Cammed 3500 Build, Rod Knock or Bad Lifter? Video

[onefastV6]

So as some of you know I bought Double0bu's car that he has for sale in the classifieds. He had indicated that he got it all back and after 45 minutes of run time the engine developed a rod knock.

Engine Mods List:
3500 engine complete tear down and inspection,new rings and bearings,multi angle valve job,1280 cam (old grind), tce double roller,ported upper and lower intake,tce 65mm tb,tce crank trigger,S&S ceramic coated headers,cold air intake,lt1 lifter springs,180 stat,LS1 MAF, ARP Rod Bolts, Aeromotive 340 fuel pump, ect. this is all new and assembled by a profesional shop.

Trans:
4t45e from 03 ga ,completely rebuilt, raybestos blues,LSD from engineered tech,3.91 final drive ratio,3000 stall converter

I got the car over to my house on Thursday and when I pulled the valve cover, all springs were good, rocker arms were tight, but the intake pushrod on cylinder #5 had popped out.






I pulled the rocker arm and checked to see if the pushrod was bent, which it was not. I proceeded to put it back together started it for a short time without the valve cover, which it started and was splashing a little oil on the headers. So I shut it down and put the valve cover back on so I could let it run. The engine runs, and sounds sounds good, until it drops down to low RPM. When it drops to lower rpm the engine surges and audible knock occurs. Bump up the RPM to about 1000-1200 and it goes away instantly. I took a video of this in hopes to get some ideas/advice before I tear into it any further.

Click Image For Video


So what do you think it is.... Lifter or Rod Bearing?

I am leaning toward a collapsed lifer due to the following:
The knock sounds like it is coming from cylinder 5, upon initial inspection cylinder 5 intake pushrod had popped out, however rocker arms were tight and valve springs were good. Everything is put back and it still knocks but the knock goes away with higher at 1000-1200 rpm. Lastly one of the mods that was done was LT1 lifter springs, potentially meaning that it did not get put back together properly.

[mfuller]

Put stock lifters in and see what happens.
It seems that modded lifters only work 50% of the time.
I know 2 of my 12 lifters with TCE springs would not pump up.

[unchained01]

Phil sounds like a lifter to me also

[NateD4]

Really hard to tell... Fortunately a good audio recording and some know how might point you in the right direction.

Get a good recording of the audio, note the RPM ranges you're in (if possible catch them with the video on the camera).

Then find a software program that lets you look at the Audio wave file (visually) and use the FFT function to look at the predominant frequencies.

For any given RPM a rod knock should be a once per revolution event... so convert the RPM you are running at to an equivalent auto frequency (in Hertz or Hz). To do this take RPM /60 this will give you the RPM number in Hertz. For 800 RPM = 13.333 Hz.

Find the range of the audio where you hear the rod knock sound and apply an FFT to it and see what the approx frequencies are.

A rod knock would be 13.333 Hz while a cam lifter would be a 13.333/2 Hz (or 6.666 Hz).

I'll try to post a rod knock sound from my 3.4 engine. It sounds a bit different than yours perhaps due to a different oil pan.


As another option, have you bought a mechanic's stethoscope? You can track the sound by finding where it's loudest. You can also hear different parts of the valve train at different areas by listening to them.

[NateD4]

* once per revolution per rod..

[AleroB888]

Really hard to tell... Fortunately a good audio recording and some know how might point you in the right direction.

Get a good recording of the audio, note the RPM ranges you're in (if possible catch them with the video on the camera).

Then find a software program that lets you look at the Audio wave file (visually) and use the FFT function to look at the predominant frequencies.

For any given RPM a rod knock should be a once per revolution event... so convert the RPM you are running at to an equivalent auto frequency (in Hertz or Hz). To do this take RPM /60 this will give you the RPM number in Hertz. For 800 RPM = 13.333 Hz.

Find the range of the audio where you hear the rod knock sound and apply an FFT to it and see what the approx frequencies are.

A rod knock would be 13.333 Hz while a cam lifter would be a 13.333/2 Hz (or 6.666 Hz).

I'll try to post a rod knock sound from my 3.4 engine. It sounds a bit different than yours perhaps due to a different oil pan.


As another option, have you bought a mechanic's stethoscope? You can track the sound by finding where it's loudest. You can also hear different parts of the valve train at different areas by listening to them.

You'd have to have a hell of a wide range microphone to record that w/o phase shift and roll off on the low end. I had a set of Earthworks that could do that at one time, but I sold them. You might then view it on a 'scope, but still likely to catch mostly the harmonic content. It could be compared to a known waveform of the failure mode if available. You might be able to use a higher RPM to test, though, if the background noise level (exhaust, belt) was low enough.

[onefastV6]

I pulled the plug wire, in which the knock did not change.

I plugged the spark plug wire back in, put the car in gear with my foot on the brake and the knock goes away completely. Gave it a little gas with my foot on the brake and it revs up without any knock.

The prior owner had to tear down the lifters to put in the LT1 lifter springs, so my guess is that for one reason or another the hydraulic lifter is not holding. I have a spare set of lifters in the garage as well as another short block, so basically if I tear the intakes off and swap out lifers I am only out a gasket set and a few hours of my time if I get it back together and it still knocks with new lifters.

Plan B = Putting together the shortblock that has been sitting in my garage.

Plan C = Pulling the engine out of my grand am that has the MPG/Torque cam and swapping it into the Malibu.

[Superdave]

sounds like a pretty hard knock to me, still worth it to pull the LIM off and check the lifters before you go too far.

it's pretty hard to screw up a lifter spring swap but you never know.

[ericjon262]

that doesn't sound like a lifter at all, I would bet it's a rod bearing. what's the oil pressure like?

[onefastV6]

I pulled the valve cover again and noticed the following.

All the pushrods were still in tact, however the pushrod that previously popped out is not getting oil and from what I can barely see the cup in the lifter is bone dry.

[trotterlg]

A rod knock is louder under load, if it goes away at higher RPM or loads then look some place else. If one lifter is not pumping oil up that could be a good clue. I would try a lifter change, or really lift hard on that rocker to see if it is pumped up right. It is not that hard to pull the pan and check the one rod bearing, but I think it will probably be good. Larry

[ericjon262]

A rod knock is louder under load, if it goes away at higher RPM or loads then look some place else. If one lifter is not pumping oil up that could be a good clue. I would try a lifter change, or really lift hard on that rocker to see if it is pumped up right. It is not that hard to pull the pan and check the one rod bearing, but I think it will probably be good. Larry

not always, I spun a rod bearing in my '79 elcamino, and it was always loud, idle, and at RPM, load/no load.

[pocket-rocket]

not always, I spun a rod bearing in my '79 elcamino, and it was always loud, idle, and at RPM, load/no load.

In-laws had an 80's LTD that had a knock. It didn't knock until it warmed up and then it knocked just like how ericjon said.

Sent from my HTC One X using Tapatalk 2

[3400-95-Modified]

I pulled the valve cover again and noticed the following.

All the pushrods were still in tact, however the pushrod that previously popped out is not getting oil and from what I can barely see the cup in the lifter is bone dry.

With what you have gathered in other info I would have to say check the lifter to see if something is wrong with it... it just doesn't sound like it's right.

That is a very harsh knocking sound but it doesn't sound like its knocking every rotation... As well as the higher the load put on the engine typically the louder a rod knock will get.

[ForcedFirebird]

Put a piece of hose on your ear to the oil pan, then to the valve cover. That should indicate where the noise is coming from.

Hard to tell from the video audio, but that sounded just like my 3.1 when the rod bearing spun.