Tapping/Knocking Noise

B

Blacktower

Member
I have a tapping/knocking noise coming from somewhere and have not been able to pinpoint it.
It is very similar to the one in this post

Some quick specs:
2000 SR5, 4WD, 3.4l engine, 238k miles.
Timing belt changed at 198K

I've crawled all over and under the engine with a stethoscope and have not got any closer to the source. It sounds like its right around the transmission bell housing / engine oil pan. But, every time think I'm getting close to the sound, it sounds louder somewhere else.

It doesn't make the noise at startup and warm up. Once the engine is warm, it will start making that noise. It will tap with a constant rhythm, but it will also skip a 'beat' here and there

When I increase the RPMs, the tapping will stop and it will come back when it comes to idle. Also it will idle for, at times, for several minutes without making the noise and then come back.

With the stethoscope, the valves sound normal, nothing on/by the timing cover, nothing on or around the exhaust. Same thing under the engine.

I put a couple videos that may or may not help :)

- YouTube
(those belts really don't sound that loud - but in the video they do!)

- YouTube
(excuse the pine needles, pre-summer clean out)

Really appreciate any insight on this one...
 
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How long has it been tapping for and is that a bearing squeal I hear in your videos? I'm thinking it could be the fan clutch or the bearing in the fan pulley bracket. The bearing squeal noise sounds familiar, as mine was squealing like crazy, but more pronounced when the weather was cold. It's possible yours is in worse shape. My problem occurred around 280k.

The fan clutch could be a problem and directly affected by engine speed. Roll up a newspaper or magazine and use it to slow down and stop the fan from spinning. Noise change or go away? If not, disconnect the 3 drive belts and run the engine for a few minutes to see if the noise goes away. Tons of good videos out there how to take the belts off, Timmy, Faye Hadley. The Asian fan clutch runs $150 from the Asian Amazon store FCT-013. The Asian fan pulley bracket is $120 from the Asian Amazon store FBT-004.

Since the knocking goes away with increasing engine speed anything with a connection to the 3 drive belts is suspect.

Worst case and unlikely, if it happened shortly after the timing belt change, was it performed by a decent mechanic? Installing the timing belt guide backwards could lead to abrasion on the timing belt and part of it could be slapping around.

I kept thinking the bearing squeal issue i had was at the bottom end. The engine bay is a fantastic wave guide for sounds, since the fan pulley is at the center of the engine. Also difficult to get a stethoscope on it since its spinning at 700 RPM, threatening to hands. If anything, this is a place to start troubleshooting.
 
Unfortunately, I don't have a lot of history with the vehicle. It's relatively new to me, had it about 6 months. The good thing it's my vehicle to play around with and not a daily driver(yet), but I have been starting it up every week and taking it on short trips.
I got it off a relative who needed to move on from it and when I asked about the tapping noise later, it was "Oh ya, that kind of started" was sort of the answer. :shocked:

I don't know who did the timing belt, but that was a thought in the back of my mind.

It sounds more like a belt squeal to me, but could easily be a bearing.

Completely agree about noises in the engine bay. Sounds bounce around and travel all over. Since I have a really long beard, I have to be extra careful in where I'm sticking my mug around spinny things (drills, mowers, truck tailgates, radial arm saws, grandkids, etc).

I'll poke around with your suggestions this morning after caffeine levels reach optimum.

Thanks for the info!
 
Got the fan belts off and ran it for just a minute. The knocking was still there. Seemed about the same without much change.

On a positive note, the fan pulley sounded a tad crunchy when I was spinning it by hand, so I will probably look to replace that.

Now that I have the skid plate completely off, I'll do some more poking around to see if I can figure out where that noise is coming from.
 
That knocking in the back sounds like the flex plate starting to tear. You can take off the inspection plate spinning the engine by hand and verify that flex plate is intact or starting to go. Seems to common in the 1999-2000 years but any year can have the flex plate going.

The other noises are all in the 3 drive belt or accessory area. Could also be the timing belt. idler etc.

Keep investigating and checking you get all the sounds gone in time. :-)
 
Looking at some other flex plate issues, it seems that might be a very likely cause. I'll take a look at in the next day or two and see if I can find any issues with it. I've never dealt with a failing flex plate, so the noise is unfamiliar.

I ordered a new fan pulley bracket to throw on there, since I already got the hardest part loose -- the power steering pump adjustment nut. Didn't know my hand bent that way, but it does now!
 
While I'm waiting on an extra set of hands, I pulled the flex plate inspection cover off and at the bottom of the bell housing was chunks of what looked like charcoal or graphite. The pieces had next to no weight to it, was not metal (magnet wouldn't pick any out) and a little bit of pressure would cause it to crumble apart. Wasn't expecting to see that...

Seeing chunks of anything is not very comforting.

For size reference, the larger piece at the bottom of the photo is about 3/4 inches along the straight edge.

Thanks again!
 
