Signs of bad lifter or valve??

[90210GTP]

Hey guys. You can check my recent post about swapping 3400 engines in my van for other backstory. Basically I'm trying to get my head rapped around possible problem with the '05 3400 I just installed. I know that trying to get diagnosis online based on sounds are difficult. I've read several posts through the years, and all most guys can do is guess based on description or their experiance. That's very understandable. All I'm hoping for is to get some other ideas running through my mind to help diagnose the problem before I break down and pull the engine for exchange.

So... here goes. There is almost no sound of knocking at idle or low RPMs. Only what I would call a muffled "flutter", but definitely nothing harsh. Normal driving I can't hear anything over road/wind noise. So it takes accelerating past 1500 to hear much of anything and it doesn't get sharp and distinct and louder until you get up into the 2300 rpm, or so. It is present in all higher rpm's that I have seen, though I have only floored it twice to redline. When setting I can rev engine with about the same results except not as sharp a knock, I kind of have to hold around 2500 and let off and on to get a sharp sound like when it is under load driving, but there is definitely a rattle/knock through the rpm's over 1500 or so.

OK. If your not bored with me yet, I 'm working on these ideas on my own. If it is a rod bearing, it is quieter than any I've ever heard and it doesn't knock at idle or dropping to idle, as the ones I've had or heard. Now, what killed my original engine was a broken camshaft. It started a much harsher sound than I hear now about 2 weeks before it seized the cam and broke it. The knocking sound came on pretty quick as my wife drives it to school all week and I got in it one Sat and heard it. I told her "When did that start? That's not going to be good" and 2weeks and 2 days later it died. But, I can almost think that it is the same sound, only about 1/2 as bad sounding at this point. Also, when I first tore the old engine down I found one of the lifters beat up and the roller part almost wouldn't turn. After that I found that rotating the engine by hand only turned 2/3 of the camshaft.

With that in mind, I'm wondering if it is possible that a roller could be not rolling right or something. Almost like it may roll with the camshaft at lower rpms but when pushed it sort of skips along the cam lobe and makes the clattering knock I hear. Or how would it be if a valve was sticking open or maybe slow to close and this let the pressure off the pushrod and lifter allowing them to knock and rattle. I just don't know.

So I hope some of you may have some ideas for me. Thanks in advance for any advice.

[trotterlg]

If a roller is stuck it will just slide around the cam until it grinds off the lobe or roller, you will just have the stuck lifter sound. Does it hammer louder if you hold the break and load it up in gear? Does it get quieter when it get hot? If it does it could be piston slap. Bad wrist pin sounds like a higher pitched bad rod bearing. I would take the oil filter off and cut it open and see what is inside. Pull one plug wire at a time and figure out what cylinder it is. Does it idle OK? Any plugs wet? Larry

[Azrael]

A bad lifter will make a loud tapping sound at any RPM. A leaking valve will cause low compression for that cylinder and the imbalance of compression/power stokes will make the engine idle rough. The roughness tends to get hidden at 2000 RPM and up.

[95Grand-Am]

I have seen alot of exhaust manifold studs break of,f could it be a leak at the manifold? Exhaust leaks at the head can sound like an engine nock. JUst something that might be worth looking into before you pull the engine apart.

[MidnightriderZ24]

how did the flexplate look when you bolted it on??

[90210GTP]

Thanks for the responses. Sound is still there, maybe slightly worse. I can hear the rattle/knock start down around 1500 rpm while driving now. It still doesn't get that scary, knocking loud, thinking you wouldn't buy a motor running this way sound until your in the 2300 - 3000 rpm range. To answer a few ?s from above; it doesn't get any quieter/louder when it heats up. It's pretty close to the same cold or hot. And it is sort of like a high pitched rod knock at the higher rpm, but nothing much at idle or a little higher. I stopped by a few mechanic shops to see if they would give a listen, and the only one that would, just said to try 10w-40 and if it quiets down, driive it. That would be fine, but I need to know this motor is dependable while I still have a warranty.

It idles and runs fine, except I scanned and found loads of KR while driving. I had never registered KR on any of my NA engines before, only the SC. I am wondering if the knock sensors are picking up this sound and showing a false KR. It doesn't seem to hurt it, but I assume the computer may be running it lean. It is getting better than my average mpg over about 350 miles this last week, though.

It doesn't seem to have any exhaust leaks that I can find, and I used my old flywheel instead on the one that came from the '05. I guess just in case there was any difference between them. So I am not sure what I'll do next. If a bad lifter knocks all the time, then it doesn't sound like that's the problem. And I assume the sound would be pretty bad if it was constantly grinding down the lobe on the cam. I will check some other things, as well as check which cylinder is the culprit. I had also thought to comprssion check for a bent valve or something. I'll let you know any results.

