phanormthtrodex

Oh boy.... So I've been hunting down this odd knocking coming from my engine. I'm at a complete loss at this point. I can make my own video and post it, but I've finally found one from another site/thread that sounds *exactly* like the noise I've got.


Unfortunately that thread never came to a conclusion; it had veered off on a tangent, since the OP had recently done some clutch work. That couldn't be it though, since I've got an automatic. And..they've got a corvette. There must be something in common here though.

Here's the facts:
1) Only occurs at idle.

Even when I first start the car, it high-idles at ~3K, then as it warms up and RPMs drop, the knocking starts up. This seems to eliminate rod knock, right?

2) Most apparent in Park.

Shifting to Reverse or Drive almost eliminates it completely, but when I come to a stop at red lights, I'll still hear a couple knocks. Then shifting back to Park in the driveway, it really starts the knocking. This makes me think it's transmission related?

3) No low oil pressure, metal flakes.

If anything it's high. Drained the oil twice and I've seen no metal chunks. So these both hopefully eliminate bearings?


Anybody heard this noise before? Or any ideas what it could be?

feilds

Hi, sounds like either your torque converter bolts are loose or you have a cracked flexplate. ive had this happen before its easy to take off the cover and inspect.

phanormthtrodex

Removed the cover. The first two bolts I checked did not seem loose at all, and I didn't see any cracks in the flexplate.

But I think you're definitely on to something here..I noticed the flexplate/converter has a bit of rotational play back and forth. Is this normal? It also makes a "clunk" when rotated each direction, that sounds suspiciously similar to the noise when the engine's running. What's up with that?

InfernalVortex

iTrader: (4)

The flexplate should be hard mounted to the crankshaft, which should not be easy to turn at all if the spark plugs are in. Maybe at the diameter of the plate it's easy enough to turn but I find it odd.

Otherwise, the clunk is likely the parking prawls in the transmission that lock it in park. The clunk isnt a concern if it's in the trans, as that's just the parking brake. Ever had to put it in park on a hill and didnt use your ebrake? It rolls a little and then clunks against the parking brake.

phanormthtrodex

Ok..well it wasn't super easy to turn, plus, like you said, it was near the outer edge, a wrench on one of the flexplate-to-torque converter bolts. When I tried to tighten the bolt, it rotated the plate/converter.

I won't worry about the back and forth play then. That makes sense, thinking about it now, it does seem just like how it would roll a bit in park on an incline.


This knock/rattle is driving me crazy though. Some additional testing found that it definitely does *not* follow the RPMs, revving the engine very slightly, and the knock can still be heard in the background, not changing frequency at all. It sounds just like a bolt tumbling around inside the engine.

I recently did the valve stem seals, and adjusted all the valves. However, it was making this same exact noise before the valve job, so loose rocker arms can be eliminated. (I actually found that some were loose, but unfortunately torquing them down did not fix it.)

Also forgot to mention, after changing the oil last time, I had it idling, trying to hunt down the knock with a screwdriver stethoscope. Realized the oil fill cap had been off the whole time, and when I put it back on, the knock just about went away! (???) So it may be some sort of vacuum problem? Related to this, once or twice I've gotten an intermittent code 33 (MAF sensor - high air flow) Which now makes sense! Seems the engine is sucking in too much air, what could cause that?

And/or an oil pressure issue? On a test drive just now, I noticed the knocks somewhat coincide with the oil pressure gauge hopping around.


Sorry if there's too much info, don't want to get off track, but it really seems like this is all inter-related. Originally, I'd suspected a timing issue, but this weekend I finally realized that this rattle is tripping the knock sensor, so the ECM goes and advances the timing as much as possibe! What on earth is the root cause here?!?

phanormthtrodex

Loose cam shaft bolt(s) seems to be the top suspect now! re: this thread

http://rennlist.com/forums/944-turbo...ing-video.html

Could it be? And do I need to remove the timing cover to get to these to check em or what?

OrangeBird

iTrader: (1)

Funny that you would mention camshaft bolts , cause , listening to the knocking Vette I was 100% sure it sounded like a badly worn timing chain slapping against it's cover , and when revved enough slack was taken from the chain to stop the rap ....

phanormthtrodex

I'll definitely keep that in mind to check the timing chain.

I'm about to pull the belts, crankshaft pulley, harmonic balancer, water pump, and timing cover now. I'll be quite disappointed if none of these dang bolts are loose! So far, it seems like a very likely culprit, some pieces I hadn't thought to mention are falling into place:

1) Wear in the middle of the distributor gear

Noticed when I swapped distributors. Had thought it was due to loose/badly seating distr. but could certainly be from a wobbly cam shaft!