Just looking at that stuff in the photo to me it looks like compacted oil soaked dirt, maybe it got stuck in a deep mud puddle and mud seeped in, but hard to say just from a photo.
 
Ya, a photo doesn't really help a bunch. At first I thought it might be just oil and debris mixed together, but I believe it would have more weight to it.
Just seems odd to me as its just like a small pieces of wood charcoal -- light density, very dry and crumbles easily.

Never seen anything like that in the bottom of a bell housing. Maybe the mice had a campfire going at one time...
 
There is some black foam that seals off the back side of the engine valley around the coolant bypass pipe that would turn into that material... but it is above the bellhousing and shouldn't be able to get to that location. There isn't that much volume/mass of it either.

-Charlie
 
Taking a look at the flex plate through a few spins, I didn't see any cracks. Of course, that doesn't mean they are not there. Cracks could be by the mounting bolts/crank where I can't see.

I'm really on the fence about pulling the transmission or having someone do it. Being lifted and bigger tires on there, it looks a bit easier than other transmissions I've pulled.

There really isn't a good reason for not doing it myself other than I just don't feel like it, but I don't feel like shelling out the cash :)
 
Blacktower said:
Taking a look at the flex plate through a few spins, I didn't see any cracks. Of course, that doesn't mean they are not there. Cracks could be by the mounting bolts/crank where I can't see.

I'm really on the fence about pulling the transmission or having someone do it. Being lifted and bigger tires on there, it looks a bit easier than other transmissions I've pulled.

There really isn't a good reason for not doing it myself other than I just don't feel like it, but I don't feel like shelling out the cash :)
Click to expand...

Rent an inspection camera to look at the bolt areas. As that is where they tear and rip is by the bolts. :-)
 
brillo_76 said:
Rent an inspection camera to look at the bolt areas. As that is where they tear and rip is by the bolts. :-)
Click to expand...

Better yet, I borrowed one out someone's tool box :)

Anyways, the view is looking at the top of one of the large circular cut out. Looks like a shift in the surface, plus a nice shiny line nearby.

Thinking that looks like a crack to me...
 
Interesting and borrowing a buddies is always the first option. :-) Is that a crack on that top by the arrows? Kinda looks like it. The I try to get different angles but is definitely a possibility. I like the inspection with the movable camera in so you can verify. If you think it is drop the starter out and see if you can see from that area. You an also verify with that starter out if the teeth weaving back and forth from the bell housing when you spin it by hand as well. You can use anything, rod with tape even. You spin and that mark is moving back and forth, you probably find your bell housing noise.
 
Having only owned vehicles with manual transmissions, I honestly didn't what a flexplate is. Searching flexplate problems in the forums, wow, I can see now what the problem is and what it can lead to. Amazing how thin the flexplate is vs a flywheel for a manual transmission. Another Flexplate PSA The video in the link for Engine Knocking is very much the same noise in your video, so I was way off thinking it was from the front end. Glad there are guys on the forum like brillo76 who know a thing or two.
 
Ben Dejo said:
Having only owned vehicles with manual transmissions, I honestly didn't what a flexplate is. Searching flexplate problems in the forums, wow, I can see now what the problem is and what it can lead to. Amazing how thin the flexplate is vs a flywheel for a manual transmission. Another Flexplate PSA The video in the link for Engine Knocking is very much the same noise in your video, so I was way off thinking it was from the front end. Glad there are guys on the forum like brillo76 who know a thing or two.
Click to expand...

There are many more then me that know a thing or 2. I just observed this over the years. I personally, never had an auto do that but many have. :-( Can happen any year of 3rd gen production. However, seems to be more common in the 1999/2000 from my observations.
 
Ben Dejo said:
Having only owned vehicles with manual transmissions, I honestly didn't what a flexplate is. Searching flexplate problems in the forums, wow, I can see now what the problem is and what it can lead to. Amazing how thin the flexplate is vs a flywheel for a manual transmission. Another Flexplate PSA The video in the link for Engine Knocking is very much the same noise in your video, so I was way off thinking it was from the front end. Glad there are guys on the forum like brillo76 who know a thing or two.
Click to expand...

I appreciate all the feedback and suggestions. That's a good forum thread that I didn't come across while searching for possible answers to the noise. The bearings on the fan bracket were on their way out and I swapped that out, so it wasn't all in vein.

The other day, I was talking with the guy who had it before me. Things kind of started when he was towing a zero turn on a trailer, it made a noise and that's when things got a little weird. He can be a little heavy on the acceleration, like John Force style, all the time :)

That would make a bit of sense that a 20+ year old flex plate would let go under those conditions.
 
Feeling a little dense here... I looked around for a bit and didn't come up with a good answer.

About ready to drop the transmission and need to get the speedometer cable out. Most of the ones I have messed with have a knob and you unscrew it.
Not seeing it on this one and not sure how it comes out.

Thanks!
 
I always just left those kick down cables connected there and disconnect and that throttle body. Bring it with the transmission ...:-)
 
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