[bob442]

these motors IME run alot nicer and quieter with 5w30. all i could say is drain the oil and crack open the filter and check for metal deposits, if so, call up the place that you got the motor from ASAP. it would be a good idea to do it now as a problem is rising concern.

[TurboGTU]

If it's never been torn open, make sure a bolt or clamp hasn't made its way behind the intake valves. Just hasn't been sucked in. Also can be a bend pushrod from overrev. I won't sound at low rpm but onece it wants to spin at high rpm, it will make noises and bind on the guide making noise. A manual oil pressure guage won't hurt either. A sticking valve can sometimes be freed by inducing trans fluid into the intake trough a small vacume port. Not saying its your problem.

[90210GTP]

If it's never been torn open, make sure a bolt or clamp hasn't made its way behind the intake valves. Just hasn't been sucked in. Also can be a bend pushrod from overrev. I won't sound at low rpm but onece it wants to spin at high rpm, it will make noises and bind on the guide making noise. A manual oil pressure guage won't hurt either. A sticking valve can sometimes be freed by inducing trans fluid into the intake trough a small vacume port. Not saying its your problem.

It was tore down as far as I changed the LIM gasket and put on new valve cover gaskets before installing. I used my UIM since it had my throttle body which had different cable linkage for my van. I rocked back the rockers one at a time to remove pushrods and kept them in order. I rotated the crank for those cylinders that were too far up in the stroke to remove rods. I looked at ends and through pushrods and rolled on table to check for bent rods. I remebered I did have one rocker slip off tool when reinstalling pushrod. It made a pinging sound and slapped away the rod that my wife was ready to slip under, but I looked over the rod ends and didn't see any damage. I don't think I rolled it to check whether it was bent, but I didn't really think at the time that it could have done that because the rod was not really under the rocker yet, it was just being held over by my wife as she was checking to see if it would fit under right as the tool slipped. Any way this could contribute? It was on the front bank, so it wouldn't be too hard to pull the valve cover and recheck the pushrods.

[bob442]

Realistically you should be able to put your ear to where the sound is coming from, from there i'd start with checking the plug to see if its firing properly. A stethiscope should help with this too, place it on each runner of the intake while its running and it will help determin what bank to go after.
Start with the simple things always like checking the plugs, if its a sticking valve, or a bent rod, this should indicate a fouled plug, or wet/dark color, also some metal deposits. Popping off the valve cover's is fairly easy for the front to check if something is wrong with a push rod or rocker, you could also have the v/c removed while the engine is running to determin where the noise is coming from. Just dont let anything drop in the motor.

[90210GTP]

Realistically you should be able to put your ear to where the sound is coming from, from there i'd start with checking the plug to see if its firing properly. A stethiscope should help with this too, place it on each runner of the intake while its running and it will help determin what bank to go after.
Start with the simple things always like checking the plugs, if its a sticking valve, or a bent rod, this should indicate a fouled plug, or wet/dark color, also some metal deposits. Popping off the valve cover's is fairly easy for the front to check if something is wrong with a push rod or rocker, you could also have the v/c removed while the engine is running to determin where the noise is coming from. Just dont let anything drop in the motor.

I used a stethescope and sound is mostly to the front and drivers side of engine. I can hear it pretty clear from the oil pan but moving around it didn't seem to vary the volume much and on top it sounds harsher, if not really louder. Don't know, because I can't use the scope all the way in my ears because they seem to sensitive. All I have to do is bump it against something and I feel like I blowed my ear drum out or something. It hurts. I guess I'll pull the front valve cover next.

[90210GTP]

I took my van to a mech. today. Don't know him, but he did seem to know a lot about 3400s and said he worked on a lot of them. He's maybe late 50's early 60's; the kind I've found know some stuff when they look at an engine. He said it is definetely valve train related but didn't sound like anything major. He said that a bad lifter should knock at lower rpm and he would not rule out sticking valve. He also said he had found some that had weak valve springs that would rattle like this one when in higher rpms. In the end he said it didn't sound like anything that would keep the engine from running, just annoy me with the sound. Well, I told him I needed to knoiw for sure before the warranty runs out so I would try to check a few things. Does anyone here think the weak valve spring idea could have merit? He said it could happen to the spring left being compressed and then setting on the shelf over time. I know the motor was listed for close to a year before I bought it. Any opinions on this?