2) Erratic oil pressure

Again - either distributor seating, cam shaft wobble, or also oil pump drive shaft.

3) Sound never stays in one place

It seems to hop around from the front to back of the engine, mostly sounded like it came from around the distributor, which makes sense that the gears are not meshing 100%.

I had wrongly been assuming it was a problem with the distributor seating, and since the oil pump going bad is unlikely, we're left with a camshaft issue.


Fingers crossed for no camshaft/lifter/etc/ damage!

phanormthtrodex

Well I am an idiot.

Reading the FSM procedure for removing the timing cover, somehow I overlooked: Step 2) Remove oil pan.

Of course this is after I've unbolted *everything* else. Thought I was about ready to pry the timing cover off, and came up to check if oil needed to be drained as I foresaw an impending massive oil spill if I just went and popped the timing cover off an engine full of oil.

Good grief what now? This sucks, I am so pissed and about ready to give up on this thing. Should I just start parting her out?

midias

No just do it right or sell it to someone who will. Owning a 30 year old car comes with repair and other mystery work.

Bob88GTA

iTrader: (2)

Good grief what now? This sucks, I am so pissed and about ready to give up on this thing. Should I just start parting her out? [/QUOTE]


No.....you get up, dust yourself off, and do step 2. Crap happens!

phanormthtrodex

Ok. After posting that, I took a step back, and regained some of my momentum. I know I can do this. It can't be that bad, and I'm nearly done. I admit, I was overreacting and almost became a quitter. And that's one thing I've never been. I was just not mentally prepared for the amount of work this is gonna take. I am now This'll be great, I'll be able to scrub all the sludge out of the pan. Anything else I should plan to do, while I've conveniently got the pan dropped?


So..I guess I need to get my hands on an engine hoist. And I really need some assistance from someone who's done this before. I think I'll be getting too deep into uncharted waters to continue alone.

Bob88GTA

iTrader: (2)

Well, I'm a little far to help ya, but its not that bad a job. Read this post, it'll help out.
https://www.thirdgen.org/forums/tech...pping-oil.html

And by ALL means...block the car up good with jackstands and wood cribbing.
Keep us posted!!!!

Check your oil pump screen and pump. Might change that out too while you're at it

phanormthtrodex

Great thanks for that thread. Some good info there. I'm not sure how invested I can get into this job right now, due to the fact that I want to take full advantage of the engine being pulled, and replace quite a few things, rusty exhaust manifolds, and lord knows what else once I pull the engine.

Unfortunately, the first suggestion of a cracked flexplate/bolts to TC did not pan out..I'm hoping I don't hit another dead end with the camshaft bolts/timing chain. Any way to check them without dropping the oil pan? Otherwise, I'm afraid my $$$-spent-to-drivability ratio could shoot through the roof. With my daily driver dying on me, I was hoping to get this beast back on the road sooner than later, but it seems like that ain't gonna happen. DD's just sprung a vicious coolant leak, and the rear differential/torque converter/axle/something is on its way out, so I thought this rattle was gonna be a lot easier to fix than all that!


And to think, this morning I'd thought I was going to unbolt the accessories, pop the cover, torque down the cam bolts and be on my merry way. The valve stem seals I did a few weeks ago seems like cake now!

phanormthtrodex

Well, seems like I've gone full circle and am back at suspecting cracks in the flexplate that I just can't see, since they've likely formed right near the flexplate-to-crankshaft bolts.

Since getting everything bolted back together, and cranking her up to listen to the sound again, I have a better description, and stronger suspicion that its the flexplate,

Very low frequency - maybe as slow as 1-3 Hz

Fairly erratic, not much of a pattern, just random occasional knocks as if someone took a hammer and tapping on the oil or trans pan. knock....knock..knockknockknock.....knock../etc/


So to check the bolts, and/or replace the flexplate -- I guess I'll need to pull the trans back away from the engine...til then, I'll continue riding the bus to work, woohoo!

(I'm assuming it's not safe to drive with a cracked flexplate, right?)

phanormthtrodex

Well, 10 points to feilds!

It absolutely was the flexplate.

TTOP350

iTrader: (8)

Yup, I have a pile of messed up flexplates, some the center fell out of it.

Bob88GTA

iTrader: (2)

I've been wondering for almost 7 months what happened to you and the knock.

Glad to hear you found the problem!

feilds

Great to hear you got it straightened out! Ive been caught out with that loose cam bolt one too, couldnt belive my eyes when i finaly found it made a real mess if my timing cover