Timing belt broke on interference engine. need advice

I have a 2002 Hyundai Sonata GLS 2.7 L V6. I was recently driving down the highway when out of nowhere my car completely stops accelerating. I step on the gas and floor it to no avail. I pull over to the side of the road and call triple A. At this point I thought it was my fuel pump due to the absence of acceleration, so I wasn’t sweating it so much as that is a fairly easy and cheap thing to fix if you do it yourself. I get my car towed to precision tune auto care. ( local shop ) where I pay around $90 after taxes for a complete diagnosis on my vehicle just to make absolute certain that it is infact my fuel pump. Then comes the bad news, they tell me that my timing belt broke and that due to the fact that my car has an interference engine, when the timing belt went, the valves crashed with the pistons and I now need a new engine. In the notes on the work order they wrote that cyl 1. Had 30 psi compression, and should be around 100. And that there was no belt on cam. The thing is the car still seems to really want to turn over. I don’t know much about this specific problem and am in desperate need of advice. Am I screwed or is there a possibility that I can work around getting a new engine/car. Is this something I can fix? Is there a possibility that I don’t need a new engine and just need to do a little bit of repairs? And how would I assess the damage myself? I kind of feel like the shop was just telling me I need a new engine reguardless if it was repairable or not. I would be doing the repairs myself if this is something I can fix. Because the shop quoted me over 3k $750 for the new engine, $155 for the new timing belt and the rest in labor costs.

I am trying to figure out how they could do a compression test if the timing belt is gone.:confused:

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I may be wrong, but I assume you’d have to pull the heads to see what actual damage was done. Pistons could be damaged, valves bent or broken. Then, the repairs would be above the skill level of a shade tree guy like myself.

perhaps they were talking about a leakdown test and providing OP with percentage numbers. OP paid $90 and the test does not take very long to perform.

This dosent make me feel great about that place or the diagnosis they gave me :neutral_face:

I once used my video scope to diagnose pitted valves and seats without removing too many components . . . pretty much the plugs only

So it might be possible to see a bent/broken valve or a piston with a hole in it without pulling heads, if you use the sideways view on the scope

Sounds like a plan. He was talking about doing it himself at one point. If it’s an interference engine, and it’s “interfered”, it’ll be beyond my skill set and more work than I’ve got time to learn how to do. That’s mainly what I was getting at. Of course, OP may be a better backyard wrench than I am.

I’m not lol, I just don’t have many options. I’m a college kid strapped for cash. I always fix whatever goes on my car…but this is by far the biggest project I have taken on if it’s something I can even do at all.

Another vote for using the borescope. If you/your mechanic don’t see obvious damage to the pistons, then it might be worth putting a new timing belt and seeing how well it runs. Even if one or two cylinders have poor compression due to bent valves, the engine will still run adequately, though it will shake at idle. If any of the pistons are cracked or broken, then I’d replace the engine or junk the car.

As a DIY project, replacing a timing belt is not too bad. The parts are not terribly expensive either, if you buy them online.

With a broken timing belt on an interference engine there is little hope. It is a disposable car, you can find similar Hyundai Sonotas for less than the cost of repairing this one, they are cheap used cars.


It’s a valid test. If no compression in some or most of cylinders then it’s a good indicator the timing belt broke. If compression is good then the belt should be good.

There’s a 1% chance the engine might be OK. But they need to scope it first.

The price they quoted is extremely low for a new engine.

I think the OP is saying $3000 to install a $750 used engine with a new timing belt, The bad news; the car is toast. The good news; the OP will have cash from scrapping this car.Not much money, and not very good news.

That’s not what he said.

“Because the shop quoted me over 3k $750 for the NEW engine, $155 for the new timing belt and the rest in labor costs.”

This is another case where it would be nice to hear what the repair shop has actually said. 750.00 dollars will not get a new engine unless it for a small riding mower.

I would not put 3000.00 into this vehicle and without a decent place and plenty of tools I certainly would not try to fix it myself.

The shop should be able to show the OP that the timing belt is broken. If that’s the case, the engine is toast, and the car is a writeoff. See what a junkyard will buy it for, and figure out how to get a new vehicle.

Me, too. The starter motor will still make the pistons go up and down, but what do you do about the valves? They are not opening and closing if the timing belt is broken.

I don’t understand the problem here. A compression test is a valid test. If you don’t have compression on several of the cylinders then you more and likely have a bad timing belt. If there is compression then the belt is good. It’s the least invasive way to tell if you have a broken belt…far easier then removing the timing belt cover for a visual inspection.


Wouldn’t a faster way to tell if the timing belt is broken be to open the oil fill hole and watch for valve train action while cranking?

But if the belt is broken and even one valve is damaged the work required to get the car back on the road is way beyond the vast majority of parking lot DIYers. I am very familiar with Hyundai engines and I wouldn’t attempt to tear into one outside of a well equipped shop.

How can a compression test be done if the valves on that cylinder are not both closed?

To do a compression test on an engine with a broken timing belt, wouldn’t you have to manually turn the camshaft to close the valves in a cylinder, then let the starter crank the engine, measure the compression, then repeat that process for each cylinder?