Can pistons hit valves

[norcals95]

You won't always here metal to metal. Why in the world would you turn the crank without the timing belt on? It absolutely will hit the valves if you do that.

[brian c]

Took a while to get that compression test done. My tester broke so I had to wait till I could get a friend to help me out.
Anyway ...all cylinders look good. compression right up near 190 lb. on all 5.

Ok so I don't think my belt slipped as much as I originally thought and I was spared the dreaded clash of piston and valves.

NOw... as far as engine noise ..... I have to admit the engine sounds a little like rods knocking rather than valves tapping. I hear it most at idle. So I'm wondering if the timing is of a little. Maybe advanced too far advanced or retarded enough to cause detonation.
Without a timing light I'm not sure how to test it. My limited knowledge is from back when engines had mechanical ignition.

When I lined up the marks on the crank and intake and exhaust cams, it seemed a little vague as to exactly where the mark was to be lined up on the plastic cam gear cover. I tried to line up the cam marks with the center or highest peak on the notch in the plastic cover, but it seems like it could easily be of by 1 tooth since the distance between the widest part of that notch is close to the width of a gear tooth.

Would anyone recommend moving the cam gear 1 tooth advanced or 1 tooth retarded? to see if the knocking disappears? Sounds like a bad idea to me, but I see where some of you have advanced the gears a little to get more power.

[Northern Chev]

I have to ask this first. It runs fine right? It's just the sound that has you perplexed?

If so then...

You are right in your gut feeling that it would be a bad idea to move the gear by a tooth either direction. At this point I'd stand back and say, "OK, let's start all over from the beginning" and rewind a bit. At this point I'd start eliminating things that we know aren't the problem.

For example:

1) Is the oil level at full? I know this is a stupid question but I've done it myself... so back to basics we go.

2) What's your oil pressure? We're SURE it's fine... but do you really know this? If you "know it's fine" without checking then we have bigger problems. Hook up a gauge and find out for sure. Never believe your dash gauges. When you find out for SURE, then you can rest assured that it's probably NOT a rod or main bearing making that noise. Although, gauging the bearings is the only real way to know for sure. If it's good then you have eliminated that possibility... not just guessed simply based on the fact that you don't think you altered anything in the oiling system that would effect that. Who knows, maybe the brand of gasket you bought blocks off one of the oil galleries partially? That would be hard to diagnose with a pressure test depending on where in the oil circuit you are measuring (before or after the blockage).

3) Check for correct belt timing 50 times if you have to, and then do it 10 more times. Just saying... Can you actually SEE the REAL timing mark on the crank snout? My bet is that you DO actually have the timing correct. Moving it a tooth may really mess things up. My guess is that it runs fine? It's just this sound has you perplexed?

4) This may also be a PEBDRAS error. Where the Problem Exists Between the Driver's Seat And Steering Wheel... you may STILL have bent parts to some capacity inside that you're allowing your non-leakdown compression test results convince you that everything's OK. Just because your regular compression test shows 190 on all cylinders doesn't mean you still don't have a valve sealing problem. Regular compression tests are an old-school way of getting a ballpark idea of what's going on. Do a LEAK DOWN compression test, not a regular compression test. Again, until you do this, you will NOT know for sure. If you do finally do a leak down test and everything's good, don't let that end result convince you that you were right in the first place by only having to do the regular compression test. They are two different types of tests.

5) What's a manifold vacuum test show? Does the needle pulsate (bob up and down a little) at idle? If so this can often be a sign of reversion, where the intake or exhaust signal is interrupted by an out of sync pulse caused by a poorly sealed valve interrupting the signal on a different phase of the stroke. Fluttering vacuum needle as you know could be a pointer to a valve problem. When diagnosing valve issues remember that it's more important what the needle DOES rather than "how much" vacuum you have. Does it float around? Does it flutter? Or is it stable?

6) You MUST check your timing with a gun... you may be right about the timing being off due to advance. Maybe the distributor timing is off? Get a light, they're 20 bucks.

7) You're running premium fuel right? Right?... You're supposed to be. And after head work it's more sensitive to this than before. And BTW cheap gas in these burns the hell out of the valves. Is that why it needed head work on this in the first place? Was it run for years on cheap gas?

