Can pistons hit valves

brian c · Post by **brian c** » 23 Jan 2012, 13:26

I have read all sorts of claims about pistons hitting valves if timing is too far off or if the timing belt breaks. I know that was the case in older engines but since timing belts are not nearly as bullet-proof as the old style timing CHAIN ....did Volvo allow clearance in the newer engines so that in the event of a timing belt failure the pistons won't collide with an open valve?

I ask because I just redid the head on my kid's 850 and when we fired up the engine it started immediately but the timing tensioner was not functioning properly so the belt jumped and of course the timing suddenly was way off and the engine died. I foolishly restarted the engine 2 more times before I saw the belt jumping around.

I reset the timing and re installed the tensioner and now everything starts and runs good but there is some tapping. Not awful but a little noisy. This car was new to me so I don't know what the engine sounded like before I redid the head. It has 130k on it and sounds to me like a well worn engine would sound but I'm wondering if I did damage or not?

anyone know for sure about the 850 and clearance?
Thanks

Post by **jblackburn** » 23 Jan 2012, 13:30

NOPE. Much more than 2 teeth off, they'll say hi to each other. That belt goes, it's usually game over for the top of the engine.

Time to run a compression test if you expect smashed valves. Sometimes the lifters can just get really ticky when you're cranking the engine over by hand a lot. That's what happened to mine. Quieted down after just a bit (on first starting it up, I freaked out and thought I'd killed it - never heard it tick that loud before).

Don't make fun of my pink duct tape.

brian c · Post by **brian c** » 23 Jan 2012, 16:09

After the incident where the belt slipped. I took the timing belt off and turned the crankshaft a few rotations by hand(with the plugs out) listening for any metal to metal sounds. I heard nothing so assumed since the
crank was turning but the cams weren't.. then probably the pistons CAN"T touch the valves open or closed.

Do you follow me? When the cams are not turning there would have to be SOME valves open so if I turned the crankshaft through a couple revolutions and heard no pistons touching valves then they MUST be unable to touch ?

Post by **jblackburn** » 23 Jan 2012, 18:08

Luck maybe? They're most definitely an interference engine and most definitely do smash valves most of the time the timing belt goes while the motor's running

Post by **JRL** » 23 Jan 2012, 18:40

Remember President Clinton
What is the definition of "is"?
It IS an interference engine. You can do all the rational BS you want, lose a T belt and you WILL lose the head

Post by **erikv11** » 23 Jan 2012, 20:12

JRL speaks the truth.

Time for a compression test, a leak down test if you have the tools. If it runs, hey, it runs, let it go, but it would be good to know what the gauge says.

brian c · Post by **brian c** » 23 Jan 2012, 20:36

thanks everyone. I'll be doing a compression test tomorrow. Still confused about how there could be NO metal to metal sound when I rotated the crank with the timing belt off. But I agree it is an interference type engine. Runs awful good!
I suppose maybe when the belt jumped during the initial start up.. maybe it only jumped on or two teeth and not enough to cause the timing to be off far enough to do damage.
I guess the compression test will tell a lot.

Northern Chev · Post by **Northern Chev** » 24 Jan 2012, 11:34

Brian, don't be confused as to why there's no "metal-to-metal" sound when you rotate the crank and you neither hear contact nor "feel" interference. What these people are telling you is true. You have an interference engine. At running speed obviously something hit, even you said yourself, "now everything starts and runs good but there is some tapping". Tapping? Well then, more than likely something hit something (at running speed). Voila! Tapping.

I may have a couple "guesses" as to why you don't think you're feeling or hearing interference when hand-cranking the engine.

1) When the engine is running it has oil pressure. When you have oil pressure the "lifters or followers" (however you may want to call them for this engine because that's not what they're called) are inflated or "pumped-up" with oil slightly - closing the lash or at the very least causing the valve-train to be at it's FULL operating height. If you have older hydraulic lifters/followers (the little pad, whatever it's called) sometimes "leak down" or drain at rest when the engine isn't running ---> AND therefore because there's no oil pressure the valvetrain does not lift the valves as far as it would at operating speed, which may explain why you don't hear or feel anything when the engine is being rotated at rest. The lifters/followers are not pumped up to full height not lifting the valves as far. If this guess isn't technically right then see my next guess.

2) Have you considered that it may not "hit" when hand-cranked because you bent it out of the way when the belt gave? Which also may explain why it "taps" at running speed... bent valve trying to seat in a flat valve seat? You're not gonna hear that at hand-cranked speed.

3) But, jblackburn's video speaks volumes... it may just need to run a while for everything to pump up. who knows you may be chasing an issue that is nothing to worry about.

Just a guess... This is not an accurate technical response nor a technical diagnosis of your or any other Volvo engine. I'm just throwing out ideas to help address your further questioning of why it doesn't do it at hand-cranked speed vs. why everyone is telling you it IS still an issue. Sometimes we just have to trust the people who are trying to help us. Especially when you get a large amount of people responding with the same answer but it may not fit our own paradigm of how we see it.

Northern Chev · Post by **Northern Chev** » 24 Jan 2012, 11:37

Also, LEAK-DOWN compression test - THAT will more accurately tell you. Regular compression tests will only give you a very tiny amount of information. To best diagnose the symptom you're asking about, you need the LEAK-DOWN test. Regular compression test won't tell but a tiny bit of the story and may lead you to believe everything is OK.

I like erikv11's response best --> "If it runs, hey, it runs, let it go"

brian c · Post by **brian c** » 24 Jan 2012, 12:26

well thanks, Northern, for your input. Just for conversation sake 1st I'd like to respond to the hydraulic lifter issue... I agree when oil pressure is down (as when I cranked by hand) the hydraulic lifters might be 'drained' and unable to 'lift' the valve fully. Only trouble with that theory is... this volvo engine surprised me when I opened it up. the lifters are not hydraulic but rather a solid looking thing between the cam lobe and the valve stem. Didn't look hydraulic at all to me but hey!.... I'm a carpenter! So what do I know??

And yep... I considered that a valve or 2 may be bent now so not making loud contact with a piston. That scenario makes me shiver! After tearing down this thing and rebuilding it only to have bent valves and/or ruined pistons on the first start up makes me sick!

Here's my hope...On first start up after rebuild the engine fired right up but then died after just a couple seconds. So..I had the boy try again ...same thing happened. that's when I realized the belt was loose and jumping. the hope part is that MAYBE the belt only jumped a couple notches...not enough to damage the valves. I can dream can't i?

Anyhow thanks for the ideas. I'll be compression testing this afternoon.

Again, though, I have to say the tapping sounds I hear are certainly no worse than the "after" portion of the video supplied above. I honestly don't think this engine I have sounds bad .. just the kind of tapping you hear on any engine with 130K on it. But I never heard it Before the original burnt valve so I have nothing to compare it to. Maybe it was quite as a mouse.