Valve bouncing?

[carts]

Hypothetically, Is it possible to crack or break a valve spring?

If so, would this cause a knock to appear in the motor over a certain rev range due to the valve starting to bounce because the spring tension of the shortened spring was no longer able to return the valve every cycle with increased speed?

What other things could cause a knock to appear after about 1600rpm?

Your thoughts would be greatly appreciated...

Cheers
Aaron

[jessie928]

yes its quite possible and it does happen , more so with increased camlobe profiles and old springs.

valve noise is usually a tappp noise not a knock... although a busted spring can indeed induce a hefty knock... Did it happen progressivly, after an overrev? or did it just appear out of the blue?

knocks are usually associated with bottom end, moreso bigends, then cam bearings then mains

did you isolate the region of the noise in the engine?

Jes

[carts]

The noise just appeared suddenly. About 5 mins b4 however, i was driving fairly hard. When it started, i had just started to slowly coast off from the lights, then it got up to about 2000rpm and from inside the car it sounded like a loud ticking/rattling noise. Had no low oil pressure warning. The motor in question is a Commodore VS V6 engine. Its got about 180k on it. I disconnected the drive belt on it to isolate all external pullies and the noise is definately in the motor somewhere.

I am just trying to eliminate the simple things b4 I go and pull the motor out.

If I keep the engine revs low below say 1600rpm, doesn't matter how much you load it up the noise is not there. Once you get it up higher it starts to rattle/knock. Its not a deep thump sound, its more like an extremely loud ticking noise.

Hope that helps..

Cheers
Aaron

[Nev62]

Check the timing. The Raider had what sound like a knock/rattle in the top end whenever there was any load on the engine and/or revs over 2200rpm. It also ticked simular to tappets bouncing up and down.

The timing was out by 4deg (advanced). Even if my timing goes out by 1deg that rattle starts when the engine is under heavy load with A/C on. I also thought the motor had broken or cracked something. Fixed the timing and all is well. Also don't put too much faith in the timing mark on the balancer as these could be out too.

[carts]

All the timing is done electronically via crank angle sensors and knock sensors. The knock sensors are actually picking up the knock and retarding the timing. I don't think I can change this. Unless a crank angle sensor has gone or something and it is causing the motor to ping really badly, i'm not sure this has anything to do with it.

Thanks for your input anyhow.

Cheers
Aaron

[Macca177]

i had the same sound or similar comein from my vn v6 motor a while
back and the thrust bearing had gave way...could b that???had heaps of momvent ...could move the harmonic balacne back and forth with hands.

[DAZZ]

I have seen this too. Crank was moving forward enough so the flex plate was hitting the nose of the starter. Some high km V6s suffer from balance shaft noise. Sounds like a rattle\knock high in the engine with the revs up.

[carts]

Some high km V6s suffer from balance shaft noise. Sounds like a rattle\knock high in the engine with the revs up.

OK. That seems to be something that a lot of people I have spoken too are pointing at. If this is the problem what needs to be done to confirm it? Would it be quicker just to chuck a 2nd hand motor in there?

BTW, I pulled the rocker covers off. Valve springs and rockers seem all good. Was a bit startled to see the amount of buildup and sludge sitting in the covers. Not a good look. Just makes me wonder whats sitting on the pickups below restricting oil flow. Have read that the oil pickup in the VS has a wire gauze on it that is designed to fix oil surge problems. The only trouble is, any grit or sludge in the oil will clog it up and cause oil pressure problems.

Cheers
Aaron