Does this sound like rod knock?

[Aurel]

I need expert ears to help me diagnose this engine noise. It is only on the driver side. I suspected valve noise or chain noise, so I readjusted the valves, and checked the tensioners. Tensioner was lower on the driver side, so I did the Jerry woods modification. After all that, the nasty noise is still here.

Some history. I had a rubber oil hose disconnect, so there may have been oil starvation, and I suspect a rod bearing suffered, but how do I know for sure? The good news is I did the top end 20,000 miles ago, but not the bottom. So if I have to split the case now, it will be a new experience...

Engine starts and runs fine besides the noise, oil pressure is normal.


Rod knock - YouTube

[James Brown]

it does still sound like valve noise. could be a bad rocker arm but just a guess

[ddinham]

May be a broken valve spring?

[Aurel]

Originally Posted by James Brown

it does still sound like valve noise. could be a bad rocker arm but just a guess

I paid attention to any abnormal play during the valve adjustment and did not notice anything. But I would much prefer that possibility...

[jpnovak]

I have a similar knock in my 3.2SS. Mine is certainly top end and the noise is isolated on #5 or #6 top endusing a drift and mechanics stethoscope. The noise can not be heard on the case (top or bottom). This means I do not suspect a problem with a rod or rod bearing.

the noise does not happen at idle. the threshold is about 1800 rpm and it intermittently clacks. Constant at 2K.

I have not found the problem after the following diagnosis.

Oil pressure is normal
Leakdown = good.
compression test = 180 +/-5 psi on all cylinders
Pulled #5 and #6 intake and exhaust rockers - slight wear on #5 intake rocker shaft - replaced; rocker faces still true and square
pulled #5 and #6 valve springs - springs intact - no problems with spring pressure
inspected cam lobes - normal wear (none)
cam spray bar working properly (intake and exhaust) - not clogged
valve stems still tight in guide

Using the borescope I do not see any damage. Minimal carbon build-up on piston crown
No wear to cylinder walls


Oil checked out clean
Oil filter is clean
no signs of spun bearing


I had no choice but the engine is out of the car. I hope to have it on the stand soon and torn down for further inspection.

I hope you find the problem. Maybe mine is similar.

[James Brown]

i agree using the stethoscope really will isolate the noise

[ddinham]

Aurel
I have a stethoscope if you want to borrow it.

Dana

[Aurel]

Originally Posted by ddinham

Aurel
I have a stethoscope if you want to borrow it.

Dana

Hi Dana! thank you for your offer. Or, since we are neighbors, I'd be happy to invite you to stop by and listen ltogether. Beer will be provided.

[saxen]

Sounds more like something in the head let go- but rod knock could still be the issue

[ddinham]

Aurel,
Will send you a PM.

Dana

[Eagledriver]

Sounds like the left side and not a rod knock to me.

-Andy

[James Brown]

i like that, use the stethoscope 5 minuets, drink beer for 5 hours

[Porshaah]

The frequency doesn't sound valve train related. Try removing spark from the suspect cylinder(s). If the knock disappears, then it is likely a rod bearing. Try to limit running it in this state to avoid further damage.

[Aurel]

We did listen to it with the sthetoscope, thanks to Dana. It seems to be coming from intake of cyl#3. I can measure compression on that cylinder, and the one next to it to see if there is a big difference. While I do that, I can also run it without the spark plug, as suggested. Those two experiments should bring a definite conclusion.

[Porshaah]

"I can also run it without the spark plug" Leave the spark plug in, just remove the spark plug wire. You can also ground the spark plug wire.

[ddinham]

After listening to Aurel's motor, a "knock" does not seem to be the appropriate descriptive word. It is more of a "ticking" than a "knocking" sound.

[911 tweaks]

Aurel...did you rebuild this motor a few yrs ago...?? There was a fellow with the same name who did a rebuild thread on here...If so, how many miles until this sound developed...??

[Aurel]

Originally Posted by 911 tweaks

Aurel...did you rebuild this motor a few yrs ago...?? There was a fellow with the same name who did a rebuild thread on here...If so, how many miles until this sound developed...??

Yes that was me. The thread is linked in my sig. I put about 20k miles on it since the rebuild. This sound developed after I had a loss of oil. It still does not sound too bad, I may just drive it for a while...

[Sboxin]

tic tic tic tic tic .................boom!

Perhaps you have a rod bearing worn making the almost rod knock sound.

It also sounds like a stuck valve lifter from the old push rod days.

We're currently rebuilding/upgrading a 964 engine that had a very worn #5 rod bearing.

Good luck,

Regards,

[Porshaah]

The term "rod knock" is misleading in that it's not refering to the sound per sai, but rather the frequency at which the sound occurrs. Even though it sounds like a tick a valve would make, it's the frequency at which it occurs that determines if it's bottom or top end related. It's a bit of a challenge to determine from the Youtube file, but it appears that the tick is of a lower frequency than what a valve would make, judging by which the engine is spinning visually. As the piston hammers on the loose bearing the tick will eventually turn into the more familiar "knock" and by that time more damage would have occurred. I think you've eliminated all the possible valve train related possibilities and I know how difficult a decision it is to drop an engine which still runs.