Weird Noise

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plumkrazee70

plumkrazee70

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Location
Medford, Oregon
68 340 block
.040 over
KB Hypers
recent rebuild (Less than 1000 miles)

Been driving often (every weekend) with no problems at all. Initial timing at 18* total 36*

We had a local "cruise" in our town a few weeks ago, so I took it there and it ran great was out for about 3 hours. I took it home, and parked it that night. Worked all week.

My wife and I were gonna head out for dinner on Friday night, so I thought I'd take the dart. Upon start up, terrible noise under hood. Checked everything and couldn't see anything obvious. Pulled Valve covers and didn't see anything broken or bent.

It sounds like a knock, but not super loud. It does go away when the throttle is lightly depressed. For example: Idle 800 rpm, if I bring it to 1k it will go away.

Sticking lifter? I am going to check converter bolts also, although with the sound going away this may not be it.

Thanks for the advice!
 
welcome to the mystery noisy lifter noise club . Does the noise stay once warm or does it come back when it idles
 
torque converter bolts can give a extra, late, knock as the engine stops. You could oull the coil wire and jog the starter to produce that knock too.
Easiest way to rule out fan, water pump, etc.. is drop those belts.
 
jerry6 said:
welcome to the mystery noisy lifter noise club . Does the noise stay once warm or does it come back when it idles
Click to expand...

I haven't warmed it up all the way yet. It will go away if I raise the RPM's just barely above idle. Idles at 800 rpm, raise to 1K... gone.

I have great oil pressure (hasn't changed) 60 psi cold.

I will see about warming it up tonight and see.
 
RedFish said:
torque converter bolts can give a extra, late, knock as the engine stops. You could oull the coil wire and jog the starter to produce that knock too.
Easiest way to rule out fan, water pump, etc.. is drop those belts.
Click to expand...

I know nothing can be ruled out, but It really sounds like the back of the motor. Now Im thinking either exhaust or Flexplate.
 
If a flex plate bolt head it too thick or if one backs out it can create a heck of a noise.
 
Alaskan_TA said:
If a flex plate bolt head it too thick or if one backs out it can create a heck of a noise.
Click to expand...

I know they aren't too thick because its been fine for this long. The noise just happened out of the blue.

Weird thing was it happened one evening when I started it, not while I was driving it. I will check to see if they are tight though.
 
If you can, get it on a hoist. "I'm normally alone" so I do crap like tie a scrap of wire to the throttle, run clip leads down and hang below to control ignition and jumper starter relay, and get under there an poke around

Use a piece of hose---almost anything---heater hose fuel hose, etc, as a stethoscope to your ear.

Pull the belts all off and run it a short time with them off FIRST

Suspect and check EVERYTHING

Exhaust rattling......already mentioned

Broken / weak motor mount or even missing support bolts

Loose/ bend / improper converter dust cover, even bell loose to engine

Inspect carefully....."its been known" LOL to dent the pan and rub the crank

These are just a few. SUSPECT.........and CHECK

If you suspect valve gear, LISTEN with your hose device........stick the hose into the oil filler, onto / into the PCV grommet, etc. Don't wast time........if you "think" you hear it "up there" yank those valve covers!!!!
 
So I went to do some checking last night. And when I started the car, the noise wasn't there? :banghead: Maybe thats a good thing? lol

Very odd. My father in law's friend has a lift in his shop, so I took it there last night. We won't be able to put it up until later this week, but I will report back what I find.

Thanks for all the suggestions.
 
Well maybe that is a good thing. I don't recall bearings repairing themselves once they go bad. Maybe something got in the combustion chamber. When a piece of my head gasket got blown into a cylinder, or maybe sucked in, whatever, it really started to pound. It destroyed the block.
 
I have had flex plate bolts back of a little and that coused a noise similar to a rod bearing or a light knock. But it was difficult to tell where the noise was coming from.
When I pulled the tranny and inspected the flex plate all the bolts were slightly loose and the holes were slightly oblonged or oval.
I think 67DART273's idea is a great way to isolate the noise.
.The noise is likely to return.
 
magnumdart said:
. I don't recall bearings repairing themselves once they go bad. .
Click to expand...

They can in a BAD way. You get a rod bearing loose and it spins. Now it's galled up the rod or the crank, or both, and the galling has balled things up in there so it doesn't knock. BAD. Damage. Carnage. "Stuff."

magnumdart said:
Maybe something got in the combustion chamber. When a piece of my head gasket got blown into a cylinder, or maybe sucked in, whatever, it really started to pound. It destroyed the block.
Click to expand...

This is a very good point
 
I hope nothing like the above happened.

When the lift gets free, I am going to go over everything to make sure its tight. (Flexplate exhaust, etc)
 
plumkrazee70 said:
Update: It was a loose flexplate bolt. Whew... I guess Ibdidnt use enough loctite. :)
Click to expand...


Did you torque them to spec with a torque wrench or just "wing it"? :banghead:


Torque wrenches are our friends.... :heart:
 
I don't know if it really matters or not, but I always turn the converter with the bolts in loose in the direction the flexplate drives the converter until it bumps against the bolts, and then tighten them down.
I always believed having the bolts centered in the holes allowed them to move and loosen up.

It's just a theory, but I have never had any come loose after doing it that way.
 
TrailBeast said:
I don't know if it really matters or not, but I always turn the converter with the bolts in loose in the direction the flexplate drives the converter until it bumps against the bolts, and then tighten them down.
I always believed having the bolts centered in the holes allowed them to move and loosen up.

It's just a theory, but I have never had any come loose after doing it that way.
Click to expand...

Good tip.
 
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