Upper end knock

[BreckAConner]

Good Morning,

I recently went through and fixed my oil pump vacuum studs, and replaced my bearings since the lack of oil and them wearing. I don't know how the studs broke but they did, and I'm just happy to have my car back up and running. In the past when I noticed the car chatter on the upper end started getting louder, I also noticed that the car started to knock on the upper end. I thought it was the bottom end but ended up being okay. Well after replacing rod/main bearings, that knock is still their. At first I thought my car started to knock on the lower end but I had totally forgot about the upper end. I have no metal shavings at all in the oil. It's nice and clean.

Anyways, I can't figure out for my life what this upper knock is. It happens any where from 1900-2300 rpm range. I'm not sure with upper RPM range, I'm afraid to go over 4k not having my new bearing broken in. I looked up in the cylinders before I put everything back together and the cylinders look fine, so I don't think it's piston slap? Could it be valves touching the piston? I'm just really confused where this knock noise comes from. I had one friend tell me it just sounds like something is look knocking against something, but the sound of it matches the speed of the cam, so I can only think it's upper end. Any ideas? It's something I would like to fix before winter when I have time.

[wildBill83]

Could it be valve float?

[BreckAConner]

Could it be valve float?

I have never heard that term, just looked it up. I bet you are right though. I will defiantly check into this. I do lack performance around 1900-2300 RPM range when this does happen.

http://www.corvetteforum.com/forums/...ienced-it.html

[wildBill83]

Basically it is usually in high mileage engines. It is more common on vehicles that have over heated or have oil sludge. It also occurs when your springs become weak and worn from years of use. It can be from the valve guides being worn or gummed up or spring fatigue or both.

In laymens terms it means the valves are taking longer to close. It can make a tick noise on the top end when the rocker comes back in contact with the cam.

[BreckAConner]

So what would the knock be?

[wildBill83]

Like I said, I suspect the rockers on the cam, take the valve cover off and inspect the cams. It's ok to start the car with the valve cover off too, only for a short while. See if you can pinpoint it.

If everything checks out there then the knock could be a detonation issue. Carbon buildup can cause early detonation. Got a video of it? How consistent is the knock?

[BreckAConner]

it's a consistent knock around that 1900-2300 rpm range.

[wagon-r]

Unlikely to be valve float. That's a high rpm issue. If the springs are so weak that the valves are floating at 2000 rpm, then the first run up to 4000 rpm should toast the engine.

And its not the valves touching the piston. Any kind of interference will bend the valve stems and you'd have a lot more than a knock to worry about.

Is this definitely a knock and not tappet noise?

Overly advanced ignition timing could cause a knock, although I don't know why that would only happen between 1900 and 2300 rpm.

[BreckAConner]

Unlikely to be valve float. That's a high rpm issue. If the springs are so weak that the valves are floating at 2000 rpm, then the first run up to 4000 rpm should toast the engine.

And its not the valves touching the piston. Any kind of interference will bend the valve stems and you'd have a lot more than a knock to worry about.

Is this definitely a knock and not tappet noise?

Overly advanced ignition timing could cause a knock, although I don't know why that would only happen between 1900 and 2300 rpm.

Beats me man, only other thing I can think of is a thrust washer between the rockers is bad or something. I will have to take the valve cover off this weekend and see what's going on.

[C91BLX7]

Have you tried adjusting the valve lash?

[johnl]

Anyways, I can't figure out for my life what this upper knock is. It happens any where from 1900-2300 rpm range. I'm not sure with upper RPM range, I'm afraid to go over 4k not having my new bearing broken in.

Bearings don't require 'breaking in', they are good to go from new. The only parts of an engine that require 'running in' are the pistons / rings / bores, and cam lobes / cam follower faces.

Are you sure the crank journals are OK? Are you certain the new bearings are the correct size for the journals? Are you sure that you have good oil pressure? Relatively unlikely, but it's possible that the little end rod bearings could be worn (which might not make noise at some rpm / load due to the cushioning affects of cylinder pressures, but might at other rpm / load).

It won't be valve float, as already said this is a high rpm issue that only increases as rpm rise. It won't be valve clearance, this will cause 'tappetty' noises at all rpm.

That the noise only occurs over a relatively narrow range of rpm tends to suggest a combustion issue (though 'rod knock' may also occur only in a narrow rpm range). Are you sure that the noise isn't combustion detonation in the cylinders, i.e. 'pinging' aka 'knocking'? Detonation may occur over a limited rpm band, typically at and around the engines highest torque output, which occurs under load when in cylinder gas pressures (and therefore temperatures) are higher than at other rpm and lesser load (high cylinder pressures are also the reason why rod knock may only occur at / near highest torque output). This could be caused by overly advanced ignition, or something else, like poor quality fuel, or overheating, or lean AFR.

[BreckAConner]

I'm going to do a valve lash when I wake up this morning, see if that makes a difference. When I hold the car at the RPM is when the knock happens, it's not as loud. Now when I rev it in between that rpm range is when the knock is loud. When taking a closer look and listening it sounds like the sound comes right from underneath the valves almost like it's in the cylinder. I thought it was a valve bent or smacking the piston. If it continues after the Valve lash, I will make a video so you guys can hear what I'm talking about. I really would just like to be done with the car. This crap would of never happend if my new oil pump hadn't failed on me. I'm the kind of guy that little problems anoy me, so you can't imagine if it's a big problem. Also I don't have any metal shavings in my oil, it's really clean and I think I'm at 700 miles with the new bearings.

One other question, if I had a bent valve I wouldn't have compression and the car would just bog/miss all the time right?

[oyajicool]

Bent valve = Low to no compression. Engine would run rough.

I would use a stethoscope to isolate the source of the noise.

You would need to remove and cut the oil filter to see if the engine is free of metal shavings or flakes.

[BreckAConner]

Here's a video if anyone can tell me what this knock noise is. I noticed, it only happens when the car is warmed up. I doesn't happen when the car is cold.



http://youtu.be/DarUvvu8oGc

[BreckAConner]

Bearings don't require 'breaking in', they are good to go from new. The only parts of an engine that require 'running in' are the pistons / rings / bores, and cam lobes / cam follower faces.

Are you sure the crank journals are OK? Are you certain the new bearings are the correct size for the journals? Are you sure that you have good oil pressure? Relatively unlikely, but it's possible that the little end rod bearings could be worn (which might not make noise at some rpm / load due to the cushioning affects of cylinder pressures, but might at other rpm / load).

It won't be valve float, as already said this is a high rpm issue that only increases as rpm rise. It won't be valve clearance, this will cause 'tappetty' noises at all rpm.

That the noise only occurs over a relatively narrow range of rpm tends to suggest a combustion issue (though 'rod knock' may also occur only in a narrow rpm range). Are you sure that the noise isn't combustion detonation in the cylinders, i.e. 'pinging' aka 'knocking'? Detonation may occur over a limited rpm band, typically at and around the engines highest torque output, which occurs under load when in cylinder gas pressures (and therefore temperatures) are higher than at other rpm and lesser load (high cylinder pressures are also the reason why rod knock may only occur at / near highest torque output). This could be caused by overly advanced ignition, or something else, like poor quality fuel, or overheating, or lean AFR.

The knocking noise, at that certain rpm range is not so bad when I hold the trottle at that range. But if I rev it between that range that's when it sounds bad. If you watch the video you will see what I mean.