isn’t really worth it, because the car isn’t worth that much anymore

Plus, there would be many parts to transfer to the “new” motor

A used motor is a possibility, but there is the uncertainty as to the condition of the used motor. What if it’s burning oil? It may also be way overdue for a timing belt. It may have more miles than yours . . .

If the pistons are indeed undamaged, it might be worth at least getting a quote for the repair of the head. It might just need a few new valves and a valve job

If you want to be sure about the diagnosis, you could have him pull the head, or perhaps use a borescope to verify the valves which are not seating

Wouldn’t it be more cost effective to slap a timing belt on it? He already has the upper cover off and the wheel well open. How long would it take to put a belt on it, 20 min? Then you’ll have a running engine that will tell you everything you need to know.

I don’t believe that any of the engine options on that year Camry are interference engines. If the timing belt broke there should be no engine damage as I think all of the dual camshafts on these engines are gear driven under the valve cover.

You state that the mechanic said the timing belt jumped. A leakdown test is pretty much pointless with a jumped timing belt unless he rotated the camshafts until the valves were closed on each cylinder as it was tested rather than doing each cylinder test based on piston position.

Sorry I can’t be of more help due to lack of info about how the test was done.
A '99 Camry with a measly 90k miles should not have a severe engine problem unless run out of oil or severely overheated.

^ OP did say mechanic rotated camshafts manually for leakdown test.

But I would still do as asemaster says, put the timing belt back on and start the engine. If it runs OK, you’re back in business.

You’re right. While pondering this I was thinking crankshaft rotation; not camshaft.

How do valves collide if the camshafts are gear driven and not out of sync with each other?

FWIW, I usually installed a new belt and attempted to start the engine in that situation. And I seem to recall that one cam was belt driven and the other driven by a gear between the cams. But it difficult to second guess from here. A leak down test is much quicker than replacing the belt…

A leak down test is much quicker than replacing the belt…

But a leakdown test improperly performed will throw you down a blind alley. In order to ensure that all the valves are closed you need to have the valve cover off to see that you are testing a cylinder with the valves in the firing position.

It’s impossible for valves to come out of time with each other on this engine.

It would be faster and more effective to throw a belt at it and see what happens.

Either something is funky in the way the leakdown test was done or there’s something lost in translation between the shop that did the test and what has been related here.
That 80%+ leakage is a major problem although the cause of it may not be major.

If the belt jumped then one has to wonder why it jumped. Faulty tensioner, timing belt in bad shape due to age, seized water pump, or maybe even a camshaft trying to seize due to oil starvation.

I think something has been lost in translation here. I’m not sure why the mechanic thinks the timing belt jumped a tooth, but I suspect that something failed in the water pump and the engine overheated. The leakdown test failure could be due to a blown headgasket and not bent valves.

Loss of compression on the two center cylinders points to a head gasket more than it does to valves. It is also possible that it didn’t overheat but that it was simply time for the gasket to fail but I’m leaning to a water pump failure and overheating.

If this is a very high mileage engine, that is over 150k miles and you like the car, a reman engine may be the best economical choice. If you have less than 100k, then a new headgasket is justified for this engine. Between 100k and 150k, its a tossup.

Edit: if you go with a new headgasket, you will also need a new timing belt and waterpump.