What's this noise(w/audio)? Is engine about to die or might this rubber thing be it?

[TimQ]

I thought I was making some progress with my 86 c-10 (86 4.3 v6 automatic with 89k original miles). The engine has never run better, started sounding good at idle after I fixed a vacuum leak, the odd knock it had went away after running some seafoam through and changing the oil a few times, the big puff of smoke it gave off on start up went away, and I even tracked down the oil leak from a bad seal on the passenger valve cover. For a few days, all was good. Then, of course, a new noise cropped up that is way different than anything I've ever heard before. I figured I'd record it and see what folks thought.

YouTube - C10 Low idle noise

When I poke around with a piece of hose to my ear, it's loudest up against the oil pan. Some other symptoms

- It's not there on startup until I blip the throttle and get it down to low idle.
- If I give it a little gas (like in the audio) the noise goes away.
- It's not there when driving until I get to really low speed or idle at a light. In fact, the truck runs fantastic at speed.
- It seems to be worse in reverse...but goes away as soon as I give it gas
- oil pressure is good...40+ psi.

I found another thread where someone had a similar description and it turned out the exhaust pipe came loose from the headers. I checked and that's not the case for me but it does sound like a few big hollow pieces of metal clanking against each other rather than something from in the engine (or perhaps thats more a hope on my part). It would just seem that if it were in the engine, it would get worse with speed/RPMs.

To add to the mystery, pictured below is a piece of rubber I found in the driveway the other day. It could be from the truck or from somewhere else. Not really sure. Might it be some sort of pad from in a mount or something that would keep two pieces of metal from rattling?





So what do you think? Is the engine about to eat itself? Is this rubber thing to blame? Something else?


Thanks!

[TimQ]

Giving this a little bump to see if there are any suggestions from the evening crowd.

[MR .T]

check to see if the torque converter bolts are tight.

[sailed2japan]

Drive it 'till it blows up, then you'll know the problem and can fix it. Sorry, but that's all I've got.

[PRattenbury]

It does sound converter/flex plate related.

[TimQ]

Originally Posted by sailed2japan

Drive it 'till it blows up, then you'll know the problem and can fix it. Sorry, but that's all I've got.

Well...on some level, that is the plan. But, if I can extend it's life a little with a bit of wrench turning and/or a few spare parts, that would be cool too.

Anyhow, I guess I now have to dive in and learn about transmissions. Never planned on learning about any of this other stuff, so why not this too!

If anyone has pointers, pictures, or other guidance on what I'd be looking for/what I need to take apart to check on the torque converter/flex plate, that would be great. It wasn't entirely clear on my first pass through the Chilton's and Haynes manuals.

Thanks for the tips.

Tim Q

[sailed2japan]

I wouldn't think it's something inside the transmission. You can access the converter to flex plate bolts by removing the dust sheild on the front of the tranny.

[Big Port Jimmy 6]

Man that really sounds nasty. Check the flex plate while you are checking the converter bolts.It should ring like a bell when you hit it with a wrench, if it has a flat clank to it it is cracked. Also take a pry bar and try to rotate it while watching the balancer. Try it both directions if it slips it is loose on the crank flange. If none of those pull the converter bolts, and crank it and see if the noise goes away, but that is an odd noise for a trans. I hope its not rod bearings letting go. On the other hand small blocks are easy and fairly cheap to rebuild. Jay

[TimQ]

Thanks for the tips. It's a cruddy rainy day here, so it will have to wait a bit till I can crawl under there and check things out. I'm totally new to this so it will be an adventure.

[TimQ]

OK, so I finally have a nice day to crawl under the truck and I'm not entirely sure on how to access the flex plate. I gather I have to remove some sort of a cover. Before I do something stupid, can I ask where this cover might be? Is it the odd shaped cover that sites between the oil pan and pan for the tansmission (the arrow in the attached picture)? Looks like it has eight bolts total (3 in a row on each side and then one each on those black support arms).

If not...can you point me in the right direction?

Anything else a complete noob needs to know before doing it?

