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Tapping/knocking noise ??

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Serviceman24

Registered Member
Joined
21 July 2005
Messages
76
Location
Baltimore, MD
OK I know that this is a long shot... Just had the car dynoed after swapping from AEM EMS to AEM FIC. During the last run at approximently 5k RPM, we developed a loud tapping/knocking noise. Lost oil pressure for a second and imeaeately shut it down. After connecting a mechanical gauge we started it back up, oil pressure good, but noise continued. Assumed it to be an issue with the oil pump/gear. Ordered billet gear, installed and reassembled. Everything that could possibly be inspected while apart was checked. Everything appeared to be fine. Reassembled and fired it back up. Guess what? The noise is still there. It's definitely a rotating noise coming from the bottom end. My mechanic is stumped. Any suggestions? What to check? I have a feeling the engine needs to be pulled and inspected.

BTW- 97 w/ BBSC

Thanks in advance!

-Wade
 
Serviceman24 said:
OK I know that this is a long shot... Just had the car dynoed after swapping from AEM EMS to AEM FIC. During the last run at approximently 5k RPM, we developed a loud tapping/knocking noise. Lost oil pressure for a second and imeaeately shut it down. After connecting a mechanical gauge we started it back up, oil pressure good, but noise continued. Assumed it to be an issue with the oil pump/gear. Ordered billet gear, installed and reassembled. Everything that could possibly be inspected while apart was checked. Everything appeared to be fine. Reassembled and fired it back up. Guess what? The noise is still there. It's definitely a rotating noise coming from the bottom end. My mechanic is stumped. Any suggestions? What to check? I have a feeling the engine needs to be pulled and inspected.

BTW- 97 w/ BBSC

Thanks in advance!

-Wade
Click to expand...

Well, I would be worried about Rod Knock as the cause of your noise. Oil starvation can do this. Have you done a compression and leak down? If your rod bearing went, then your pistons would have scored the walls of the offending cylinder and you should detect it as a worn ring and scored cylinder wall that leaks oil and thus air on a leakdown. Good luck.
 
roondogg said:
If your rod bearing went, then your pistons would have scored the walls of the offending cylinder and you should detect it as a worn ring and scored cylinder wall that leaks oil and thus air on a leakdown. Good luck.
Click to expand...

That is in NO WAY true.

If the oil pan was off, did you take the time to remove and inspect each and every rod bearing?

It is true it is most likely a rod bearing but I cannot see how a rod bearing could possibly have any effect on a cylinder wall. If you have not actually visually inspected the rod bearings then do it immediately.

A good trick to find out if its a rod bearing without taking the engine apart is to one by one unplug the ignition coils, very slightly raise the RPMs and listen for the knock to go away - (no combustion = no noise) if it is something else then unplugging the coils will not change the sound.


BTW - were the oil pump gears broken? What caused the drop in oil pressure?
 
Last edited:
angus said:
That is in NO WAY true.

If the oil pan was off, did you take the time to remove and inspect each and every rod bearing?

It is true it is most likely a rod bearing but I cannot see how a rod bearing could possibly have any effect on a cylinder wall. If you have not actually visually inspected the rod bearings then do it immediately.
Click to expand...

Well, I respectfully disagree. Rod bearing destruction and overheating at it's worse will allow excessive piston travel in the axial direction and in side loading. This will cause combustion problems that can lead to contact with the valves or with detonation. I am no expert, but common sense reasons that heat transfer from worn bearings causes damage in the cylinder in many respects.

"Bad rod knocks may double knock if enough rod bearing material has been worn away allowing the piston to whack the cylinder head in addition to the big end of the connecting rod banging on the crankshaft rod journal. It will sound like a hard metallic knock (rod) with an alternating and somewhat muffled aluminum (piston) klock sound."

I got this from some source...

If this motor comes apart, I would be interested in pictures of the cylinder walls. I would also like to see that leak down result in that cylinder.

Here is a video of some DSM with rod knock. This is a worst case scenario. I honestly know nothing about this motor, but the video is self explanatory.
http://www.youtube.com/watch?v=lpzff1Rm-Gg

This web site is a good read. http://www.hydraulicspneumatics.com/200/Issue/Article/False/85214/Issue
RD
 
Last edited:
NetViper said:
Sort of sounds like what happened with mine. I had to buy a new motor. :frown:
Click to expand...

