Best practice to tell if an interference engine has bent valves?

Question

I have a 2003 Mitsubishi Galant 2.4L SOHC engine with 251k miles on it. While I was driving it all of sudden the engine just died. I pulled off the road and then had it towed to a local mechanic. They pulled off the oil filler cap and looked in while someone cranked the engine. Nothing moved inside on the engine, so they assumed it was a broken timing belt. Since it's an interference engine and it had high miles, they said to scrap the car.

Moreover, I've read that 70% of the cars on the road have interference engines, so this is something I want to make sure I understand.

I got it towed home anyway, pulled the timing belt cover and there wasn't any broken belt, but when I did the same visual test looking through the oil filler cap, nothing in the engine moved when I tried to start it either, which I assume is due to no compression from bent values, but I'm not sure. I also assume that the belt has slipped and that is why it won't start.

Then I watched a video by Eric the Car guy What to do when your timing belt breaks where he had a Honda (which has an interference engine) with a broken timing belt. He said he has had great success by putting a new timing belt on and then firing up the engine. In the video he did it and it started and ran fine!

I have a compression tester and I'm going to test the cylinders, but if the belt slipped I'm thinking a zero reading may be because things are out of alignment for the compression stroke to work. However, that is guesswork right now until I actually do the test.

What am I missing here? I've always heard if you break a timing belt on an interference engine and in some rare cases even an interference engine, the values are bent, period.

If all it takes is another timing belt because this one slipped, I can do that work, but I don't want to waste the time and effort on it if the values are bent and I have to get the head redone at the same time due to the cost for an older car.

So my question is this, is there a better simple test for this or is the only way to tell for sure is to pull the head and look at the values?

Aftermath: I found a video online for 2003 Mitsubishi Galant Timing Belt Installation, where the belt had actually broke, however, the driver had only been going about 5 mph and after he replaced the belt, everything was fine.

In my case I had been going about 20 to 25 mph and the belt slipped. When I got to the belts I found about 4" of the groves on the belt sheared off, but the belt held. I thought I had a bad tensioner, but it turned out that oil had leaded under the timing belt cover from the oil filter housing gasket. One of the bolts that holds that on is under the lower timing belt cover. I replaced the belts, pulleys, and tensioner and that fixed it. So pulling the timing belt covers is another methold, albeit more labor intensive.

By the way, after I put the new timing belts on, the car fired right up!

Answer 1

Simplest test I can think of is check the timing gear is intact and properly aligned then perform a compression test. If there is no compression on one or more cylinders, it's safe to assume it's got damaged valve gear.

Answer 2

Without pulling the head you can do a leak down test.

1. Set cylinder 1 to TDC make sure the cam and crank align.
2. Pull the intake tube and open the throttle.
3. Hook up a leak down testing kit.
4. Listen for air.

If it's coming out of the intake you have bent valves. If it's coming out the exhaust you have bent valves.

An alternative would be to use a boroscope with a 90° mirror and visually inspect the valves with the cam and crank aligned at TDC.

Answer 3

I am concerned when you say "nothing in the engine moved" - can you see parts that rotate? Does the belt move when the crankshaft is rotated? if not, then check belt / crank pulley etc If yes, then make sure camshaft rotates and is timed correctly and then you can do the compression test. After that then if it does not start you need to investigate other issues.