Because it all comes down to this ---> All these things above may seem silly but getting down to the basics is the point you're at in this repair. It sounds like you're at your wits-end with this. Since the advanced stuff isn't helping find an easy answer, let's try some of the basics to help REMOVE some of the other possibilities. I say this because I think it's going to lead you back to what you don't want to hear. And that's that you still probably have bent valve parts to some capacity. Regardless of how far you want to believe your belt slipped and regardless of what your "regular" compression test leads you to believe. I HOPE NOT though. I hope you find the answer quickly and I hope it's something simple. This has to be bugging you.

[rspi]

I'd say get it as close as you can and leave it be. The computer is suppose to adjust timing so start the car and let it have it's way. It is also suppose to have 91+ octane run in it so if you run lower octane fuel, like 87, it may retard the timing to avoid knock.

My suggestion is to put in 91+ octane fuel or fuel octane booster, dump in some fuel injector cleaner, start the car and drive it for at least 30 minutes. If it has valve problems, you'll know it. Driving it will put a real load on it and the different RPM's will give it the chance to adjust timing all over the range. It will also heat up the oil and allow it to circulate the oil through the lifters, etc. to get sticky lifters freed up, hopefully no more tapping.

On the other hand, if the valves are damaged you'll know it because the valves wont seat and you'll see smoking, etc. I assume you replaced the hydraulic tensioner???

[rspi]

On another note, you did the HEAD in the first place because you had a burnt valve??? A burnt valve on a motor with only 130,000 miles on it is not good nor normal. What caused the burnt valve? Has that problem been corrected?

[erikv11]

Put the crank mark *exactly* on the block mark, then post up pictures of the cam marks in the notches. We can definitely help you interpret whether or not the cams are off by a tooth.

[brian c]

thanks for the replies guys. I just now saw that there were several replies. Something haywire with my computer.

I am assuming at this point that there is no valve damage.(and yes...I have oil in the engine) I may be wrong but I want to proceed from the assumption that I didn't damage the valves or pistons..

Eric..I see that you asked for photos. I'll get right on that ....but in the meantime..... to your question about the head job:

My kid bought this car and brought it home with # 4 cylinder missing and no compression in that one.
Yeah, I pulled the head but only replaced the bad exhaust valve in that cylinder. Oh, and I also replaced all the valve seals while I had the head off.
I agree, at 130k it seems odd that a valve would go bad but it had a hole the size of an apple seed in it. Anyhow...that is done.
I never got to hear this engine run before my kid bought it but he says it was running fine until the check engine light went on and it started missing badly. So, I don't know if there was a knock before the valve went or not.

All I know is it runs real nice since I replaced the valve but there is somewhat of a knock ...mostly at idle. To me the knock sounds like detonation and as I said before lining up the marks on the cam gears with the cut outs on the plastic gear cover looks like a possible problem. Looks to me like a guy could be off by the width of a tooth causing possible detonation.
I'll try to get a couple photos of the cam gear lineup if I can ever find the microscopic "mark" on the crank gear again!

[taxi]

Is it hard to find crank/cam locking tools? They are cheap here, and its comforting to know the timing is perfect without looking much at the marks. Couldnt even find my crank mark.
And remember: the cam gears are adjustable, can you really trust those marks?
Good luck!

[brian c]

I took a shot of the cam marks. They look right to me but as you can see the intake is a little farther advanced than the exhaust. But after looking at it again I guess if I were off by one lug on the belt or one tooth it would be obvious.

So if this is how it's supposed to look, what about the guys who say they advance their gears by 1 or 2 teeth to improve performance? I take that to mean 1 or 2 teeth is not enough off of factory timing to be dangerous.

the old way of timing was to advance the timing till you could hear a knock ....then retard it a couple of degrees. That's where I got the idea that I might get rid of the slight knock by a one tooth adjustment.

Thanks again to you guys. Some of you sound like real fine fellers trying to keep an old carpenter from screwing up too badly. Like they say... a little knowledge is dangerous! That's me!

[erikv11]

Your thinking on the marks is crystal clear. Those marks are good.

I did a timing belt job a couple days ago where the marks looked almost exactly like that when I pulled the old belt. I think that if the timing belt is really old it can actually stretch a little. Stretch on the tensioner side is taken up by the tensioner, but stretch between the sprockets has nowhere to go. So when you put the new one on, the intake cam may move back a hair counterclockwise. That's how it went for me on that job; the belt was original (16 years old) and had 92k on it.

When you adjust timing you move a few degrees, not a few teeth. Timing will run poorly if off by a tooth, maybe not at all if off by two teeth. The degree adjustments come from loosening the three bolts that fasten the sprockets to the camshafts.