Makes me not want to go fi, I dont want to spend 15 k lol. How did you guys both mess up the motors?
 
roondogg said:
Well, I respectfully disagree. Rod bearing destruction and overheating at it's worse will allow excessive piston travel in the axial direction and in side loading. This will cause combustion problems that can lead to contact with the valves or with detonation. I am no expert, but common sense reasons that heat transfer from worn bearings causes damage in the cylinder in many respects.

"Bad rod knocks may double knock if enough rod bearing material has been worn away allowing the piston to whack the cylinder head in addition to the big end of the connecting rod banging on the crankshaft rod journal. It will sound like a hard metallic knock (rod) with an alternating and somewhat muffled aluminum (piston) klock sound."

I got this from some source...

If this motor comes apart, I would be interested in pictures of the cylinder walls. I would also like to see that leak down result in that cylinder.

Here is a video of some DSM with rod knock. This is a worst case scenario. I honestly know nothing about this motor, but the video is self explanatory.
http://www.youtube.com/watch?v=lpzff1Rm-Gg

This web site is a good read. http://www.hydraulicspneumatics.com/200/Issue/Article/False/85214/Issue
RD
Click to expand...


Rod bearing damage will NOT cause extra piston travel. The rod bolts would prevent this. Extreme rod bearing failure leading to rod failure could though, but this is not the case. Rod bearings are cheap (considering) and it is worth the peace of mind to check and replace. This is likely the culprit. I would not fire the motor up again until you inspect the rod bearings. Use plastigauge. Good luck.
 
I believe that is exactly what the post that you quoted reads. It is, of course, a worst case scenario and probably not the usual outcome. I would inspect, not only the rod bearing, but also the piston and its involved cylinder.
 
Happened to me the first track event of the year. Went out first session not even two laps and heard the knock I went right into the paddock and shut her down. Let it sit for an hour started it up sounded fine until we reved it up and the noise was still there. Had it flat beded to Acura of Brookfield and this is what they found after dropping the oil pan :eek: I was lucky most of the engine was still not trashed and a friend of mine wanted to buy it for a big build so I sold it to him. I was very lucky to find a low mileage bone stock motor and swapped what we could off the old and now runs stronger than ever.
 
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Sometimes if you turn the crank over by hand with the oil pan off you can see excessive movement (up & down) from a rod if the bearing is bad, but the only way to be sure is to pull the cap off each rod and manually inspect each bearing. Hopefully since you shut it down quickly that the damage is minimal.
 
Update... Pulled caps and inspected all bearings. Two of them have some minimal wear; however none of them are out of spec or spun???? What's next? I guess the motor gets pulled and we go from there.
 
Are you certian its the bottom end? I've had a few proteges (I'm a mazda tech) that have the "rod knock" noise and it was actually from screws that fell out of the intake manifold valves and were on top of the pistons, jamming between the top of the piston & cylinder head. I'm not for certian that the intake valves on the nsx have screws, someone who has had one apart would know better than myself, but just a thought. Its hard to say with out seeing/hearing for one's self. It's just that it would be unfourtunate to replace your engine for a possible simple/cheaper fix.
 
How loud is this noise? Could it be valvetrain? Is it due for an adjustment.
Also, what caused the oil pressure issue....
 
I don't believe that he has done a leak down test yet? What should I be looking for?

Not sure what caused the oil pressure to drop? Assumed that it was the gear that had expanded/slipped at high RPM. The gear didn't break; however was was worn and sloppy on the crank.

It's fairly loud, and appears to be coming from the bottom. When you scope it, the sound comes from the bottom and not the top. Don't think it's the valve train; however my mechanic said it may be a stuck valve? Valves were adjusted a few thousand miles ago.
 
If the valves were adjusted too tight they could potenially hit the piston at high rpms.... is the noise always there now or just when the revs are higher?
 
Update... Motor pulled and disassembled for inspection. And the culprit is... Broken valve guide!! Head going to machine shop tomorrow for inspection and repair. It doesn't appear that there was any damage to the piston, or cylinder wall. Mechanic was to inspect both today. I have my fingers crossed.

Any suggestions on anything to check and or replace while the motor is out....
 
Serviceman24 said:
Update... Motor pulled and disassembled for inspection. And the culprit is... Broken valve guide!! Head going to machine shop tomorrow for inspection and repair. It doesn't appear that there was any damage to the piston, or cylinder wall. Mechanic was to inspect both today. I have my fingers crossed.

Any suggestions on anything to check and or replace while the motor is out....
Click to expand...

You could think about cams, valvetrain, port and polish, adj cam gears, timing belt, water pump. Any of those things would be nice when the head is off.
 

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