4L60E knock in bell housing or not

[i6pwr]

This is a 2004 Trailblazer, 4.2 I6 and there is a "light knock" in the bell housing area. You can't really hear it from the front of the vehicle, but along the side you can. Obviously under the vehicle close to the motor it's very obvious.

The sequence of the taps sounds like a rod bearing, motor has 200K. I think it's the very early stage of a rod bearing failure but curious of this could be a flex plate. I cannot see any cracks and all the converter bolts are tight.

I did pull the pan and have around
0018-0019" clearance on #5&6, haven't made it to the rest yet.

There was a little glitter in the oil.

Hopefully @clinebarger can let me know if he has heard this from a 4L60E.

 

[Lubener]

Use a stethoscope, call under and determine for yourself. There's no way anyone can tell from your video unless they are guessing.

 

[i6pwr]

I did, didn't get a pronounced sound along the pan or head, my concern is the frequency of the knocking. It's fast enough for a double-knock at the 5hz for a 600 RPM idle speed, but, rods generally have one knock every other rev, unless it's two rods...lol, not common though for sure.

I figured if it was in the trans it would be easily identifiable, just a hunch though.

 

[The_Eric]

That noise is only when fully warmed? The video was taken at idle? 600rpm? Does it change when the revs go up?


Unplug coil or injectors, that will take away the explosive force and quiet any noise from a rod bearing

 

[PontiacHO]

Has the torque converter to flex plate bolts been checked?

 

[bullwinkle]

Flex plate will knock cold or hot, rod bearings will be worse hot. Take the RPMs to 2500 or so, hold them there when fully warmed up-that's when a rod knock will be loudest. Thicker oil will mask the sound too, unless it's ready to throw one.

 

[Opelman]

I've heard the double knock on worn full floating wrist pin bushings. I don't know if yours are pressed into the rod or floating. Isolating it by killing one cylinder at a time might point you in the right direction.

 

[i6pwr]

That noise is only when fully warmed? The video was taken at idle? 600rpm? Does it change when the revs go up?


Unplug coil or injectors, that will take away the explosive force and quiet any noise from a rod bearing

I did pull the coil on 5 & 6, not really much change, only a very small amount, I know to check all of them but this is in the back of the motor.

Has the torque converter to flex plate bolts been checked?

Yes

I've heard the double knock on worn full floating wrist pin bushings. I don't know if yours are pressed into the rod or floating. Isolating it by killing one cylinder at a time might point you in the right direction.

Yeah, this has floating pins with bronze bushings, we ran out of time but I will get in there and see if the rods have play in the pins.

Edit to add: I ran a test tone generator and it mimics a square wave at 6 hz, little faster than what it should be at idle of 600 RPM, but I don't really hear a double-tap to the point being very noticeable. Religious oil changes at 5-6K with Mobil 1.

 

[i6pwr]

Wouldn't a wrist pin be at 10 hz if a 600 RPM idle? Or possibly the 2nd tap is weak.

 

[clinebarger]

Cracked flexplate would me more of a "tinny" sound.

 

[mattd]

Doesn’t really sound like a rod to me. It could be a possible wrist pin. Flexplate crack typically sounds different than that. If you found metal in the oil you know where to look.

 

[i6pwr]

Doesn’t really sound like a rod to me. It could be a possible wrist pin

I was able to get a handle on a few rods, 4,5&6 and they seem tight, no wobble.

I agree it has that extra tap like a pin but I'm thinking it's the very early stage of a rod knock. When I lay under it, my focus is directly on the bell housing, that's where the sound comes from.
But the sounds will travel and the bell housing is just a megaphone.

 

[i6pwr]

I cut the oil filter tonight.....barely saw any bits of metal, however there was what seems to be a decent amount in the oil. Could have been residue from the pan as we ran 1qt of ATF for about 15 min. Also the oil was drained a few times with the front in the air so maybe some flakes that never drained out.

Either way, that's alot of racket with a relatively clean filter media.

I looked as good as I could with a borescope and could not see any cracks in the flexplate.

Can I loosen the converter and push it into the trans enough to look at the crank bolts?

Drained oil pics:

Filter media:

 

[bullwinkle]

Still think I would try a little 15W40 or 20W50 in it, just for a test. Good news is, there seems to be a lot of 4.2 equipped trucks in the boneyard, the Trailblazers, etc. seem to readily disintegrate (at least my brother’s ‘07 is). Flexplates seem to crack at the crankshaft bolts, not sure the cracks can be seen without pulling the tranny.

 

[i6pwr]

Still think I would try a little 15W40 or 20W50 in it, just for a test. Good news is, there seems to be a lot of 4.2 equipped trucks in the boneyard, the Trailblazers, etc. seem to readily disintegrate (at least my brother’s ‘07 is). Flexplates seem to crack at the crankshaft bolts, not sure the cracks can be seen without pulling the tranny.

I'm hoping to not have to swap motors, I have the pan off trying to see what's going on. Haven't checked all the bearings yet but #5&6 are about .0018" and that's not terrible. I don't know how number 1-4 can be heard only in the bellhousing but maybe so..still need to check them.

 

[mattd]

More than likely you’d be wasting your time unbolting the converter to check things flexplate bolts . Being you still have debris in the oil associated with noise there is a mechanical issue internal at work here. IMO

 

[Opelman]

How does the crank endplay look?

 

[mattd]

Tough to tell from pictures but almost looks like bronze bushing type material with gold ish pieces.

 

[i6pwr]

How does the crank endplay look?

Looks good from what I can tell, all rod side clearance were within spec, I will double check the crank play.

 

[i6pwr]

Tough to tell from pictures but almost looks like bronze bushing type material with gold ish pieces.

That my fear that it's a wrist pin.