[sailed2japan]

Sounds like you're in the right spot, but the picture is MIA.

[TimQ]

Ooops...here's the pic. I'm now fighing with a non-starting lawn mower but will check back when that is fixed.

Thanks.

[PRattenbury]

That looks like the right pan. With that pan removed you'll be able to check the torque on the torque converter bolts. But unless you pull your driveshaft out, unbolt your tranny from the crossmember, take the crossmember down, get a jack under the engine and one under the tranny, disconnect the tranny cooling tubes, the shift linkage, reverse light wire, kick down cable, remove the torque converter bolts from the flywheel, disconnect the battery, drop the starter (you can prolly leave the wires hooked up), and then removethe bolts on the bell housing that hold the tranny to the engine, and then carefully and slowly pulling the tranny back away from the engine, you won't be able to inspect the flex plate. Typically they crack or break where it bolts to the crank shaft.

[sailed2japan]

You don't need to do all that if you have a boroscope. also if you can squirt some degreaser in there and wipe it down with a rag on a screw driver, the oil and nastiness will stay in the cracks and you may be able to detect them.

[PRattenbury]

Have you priced borescopes? The less expensive ones are bigger diameter and not controllable. To get onethat's small and controllable you're looking at a king's ransom. I'd love to own one, though.

[tucsonjwt]

It sounds deep in the engine, like a rod knocking, but audio on the internet is never like real life.
First, be careful where you put your hands and head when the engine is running, especially near the fan.
Before you go into major surgery, point a good flashlight on the water pump/crank pulley/balancer area in the front of the engine behind the fan while the engine is running and see if you notice any wobbly movement on any of those parts while the engine is running or being revved up. Also check your water level when the engine is cold.
I had a lose bolt on my crank pulley last summer and the crank literally flew off the engine when all of the bolts came loose. It sounded like a water pump about to go out (clank, clank) but it was the crank pulley.
That piece you found in the driveway is about the diameter of a freeze plug (on the bottom sides of the engine block -intended to blow out if the engine is exposed to subfreezing temperatures without antifreeze and the water expands when forming ice and cracks the block.) Some aftermarket freeze plugs have a hole in the middle with a bolt in the middle that turns and expands a rubber plug to seal the freeze plug hole. The problem is your piece of rubber is too thin - a freeze plug would have a metal washer about that size, over a thick rubber plug. The factory plugs are just metal dish shaped pieces that seal the hole, like a miniature pie plate.
Look at the ends of your upper and lower control arm rods and other under hood area chassis suspension parts. That piece you found is about the right diameter to be a cap for one of them, except it is flat and not cupped. Look at the suspension parts on one side of the truck and then look at the other side to see if there is a piece missing that looks like the piece you found.
Check your water pump. It will have at least one "weep hole" on it. This is about a 1/8" diameter hole which will leak water when the seal in the pump is broken. If the pump is bad, you should see a trail from the weep hole where there is a rusty water mark, or maybe even see the water leaking out when the engine is running. Haynes has a picture of this water pump weep hole and diagnosis. Any traces of rusty water around the water pump are suspect. Obviously,also check engine temperature when the engine is warm and you are idling. Bad water pumps will make a clanking noise until they fail and allow the engine to overheat because no water is circulating through the block and cooling it. Bad water pumps are usually only heard at idle because the noise of higher engine speeds masks the clanking sounds of a bad pump bearing or impeller.

[Camaro_nut2001]

I am leaning against a rod knock as it should knock louder the higher you rev. It really doesn't sound like a main bearing knock. It kinda sounds like a wrist pin knock & that would explain why it goes away when revved but from what I could make out it sounds like maybe the flywheel or converter as stated before. You should be able to take the three converter bolts out, push the converter back in the front pump enough to see the bottom flywheel bolt. Unplug your dist. & turn the motor over while checking each bolt that holds the flywheel to the crank. If you can't see any cracks, plug your dist. back up & fire her up to see if the noise is still there. As far as the rubber peice, I don't have a clue. Let us know what ya find out.