Help with sudden engine knocking and clanking

[BRetty]

All,

My 350 SBC (TH350C trans, just rebuilt 2 months ago) has a steady RPM-based tick/click that starts after about 30 seconds of startup/idle. Putting it in gear makes it worse, applying throttle it becomes a very loud horrible clank-clank -- but the sound immediately backs off when I coast in gear.

It sounds like fan blades clipping a hard line, in fact a similar staggered 5-blade rhythm, but I checked and nothing is obviously interfering.

I has the rear end off the ground on stands and ran it in gear, didn't notice any odd noises then.

Started it just now after 2hrs and engine sounds fine, revs up and down in Park with no problem

On Sunday I changed my spark plugs, and after fixing a couple mistakes -- I had switched wires 6 and 8, found that within 100 yards of driving -- then #1 was loose, connected it securely and stumble vanished -- I drove home all was good

Monday driving into work, I started to feel the rattle and lose power, so I pulled off (*) one plug wire was burnt through, I replaced it. I WAS VERY LOW ON OIL, ADDED 2 QUARTS. From the jug I had bought meaning to change oil....

when changing spark p,ugs, I had to jump in engine and thought maybe I had stomped something loose in the fender wells....

From under the truck, it sure feels like the flexplate or oil pan is source of rattle, not back by the driveshaft/diff. U-joints look fine. I know I need to replace diff ring/pinion soon.

My crank pulley looks pretty eccentric, I need to take off belts and see if it's pulley or balancer or what.

I checked vac gauge, my vac is low (~14in, has been 16-ish) but there's no dip or stumble lime a broken rod or lifter. I have not removed valve covers to check yet since I think it's dkwn below.

* Any thoughts on what to check next would be appreciated. *

I'm going to trans shop to have them re-check my flexplate and torque converter. After that I'm taking it to the local Armenians with their lift to get a good look.

Rattled,
BRetty

* -- Just a PSA, times have changed. Stopping right in front of a High School at 7am on Monday, popping the hood on your 50-yo truck and staying there for 30 minutes is NOT COOL. Apparently some Seniorita Manicure called the cops about a "suspicious vehicle". Called from her leased SUV no doubt. Fortunately one of the cops had (or used to have - I was talking to his shoes) a 70's chevelle or Nova so they just asked me to move it quick b/c traffic.

I actually thought about this when I stopped, but looking at the sorry state of the building and grounds, I was 90% certain the place was abandoned. Seriously.

 

[scrap--metal]

Putting it in gear makes it worse, applying throttle it becomes a very loud horrible clank-clank -- but the sound immediately backs off when I coast in gear.

You might be on to something with the cracked flex plate idea. I had a cracked flex plate once, and if I remember correctly the sound did change depending on how it was loaded (e.g. acceleration, coasting, idle, etc.). To me, it did sound almost like an engine knock.

I'm not sure why it would start making noise after idling for 30 second though. Maybe engine vibrations take a few cycles to get the material on either side of the crack to start popping beck and forth against one another and making the noise.

With the flex plate cover off, you should be able to get a good look at the flex plate. You'll have to turn the engine over to look at the whole flex plate though.

2+ quarts low on oil can make some knocking too, with a noticeable loss of power like you described. Been there and done that too. As long as it wasn't run too long while low on oil, filling it back up should quiet it down. That's been on my experience anyway. It's hard to say if your burnt plug wire could've been responsible though.

Good luck, and ignore the overprotective parents/teachers out there. You're doing nothing wrong.

 

[BRetty]

Update -- I took it to the trans shop who rebuilt my transmission. It was just the flexplate cover come loose and something there contacting the flywheel. Prob happened when I jumped in like a paratrooper to get at those #6 and #8 spark wires

It's not FIXED -- they are moving to a new shop and busy packing up. But the tech assured me it was just something being nicked by the flywheel, nothing in the driveline. I'll get her home and pull the cover without worrying my engine will explode.

Sorry for the false alarm.

Oh -- I could have very easily ended up in jail Monday morning. "You can't be too safe" justifies "taking you in" to keep kids from harm. A white man working on an old car is highly unlikely in Los Angeles unless you are Jay Leno and Leno has teams of mechanics who do all that. I also had gasoline, motor oil, electrical thingamabobs, aka "bomb-making-materials".

I'm not joking. Beware of appearances because that's all that matters.

I really did think the school was derelict, deserted at 645am until the parents started rolling in. It's right by the major landfill and sewage treatment plant too. Tumbleweeds on playground and not painted in 15 years I'll guess.

 

[DoubleDingo]

The way you describe the school is exactly what I envision when I think a Los Angeles school.

Glad you found the ticking problem

 

[BRetty]

Well, jacking her up and getting under there, it sounds like my starter is contacting the flexplate, making the terrible clacking.

So starter would need to move forward, towards the radiator, about 1mm.

I've read the threads here on these problems. I'll try to get a pic of my clearance betw starter/flywheel.

BR

 

[Ricko1966]

As many school shootings as have happened. I'm glad somebody checked you out. No one but you knew that you were not a threat.

 

[RecklessWOT]

As many school shootings as have happened. I'm glad somebody checked you out. No one but you knew that you were not a threat.

I mean yeah, while I hear you there, come on dude was working on an old truck. He wasn't putting on body armor or loading a rifle.

If he was just sitting in the truck on the phone slouched down low, or pacing back and forth in the parking lot looking around and whatnot, yeah that's sketchy. But if he's clearly hanging out under the hood wrench in hand, that should be pretty self explanatory. Old cars need to get fixed sometimes. Sorry for breaking down near a school instead of an auto parts store...

 

[Ricko1966]

I mean yeah, while I hear you there, come on dude was working on an old truck. He wasn't putting on body armor or loading a rifle.

If he was just sitting in the truck on the phone slouched down low, or pacing back and forth in the parking lot looking around and whatnot, yeah that's sketchy. But if he's clearly hanging out under the hood wrench in hand, that should be pretty self explanatory. Old cars need to get fixed sometimes. Sorry for breaking down near a school instead of an auto parts store...

Look at the crap people do today, typing man poses as ups driver just seemed like fun. Got many hits, didnt think to type man poses as stranded motorist, going to try that next. But come on man the world isn't the same place it used to be.

 

[Ricko1966]

Hmmm, seems like the bad guys arent very honest, kinda sneaky.

 

[Wallace6]

You probably just need a starter shim. Cheap and easy to find. Good luck