Likeliness of broken camshaft?

[logikfive]

Well, early in the spring this year I had my '97 LTZ give up on me on the interstate and require a tow. I can't remember if I made a post over here or not, but I assumed at the time that the timing chain jumped a tooth (The engine has 219,000 miles on it, and all maintenance records show no replacement of chain). Until now I haven't had the chance to get around to fixing it, and could drive one of my other vehicles for the rest of the summer. Now that winter is closing in I need it again.

But anyway, as the (thought) that the timing chain jumped a tooth, I assumed that the whirring noise it made was the tensioner being broken and chewed up (by the chain) in the fit of rage given by the timing chain; which I actually saw happen to a GM 2.2L I4. To my amazement when I pulled the front of the motor down, the timing chain is a tad bit loose but not enough for it to be even possible it jumped timing. I decided I'd run a quick compression test on the left side of the engine (front of engine bay) and see if I can see any problems. First 2 cylinders had GREAT compression, the rear one I couldn't get anything out of it.

That leads me to believe either a) the cam is broken, or b) the rings failed (not likely, I'm sure)

I did a quick search here but didn't come up with anything, other than the question of intake gasket failure. Yes, this engine has had gasket failure at 216,000 miles but that was 3,000 miles ago, and never gave any indication of problem.

Anyone think it's likely it has a broken cam? I'm going to pull one of the valve covers tomorrow and see if all the rockers are moving or not. If they don't, is it safe to assume that the valves aren't damaged by the cam breakage (if broken)? How close are the tolerances on the 3100?

[3100 MPFI]

pulling the valve cover is the easiest way to check. Once you do that, you can easily tell.

The likelyhood of bent valves is low. The 3100 is not an interferance engine, but it is possilbe to do damage.

If the cam is broken, you can put a new one in and do a compression test.

[logikfive]

I've had people tell me it's a interference engine, and other people tell me it isn't. Being the optimistic self I am, I assumed it wasn't. Since it was only turning about 2,000rpm at 75mph when it all happened, I figured the chances of it doing damage was slim anyway. I'll probably pull the engine if it's indeed a cam issue. For the cost of doing the repairs, I'll likely be in the range of a new engine. It wouldn't make sense to repair what is in the car. Shame too , because I really wanted to see how long this engine would last.

But anyway, I just wondered how common broken cams are in these engines?

[CNCguy]

They do break sometimes as they are an assembled camshaft made from a hollow tube with pressed on lobes. Every break that I have seen has been around cylinders 5 and 6. Many people say they only fail when the LIM gasket fails but I have one here with a broken cam and no water in the oil. I thought they were interference engines. Also, there could be bearing damage depending on how long it ran after breaking since the oil pump is driven by the cam and stops pumping when the cam breaks.

[loner666]

If they don't, is it safe to assume that the valves aren't damaged by the cam breakage (if broken)? How close are the tolerances on the 3100?

no..my alignment pin on my cam broke taking out some valves but everything still moved up and down