Non-Rotation Based Stuttering Knock

**excrider121** · 10-24-2012, 06:38 PM

98 T/A 1k miles on engine rebuild (no excessive metal in the oil)

Since about 100 miles, there's been a non-rotational knock on the passenger side that's been steadily getting louder and louder.

I say non-rotational because sometimes it's there, then it's not, only to have it come right back. Unpredictable.

I also noticed today when I was headed home that during deceleration it goes away completely until DFCO disengages or I touch the gas again.

I think I'm going to remove the belt and see if it's maybe a rotating accessory? That would also tell me if it's something internal.

Any other ideas?

**pajeff02** · 10-25-2012, 02:47 AM

Rod knock can come and go based upon the engine load. The fact that it is getting louder is of concern. You can drop the belts, but it is unlikely that an accessory would be doing that. If it is steady in tempo and increases/decreases with engine rpm, then it is probably "rotational". Other option is an exhaust leak, however, this usually is more associated with a "tick" rather than a "knock".

**Knight** · 10-25-2012, 11:52 AM

You might also inspect the drivetrain and see if something isn't worn or making contact with something.

***SMWS6TA*** · 10-25-2012, 12:05 PM

did you do the build or did you have a shop do it?

**excrider121** · 10-25-2012, 04:51 PM

The knock isn't loud enough to turn heads, but after listening to the engine run 5-10min it becomes apparent. The knock also gets worse when put in drive/reverse.

Would any portion of the drivetrain make any knocking noises when the engine is in park/neutral?

I did the engine build myself, it was my first LS1 rebuild, definitely not the first engine build though.

I had a coworker today say that it's possible with upped compression and advanced timing that it might be a little bit of detonation and since we've desensitized the knock sensors they aren't being tripped.

**cammed goat** · 10-25-2012, 06:27 PM

Have the knock sensors reactivated. Probably just me, but I am not a fan of running an engine without functioning knock sensors.

**pajeff02** · 10-25-2012, 06:48 PM

Detonation at idle or when revved while not under load would have to mean that something is way wrong.

**cammed goat** · 10-25-2012, 07:13 PM

How is your oil pressure at idle? At accel? I ask as there is another member who lost oil pressure and upon disassembly, discovered the bearings were toast.

**excrider121** · 10-26-2012, 06:41 PM

The knock sensors are still functioning but have been desensitized. This being that when engine load is ramped up in any gear, aggressiveness of the cam combined with solid motor mounts will trick the sensors into thinking that engine is realistically knocking. (So I'm told, I know nothing about tuning)

The sound is more noticeable once the engine warms up but, but is always there, unless the engine is decelerating.

Before the engine was rebuilt, the lowest oil pressure I ever observed was 40lb. After rebuild, since Felpro doesn't include the little piece of paper that says which o-ring is the correct one for the LS1 pick up tube, I've had no lower than 20lb of oil pressure. The moment the gas is touched (even creeping away from a stop sign), the oil jumps to 30lb.

A thought that occurred to me earlier, compression was upped to approx 11.5:1 (as per Trickflow numbers) timing is advanced and the fuel (super) that's in the tank is 2-3 weeks old, could it be possible that the noise is brought on by old fuel?

**04yellowjacket** · 10-26-2012, 07:02 PM

what transmission do you have. i have seen at my shop many times that the flywheel can crack between two bolt holes. and that will cause a knock sound that can sound like a early rod knock. if it is a 6sp make sure all the bolts are tight.

**pajeff02** · 10-27-2012, 01:54 AM

It takes months, not weeks, for fuel to degrade enough to impact how an engine runs.

**jrbonds** · 10-27-2012, 12:07 PM

I just went through this myself.

Fresh rebuild, low oil pressure, little bit of a knock at only 2100 rpm's...driving or idling, as long as it got into the 2100 range.

So guess what it was?

Several of my rod bearings fell out into pieces.

You really should pull that motor out and inspect the bottom end before you do anymore serious damage.

And seriously...knock sensors are there for a reason.

**jrbonds** · 10-27-2012, 12:11 PM

Originally Posted by cammed goat

How is your oil pressure at idle? At accel? I ask as there is another member who lost oil pressure and upon disassembly, discovered the bearings were toast.

Me?

**excrider121** · 10-27-2012, 04:45 PM

I appreciate everyone's input and suggestions. I managed to secure another vehicle I could use today while I disassemble the engine once again. I'll report back with pictures and of what ever it is that I find.

**excrider121** · 10-27-2012, 04:46 PM

Originally Posted by 04yellowjacket

what transmission do you have. i have seen at my shop many times that the flywheel can crack between two bolt holes. and that will cause a knock sound that can sound like a early rod knock. if it is a 6sp make sure all the bolts are tight.

4l60e

The transmission will come out with the motor, so I'll be able to check it then.